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k, , IITK - bmPc, , EARTHQUAKE TIP, Learning Earthquake Design and Construction, , "a., h, , V. R. MURTY, , •partment of Civil Engineering, lian Institute of Technology Kanpur, inpur, , lilding Material and Technology Promotion Council, ustry of Urban Development & Poverty Alleviation, Government of India, ?w Delhi, , September 2005

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IITK - BUM, , EARTHQUAKE TIPS, Learning Earthquake Design and Construction, , C. V. R. MURTY, , -,•.*.•:;•., , yvWit^M^^ywwiii'iN'v^H^^, , Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, , Building Material and Technology Promotion Council, , Ministry ofUrban Development & Poverty Alleviation, Government ofIndia, New Delhi

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PREFACE, , The Republic Day earthquake of 26 January 2001 in Gujarat clearly demonstrated the earthquake, vulnerability profile of our country. It created a considerable interest amongst the professionals, associated with construction activities in any form, as well as the non-professionals regarding the, earthquake safety issues. While the subject of earthquake engineering has its own sophistication and a lot, of new research is being conducted in this very important subject, it is also important to widely, disseminate the basic concepts of earthquake resistant constructions through simple language. With this, objective, the Indian Institute of Technology Kanpur (IITK) and the Building Materials and Technology, Promotion Council (BMTPC), a constituent of the Ministry of Urban Development & Poverty Alleviation,, Government of India, launched the IITK-BMTPC Series on Earthquake Tips in early 2002. Professor C. V. R., Murty was requested to take up the daunting task of expressing difficult concepts in very simple, language, which he has very ably done., , This publication, containing all the 24 Tips, is targeted at persons interested in building, construction. The Tips cover topics such as basic introduction to earthquakes and terminology such as, magnitude and intensity, concepts of earthquake resistant design, and aspects of a seismic design and, construction of buildings. Utmost care is taken to ensure that despite complexity of the concepts, the Tips, are simple and unambiguous. To ensure the highest quality of technical contents, ever)' Tip is carefully, reviewed by two or more experts, both within and outside India and thru feedback is used before, , finalizing the Tips., The Tips are released for publication to all interested journals, magazines, and newspapers. The, Tips are also placed at the web site of the National Information Centre of Earthquake Engineering (NICEE), (www.nieee.org) and Building Materials & Technology Promotion Council (BMTPC) (wano.bmtpc.org). The, project has succeeded way beyond our own expectations: a large number of journals of architecture,, construction and structural engineering, and many prestigious newspapers have published some or all, the Tips., , Seeing the interest of the readers in the Tips, we are happy to place all the twenty four Tips in this, single cover for facilitating their usage. We are grateful to Professor C. V. R. Murty for the dedication, with which he worked on this project. We also take this opportunity to thank the numerous reviewers, who have willingly spent time in reviewing the Tips. But, a special mention may be made here for Ms., Alpa R. Sheth of Mumbai and Professor Svetlana N. Brzev of Vancouver (Canada), who have reviewed, very substantial number of these Tips. Finally, we must thank numerous newspapers, journals and, magazines who came forward to publish these Tips, at times making an exception to their editorial policy, on exclusivity., Development of the Tips was financially supported by the BMTPC New Delhi. Financial support, for this reprint and dissemination was provided by the National Programme on Earthquake Engineering, Education (jmow.nicee.org/hpeee) and the Joan and Haresh Shah family funds, respectively, which is, gratefully acknowledged., , We hope that the readers will find the Tips useful when constructing buildings in earthquake, prone areas and will consult the expert for finalising their design and construction details. We welcome, comments and suggestions; please email to [email protected]., , Sudhir K. Jain, Coordinator, National Information Center of Earthquake Engineering &, Professor of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur208016, September 2005

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UST OF REVIEWERS, We are grateful to the following experts who reviewed one or more Earthquake, Tip and made valuable feedback., Ms. Alpa R. Sheth, Vakil Mehta Sheth Consulting Engineers, Mumbai, Professor Andrew Charleson, Victoria University of Wellington, NEW ZEALAND, Dr. C. P. Rajendran, Centre for Earth Science Studies, Trivandrum, , Professor Christopher Arnold, Building Systems Development, USA, Professor Durgesh C. Rai, Indian Institute of Technology Kanpur, Kanpur, Professor K. N. Khattri, Wadia Institute of Himalayan Geology, Dehradun, Dr. Leonardo Seeber, Lamont-Doherty Earth Observatory, USA, Dr. Praveen K. Malhotra, Factory Mutual Research Corporation, USA, Professor Robert D. Hanson, The University of Michigan, USA, Professor Sri Krishna Singh, Institute De Geofisica, MEXICO, Professor Sudhir K. Jain, Indian Institute of Technology Kanpur, Kanpur, Professor Svetlana N. Brzev, British Columbia Institute of Technology, CANADA, Professor Thomas Paulay, University of Canterbury, NEW ZEALAND, Mr. T. N. Gupta, BMTPC, New Delhi

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CONTENTS, , Preface, , List of Reviewers, Tip 01: What Causes Earthquake?, Tip 02: How the Ground Shakes?, , 1, 3, , Tip 03: What are Magnitude and Intensity?, Tip 04:Where are Seismic Zones in India?, Tip 05:What are the Seismic Effects on Structures?, Tip 06: How Architectural Features Affects Buildings During Earthquakes?, Tip 07: How Buildings Twist During Earthquakes?, Tip OS: What is the Seismic Design Philosophy for Buildings?, Tip 09: How to Make Buildings Ductile for Good Seismic Performance?, Tip 10: How Flexibility of Buildings affects their Earthquake Response?, Tip II: What are the Indian Seismic Codes?, Tip 12: How do Brick Masonry Houses behave during Earthquake?, Tip 13: Why should Masonry Buildings have simple Structural Configuration?, , 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, , Tip 14: Why are horizontal bands necessary in masonry buildings?, Tip 15: Why is vertical reinforcement required in masonry buildings?, Tip 16: How to make Stone Masonry Buildings Earthquake Resistant?, Tip 17: How do Earthquake affect Reinforced Concrete Buildings?, , 27, 29, 31, 33, , Tip 18: How do Beams in RC Buildings Resist Earthquakes?, Tip 19: How do Columns in RC Buildings Resist Earthquakes?, , 35, 37, , Tip 20: How do Beam-Column Joints in RC Buildings Resist Earthquakes?, Tip 21: Why are Open-Ground Storey Buildings Vulnerable in Earthquakes?, Tip 22: Why are Short Columns more Damaged During Earthquakes?, Tip 23: Why are Buildings with Shear Walls Preferred in Seismic Regions?, Tip 24: How to Reduce Earthquake Effects on Buildings?, , 39, 41, 43, 45, 47

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Learning, Earthquake Design, , HTK - bnflpc, Earthquake Tip, , and, Construction, , What Causes Earthquakes?, The Earth and its Interior, , Long time ago, a large collection of material, masses coalesced to form the Earth. Large amount of, heat was generated by this fusion, and slowly as the, Earth cooled down, the heavier and denser materials, , sank to the center and the lighter ones rose to the top., The differentiated Earth consists of the Inner Core, , (radius ~1290*rm), the Outer Core (thickness ~2200A-;h),, the Mantle (thickness -2900Aw) and the Crust, (thickness ~5 to 40Aw). Figure 1 shows these layers., The Inner Core is solid and consists of heavy metals, (e.g., nickel and iron), while the Crust consists of light, materials (e.g., basalts and granites). The Outer Core is, liquid in form and the Mantle has the ability to flow., At the Core, the temperature is estimated to be, ~2500°C, the pressure ~4 million atmospheres and, density -13.5 gm/cc; this is in contrast to ~25°C, 1, atmosphere and 1.5 gm/cc on the surface of the Earth., Crust, , Figure 2:, Local Convective Currents in the Mantle, , Plate Tectonics, The convective flows of Mantle material cause the, , Crust and some portion of the Mantle, to slide on the, hot molten outer core. This sliding of Earth's mass, takes place in pieces called Tectonic Plates. The surface, of the Earth consists of seven major tectonic plates and, many smaller ones (Figure 3). These plates move in, different directions and at different speeds from those, , of the neighbouring ones. Sometimes, the plate in the, front is slower; then, the plate behind it comes and, collides (and mountains are formed). On the other, , hand, sometimes two plates move away from one, Figure 1:, Inside the Earth, , The Circulations, , Convection currents develop in the viscous, Mantle, because of prevailing high temperature and, pressure gradients between the Crust and the Core,, like the convective flow of water when heated in a, , beaker (Figure 2). The energy for the above, circulations is derived from the heat produced from, the incessant decay of radioactive elements in the, rocks throughout the Earth's interior. These convection, , another (and rifts are created). In another case, two, plates move side-by-side, along the same direction or, in opposite directions. These three types of inter-plate, , interactions are the convergent, divergent and transform, boundaries (Figure 4), respectively. The convergent, boundary has a peculiarity (like at the Himalayas) that, sometimes neither of the colliding plates wants to sink., , The relative movement of these plate boundaries, varies across the Earth; on an average, it is of the order, of a couple to tens of centimeters per year., , currents result in a circulation of the earth's mass; hot, , molten lava comes out and the cold rock mass goes, into the Earth. The mass absorbed eventually melts, under high temperature and pressure and becomes a, part of the Mantle, only to come out again from, another location, someday. Many such local, circulations are taking place at different regions, underneath the Earth's surface, leading to different, portions of the Earth undergoing different directions, of movements along the surface., , Figure 3:, , ^Major Tectonic Plates on the Earth's surfacey

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IITK-BMTPC Earthquake Tip 1, What Causes Earthquakes?, , Transform Boundary, , j>age2, The sudden slip at the fault causes theearthquake...., a violent shaking of the Earth when large elastic strain, energy released spreads out through seismic waves, that travel through the body and along the surface of, the Earth. And, after the earthquake is over, the, process of strain build-up at this modified interface, between the rocks starts all over again (Figure 6). Earth, scientists know this as the Elastic Rebound Tlieory. The, material points at the fault over which slip occurs, usually constitute an oblong three-dimensional, volume, with its long dimension often running into, tens of kilometers., , Figure 4: Types of, , Inter-Plate Boundaries^^, , Divergent Boundary, , The Earthquake, Rocks are made of elastic material, and so elastic, , strain energy is stored in them during the, deformations that occur due to the gigantic tectonic, plate actions that occur in the Earth. But, the material, contained in rocks is also very brittle. Thus, when the, rocks along a weak region in the Earth's Crust reach, their strength, a sudden movement takes place there, (Figure 5); opposite sides of the fault (a crack in the, rocks where movement has taken place) suddenly slip, and release the large elastic strain energy stored in the, interface rocks. For example, the energy released, during the 2001 Bhuj (India) earthquake is about 400, times (or more) that released by the 1945 Atom Bomb, dropped on Hiroshima!!, , Types of Earthquakes and Faults, Most earthquakes in the world occur along the, boundaries of the tectonic plates and are called Interplate Earthquakes (e.g., 1897 Assam (India) earthquake)., A number of earthquakes also occur within the plate, itself away from the plate boundaries (e.g., 1993 Latur, (India) earthquake); these are called Intra-plate, Earthquakes. In both types of earthquakes, the slip, generated at the fault during earthquakes is along both, vertical and horizontal directions (called Dip Slip) and, lateral directions (called Strike Slip) (Figure 7), with, one of them dominating sometimes., , Figure 5:, Elastic Strain Build-Up, , Figure 7: Type of Faults J, , and Brittle Rupture, , Sla ;e C, , Reading Material, BolLB.A., (1999), Earthquakes, Fourth Edition, W. H. Freeman and, Company, New York, USA, , http://earthquake.usgs.gov/faq/, http://neic.usgs.gov/neis/general/handouts/, general_seismicity.html, , y -g~, , http:// www.fema.gov/ kids/quakeJitm, , Authored by:, R.Murtv, , O .-, , Lt., , „ a, » Strength, , $, , 5>, , i?, , c, Energy, Build-Up JD, , t Time, , (years), , jrSl Energy, , Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by:, , Building Materials and Technology Promotion, Council, New Delhi, India, , ".« l/Q*, , c6^, , Figure 6: Elastic Rebound Theory, , •Time, (years), Time, , This release is a property of UT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicee'aulk.ac.in. Visit www.nicee.org or, www.bmtpc.orp. to seeprevious IITK-BMTPC Earthquake Tips., Avril 2002

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IITK - bmTPC, , Earthquake Tip, How the ground shakes?, Seismic Waves, , Large strain energy released during an earthquake, , P'-Waves, , Push and pull, , travels as seismic waves in all directions through the, , Earth's layers, reflecting and refracting at each, interface. These waves are of two types - body waves, , and surface waves; the latter are restricted to near the, Earth's surface (Figure 1). Body waves consist of, Primary Waves (P-waves) and Secondary Waves (Swaves), and surface waves consist of Love waves and, Rayleigh waves. Under P-waves, material particles, undergo extensional and compressional strains along, , Extension, , S-Waves, , Compression, , Up and down, , direction of energy transmission, but under S-waves,, oscillate at right angles to it (Figure 2). Love waves, cause surface motions similar to that by S-waves, but, , Side to side, , with no vertical component. Rayleigh wave makes a, , material particle oscillate in an elliptic path in the, vertical plane (with horizontal motion along direction, of energy transmission)., , f, , Direction of, , Energy Transmission, Love Waves, , Sideways in horizontal plane, , Structure, , Surface Waves, , Rayleigh Waves, Elliptic in vertical plane, , Figure 2:, , Motions caused by Body and Surface Waves, , Figure 1: Arrival of Seismic Waves at a Site, , (Adapted from FEMA 99, Non-Technical, Explanation of the NEHRP Recommended, Provisions), , P-waves are fastest, followed in sequence by S-,, , Love and Rayleigh waves. For example, in granites, Pand S-waves have speeds ~4.8 km/sec and, ~3.0km/sec, respectively. S-waves do not travel, , through liquids. S-waves in association with effects of, Love waves cause maximum damage to structures by, , their racking motion on the surface in both vertical, and horizontal directions. When P- and S-waves reach, , the Earth's surface, most of their energy is reflected, back. Some of this energy is returned back to the, , surface by reflections at different layers of soil and, rock. Shaking is more severe (about twice as much) at, the Earth's surface than at substantial depths. This is, often the basis for designing structures buried, , Measuring Instruments, The instrument that measures earthquake shaking,, , a seismograph, has three components - the sensor, the, recorder and the timer. The principle on which it works, , is simple and is explicitly reflected in the early, seismograph (Figure 3) - a pen attached at the tip ofan, oscillating simple pendulum (a mass hung by a string, from a support) marks on a chart paper that is held on, a drum rotating at a constant speed. A magnet around, , the string provides required damping to control the, amplitude of oscillations. The pendulum mass, string,, magnet and support together constitute the sensor; the, drum, pen and chart paper constitute the recorder; and, , underground for smaller levels of acceleration than, , the motor that rotates the drum at constant speed, , those above the ground., , forms the timer.

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IITK-BMTPC Earthquake Tip 2, How the ground shakes?, , jmge_2, , local soil (Figure 1). They carry distinct information, , regarding ground shaking; peak amplitude, duration of, strong shaking, frequency content (e.g., amplitude of, , shaking associated with each frequency) and energy, content (i.e., energy carried by ground shaking at each, frequency) areoften used todistinguish them., Peak amplitude (peak ground acceleration, PGA) is, physically intuitive. For instance, a horizontal PGA, value of 0.6g (= 0.6 times the acceleration due to, , Support, , gravity) suggests that the movement oftheground can, cause a maximum horizontal force on a rigid structure, equal to 60% of its weight. In a rigid structure, all, points in it move with the ground by the same, amount, and hence experience the same maximum, , s,Figure 3:, , Schematic of Early Seismograph, , One such instrument is required in each of the two, orthogonal horizontal directions. Of course, for, measuring vertical oscillations, the string pendulum, , (Figure 3) is replaced with a spring pendulum, , acceleration of PGA. Horizontal PGA values greater, than l.Og were recorded during the 1994 Northridge, Earthquake in USA. Usually, strong ground motions, carry significant energy associated with shaking of, frequencies in the range 0.03-30Hz (i.e., cycles per sec)., g, , oscillating about a fulcrum. Some instruments do not, , 1985 Mexico Earthquake (SCTIA. N90E), , 1940 Imperial Valley Earthquake (El Centra; S00E), , have a timer device (i.e., the drum holding the chart, paper does not rotate). Such instruments provide only, , jaw, , the maximum extent (or scope) of motion during the, earthquake; for this reason they are called seismoscopes., , », , ,, , uake (Pacoima Dam; N76W), , 50, , The analog instruments have evolved over time,, , 60, , Time (sec), , but today, digital instruments using modern computer, technology are more commonly used. The digital, instrument records the ground motion on the memory, of the microprocessor that is in-built in the instrument., Strong Ground Motions, Shaking of ground on the Earth's surface is a net, , ^V, , ~~^—^WW-VVW\/\/Vv^^\rv v-, , ^1997 Uttarkashi Earthquake (Uttarkash,. N7SE), »»•, , |—, , Figure 4::, , Some typical recorded accelerograms, , the fault. These waves arrive at various instants of, , Generally, the maximum amplitudes of horizontal, motions in the two orthogonal directions are about the, same. However, the maximum amplitude in the, vertical direction is usually less than that in the, , time, have different amplitudes and carry different, levels of energy. Thus, the motion at any site on, , design acceleration is taken as V2 to 2/3 of the, , consequence of motions caused by seismic waves, generated by energy release at each material point, , within the three-dimensional volume that ruptures at, , ground is random in nature with its amplitude and, direction varying randomly with time., , Large earthquakes at great distances can produce, weak motions that may not damage structures or even, be felt by humans. But, sensitive instruments can, record these. This makes it possible to locate distant, , earthquakes. However, from engineering viewpoint,, , horizontal direction. In design codes, the vertical, horizontal design acceleration. In contrast, the, maximum horizontal and vertical ground accelerations, in the vicinity of the fault rupture do not seem to have, such a correlation., , Resource Material, , BoIt.B.A., (1999), Earthquakes, Fourth Edition, W. H. Freeman and, Company, New York, USA, , strong motions that can possibly damage structures, are of interest. This can happen with earthquakes in, the vicinity or even with large earthquakes at, , Authored by:, C.V.R.Miirtv, , reasonable medium to large distances., , Indian Institute ofTechnology Kanpur, , Characteristics of Strong Ground Motions, The motion of the ground can be described in, terms of displacement, velocity or acceleration. The, variation of ground acceleration with time recorded at, a point on ground during an earthquake is called an, , accelerogram. The nature of accelerograms may vary, (Figure 4) depending on energy released at source,, , type of slip at fault rupture, geology along the travel, path from fault rupture to the Earth's surface, and, , Kanpur, India, , Sponsored by:, Building Materials and Technology Promotion, , ^5, , Council, New Delhi, India, , This release is a property of UT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, , and with due acknowledgement. Suggestions/comments, , may be sent to: niceetaiitk.ac.in. Visit www.nicee.org or, www.bmlpc.orB. to see previous IITK-BMTPC Earthquake Tips., May 2002

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Learning, Earthquake Design, , HTK - timfc, Earthquake Tip, , and, Construction, , What are Magnitude and Intensity?, Terminology, The point on the fault where slip starts is the Focus, or Hypocenter, and the point vertically above this on, the surface of the Earth is the Epicenler (Figure 1). The, depth of focus from the epicenter, called as Food Depth,, is an important parameter in determining the, damaging potential of an earthquake. Most of the, damaging earthquakes have shallow focus with focal, depths less than about 70km. Distance from epicenter, to any point of interest is called epicentral distance., Epicentral Distance, , released goes into heal and fracturing the rocks, and, only a small fraction of it (fortunately) goes into the, seismic waves that travel to large distances causing, shaking of the ground en-route and hence damage to, structures. (Did you know? The energy released bv a, M6.3 earthquake is equivalent to that released by the, 1945 Atom Bomb dropped on Hiroshima!!), Earthquakes are often classified into different, groups based on their size (Table 1). Annual average, number of earthquakes across the Earth in each of, these groups is also shown in the table; it indicates that, on an average one Great Earthquake occurs each year., Table 1: Global occurrence of earthquakes, Group, , Magnitude, , Great, , 8 and higher, , 1, , Major, , 7-7.9, , 18, , Strong, , 6-6.9, , 120, , Moderate, , 5 - 5.9, , Mill, , Annual Average Number, , Light, , 4-4.9, , Minor, , 3-3.9, , 6,200 (estimated), 49.000 (estimated), , Very Minor, , <3.0, , M2-3: -1,000/day; Ml-2: -8,000/dav, , Source: http::/neic.usgs.gov/neis/eqlists/eqstats.html, , Intensity, A number of smaller size earthquakes take place, , before and after a big earthquake (i.e., the Miin Shock)., Those occurring before the big one are called, Foreshocks, and the ones after are called Aftershocks., , Magnitude, Magnitude is a quantitative measure of the actual, size of the earthquake. Professor Charles Richter, noticed that (a) at the same distance, seismograms, , (records of earthquake ground vibration) of larger, earthquakes have bigger wave amplitude than those of, smaller earthquakes; and (b) for a given earthquake,, seismograms at farther distances have smaller wave, amplitude than those at close distances. These, , prompted him to propose the now commonly used, magnitude scale, the Richter Scale. It is obtained from, , Intensity is a qualitative measure of the actual, shaking at a location during an earthquake, and is, assigned as Roman Capital Numerals. There are manv, intensity scales. Two commonly used ones are the, Modified Mercalli Intensity (MM!) Scale and the MSK, Scale. Both scales are quite similar and range from I, (least perceptive) to XII (most severe). The intensity, , scales are based on three features of shaking perception by people and animals, performance of, , buildings, and changes to natural surroundings. Table, 2 gives the description of Intensity VIII on MSK Scale., The distribution of intensity at different places, during an earthquake is shown graphically using, isoseismals, lines joining places with equal seismic, intensity (Figure 2)., , the seismograms and accounts for the dependence of, waveform amplitude on epicentral distance. This scale, is also called Local Magnitude scale. There are other, magnitude scales, like the Body Wave Magnitude,, , Surface Wave Magnitude and Wave Energy Magnitude., These numerical magnitude scales have no upper and, lower limits; the magnitude of a very small earthquake, can be zero or even negative., , An increase in magnitude (M) by 1.0 implies 10, times higher waveform amplitude and about 31 times, , higher energy released. For instance, energy released, in a M7.7 earthquake is about 31 times that released in, a M6.7 earthquake, and is about 1000 (*31x31) times, , that released in a M5.7 earthquake. Most of the energy, , Figure 2: Isoseismal Map of the 2001 Bhuj (India), Earthquake (MSK Intensity), Source:, , http::/www.nicee.org/nicee/EQReports/Bhuj/isoseismal.html

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IITK-BMTPC Earthquake Tip 3, What are Magnitude and Intensity?, Table 2: Description of shaking intensity VIII as per, MSK scale, , Intensity VIII -. Destruction of Building*, (a) Fright and panic. Also, persons driving motorcars are, disturbed. Here and there branches of trees break off. Even, , heavy furniture moves and partly overturns. Hanging, lamps are damaged in part., (b) Most buildings of Type C suffer damage of Grade 2, and, few of Grade 3. Most buildings of Type B suffer damage of, Grade 3, and most buildings of Type A suffer damage of, Grade 4. Occasional breaking of pipe seams occurs., Memorials and monuments move and twist. Tombstones, , overturn Stonewalls collapse., , (c) Small landslips occur in hollows and on banked roads on, steep slopes; cracks develop in ground up lo widths of, several centimeters. Water in lakes becomes turbid. New, , reservoirs come into existence. Dry wells refill and existing, , wills become drv. In many cases, changes in (low and level, ol water are observed., , Hat, Type A slim lures - rural constructions; Type B - ordinary, , masonry constructions; Type C- Well-builtstructures, Rev - about 5%;Many- about 50%;Most - about 75%, 11 Damage - Slight damage; Grade 2 - Moderate, damage; Grade 3 - Heavy damage; Grade 4 - Destruction;, Grade 5 - Total damage, , P»ffc 2, enclosed by the isoseismal VIII (Figure 2) may have, experienced a PGA of about 0.25-0.30g. However, now, strong ground motion records from seismic, instruments are relied upon to quantify destructive, ground shaking. These are critical for cost-effective, earthquake-resistant design., Table 3: PGAs during shaking of different intensities, VI, , VII, , VIII, , IX, , Wm, Source: B.A.BoIt. Earthquakes. W.H.Freeman and Co., New York. 1993, 0.03-0.04, , 0.06-0.07, , 0.10-0.15, , 0.25-0.30 0.50-0.55, , >0.60, , Based on data from past earthquakes, scientists, , Gutenberg and Richter in 1956 provided an, approximate correlation between the Local Magnitude, Mi of an earthquake with the intensity In sustained in, the epicentral area as: Ml =% lo + 1. (For using this, equation, the Roman numbers of intensity are replaced, with the corresponding Arabic numerals, e.g., intensity, IX with 9.0). There are several different relations, proposed by other scientists., , Basic Difference! Magnitude versus Intensity, , 100 Watt Bulb, , Magnitude of an earthquake is a measure of its size., For instance, one can, , measure the size of an, , earthquake by the amount of strain energy released by, the fault rupture. This means that the magnitude of the, earthquake is a single value for a given earthquake. On, the other hand, intensity is an indicator of the severity, of shaking generated at a given location. Clearly, the, seventy of shaking is much higher near the epicenter, than farther away. Thus, during the same earthquake, of a certain magnitude, different locations experience, , Near, , Bright, , (100 lumens), , different levels of intensity., To elaborate this distinction, consider the analogy, of an electric bulb (Figure 3). The illumination at a, location near a 100-Watl bulb is higher than that, , Normal, , (50 lumens), , farther awav from it. While the bulb releases 100 Watts, , Dull, , of energy, the intensity of light (or illumination,, , (20 lumens), , measured in lumens) at a location depends on the, , Figure 3: Reducing illumination with distance, , wattage of the bulb and its distance from the bulb., , from an electric bulb, , Here, the size of the bulb (WO-Watt) is like the, , magnitude of an earthquake, and the illumination at a, location like the intensity of shaking at that location., , Magnitude and Intensity in Seismic Design, One often asks: Can my building withstand a, , magnitude 7.0 earthquake? But, the M7.0 earthquake, causes different shaking intensities at different, locations, and the damage induced in buildings at, these locations is different. Thus, indeed it is particular, levels of intensity of shaking that buildings and, , structures are designed to resist, and not so much the, magnitude. The peak ground acceleration (PGA), i.e.,, maximum acceleration experienced by the ground, during shaking, is one way of quantifying the severity, of the ground shaking. Approximate empirical, correlations are available between the MM intensities, , and the PGA that may be experienced (e.g., Table 3)., For instance,during the 2001 Bhuj earthquake, the area, , Resource Material, , Richter.CF., (1958), Elementary Seismology, W. H. Freeman and, Company Inc, USA (Indian Reprint in 1969by Eurasia Publishing, House Private Limited, New Delhi), , http://neic.usgs.gov/neis/general/handouts/magnitude_intensity., html, , Authored by:, , C.V.R.Murty, Indian Institute of Technology Kanpur, Kanpur, India, , Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicee(ajitk.ac.in. Visit www.nicec.org or, www.bmtpc.orc tosee previous IITK-BMTPC Earthquake Tips., June 2002, , 6

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IITK - bnflpc, Earthquake Tip, Where are the Seismic Zones in India?, Basic Geography and Tectonic Features, India lies at the northwestern end of the Indo-, , Australian Plate, which encompasses India, Australia, a, major portion of the Indian Ocean and other smaller, countries. This plate is colliding against the huge, Eurasian Piute (Figure 1) and going under the Eurasian, Plate; this process of one tectonic plate getting under, another is called subditclion. A sea, Tetln/s, separated, these plates before they collided. Part of the, , lithosphere, the Earth's Crust, is covered by oceans, and the rest by the continents. The former can undergo, subduction at great depths when it converges against, another plate, but the latter is buoyant and so tends to, remain close to the surface. When continents converge,, large amounts of shortening and thickening takes, place, like at the Himalayas and the Tibet., , across the central part of peninsular India leaving, layers of basalt rock. Coastal areas like Kachchh show, marine deposits testifying to submergence under the, sea millions of years ago., , Prominent Past Earthquakes in India, A number of significant earthquakes occurred in, and around India over the past century (Figure 2)., Some of these occurred in populated and urbanized, areas and hence caused great damage. Many went, unnoticed, as they occurred deep under the Earth's, surface or in relatively un-inhabited places. Some of, the damaging and recent earthquakes are listed in, Table 1. Most earthquakes occur along the Himalayan, plate boundary (these are inter-plate earthquakes), but, a number of earthquakes have also occurred in the, peninsular region (these are intra-plate earthquakes)., , r, , Figure 1: Geographical Layout and, Tectonic Plate Boundaries at India, , Three chief tectonic sub-regions of India are the, mighty Himalayas along the north, the plains of the, Ganges and other rivers, and the peninsula. The, Himalayas consist primarily of sediments accumulated, over long geological time in the Tethys. The IndoGangetic basin with deep alluvium is a great, depression caused by the load of the Himalayas on the, continent. The peninsular part of the country consists, of ancient rocks deformed in the past Himalayan-like, collisions. Erosion has exposed the roots of the old, mountains and removed most of the topography. The, rocks are very hard, but are softened by weathering, near the surface. Before the Himalayan collision,, several tens of millions of years ago, lava flowed, , Figure 2: Some Past Earthquakes, , Four Great earthquakes (M>8) occurred in a span, of 53 years from 1897 to 1950; the January 2001 Bhuj, earthquake (M7.7) is almost as large. Each of these, caused disasters, but also allowed us to learn about, , earthquakes and to advance earthquake engineering., For instance, 1819 Cutch Earthquake produced an, unprecedented ~3m high uplift of the ground over, WOkm (called Allah Bund). The 1897 Assam Earthquake, caused severe damage up to 500km radial distances;, the type of damage sustained led to improvements in, the intensity scale from I-X to I-XII. Extensive, , liquefaction of the ground took place over a length of, 300km (called the Slump Belt) during 1934 Bihar-Nepal, earthquake in which many structures went afloat., •, , 7

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IITK-BMTPC Earthquake Tip 4, Where are the Seismic Zones in India?, , page 2, , Table 1: Some Past Earthquakes in India, , 1967 and again in 1970. The map has been revised, again in 2002 (Figure 4), and it now has only four, seismic zones - II, III, IV and V. The areas falling in, seismic zone I in the 1970 version of the map are, merged with those of seismic zone II. Also, the seismic, zone map in the peninsular region has been modified., Madras now comes in seismic zone III as against in, zone II in the 1970 version of the map. This 2002, , Dale, , Event, , 16 June 1819 Cutci, 12 June 1897 AsS.llll, , Time Magnitude, , Max., , Intensity, , Deaths, , IlMKI, , 8.3, , VIII, , 1.500, , 17:11, , 8.7, , XII, , 1,500, , 8 Feb. 1900, , Coimbatore, , 03:11, , 6.0, , X, , Nil, , 4 Apr. 1905, , Kangra, Bihar-Nepal, , 06:20, , 8.6, , X, , 19,000, , 15 Jan. 1934, , 14:13, , 8.4, , X, , 11,000, , 31 Max 1935 Quetta, , 03:03, , 7.6, , X, , 10,000, , 15 Aug 1950, , 19:31, , 8.5, , X, , 1,530, , 21 Jul. 1956 JAnjar, , 21:02, , 7.0, , IX, , 115, , 10 Dec 1967 JKovna, , 04:30, , 6.5, , VIII, , 200, , 20:56, , 5.4, , VII, , 30, , 04:39, , 6.6, , IX, , 1,004, , Assam, , 23 Mar 1970 Bharuch, , 21 Aug 19881 Bihar-Nepal, 20Oct 1991 luttarkashi, , 02:53, , 6.6, , IX, , 768, , 30 Sep 1993 •Killari (Latur) 03:53, 22 Mav 1997 Jabalpur, 04:22, , 6.4, , IX, , 7.928, , 6.0, , VIII, , 38, , 29 Mar 1999 Chamoh, , 12:35, , 6.6, , VIII, , 63, , 26 Jan. 2001, , 08:46, , 7.7, , X, , 13,805, , Bhuj, , The tirr ing, , of the ^;arthimake duri ng the c ay, , seismic zone map is not the final word on the seismic, hazard of the country, and hence there can be no sense, , of complacency in this regard., , anc, , during the year critically determines the number of, casualties. Casualties are expected to be high for, earthquakes that strike during cold winter nights,, when most of the population is indoors., Seismic Zones of India, , The varying geology at different locations in the, country implies that the likelihood of damaging, earthquakes taking place at different locations is, different. Thus, a seismic zone map is required to, identify these regions. Based on the levels of intensities, sustained during damaging past earthquakes, the 1970, version of the zone map subdivided India into five, zones - I, II, III, rV and V (Figure 3). The maximum, Modified Mercalli (MM) intensity of seismic shaking, expected in these zones were V or less, VI, VII, VIII,, and IX and higher, respectively. Parts of Himalayan, boundary in the north and northeast, and the Kachchh, area in the west were classified as zone V., , Figure 4: Indian Seismic Zone Map as per, IS: 1893 (Part 1)-2002, ., , The national Seismic Zone Map presents a largescale view of the seismic zones in the country. Local, variations in soil type and geology cannot be, represented at that scale. Therefore, for important, projects, such as a major dam or a nuclear power plant,, the seismic hazard is evaluated specifically for that, site. Also, for the purposes of urban planning,, metropolitan, , areas, , are, , microzoned., , Seismic, , microzonation accounts for local variations in geology,, local soil profile, etc,., Resource Material, , BMTPC, (1997), Vulnerability Atlas of India, Building Materials and, Technology Promotion Council, Ministry of Urban Development,, Government of India, New Delhi, , Dasgupta,S., et al, (2000), Seismotectonic Atlas of Imiian and its, Environs, Geological Survey of India, IS:1893, (1984), Indian Standard Criteria for Earthquake Resistant, Design of Structures, Bureau of Indian Standards, New Delhi, , Authored by., CV.R.Murty, Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, , The seismic zone maps are revised from time to, time as more understanding is gained on the geology,, the seismotectonics and the seismic activity in the, , This release is a property of IIT Kanpur and BMTPC New, , country. The Indian Standards provided the first, seismic zone map in 1962, which was later revised in, , may be sent to: nicee(aiitk.ac.in. Visit www.nicee.org or, , 8, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , .>. u ,\ bmtpc.org.tosee previous IITK-BMTPC Earthquake Tips., July 2002: August 2004

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Learning, Earthquake Design, , HTK - bmlPC, Earthquake Tip, , and, , Construction, What are the Seismic Effects on Structures?, Inertia Forces in Structures, , Earthquake causes shaking of the ground. So a, building resting on it will experience motion at its, , base. From Newton's First Lino of Motion, even though, the base of the building moves with the ground, the, roof has a tendency to stay in its original position. But, since the walls and columns are connected to it, they, drag the roof along with them. This is much like the, situation that you are faced with 'when the bus you are, standing in suddenly starts; yourfeet move with the bus,, but your upper body tends to stay back making you fall, backwards!! This tendency to continue to remain in the, previous position is known as inertia. In the building,, , would like to come back to the straight vertical, position, i.e., columns resist deformations. In the, straight vertical position, the columns carry no, horizontal earthquake force through them. But, when, forced to bend, they develop internal forces. The larger, is the relative horizontal displacement u between the, top and bottom of the column, the larger this inlernal, force in columns. Also, the stiffer the columns are (i.e.,, bigger is the column size), larger is this force. For this, reason, these internal forces in the columns are called, , stiffness forces. In fact, the stiffness force in a column is, the column stiffness times the relative displacement, between its ends., , since the walls or columns are flexible, the motion of, , Inertia Force, , the roof is different from that of the ground (Figure1)., , III, Roof, , \\, Column, , Foundation, , Figure 1: Effect of Inertia in a building when, shaken at its base, , Consider a building whose roof is supported on, columns (Figure 2). Coining back to the analogy of, yourself on the bus: when the bus suddenly starts, you are, thrown backwards as if someone has applied a force on the, upper body. Similarly, when the ground moves, even, the building is thrown backwards, and the roof, experiences a force, called inertia force. If the roof has a, mass M and experiences an acceleration a, then from, Newton's Second Law of Motion, the inertia force F, is, mass M times acceleration a, and its direction is, , opposite to that of the acceleration. Clearly, more mass, means higher inertia force. Therefore, lighter buildings, sustain the earthquake shaking better., Effect of Deformations in Structures, , The inertia force experienced by the roof is, , transferred to the ground via the columns, causing, forces in columns. These forces generated in the, columns can also be understood in another way., During earthquake shaking, the columns undergo, relative movement between their ends. In Figure 2,, this movement is shown as quantity u between the, roof and the ground. But, given a free option, columns, , Soil, , >, Acceleration, , Figure 2: Inertia force and relative motion within, a building, , Horizontal and Vertical Shaking, Earthquake causes shaking of the ground in all, three directions - along the two horizontal directions, , (Xand Y, say), and the vertical direction (Z, say) (Figure, 3). Also, during the earthquake, the ground shakes, randomly back andforth (- and +) along each of these X,, Y and Z directions. All structures are primarily, designed to carry the gravity loads, i.e., they are, designed for a force equal to the mass M (this includes, mass due to own weight and imposed loads) times the, acceleration due to gravity g acting in the vertical, downward direction (-Z). The downward force Mg is, , called the gravity load. The vertical acceleration during, ground shaking either adds to or subtracts from the, , acceleration due to gravity. Since factors of safety are, used in the design of structures to resist the gravity, loads, usually most structures tend to be adequate, against vertical shaking.

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IITK-BMTPC Earthquake Tip 5, What are the Seismic Effects on Structures?, , _pagc2, have been observed in many earthquakes in the past, (e.g., Figure 5a). Similarly, poorly designed and, constructed, , reinforced, , concrete, , columns, , can, , be, , disastrous. The failure of the ground storey columns, resulted in numerous building collapses during the, 2001 Bhuj (India) earthquake (Figure 5b)., , Figure 3: Principal directions of a building, , However, horizontal shaking along X and Y, directions (both + and - directions of each) remains a, , concern. Structures designed for gravity loads, in, general, may not be able to safely sustain the effects of, horizontal earthquake shaking. Hence, it is necessary, to ensure adequacy of the structures against horizontal, earthquake effects., Flow of Inertia Forces to Foundations, Under horizontal shaking of the ground,, , horizontal inertia forces are generated at level of the, mass of the structure (usually situated at the floor, levels). These lateral inertia forces are transferred by, , (a) Partial collapse of stone masonry walls, during 1991 Uttarkashi (India) earthquake, , the floor slab to the walls or columns, to the, , foundations, and finally to the soil system underneath, (Figure 4). So, each of these structural elements (floor, slabs, walls, columns, and foundations) and the, connections between them must be designed to safely, transfer these inertia forces through them., Inertia Forces, , (b) Collapse of reinforced concrete columns (and, , building) during 2001 Bhuj (India) earthquake, Figure 5: Importance of designing walls/columns, for horizontal earthquake forces., , Resource Material, Chopra.A.K., (1980), Dynamics of Structures - A Primer, EERI, , Monograph, Earthquake Engineering Research Institute, USA, , Next Upcoming Tip, What is the Influence of Architectural Features on Earthquake, Behaviour of Buildings?, Earthquake Shaking, , Authored by:, Figure 4: Flow of seismic inertia forces through, all structural components., Walls or columns are the most critical elements in, , C.V.R.MuiU, , Indian Instituteof lechnology Kanpur, Kanpur, India, Sponsored by:, , transferring the inertia forces. But, in traditional, , Building Materials and Technology Promotion, , construction, floor slabs and beams receive more care, , Council, New Delhi. India, , and attention during design and construction, than, walls and columns. Walls are relatively thin and often, made of brittle material like masonry. They are poor in, carrying horizontal earthquake inertia forces along the, direction of their thickness. Failures of masonry walls, , This release is a property of IIT Kanpur and BMTPC New, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicee(uiitk.ac.in. Visit www.nicee.org or, www.bmtpc.org. lo seeprevious IITK-BMTPC Earthquake Tips, August 2002, , 10

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IITK - bnflpc, Earthquake Tip, How Architectural Features Affect Buildings During Earthquakes?, Importance of Architectural Features, The behaviour of a building during earthquakes, depends critically on its overall shape, size and, geometry, in addition to how the earthquake forces are, carried to the ground. Hence, at the planning stage, itself, architects and structural engineers must work, together to ensure that the unfavourable features are, avoided and a good building configuration is chosen., The importance of the configuration of a building, was aptly summarised by Late Henry Degenkolb, a, noted Earthquake Engineer of USA, as:, "If-we have a poor configuration to start with, all the, engineer can do is to provide a band-aid - improve a, basically poor solution as best as he can. Conversely, if, we start-offwith a good configuration and reasonable, framing system, even a poor engineer cannot harm its, ultimate performance too much.", , Horizontal Layout of Buildings: In general,, buildings with simple geometry in plan (Figure 2a), have performed well during strong earthquakes., Buildings with re-entrant corners, like those U, V, H, and + shaped in plan (Figure 2b), have sustained, significant damage. Many times, the bad effects of, these interior corners in the plan of buildings are, avoided by making the buildings in two parts. For, example, an L-shaped plan can be broken up into two, rectangular plan shapes using a separation joint at the, junction (Figure 2c). Often, the plan is simple, but the, columns/walls are not equally distributed in plan., Buildings with such features tend to twist during, earthquake shaking. A discussion in this aspect will be, presented in the upcoming IITK-BMTPC Earthquake Tip, 7 on How Buildings Twist During Earthquakes?, , Architectural Features, , A desire to create an aesthetic and functionally, efficient, , structure, , drives, , architects, , to, , conceive, , wonderful and imaginative structures. Sometimes the, sliape of the building catches the eye of the visitor,, sometimes the structural system appeals, and in other, occasions both shape and structural system work together, to make the structure a marvel. However, each of these, , choices of shapes and structure has significant bearing, on the performance of the building during strong, earthquakes. The wide range of structural damages, observed during past earthquakes across the world is, very educative in identifying structural configurations, that are desirable versus those which must be avoided., , Size of Buildings: In tall buildings with large, height-to-base size ratio (Figure la), the horizontal, movement of the floors during ground shaking is, large. In short but very long buildings (Figure lb), the, damaging effects during earthquake shaking are, many. And, in buildings with large plan area like, warehouses (Figure lc), the horizontal seismic forces, can be excessive to be carried by columns and walls., taccoocaoocc, I I :, , 1, , ;, , •, , dd•a, , o, , u, , n, , n, , n, , d, , n, , P (b) too long, , I'l'I'I'I'I'I'I'I'I'I'I'I'I'T'I'l'I'I'I'l, [•l-M-l-M-l-l>l-M-M*M-M-t-l-l, , (a) too tall, , •*•'$) f00 iarge /n p/an, , Figure 1: Buildings with one of their overall sizes, much larger or much smaller than the other, , two, do not perform well during earthquakes., , (b) Corners, and Curves, :: poor, , (c) Separation joints make complex plans, into simple plans, , Figure 2: Simple plan shape buildings do well, during earthquakes., , Vertical Layout of Buildings: The earthquake, forces developed at different floor levels in a building, need to be brought down along the height to the, ground by the shortest path; any deviation or, discontinuity in this load transfer path results in poor, performance of the building. Buildings with vertical, setbacks (like the hotel buildings with a few storeys, wider than the rest) cause a sudden jump in, earthquake forces at the level of discontinuity (Figure, 3a). Buildings that have fewer columns or walls in a, , particular storey or with unusually tall storey (Figure, 3b), tend to damage or collapse which is initiated in, 11

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IITK-BMTPC Earthquake Tip 6, How Architectural Features Affect Buildings During Earthquakes?, W 2, that storey. Many buildings with an open ground, Adjacency of Buildings: When two buildings are, store)- intended for parking collapsed or were severely, too close to each other, they may pound on each other, damaged in Gujarat during the 2001 Bhuj earthquake., during strong shaking. With increase in building, Buildings on slopy ground have unequal height, height, this collision can be a greater problem. When, columns along the slope, which causes ill effects like, building heights do not match (Figure 4), the roof of, twisting and damage in shorter columns (Figure 3c)., the shorter building may pound at the mid-height of, Buildings with columns that hang or float on beams at, the column of the taller one; this can be very, an intermediate storey and do not go all the way to the, dangerous., foundation, have discontinuities in the load transfer, , path (Figure 3d). Some buildings have reinforced, concrete walls to carry the earthquake loads to the, foundation. Buildings, in which these walls do not go, all the way to the ground but stop at an upper level,, are liable to get severely damaged during earthquakes., , «, , i, , r, , ^, , *>, , H"W, , ,, , •••, , •, , •, , r, , ,, , "., , •, , >, , ', , **, , 1, , ., , ,, , p, , TV, , '•, , DODDDDDODU, , Figure 4: Pounding can occur between adjoining, buildings due to horizontal vibrations of the, two buildings., , DDDDDDDDDD, DDDDODDODD, OOOOODDDOO, , (a) Setbacks, , Building Design and Codes..., , • •••, DDDD, nana, , D, m, , I Unusually, Tall, , Storey, , (b) Weak or Flexible Storey, , 1, , JLH, (c) Slopy Ground (d) Hanging or Floating Columns, , Looking ahead, of course, one will continue to, make buildings interesting rather than monotonous., However, this need not be done at the cost of poor, behaviour and earthquake safety of buildings., Architectural, , features, , that, , are, , detrimental, , to, , earthquake response of buildings should be avoided. If, not, they must be minimised. When irregular features, are included in buildings, a considerably higher level, of engineering effort is required in the structural, design and yet the building may not be as good as one, with simple architectural features., Decisions made at the planning stage on building, configuration are more important, or are known to, have made greater difference, than accurate, determination of code specified design forces., Resource Material, , Amold.C. and Reitherman.R., (1982), Building Configuration and, Seismic Design, John Wiley, USA, Lagorio.HJ, (1990), EARTHQUAKES An Architect's Guide to NonStructural Seismic Hazard, John Wiley & Sons, Inc., USA, , Next Upcoming Tip, How Buildings Twist During Earthquakes?, , Reinforced, Concrete Wall, Discontinued in, , Ground Storey, , r, , r, , i, , TT, , (e) Discontinuing Structural Members, , |Figure 3: Sudden deviations in load transfer path, along the height lead to poor performance of, buildings., , (i Authored by:, C.V.R.Murty, Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of ITT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceeiaiitk.ac.in. Visit www.nicee.org or, www.bmtpc.org. tosee previous IITK-BMTPC Earthquake Tips., September 2002, , 12-

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Learning, Earthquake Design, , HTK - hmlPC, Earthquake Tip, , ami, Construction, , How Buildings Twist During Earthquakes?, Why a Building Twists, In your childhood, you must have sat on a rope, swing - a wooden cradle tied with coir ropes to the, sturdy branch of an old tree. The more modern, versions of these swings can be seen today in the, children's parks in urban areas; they have a plastic, , Uniform Movement, of Floor, , cradle tied with steel chains to a steel framework., , Consider a rope swing that is tied identically with two, equal ropes. It swings equally, when you sit in the, middle of the cradle. Buildings too are like these rope, swings; just that they are inverted swings (Figure 1)., The vertical walls and columns are like the ropes, and, the floor is like the cradle. Buildings vibrate back and, forth during earthquakes. Buildings with more than, one storey are like rope swings with more than one, cradle., , Identical Vertica., Members, , Figure 2: Identical vertical members placed, , uniformly in plan of building cause all points |, on the floor to move by same amount., , Again, let us go back to the rope swings on the, tree: if you sit at one end of the cradle, it hoists (i.e.,, moves more on the side you are sitting). This also, happens sometimes when more of your friends bunch, together and sit on one side of the swing. Likewise, if, the mass on the floor of a building is more on one side, (for instance, one side of a building may have a storage, or a library), then that side of the building moves more, under ground movement (Figure 3). This building, moves such that its floors displace horizontally as well, as rotate., , ^s^_/, , -:S:y:y:y:S:y:y:y:y:y:y:y:y:y:y:y:y:y:y:::----, , --.••.••.••.•.•.••.••.•, , (a) Single-storey building (b) Three-storey building, Figure 1: Rope swings and buildings, both swing, back-and-forth when shaken horizontally. The, former are hung from the top, while the latter, are raised from the ground., , Thus, if you see from sky, a building with identical, vertical members and that are uniformly placed in the, two horizontal directions, when shaken at its base in a, , certain direction, swings back and forth such that all, points on the floor move horizontally by the same, amount in the direction in which it is shaken (Figure 2)., , /, Light Side, of Building, , •, , •, , •, , •, , •, , •, , •, •, , •, , •, , •, , •, , •, , Earthquake, Ground Shaking, , f, , •, , •, , a], , •, , •, •, •, , •, , •, , •, , •, , •, , •, , •, , •, Heavy Side, of Building, , Figure 3: Even if vertical members are placed, uniformly in plan of building, more mass on, one side causes the floors to twist., -13

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IITK-BMTPC Earthquake Tip 7, How Buildings Twist During Earthquakes?, Once more, let us consider the rope swing on the, tree. This time let the two ropes with which the cradle, is tied to the branch of the tree be different in length., Such a swing also twists even if you sit in the middle, (Figure 4a). Similarly, in buildings with unequal, structural members (i.e., frames and/or walls) also the, floors twist about a vertical axis (Figure 4b) and, displace horizontally. Likewise, buildings, which have, walls only on two sides (or one side) and flexible, frames along the other, twist when shaken at the, ground level (Figure 4c)., , JhUBL, , IEarthquake, Ground, , Shaking, , Figure 5: One-side open ground storey building, twists during earthquake shaking., , What Twist does to Building Members, Twist in buildings, called torsion by engineers,, makes different portions at the same floor level to, move horizontally by different amounts. This induces, more damage in the frames and walls on the side that, moves more (Figure 6). Many buildings have been, severely affected by this excessive torsional behaviour, during past earthquakes. It is best to minimize (if not, completely avoid) this twist by ensuring that buildings, have symmetry in plan (i.e., uniformly distributed, mass and uniformly placed lateral load resisting, systems). If this twist cannot be avoided, special, , •.•«§f$g£3.«<, , (a) Swing with unequal ropes, , calculations, , need, , to be done to account for, , this, , additional shear forces in the design of buildings; the, Indian seismic code (IS 1893, 2002) has provisions for, such calculations. But, for sure, buildings with twist, will perform poorly during strong earthquake shaking., , Vertical Axis about, , which building twists, , TT, , Earthquake, Ground, Movement, , t, , TT, , TT, , •, , D, , D, , Earthquake, , iUl, , Ground, , .£>«, , ...,, , TT, •, , •:•", , -D., , Movement, , (b) Building on slopy ground, , These columns are more vulnerable, , Figure 6: Vertical members of buildings that move, more horizontally sustain more damage., , '. Wall, , Wall, , Resource Material, Arnold.C, and Reitherman.R., (1982), Building Configuration and, Seismic Design,John Wiley, USA, , Lagorio.HJ, (1990), EARTHQUAKES An Architect's Guide to NonStructural Seismic Hazard. John Wiley & Sons, Inc., USA, , Next Upcoming Tip, , Wall, , What is the Seismic Design Philosophy for Buildings?, Beam, , Beam^, , Columns, , (c) Buildings with walls on two/one sides (in plan), Figure 4: Buildings have unequal vertical, members; they cause the building to twist, about a vertical axis., , Buildings that are irregular shapes in plan tend to, twist under earthquake shaking. For example, in a, propped overhanging building (Figure 5), the, overhanging portion swings on the relatively slender, columns under it. The floors twist and displace, horizontally., 14, , Authored by:, C.V.R.Murtv, , Indian Instituted Irchnology Kanpur, Kanpur, India, Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of ITT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceeiaiitk.ac.in. Visit www.nicee.urg or, wtvw.bmlpc.org. to seeprevious IITK-BMTPC Earthquake Tips., October 2002; September 2005

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Learning, Earthquake Design, , HTK - bmlc, Earthquake Tip, , and, , Construction, , What is the Seismic Design Philosophy for Buildings?, The Earthquake Problem, Severity of ground shaking at a given location, during an earthquake can be minor, moderate and, , may sustain severe (even irreparable) damage, but, the building should not collapse., , strong. Relatively speaking, minor shaking occurs, frequently, moderate shaking occasionally and strong, shaking rarely. For instance, on average annually, about 800 earthquakes of magnitude 5.0-5.9 occur in, the world while the number is only about 18 for, magnitude range 7.0-7.9 (see Table 1 of IITK-BMTPC, Earthquake Tip 03 at ivww.nicee.org). So, should we, design and construct a building to resist that rare, earthquake shaking that may come only once in 500, years or even once in 2000 years at the chosen project, site, even though the life of the building itself may be, only 50 or 100 years? Since it costs money to provide, additional earthquake safety in buildings, a conflict, arises: Should we do away with the design of buildingsfor, earthquake effects? Or should we design the buildings to be, "earthquake proof wherein there is no damage during the, strong but rare earthquake shaking? Clearly, the former, approach can lead to a major disaster, and the second, approach is too expensive. Hence, the design, philosophy should lie somewhere in between these, two extremes., , Earthquake-Resistant Buildings, The engineers do not attempt to make earthquakeproof buildings that ivill not get damaged even during, the rare but strong earthquake; such buildings will be, too robust and also too expensive. Instead, the, engineering intention is to make buildings earthquakeresistant; such buildings resist the effects of ground, shaking, although they may get damaged severely but, would not collapse during the strong earthquake., Thus, safety of people and contents is assured in, earthquake-resistant buildings, and thereby a disaster, is avoided. This is a major objective of seismic design, codes throughout the world., , Earthquake Design Philosophy, The earthquake design philosophy may be, summarized as follows (Figure 1):, (a) Under minor but frequent shaking, the main, members of the building that carry vertical and, horizontal forces should not be damaged; however, building parts that do not carry load may sustain, repairable damage., (b) Under moderate but occasional shaking, the main, members may sustain repairable damage, while the, other parts of the building may be damaged such, that they may even have to be replaced after the, earthquake; and, (c) Under strong but rare shaking, the main members, , Figure 1: Performance objectives under different, intensities of earthquake shaking - seeking, , low repairable damage under minor shaking and, collapse-prevention under strong shaking., , Thus, after minor shaking, the building will be, fully operational within a short time and the repair, costs will be small. And, after moderate shaking, the, building will be operational once the repair and, strengthening of the damaged main members is, completed. But, after a strong earthquake, the building, may become dysfunctional for further use, but will, stand so that people can be evacuated and property, recovered., , The consequences of damage have to be kept in, view in the design philosophy. For example, important, buildings, like hospitals and fire stations, play a critical, role in post-earthquake activities and must remain, functional immediately after the earthquake. These, structures must sustain very little damage and should, be designed for a higher level of earthquake, protection. Collapse of dams during earthquakes can, cause flooding in the downstream reaches, which itself, can be a secondary disaster. Therefore, dams (and, similarly, nuclear power plants) should be designed, for still higher level of earthquake motion., , Damage in Buildings: Unavoidable, Design of buildings to resist earthquakes involves, controlling the damage to acceptable levels at a reasonable, , cost. Contrary to the common thinking that any crack, in the building after an earthquake means the building, is unsafe for habitation, engineers designing, earthquake-resistant buildings recognize that some, 15

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IITK-BMTPC Earthquake Tip 8, What is the Seismic Design Philosophy for Buildings?, , damage is unavoidable. Different types of damage, (mainly visualized though cracks; especially so in, concrete and masonry buildings) occur in buildings, during earthquakes. Some of these cracks are, acceptable (in terms of both their size and location),, , page 2, , factors affecting the building performance. Thus,, earthquake-resistant design strives to predetermine, the locations where damage takes place and then to, provide good detailing at these locations to ensure, , ductile behaviour of the building., , while others are not. For instance, in a reinforced, , concrete frame building with masonry filler walls, , Ductile, , between columns, the cracks between vertical columns, , Performpnc^, , and masonry filler walls are acceptable, but diagonal, cracks running through the columns are not (Figure 2)., In general, qualified technical professionals are, knowledgeable of the causes and severity of damage, in earthquake-resistant buildings., , Brittle, , Collapse, , 17, Horizontal Movement of Roof of Building, relative to its base, , (a) Building performances during earthquakes:, two extremes - the ductile and the brittle., , Figure 2: Diagonal cracks in columns jeopardize, , vertical load carrying capacity of buildings unacceptable damage., , Earthquake-resistant design is therefore concerned, , about ensuring that the damages in buildings during, earthquakes are of the acceptable variety, and also that, they occur at the right places and in right amounts., This approach of earthquake-resistant design is much, like the use of electrical fuses in houses: to protect the, entire electrical wiring and appliances in the house, you, sacrifice some small parts of the electrical circuit, called, fuses; these fuses are easily replaced after the electrical overcurrent. Likewise, to save the building from collapsing,, you need to allow some pre-determined parts to, undergo the acceptable type and level of damage., , Acceptable Damage: Ductility, So, the task now is to identify acceptable forms of, damage and desirable building behaviour during, earthquakes. To do this, let us first understand how, , I, , •JW~, (b) Brittle failure of a reinforced concrete, column, , Figure 3: Ductile and brittle structures - seismic, , design attempts to avoid structures of the latter, kind., Resource Material, , Naeim.F., Ed., (2001), The Seismic Design Handbook, Kluwer Academic, Publishers, USA, , Ambrose,J., and Vergun.D., (1999), Designfor Earthquakes, John Wiley, & Sons, Inc., USA, , Next Upcoming Tip, How to make buildings ductile for good seismic performance?, , different materials behave. Consider white chalk used, , to write on blackboards and steelpins with solid heads, used to hold sheets of paper together. Yes... a chalk, breaks easily'.'. On the contrary, a steel pin allows it to be, bent back-and-forth. Engineers define the property that, allows steel pins to bend back-and-forth by large, amounts, as ductility; chalk is a brittle material., Earthquake-resistant buildings, particularly their, main elements, need to be built with ductility in them., Such buildings have the ability to sway back-and-forth, during an earthquake, and to withstand earthquake, effects with some damage, but without collapse, (Figure 3). Ductility is one of the most important, , Authored by:, C.V.R.Mum, , Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by:, Building Materials and Technology Promotion, Council. New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicee(aiitk.ac.in. Visit www.nicee.org or, www.bmtpc.org. to seeprevious IITK-BMTPC Earthquake Tips., November 2002, , 16

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IITK - bmfc, Earthquake Tip, How to Make Buildings Ductile for Good Seismic Performance?, Construction Materials, , In India, most non-urban buildings are made in, masonry. In the plains, masonrv is generally made of, burnt clay bricks and cement mortar. However, in hilly, areas, stone masonry with mud mortar is more, prevalent; but, in recent times, it is being replaced with, cement mortar. Masonry can carry loads that cause, compression (i.e., pressing together), but can hardly take, load that causes tension (i.e.. pulling apart) (Figure 1)., , Compression, , Concrete is used in buildings along with steel, reinforcement bars. This composite material is called, reinforced cement concrete or simplv reinforced concrete, (RC). The amount and location of steel in a member, should be such that the failure of the member is by, steel reaching its strength in tension before concrete, reaches its strength in compression. This type of, failure is ductile failure, and hence is preferred over a, failure where concrete fails first in compression., Therefore, contrary to common thinking, providing, too much steel in RC buildings can be harmful even!!, , Capacity Design Concept, , Tension, , Let us take two bars of same length and crosssectional area - one made of a ductile material and, , another of a brittle material. Now, pull these two bars, , until they break!! You will notice that the ductile bar, elongates bv a large amount before it breaks, while the, brittle bar breaks suddenlv on reaching its maximum, strength at a relatively small elongation (Figure 2)., Amongst the materials used in building construction,, steel is ductile, while masonrv and concrete are brittle., , Strong, , Figure 1: Masonry is strong in compression but, weak in tension., , Concrete, , is, , another, , material, , that, , has, , been, , popularly used in building construction particularly, over the last four decades. Cement concrete is made of, , crushed stone pieces (called aggregate), sand, cement, and water mixed in appropriate proportions. Concrete, , is much stronger than masonry under compressive, loads, but again its behaviour in tension is poor. The, properties of concrete critically depend on the amount, of water used in making concrete; too much and too, little water, both can cause havoc. In general, both, masonry and concrete are brittle, and fail suddenly., Steel is used in masonry and concrete buildings as, , reinforcement bars of diameter ranging from 6mm to, , Final, , Elongation, is large, , Elongation of Bar, , 40mm. Reinforcing steel can carrv both tensile and, compressive' loads. Moreover, steel is a ductile material., , This important property of ductility enables steel bars, to undergo largeelongation beforebreaking., , Figure 2: Tension Test on Materials - ductile, versus brittle materials., , •17

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IITK-BMTPC Earthquake Tip 9, How to Make Buildings Ductile for Good Seismic Performance?, , PaSe2, , Now, let us make a chain with links made of brittle, , Weak Beam, , and ductile materials (Figure 3). Each of these links will, fail just like the bars shown in Figure 2. Now, hold the, , L, , last link at either end of the chain and apply a force F., , t, , Since the same force F is being transferred through all, , -Weak Column, , m, , the links, the force in each link is the same, i.e., F. As, , more and more force is applied, eventually the chain, , ductile link is the iveak one (i.e., its capacity to take load, is less), then the chain will show large final elongation., Instead, if the brittle link is the weak one, then the, , i, , Strong, , will break when the weakest link in it breaks. If the, , 'Column, , u, , chain will fail suddenly and show small final, elongation. Therefore, if we want to have such a ductile, , 5fong-Column, , chain, we have to make the ductile link to be the, , Design, , Weak-Beam, , weakest link., , Strong, Beam, , i, , 1/, , Strong-Beam, Design, , 7, , Figure 4: Reinforced Concrete Building Design:, , Original Chain, , the beams must be the weakest links and not, , the columns - this can be achieved by, appropriately sizing the members and providing, correct amount of steel reinforcement in them., Brittle Links, , Ductile Link, , Quality Control in Construction, The capacity design concept in earthquakeresistant design of buildings will fail if the strengths of, , Loaded Chain, , the brittle links fall below their minimum assured, , Brittle Links, Ductile Link, , stretches by, yielding before, breaking, , do not yield, , Figure 3: Ductile chain design., , Earthquake-Resistant Design of Buildings, Buildings should be designed like the ductile, chain. For example, consider the common urban, residential apartment construction - the multi-storey, building made of reinforced concrete. It consists of, horizontal and vertical members, namely beams and, columns. The seismic inertia forces generated at its, floor levels are transferred through the various beams, and columns to the ground. The correct building, components need to be made ductile. The failure of a, column can affect the stability of the whole building,, but the failure of a, , beam causes localized effect., , values. The strength of brittle construction materials,, like masonry and concrete, is highly sensitive to the, quality of construction materials, workmanship,, supervision, and construction methods. Similarly,, special care is needed in construction to ensure that, the elements meant to be ductile are indeed provided, with features that give adequate ductility. Thus, strict, adherence to prescribed standards of construction, materials and construction processes is essential in, assuring an earthquake-resistant building. Regular, testing of construction materials at qualified, laboratories (at site or away), periodic training of, workmen at professional training houses, and on-site, evaluation of the technical work are elements of good, quality control., Resource Material, , Paulay.T., and Priestley,M.J.N„ (1992), Seismic Design of Reinforced, Concrete Buildings and Masonry. John Wiley, USA, , Mazzolani.F.M., and Piluso.V., (19%), Theory and Design of SeismicResistant Steel Frames, E&FN Spon, UK, , Next Upcoming Tip, How flexibility of buildings affects their earthquake response?, , Therefore, it is better to make beams to be the ductile, , weak links than columns. This method of designing RC, buildings is called the strong-column weak-beam design, method (Figure 4)., , By using the routine design codes (meant for, design against non-earthquake effects), designers may, , Authored by:, C \ R Murty, , Indian Institute of Technology Kanpur, Kanpur, India, , Sponsored by:, , not be able to achieve a ductile structure. Special, , Building Materials and Technology Promotion, , design provisions are required to help designers, improve the ductility of the structure. Such provisions, are usually put together in the form of a specialseismic, design code, e.g., IS:13920-1993 for RC structures., , Council, New Delhi, India, , These codes also ensure that adequate ductility is, , provided in the members where damage is expected., 18, , This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceejaiitk.ac. in. Visit www.nicee.orp or, , www.bmtpc.org, t<> seeprevious IITK-BMTPC Earthquake Tips., December 2002

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IITK - brnlpc, Earthquake Tip, How Flexibility of Buildings Affects their Earthquake Response?, Oscillations of Flexible Buildings, When the ground shakes, the base of a building, moves with the ground, and the building swings backand-forth. If the building were rigid, then every point, in it would move by the same amount as the ground., But, most buildings are flexible, and different parts, move back-and-forth by different amounts., Take a fat coir rope and tie one end of it to the roof, of a building and its other end to a motorized vehicle, (say a tractor). Next, start the tractor and pull the, building; it will move in the direction of pull (Figure, la). For the same amount of pull force, the movement, is larger for a more flexible building. Now, cut the, rope! The building will oscillate back-and-forth, horizontally and after some time come back to the, original position (Figure lb); these oscillations are, periodic. The time taken (in seconds) for each complete, cycle of oscillation (i.e., one complete back-and-forth, motion) is the same and is called Fundamental Natural, Period T of the building. Value of T depends on the, building flexibility and mass; more the flexibility, the, longer is the T, and more the mass, the longer is the T., In general, taller buildings are more flexible and have, larger mass, and therefore have a longer T. On the, contrary, low- to medium-rise buildings generally, have shorter T (less than 0.4 sec)., , Fundamental natural period T is an inherent, property of a building. Any alterations made to the, building will change its T. Fundamental natural, periods T of normal single storey to 20 storey, buildings are usually in the range 0.05-2.00 sec. Some, examples of natural periods of different structures are, shown in Figure 2., , 15 Storey Building:, 1 sec, Reinforced, Concrete, , Chimney:, 2 sec, , L, Elevated Water Tank: 4 sec, , m, Large, , Concrete Gravity Dam:, O.Bsec, , mymmmmmmm^^^^^M, (a) Building pulled with a rope tied at its roof, Root, , Displacement, , Suspension Bridge: 6 sec, MMtrtf"""- Newmark. (1970), Currenttrends in the SeismK, , Anal/sisandDesign ot High RiseStructures, Chapter IS, In, Mflegel. (1970), Earthquake Engineering, Prentice Hall. USA., Inverted Pendulum Model, , (b) Oscillation of building on cutting the rope, , Figure 1: Free vibration response of a building:, the back-and-forth motion is periodic., ,, , Figure 2: Fundamental natural periods of, structures differ over a large range. The, naturalperiod values are only indicative;, depending on actual properties of the structure,, , natural period may vary considerably., -19

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IITK-BMTPC Earthquake Tip 10, _page2, , How Flexibility of Buildings Affects their Earthquake Response?, , Importance of Flexibility, The ground shaking during an earthquake, contains a mixture of many sinusoidal waves of, different frequencies, ranging from short to long, periods (Figure 3). The time taken by the wave to, complete one cycle of motion is called period of the, earthquake wave In general, earthquake shaking of the, ground has waves whose periods vary in the range, 0.03-33sec. Even within this range, some earthquake, waves are stronger than the others. Intensity of, , ••/••/•-/••.••7-V'V-v, , Earthquake Shaking £££££:, (a) Buildings in a city lie on different soils, , earthquake waves at a particular building location, depends on a number of factors, including the, magnitude of the earthquake, the epicentral distance, and, the type of ground that the earthquake waves travelled, through before reaching the location of interest., , 50, , 10-14 Storey, Buildings, , .)-., , 3-5 Storey, , Buildings, , Short, , 20, , I, , Time, , Period, Wave, , f., , 10, 50, , 100, , 150, , 200, , Long, , l/TX, , Wave, , r^7, , 300, , (b) Intensity of damage depends on thickness of, underlying soil layer: 1967 Caracas Earthquake, Figure 4: Different Buildings Respond Differently, , Amplitude, Period, , 250, , Depth of Soil (m), , Time, , to Same Ground Vibration., Time, , In a typical city, there are buildings of many, different sizes and shapes. One way of categorizing, them is by their fundamental natural period T. The, ground motion under these buildings varies across the, city (Figure 4a). If the ground is shaken back-and-forth, , Flexible buildings undergo larger relative, horizontal displacements, which may result in damage, to various nonstructural building components and the, contents. For example, some items in buildings, like, glass windows, cannot take large lateral movements,, and are therefore damaged severely or crushed., Unsecured shelves might topple, especially at upper, stories of multi-storey buildings. These damages may, not affect safety of buildings, but may cause economic, losses, injuries and panic among its residents., , by earthquake waves that hJRre short periods, then, , Related IITK-blfiTPC Tip, , ' long, , Figure 3: Strong Earthquake Ground Motion is, transmitted by waves of different periods., -, , short period buildings will have large, , response., , Similarly, if the earthquake ground motion has long, period waves, then long period buildings will have, larger response. Thus, depending on the value of T of, the buildings and on the characteristics of earthquake, ground motion (i.e., the periods and amplitude of the, earthquake waves), some buildings will be shaken, more than the others., , IITK-BMTPC Earthquake lip 2: time the Ground Shakes?, , IITK-BMTPC Earthquake Tip 5: What are the Seismic Effects on, Structures?, , Resource Material, , Wiegel.R., (1970), Earthquake Engineering, Prentice Hall Inc., USA, Chopra.A.K... (1980), Dynamics of Structures - A Primer. Earthquake, Engineering Research Institute. USA, , Next Upcoming Tip, What are the Indian Seismic Gules?, , During the 1967 Caracas earthquake in South, America, the response of buildings was found to, depend on the thickness of soil under the buildings., Figure 4b shows that for buildings 3-5 storeys tall, the, damage intensity was higher in areas with underlying, , Authored by:, C.V.R.Murty, Indian Institute of Technology Kanpur, Kanpur, India, , soil cover of around 40-60m thick, but was minimal in, , areas with larger thickness of soil cover. On the other, hand, the damage intensity was just the reverse in the, case of 10-14 storey buildings; the damage intensity, was more when the soil cover was in the range 150300m. and small for lower thickness of soil cover., , Here, the soil layerunder the buildingplays the roleof, a filter, allowing some ground waves to pass through, and filtering the rest., 20, , Sponsored by., Building Materials and Technology Promotion, , ^, , Council, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceetaiitk.ac.in. Visit www.nicee.org or, , www.bmtpc.org, tosee previous IITK-BMTPC Earthquake Tips., January 2003

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Learning, Earthquake Design, , HTK - hlnlPC, Earthquake Tip, , and, , Const ruction, What are the Indian Seismic Codes?, Importance of Seismic Design Codes, Ground, , vibrations during earthquakes cause, , forces and deformations in structures. Structures need, , to be designed to withstand such forces and, deformations. Seismic codes help to improve the, behaviour of structures so that they may withstand the, earthquake effects without significant loss of life and, property. Countries around the world have, procedures outlined in seismic codes to help design, engineers in the planning, designing, detailing and, constructing of structures. An earthquake-resistant, building has four virtues in it, namely:, (a) Good Structural Configuration: Its size, shape and, structural system carrying loads are such that they, ensure a direct and smooth flow of inertia forces to, , the ground., (b) Lateral Strength: The maximum lateral (horizontal), force that it can resist is such that the damage, induced in it does not result in collapse., (c) Adequate Stiffness: Its lateral load resisting system is, such that the earthquake-induced deformations in, it do not damage its contents under low-tomoderate shaking., (d)G(H>d Ductility: Its capacity to undergo large, deformations under severe earthquake shaking, even after yielding, is improved by favourable, design and detailing strategies., Seismic codes cover all these aspects., , IS 13935, 1993, Indian Standard Guidelines for Repair and, SeismicStrengthening of Buildings, The regulations in these standards do not ensure, that structures suffer no damage during earthquake of, all magnitudes. But, to the extent possible, they ensure, that structures are able to respond to earthquake, shakings of moderate intensities without structural, , damage and of heavy intensities without total collapse., IS 1893, , IS 1893 is the main code that provides the seismic, zone map (Figure 1) and specifies seismic design force., This force depends on the mass and seismic coefficient, of the structure; the latter in turn depends on, properties like seismic zone in which structure lies,, importance of the structure, its stiffness, the soil on, which it rests, and its ductility. For example, a, building in Bhuj will have 2.25 times the seismic, design force of an identical building in Bombay., Similarly, the seismic coefficient for a single-storey, , building may have 2.5 times that of a 15-storey, building., , Indian Seismic Codes, , Seismic codes are unique to a particular region or, country. Thev take into account the local seismology,, accepted level of seismic risk, building typologies, and, materials and methods used in construction. Further,, , they are indicative of the level of progress a country, has made in the field of earthquake engineering., The first formal seismic code in India, namely IS, 1893, was published in 1962. Today, the Bureau of, Indian Standards (BIS) has the following seismic codes:, IS 1893 (Part I), 2002, Indian Standard Criteria for, Earthquake Resistant Design of Structures (5ln Revision), IS 4326, 1993, Indian Standard Code of Practice for, Earthquake Resistant Design and Construction of, Buildings (2nd Revision), IS 13827, 1993, Indian Standard Guidelines for Improving, Earthquake Resistance of Earthen Buildings, IS 13828, 1993, Indian Standard Guidelines for Improving, Earthquake Resistance of Low Strength Masonry, Buildings, IS 13920, 1993, Indian Standard Code of Practice for, Ductile Detailing of Reinforced Concrete Structures, Subjected to Seismic Forces, , Seismic, Zone, , Figure 1: Seismic Zone Map of India showing, four seismic zones - over 60% of India s land, under seismic zones III. IV and V., , 21

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IITK-BMTPC Earthquake Tip 11, _page2, , What are the Indian Seismic Codes?, , The revised 2002 edition, Part 1 of IS1893, contains, , provisions that are general in nature and those, applicable for buildings. The other four parts of IS, 1893 will cover: Liquid-Retaining Tanks, both elevated, and ground supported (Part 2); Bridges and Retaining, Walls (Part 3); Industrial Structures including StackLike Structures (Part 4); and Dams and Embankments, (Part 5) These four documents are under preparation., In contrast, the 1984 edition of IS1893 had provisions, for all the above structures in a single document., Provisionsfor Bridges, Seismic design of bridges in India is covered in, three codes, namely IS 1893 (1984) from the BIS, 7RC 6, (2000) from the Indian Roads Congress, and Bridge, Rules i!964) from the Ministry of Railways. All, highway bridges are required to comply with IRC 6,, and all railway bridges with Bridge Rules. These three, codes are conceptually the same, even though there, are some differences in their implementation. After the, 2001 Bhuj earthquake, in 2002, the IRC released, interim, provisions, that, make, significant, improvements to the IRC6 (2000) seismic provisions., IS 4326, 1993, , This code covers general principles for earthquake, resistant buildings. Selection of materials and special, features of design and construction are dealt with for, the following types of buildings: timber constructions,, masonry constructions using rectangular masonry, units, and buildings with prefabricated reinforced, concrete roofing/flooring elements., , IS 13935, 1993, , These guidelines cover general principles of, seismic strengthening, selection of materials, and, , techniques, , for repair/seismic, , strengthening of, , masonry and wooden buildings. The code provides a, brief coverage for individual reinforced concrete members, in such buildings, but does not cover reinforced concrete, frame or shear wall buildings as a whole. Some, guidelines are also laid down for non-structural and, , architectural components of buildings., In Closure..., , Countries with a history of earthquakes have well, developed earthquake codes. Thus, countries like, Japan, New Zealand and the United States of America,, , have detailed seismic code provisions. Development of, building codes in India started rather early. Today,, India has a fairly good range of seismic codes covering, a variety of structures, ranging from mud or lowstrength masonry houses to modern buildings., However, the key to ensuring earthquake safety lies in, having a robust mechanism that enforces and, implements these design code provisions in actual, constructions., , Related IITK-HfflK Tip, Tip 4: Whereare the seismic zones in Imlia?, , Tip8: What is theseismicdesign philosophyof buildings?, Tip 9:How to make buildingsductilefor good seismic performance?, Tip10:How flexibility of buildingsaffects their earthquake, response?, , Resource Material, , IS 13827, 1993 and IS 13828, 1993, , Guidelines in IS 13827deal with empirical design, and construction aspects for improving earthquakeresistance of earthen houses, and those in IS 13828 with, , BMTPC, (2000), Guidelines: Improving Earthquake Resistance of Housing,, Building Materials and Technology Promotion Council, New, Delhi, , Bridge Rules, (1964), Rules Specifying the 1-oadsfor the Design of SuperStructure and Sub-Structure of Bridges and for Assessment of the, Strength of Existing Bridges, Government of India, Ministry of, , general principles of design and special construction, features for improving earthquake resistance of, buildings of low-strength masonry. This masonry, includes burnt clay brick or stone masonry in weak, mortars, like clay-mud. These standards are applicable, , IS 456, (2000), Indian Standard Code of Practicefor Plain and Reinforced, , in seismic zones III, IV and V. Constructions based on, , SP 22 (S&T), (1982), Explanatory Handbook on Codes for Earthquakes, , them are termed non-engineered, and are not totally, free from collapse under seismic shaking intensities, VIII (MMI) and higher. Inclusion of features, mentioned in these guidelines may only enhance the, seismic resistance and reduce chances of collapse., India,, , reinforced, , concrete, , structures, , are, , designed and detailed as per the Indian Code IS 456, (2002) However, structures located in high seismic, regions require ductile design and detailing. Provisions, for the ductile detailing of monolithic reinforced, concrete frame and shear wall structures are specified, in IS 13920 (1993). After the 2001 Bhuj earthquake, this, code has been made mandatory for all structures in, zones III, IV and V. Similar provisions for seismic, design and ductile detailing of steel structures are not, yet available in the Indian codes., 22, , Delhi, , Concrete, Bureau of Indian Standards, New Delhi., , Engineering - IS 1893:1975 and IS 4326:1976, Bureau of Indian, Standards. New Delhi, , Next Upcoming Tip, How do masonry buildings behave during earthquakes?, , Authored by., , IS 13920, 1993, In, , Railways (Railway Board), , IRC 6, (2000), Standard Specifications and Code of Practice for Road, Bridges - Section II: Loads and Stresses, Indian Roads Congress, New, , C.V.K.Murh, , Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by., , Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of ITT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, , and with due acknowledgement. Suggestions/comments, , may be sent to: niceeajitk. ac.in. Visit www.nicee.org or, www.bmtpc.org, to seeprevious IITK-BMTPC Earthquake Tips., February 2003

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htk - am, Earthquake Tip, How do brick masonry houses behave during earthquakes?, Behaviour of Brick Masonry Walls, Masonry buildings are brittle structures and one of, the most vulnerable of the entire building stock under, strong earthquake shaking. The large number of, human fatalities in such constructions during the past, earthquakes in India corroborates this. Thus, it is very, important to improve the seismic behaviour of, masonry buildings. A number of earthquake-resistant, features can be introduced to achieve this objective., Ground vibrations during earthquakes cause, inertia forces at locations of mass in the building., These forces travel through the roof and walls to the, foundation. The main emphasis is on ensuring that, these forces reach the ground without causing major, damage or collapse. Of the three components of a, masonry building (roof, wall and foundation) (figure, la), the walls are most vulnerable to damage caused, ^\, , by horizontal forces due to earthquake. A wall topples, down easily if pushed horizontally at the top in a, direction perpendicular to its plane (termed weak, direction), but offers much greater resistance if pushed, along its length (termed strong direction) (Figure lb)., The ground shakes simultaneously in the vertical, and two horizontal directions during earthquakes, (IITK-BMTPC Earthquake Tip 5). However, the, horizontal vibrations are the most damaging to normal, masonry buildings. Horizontal inertia force developed, at the roof transfers to the walls acting either in the, weak or in the strong direction. If all the walls are not, tied together like a box, the walls loaded in their weak, direction tend to topple (Figure 2a)., To ensure good seismic performance, all walls, must be joined properly to the adjacent walls. In this, , way, walls loaded in their weak direction can take, advantage of the good lateral resistance offered by, walls loaded in their strong direction (Figure 2b)., Further, walls also need to be tied to the roof and, , Walls, , foundation to preserve their overall integrity., , Roof, , Toppling, , . - ' S ' S ' .•..•- f . f . t . f . t . J . f . * ., , (a) Basic components of a masonry building, Pushed in the plane of the wall, , J§8r D'rec,'on of, , gJa&*, , earthquake, shaking, , ^^mmmmmmw^, (a) For the direction of earthquake shaking shown., wall B tends to fail, , , Toothed joints, in masonry, , ;A^, , courses, , or L-shaped, , Direction of, , earthquake shaking, , Strong, , S'S' ^^, , dowel bars, , £M, , Toppling, , Direction, , Pushed perpendicular, to the plane of the wall, , ^•'Direction ol, earthquake, shaking, , (b) Direction of force on a wall critically determines, its earthquake performance, Figure 1: Basic components of a masonry, building - walls are sensitive to direction of, earthquake forces., , Direction ol, , ^mmmmm^^, (b) WallB properly connected to WallA (Note: roof, earthquake, , shaking, , is not shown): Walls A (loadedin strong direction), support Walls B (loaded in weak direction), Figure 2: Advantage sharing between walls only possible if walls are well connected., 23

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IITK-BMTPC Earthquake Tip 12, How do brick masonry houses behave during earthquakes?, , How to Improve Behaviour of Masonry Walls, Masonry walls are slender because of their small, , thickness compared to their height and length. A, simple way of making these walls behave well during, earthquake shaking is by making them act together as, a box along with the roof at the top and with the, foundation at the bottom. A number of construction, , aspects are required to ensure this box action. Firstly,, connections between the walls should be good, this, can be achieved by (a) ensuring good interlocking of, the, , masonry courses at the junctions, and (b), horizontal bands at various levels,, particularly at the lintel level. Secondly, the sizes of, door and window openings need to be kept small. The, smaller the openings, the larger is the resistance, offered by the wall. Thirdly, the tendency of a wall to, topple when pushed in the weak direction can be, reduced by limiting its length-to-thickness and heightto-thickness ratios (Figure 3). Design codes specify, limits for these ratios. A wall that is too tall or too long, in comparison to its thickness, is particularly, vulnerable to shaking in its weak direction (Figure 3)., emplo\ ing, , V^2, , Choice and Quality of Building Materials, Earthquake performance of a masonrv wall is very, sensitive to the properties of its constituents, namely, masonry units and mortar. The properties of these, materials vary across India due to variation in raw, materials and construction methods. A variety of, masonry units are used in the country, e.g., clay bricks, (burnt and unburnt), concrete blocks (solid and, hollow), stone blocks. Burnt clay bricks are most, commonly used. These bricks are inherently porous,, and so they absorb water. Excessive porosity is, detrimental to good masonry behaviour because the, bricks suck away water from the adjoining mortar,, which results in poor bond between brick and mortar,, and in difficulty in positioning masonry units. For this, reason, bricks with low porosity are to be used, and, they must be soaked in water before use to minimise, the amount of water drawn away from the mortar., Various mortars are used, e.g., mud, cement-sand,, or cement-sand-lime. Of these, mud mortar is the, , weakest; it crushes easily when dry, flows outward, and has very low earthquake resistance. Cement-sand, mortar with lime is the most suitable. This mortar mix, , Overturning, , provides excellent workability for laying bricks,, stretches without crumbling at low earthquake, shaking, and bonds well with bricks. The earthquake, response of masonry walls depends on the relative, strengths of brick and mortar. Bricks must be stronger, than mortar. Excessive thickness of mortar is not, , Overturning, , wsoirmm, , Soil, , «MiMrWi, , Thick Wall(l'ibnck) 1, , Short Wall 11 brick), , desirable. A 10mm thick mortar layer is generally, satisfactory, from, practical, and, aesthetic, considerations. Indian Standards prescribe the, preferred types and grades of bricks and mortars to be, used in buildings in each seismic zone., , Related ISffllg-HH Earthquake Tip, Tip 5: Whatare the seismic effects on structures?, Resource Material, , Thin Wall (1 brick), , IS 1905, (1987), Indian Standard Code of Practice for Structural Use of, Unretnforced Masonry, Bureau of Indian Standards, New Delhi, IS4326, (1993), Indian Standard Code of Practice for Earthquake Resistant, Design and Construction of Building*, Bureau of Indian Standards,, New Delhi, , Largeportion of wallt, , IS 13828, (1993), Indian Standard Guideline? fur Improving Earthquake, Resistance of LotO-Strengttt Masonry Buildings, Bureau ol Indian, , not supported by, cross walls, , Standards, New Delhi, Cross Wall, , PauIay.T., and PriestleyA1.J.N., (1992), Seismic Design of Reinforced, Concrete and Masonry Buildings, lolui Wilev & Son-.. I IS \, , Next Upcoming Tip, Why should masonry houses have simple structural configuration?, , -0, , Authored by., C.V.R.Murty, , \\f#, lwvm, , mn Short Wall, , Good support offered ,#:••;•&, by cross walls ';-'v;vJv;, , Figure 3: Slender walls are vulnerable - height, and length to be kept within limits. Note: In this, figure, the effect of roof on walls is not shown., , Indian Institute ol Technology Kanpux, Kanpur, India, Sponsored by., Building Materials and technology Promotion, C uuncil, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicee(aiitk.ac.in, , Visit www.nicee.org or, , www.bmtpc.oru, tosee previous IITK-BMTPC Earthquake Tips., March 2003, , 24

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Learning, , HTK - hrnlBE, Earthquake Tip, , Earthquake Design, and, Construction, , Why should masonry buildings have simple structural configuration?, Box Action in Masonry Buildings, Brick masonry buildings have large mass and, hence attract large horizontal forces during earthquake, shaking. They develop numerous cracks under both, compressive and tensile forces caused by earthquake, , shaking. The focus of earthquake resistant masonry, building construction is to ensure that these effects are, sustained without major damage or collapse., Appropriate choice of structural configuration can, help achieve this., , The structural configuration of masonry buildings, includes aspects like (a) overall shape and size of the, building, and (b) distribution of mass and (horizontal), lateral load resisting elements across the building., Large, tall, long and unsymmetric buildings perform, poorly during earthquakes (IITK-BMTPC Earthquake, Tip 6). A strategy used in making them earthquakeresistant is developing good box action between all the, elements of the building, i.e., between roof, walls and, foundation (Figure 1). Loosely connected roof or, unduly slender walls are threats to good seismic, behaviour. For example, a horizontal band introduced, at the lintel level ties the walls together and helps to, make them behave as a single unit., , consider a four-wall system of a single storey masonry, building (Figure 2). During earthquake shaking, inertia, forces act in the strong direction of some walls and in, the weak direction of others (See IITK-BMTPC, Earthquake Tip 12). Walls shaken in the weak direction, seek support from the other walls, i.e., walls Bl and B2, , seek support from walls Al and A2 for shaking in the, direction shown in Figure 2. To be more specific, wall, Bl pulls walls Al and A2, while wall B2 pushes, against them. At the next instance, the direction of, shaking could change to the horizontal direction, perpendicular to that shown in Figure 2. Then, walls A, and B change their roles; Walls Bl and B2 become the, strong ones and Al and A2 weak., Thus, walls transfer loads to each other at their, , junctions (and through the lintel bands and roof)., , Hence, the masonry courses from the walls meeting at, corners must have good interlocking. For this reason,, openings near the wall corners are detrimental to good, seismic performance. Openings too close to wall, corners hamper the flow of forces from one wall to, another (Figure 3). Further, large openings weaken, walls from carrying the inertia forces in their own, plane. Thus, it is best to keep all openings as small as, , possible and as far away from the corners as possible., Good, connection, between roof, , Roof that stays together as a single, 'integral unit during earthquakes, , and walls, Walls with, small, , Inertia force, fmm roof, Inertia force, , from roof, , openings, , Good, connection, "•..•..'.••.., , '.•'.• ,.-,..,.-,..,..,..,..,.."..'..M*..\.<..•..•..•', , Good connection, , between, walls and, foundation, , Regions, , at wall corners', , Figure 1: Essential requirements to ensure box, action in a masonry building., , where load, transfer, , earthquake, , takes place, , shaklna, , from one, wall to, , Influence of Openings, Openings are functional necessities in buildings., However, location and size of openings in walls, assume significance in deciding the performance of, masonry buildings in earthquakes. To understand this,, , another, , Figure 2: Regions of force transfer from weak, , walls to strong walls in a masonry building wall B1 pulls walls A1 and A2, while wall B2, pushes walls A1 and A2., 25

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IITK-BMTPC Earthquake Tip 13, Why should masonry buildings have simple structural configuration?, , jnigc2, , Large window, opening, reduces the, , wall strength, in its strong, direction, , Damage, , Diagonal, bracing, effect, , •^Door opening close to wall corner, weakens the connection between walls, , Figure 3: Openings weaken walls in a masonry, , building -a single closed horizontal band must, be provided above all of them., , Earthquake-Resistant Features, Indian Standards suggest a number of earthquakeresistant measures to develop good box-type action in, masonry buildings and improve their seismic, performance. For instance, it is suggested that a, building having horizontal projections when seen, from the top, e.g., like a building with plan shapes L, T,, E and Y, be separated into (almost) simple rectangular, blocks in plan, each of which has simple and good, earthquake behaviour (IITK-BMTPC Earthquake Tip 6)., During earthquakes, separated blocks can oscillate, independendy and even hammer each other if they are, too close. Thus, adequate gap is necessary between, these different blocks of the building. The Indian, Standards suggest minimum seismic separations, between blocks of buildings. However, it may not be, necessary to provide such separations between blocks,, if horizontal projections in buildings are small, say up, to -15-20% of the length of building in that direction., Inclined staircase slabs in masonry buildings offer, another concern. An integrally connected staircase slab, acts like a cross-brace between floors and transfers, , large horizontal forces at the roof and lower levels, (Figure 4a). These are areas of potential damage in, masonry buildings, if not accounted for in staircase, design and construction. To overcome this, sometimes,, staircases are completely separated (Figure 4b) and, built on a separate reinforced concrete structure., Adequate gap is provided between the staircase tower, and the masonry building to ensure that they do not, pound each other during strong earthquake shaking., Resource Material, , IS 1905, (1987), Indian Standard Code of Practice for Structural Use of, , Unranforccd Masonry, Bureau of Indian Standards, New Delhi, IS 42326. (1993), button Standard Code of Practice for Earthquake, , Resistant Design and Construction of Buildings, Bureau of Indian, , ^^mSDamage, , MtMNMNMMMMMW, (a) Damage in building with rigidly built-in staircase, Reinforced Concrete, Stair Case Tower, , (or Mumly), , (b) Building with separated staircase, Figure 4: Earthquake-resistant detailing of, staircase in masonry building, , - must be carefully designed and constructed., , Related IITK - bHilPE Earthquake Tip, Tip 5: Wliat arethe seismic effects on structures?, Tip 6: How ardiitectural features affect buildings during earthquakes?, Tipl2: How brick masonry houses beltave during earthquakes?, , Next Upcoming Tip, Why are horizontal bands necessary in masonry buildings?, , Authored by:, CV.R.Murtx, , Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by:, , Building Materials and Technology Promotion, Council, New Delhi, India, , Standards, New Delhi, , IS 13828, (1993), Indian Standard Guidelines for Improving Earthquake, , Resistance of Low-strength Masonry Buildings, Bureau of Indian, Standards, New Delhi, , TomazevicM.. (1999), Earthquake Resistant Design of Masonry, , Buildings, Imperial College Press,UK, , This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, may be sent to: mceeiaiitk.ac. in. Visit www.niciv.org or, , www.bmtpc.org. to seeprevious IITK-BMTPC Earthquake Tips., April201)3, , 26

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IITK - bnflPC, Earthquake Tip, , Learning, Earthquake Design, and, Construction, , Why are horizontal bands necessary in masonry buildings?, Role of Horizontal Bands, , flat timber or CGI sheet roof, roof band needs to be, , Horizontal bands are the most important, earthquake-resistant feature in masonry buildings. The, bands are provided to hold a masonry building as a, single unit by tying all the walls together, and are, similar to a closed belt provided around cardboard, boxes. There are four types of bands in a typical, masonry building, namely gable band, roof band, lintel, band and plinth band (Figure 1), named after their, location in the building. The lintel band is the most, important of all, and needs to be provided in almost all, buildings. The gable band is employed only in, buildings with pitched or sloped roofs. In buildings, , provided. In buildings with pitched or sloped roof, the, roof band is very important. Plinth bands are, primarily used when there is concern about uneven, , with flat reinforced concrete or reinforced brick roofs, the, , roof band is not required, because the roof slab also, plays the role of a band. However, in buildings with, , settlement of foundation soil., , The lintel band ties the walls together and creates, a support for walls loaded along weak direction from, walls loaded in strong direction. This band also, reduces the unsupported height of the walls and, thereby improves their stability in the weak direction., During the 1993 Latur earthquake (Central India), the, intensity of shaking in Killari village was IX on MSK, scale. Most masonry houses sustained partial or, complete collapse (Figure 2a). On the other hand, there, was one masonry building in the village, which had a, lintel band and it sustained the shaking very well with, hardly any damage (Figure 2b)., , Roof, , MasonryJ, , C, , above linten, Lintel Band «, , Masonry, below lintel, Wall, , Plinth Band, Foundation, •^^T^J*': •':, , (a) Building with Flat Roof, , Gable-mot, connection, , Root, Band, , Floor-walls, connectioi, , '6:::v6v/y^fifi^J^!fS^enPheral wall, (b) Two-storey Building with Pitched Roof, , Figure 1: Horizontal Bands in masonry building Improve earthquake-resistance., , (b) A building with horizontal lintel band in Killari, village: no damage, , Figure 2: The 1993 Latur Earthquake (Central, India) - one masonry house in Killari village had, horizontal lintel band and sustained the shaking, without damage., 27

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IITK-BMTPC Earthquake Tip 14, Why are horizontal bands necessary in masonry buildings?, , PaSe2, , Design of Lintel Bands, During earthquake shaking, the lintel band, undergoes bending and pulling actions (Figure 3). To, resist these actions, the construction of lintel band, , Wood, , requires special attention. Bands can be made of wood, (including bamboo splits) or of reinforced concrete, (RC) (Figure 4); the RC bands are the best. The straight, lengths of the band must be properly connected at the, wall corners. This will allow the band to support walls, loaded in their weak direction by walls loaded in their, strong direction. Small lengths of wood spacers (in, wooden bands) or steel links (in RC bands) are used to, make the straight lengths of wood runners or steel, bars act together. In wooden bands, proper nailing of, straight lengths with spacers is important. Likewise, in, RC bands, adequate anchoring of steel links with steel, bars is necessary., , Runners, , Pulling of, , Bending of, , Lintel Band, , 'Lintel Band, , (b) RC Band, Figure 4: Horizontal Bands in masonry buildings, - RC bands are the best., , >Wj-S>'i'-"', Direction of, , Related llftKr- inlPC Earthquake Tip, , earthquake, shaking, , Tip 5: Whatare the seismic effects on structures?, Tipl2: How brickmasonry houses behave duringearthquakes?, Tipl3: Why masonry buildings should have simple structural, , configuration?, , J 751, , 150, , !, , mm, , Resource Material, IAEE, (1986), Guidelines for Earthquake Resistant Non-Engineered, , e—^, , Construction,, , International, , Association, , for, , Earthquake, , Engineering, Tokyo, available on www.nicee.org, IS 4326, (1993), Indian Standard Code of Practicefor Earthquake Resistant, , Design and Construction of Buildings, Bureau of Indian Standards,, New Delhi, , Large, , Small, , IS 13828, (1993), Indian Standard Guidelines for Improving Earthquake, , Resistance of Low-strength Masonry Buildings, Bureau of Indian, Standards, New Delhi, , Cross-section of, , Lintel Bands, , Next Upcoming Tip, Why is vertical reinforcement required in masonry buildings?, , Figure 3: Bending and pulling in lintel bandsBands must be capable of resisting these., ^, , ft Authored by:, "•, , Indian Standards, The Indian Standards IS:4326-1993 and IS:13828, , (1993) provide sizes and details of the bands. When, wooden bands are used, the cross-section of runners is, , to be at least 75mmx38mm and of spacers at least, 50mmx30mm. When RC bands are used, the minimum, , thickness is 75mm, and at least two bars of 8mm, , diameter are required, tied across with steel links of at, least 6mm diameter at a spacing of 150mm centers., , C.V.R.MuiK, , Indian Institute of Technology Kanpur, , Kanpur, India, Sponsored by., Building Materials and Technology Promotion, Council, New Delhi, India, , This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nicceiaiitk.ac.in. Visit www.nicee.orB or, , www.bmtpc.org,to see previous IITK-BMTPC Earthquake Tips., May 2003, , 28

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Learning, Earthquake Design, , HTK - bnflpc, Earthquake Tip, , and, , Construction, , Why is vertical reinforcement required in masonry buildings?, Response of Masonry Walls, Horizontal bands are provided in masonry, buildings to improve their earthquake performance., These bands include plinth band, lintel band and roof, band. Even if horizontal bands are provided, masonry, buildings are weakened by the openings in their walls, (Figure 1). During earthquake shaking, the masonry, walls get grouped into three sub-units, namely, spandrel masonry, wall pier masonry and sill masonry., , Lintel, Band, , Plinth^^i^i>ii^i^iili^^(^i^^^ti^^^ Masonry, , Roof, , Band ' •' :::(a) Building Components, , Pier, , Spandrel, Masonry, Lintel, Level, Wall Pier, , *•Masonry, Sill, Level, , Sill, , ' Masonry, Plinth, Level, Foundation, , mmmmm, , r '• '.'• :'• '.*•*.*• *.*•*.*•'.*•*„'•7, Uplifting offtRRRRSUOS, , mSSmmMWm, , masonry, , (b) Rocking of Masonry Piers, , Figure 1: Sub-units in masonry building - walls, behave as discrete units during earthquakes., , Consider a hipped roof building with two window, openings and one door opening in a wall (Figure 2a). It, , X-Cracking, of Masonry, Piers, , has lintel and plinth bands. Since the roof is a hipped, one, a roof band is also provided. When the ground, shakes,, , the, , inertia, , force, , causes, , the, , small-sized, , masonry wall piers to disconnect from the masonry, above and below. These masonry sub-units rock back, and forth, developing contact only at the opposite, diagonals (Figure 2b). The rocking of a masonry pier, can crush the masonry at the corners. Rocking is, possible when masonry piers are slender, and when, weight of the structure above is small. Otherwise, the, piers are more likely to develop diagonal (X-type), shear cracking (Figure 2c); this is the most common, failure type in masonry buildings., In un-reinforced masonry buildings (Figure 3), the, cross-section area of the masonry wall reduces at the, opening. During strong earthquake shaking, the, building may slide just under the roof, below the lintel, , Foundation, , &sij$iliiP, , •2&^#si.Smi$!$M., , (c) X-Cracking of Masonry Piers, Figure 2: Earthquake response of a hipped roof, masonry building - no vertical reinforcement, , ^/sprowotec^nwa//s^^^^^^^^^^^^^^^^, Roof, , Earthquakeinduced inertia, force, , Sliding, , band or at the sill level. Sometimes, the building may, also slide at the plinth level. The exact location of, , sliding depends on numerous factors including, building weight, the earthquake-induced inertia force,, the area of openings, and type of doorframes used., , Foundation, , Figure 3: Horizontal sliding at sill level in a, masonry building - no vertical reinforcement., 29

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IITK-BMTPC Earthquake Tip 15, Why is vertical reinforcement required in masonry buildings?, , How Vertical Reinforcement Helps, Embedding vertical reinforcement bars in the, edges of the wall piers and anchoring them in the, , jmge2, , Earthquake-induced inertia force, , foundation at the bottom and in the roof band at the, , top (Figure 4), forces the slender masonry piers to, undergo bending instead of rocking. In wider wall piers,, the vertical bars enhance their capability to resist, horizontal earthquake forces and delay the X-cracking., Adequate cross-sectional area of these vertical bars, prevents the bar from yielding in tension. Further, the, vertical bars also help protect the wall from sliding as, well as from collapsing in the weak direction., , *%$&, (a) Cracking in building with no corner reinforcement, , Lintel Band, , Bending, , Reinforcement, Bars, , of Pier, Sill Band, , (Similar to ^^, Untel Band.^™, but discontinued, , *wm, , Vertical steel bars anchonad iri!'\, foundation and roof band, , (a) Vertical reinforcement causes bending of, masonry piers in place of rocking (See Figure 2)., , (b) No cracks in building with vertical reinforcement, Figure 5: Cracks at corners of openings in a, masonry building - reinforcement around them, helps., , Related IITK - HuTO Earthquake Tip, Tip5: Whatare the seismic effects on structures?, Tipl2: How brick masonry houses behave during earthquakes?, Tipl3: Why masonry buildings should have simple structural, , configuration?, Tipl4: Why horizontal bandsare required in masonry buildings?, , i1""""""'"": !>, (b) Vertical reinforcement prevents sliding in walls, (See Figure 3)., Figure 4: Vertical reinforcement in masonry walls, - wall behaviour is modified., , Protection of Openings in Walls, Sliding failure mentioned above is rare, even in, unconfined masonry buildings. However, the most, common damage, observed after an earthquake, is, diagonal X-cracking of wall piers, and also inclined, cracks at the corners of door and window openings., When a wall with an opening deforms during, earthquake shaking, the shape of the opening distorts, and becomes more like a rhombus - two opposite, corners move away and the other two come closer., Under this type of deformation, the corners that come, closer develop cracks (Figure 5a). The cracks are bigger, when the opening sizes are larger. Steel bars provided, in the wall masonry all around the openings restrict, these cracks at the corners (Figure 5b). In summary,, lintel and sill bands above and below openings, and, vertical reinforcement adjacent to vertical edges,, , provide protection against this type of damage., 30, , •, , Resource Material, Amrose.J., (1991), Simplified Design of Masonry Structures. John Wiley, & Sons, Inc., USA, , BMTPC, (2000), Guidelines: Improving Earthquake Resistance of, Housing, Building Materials and Technology Promotion Council,, New Delhi, , IS 4326, (1993), Indian Standard Code of Practicefor Earthquake Resistant, Design and Construction of Buildings, Bureau of Indian Standards,, New Delhi, , IS 13828, (1993), Indian Standard Guidelines for Improving Earthquake, Resistance of Low-strength Masonry Buildings, Bureau of Indian, Standards, New Delhi, , Next Upcoming Tip, How to improve seismic behaviour of stone masonry buildings1, , Authored by:, C.V.R.Muitv, , Indian Institute of Technology Kanpur, Kanpur, India, Sponsored by., Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceetaiitk.ac.in. Visit www.nicee.ore or, , www.bmtpc.org. to seeprevious IITK-BMTPC Earthquake Tips., June 200.!

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Learning, Earthquake Design, , HTK - bmliic, Earthquake Tip, , and, , Construction, , How to make Stone Masonry Buildings Earthquake Resistant?, Behaviour during Past India Earthquakes, Stone has been used in building construction in, India since ancient times since it is durable and locally, available. There are huge numbers of stone buildings, in the country, ranging from rural houses to royal, palaces and temples. In a typical rural stone house,, there are thick stone masonry walls (thickness ranges, from 600 to 1200 mm) built using rounded stones from, riverbeds bound with mud mortar. These walls are, , constructed with stones placed in a random manner,, and hence do not have the usual layers (or courses), , masonry dwellings. Likewise, a majority of the over, 13,800 deaths during 2001 Bhuj (Gujarat) earthquake is, attributed to the collapse of this type of construction., The main patterns of earthquake damage include:, (a) bulging/separation of walls in the horizontal, direction into two distinct wythes (Figure 2a), (b), separation of walls at corners and T-junctions (Figure, 2b), (c) separation of poorly constructed roof from, walls, and eventual collapse of roof, and (d), disintegration of walls and eventual collapse of the, whole dwelling., , seen in brick walls. These uncoursed walls have two, , exterior vertical layers (called wythes) of large stones,, filled in between with loose stone rubble and mud, , mortar. A typical uncoursed random (LICR) stone, masonry wall is illustrated in Figure 1. In many cases,, these walls support heavy roofs (for example, timber, root with thick mud overlay)., Vertically split, layer of wall, , Vertical gap, , Vertically split layer, of wall, , <r=3, , Mud mortar, , ^r^, "y Outward bulging, /, , of vertical wall, , layer, Half-dressed, , oblong stones, , Figure 1: Schematic of the wall section of a, traditional stone house - thick walls without, , stones that go across split into 2 vertical layers., , Laypersons may consider such stone masonry, buildings robust due to the large wall thickness and, robust appearance of stone construc'ion. But, these, buildings are one of the most deficient building, systems from earthquake-resistance point of view. The, main deficiencies include excessive wall thickness,, , absence of any connection between the two wythes of, the wall, and use of round stones (instead of shaped, ones). Such dwellings have shown very poor, performance during past earthquakes in India and, other countries (e.g., Greece, Iran, Turkey, former, Yugoslavia). In the 1993 Killari (Maharashtra), earthquake alone, over 8,000 people died, most of, them buried under the rubble of traditional stone, , Earthquake Resistant Features, Low strength stone masonry buildings are weak, against earthquakes, and should be avoided in high, seismic, , zones., , The, , Indian Standard, , IS:13828-1993, , states that inclusion of special earthquake-resistant, design and construction features may raise the, earthquake resistance of these buildings and reduce, the loss of life. However, in spite of the seismic, features these buildings may not become totally free, from heavy damage and even collapse in case of a, major earthquake. The contribution of the each of, these features is difficult to quantify, but qualitatively, these features have been observed to improve the, performance of stone masonry dwellings during past, earthquakes. These features include:, 31

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IITK-BMTPC Earthquake Tip 16, How to make Stone Masonry Buildings Earthquake Resistant?, JUlgeJ, (a) Ensure proper wall construction The wall thickness, resistance, its extensive use is likely to continue due to, should not exceed 450mm. Round stone boulders, tradition and low cost. But, to protect human lives and, should not be used in the construction! Instead, the, property in future earthquakes, it is necessary to, stones should be shaped using chisels and, follow proper stone masonry construction as described, hammers. Use of mud mortar should be avoided in, above (especially features (a) and (b) in seismic zones, higher seismic zones. Instead, cement-sand mortar, III and higher). Also, the use of seismic bands is highly, should be 1:6 (or richer) and lime-sand mortar 1:3 (or, recommended (as described in feature (c) above and in, richer) should be used., IITK-BMTPC Earthquake Tip U)., (b) Ensure proper bond in masonry courses: The masonry, walls should be built in construction lifts not, , exceeding 600mm. Tlirough-stones (each extending, over full thickness of wall) or a pair of overlapping, bond-stones (each extending over at least %ths, thickness of wall) must be used at every 600mm, along the height and at a maximum spacing of 1.2m, along the length (Figure 3)., Wall, , Alternatives to, , Section, , Through Stones, Wood, , < 800mm, , plank \ts., Hooked, ~t>', steel link "=J>, , < BOOmm, Floor, , !••, , Pair of overlapping stones, (each of length at least, Xt*s the wall thickness), , Figure 4: Horizontal lintel band is essential in, random rubble stone masonry walls -, , provides integrity to the dwelling, and holds the, walls together to resist horizontal earthquake, effects., , Related IITK - tifflPC Earthquake Tip, Tipl4: Whyhorizontal bandsare required in masonry buildings?, Resource Material, , Figure 3: Use of "through stones" or "bond, stones" in stone masonry walls - vital in, preventing the wall from separating into wythes., , (c) Prox'ide horizontal reinforcing elements: The stone, masonry dwellings must have horizontal bands, (See IITK-BMTPC Earthquake Tip U for plinth, lintel,, roof and gable bands). These bands can be, constructed out of wood or reinforced concrete, and, , chosen based on economy. It is important to, provide at least one band (either lintel band or roof, band) in stone masonry construction (Figure 4)., (d) Control on overall dimensions and heights: The, unsupported length of walls between cross-walls, should be limited to 5m; for longer walls, cross, supports raised from the ground level called, buttresses should be provided at spacing not more, than 4m. The height of each storey should not, exceed 3.0m. In general, stone masonry buildings, should not be taller than 2 storeys when built in, cement mortar, and 1 storey when built in lime or, mud mortar. The wall should have a thickness of at, , least one-sixth its height., Although, this type of stone masonry construction, practice is deficient with regards to earthquake, , Brzev,S., Greene.M. and Sinha.R. (2001), "Rubble stone masonry, walls with timber walls and timber roof," Worid Housing, Encyclopedia (mmv.uwrld-housmg.net), India/Report 18,, published by EERI and IAEE, , IAEE, (1986), Guidelines for Earthquake Resistant Non-Engineered, Construction, The ACC Limited, Thane, 2001 (See wwiv.niccee.org)., IS 13828, (1993), Indian Standard Guidelines - Improving Earthquake, Resistance of Low-Strength Masonry Buildings, Bureau of Indian, Standards, New Delhi, , Publications of Building Materials and Technology Promotion Council,, New Delhi (www.bmtpc.org):, , (a) Retrofitting of Stone Houses in Marathwada Area ofMaliarashtra, (b) Guidelines For Improving Earthquake Resistance of Housing, (c) Manual for Repair and Reconstruction of Houses Damaged in, , Earthquake in October 1991 in the Garhwal Region of UP, , Next Upcoming Tip, What are the seismic effects on RC frame buildings?, , Authored by., I \ K Murty, Indian Institute ol technology Kanpur, Kanpur, India, , Sponsored by., Building Materials and Technology Promotion, Council, New Delhi, India, This release is a properly of DT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, may be sent to: nice&iiiitk. ac. in. Visit www.nicee.ore or, , www.bmtpc.org, to see previous IITK-BMTPC Earthquake Tips., ]uly 2003, , 32

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Learning, Earthquake Design, , HTK - bnflpc, Earthquake Tip, , and, , Construction, , How do Earthquakes Affect Reinforced Concrete Buildings?, Reinforced Concrete Buildings, In recent times, reinforced concrete buildings have, become common in India, particularly in towns and, cities. Reinforced concrete (or simply RC) consists of, two primary materials, namely concrete with reinforcing, , In most buildings, the geometric distortion of the slab, is negligible in the horizontal plane; this behaviour is, known as the rigid diaphragm action (Figure 2b)., , Structural engineers must consider this during design., , steel bars. Concrete is made of sand, crushed stone (called, , aggregates) and cement, all mixed with pre-determined, amount of water. Concrete can be molded into any, desired shape, and steel bars can be bent into many, shapes. Thus, structures of complex shapes are, possible with RC., A typical RC building is made of horizontal, , members (beams and slabs) and vertical members, (columns and walls), and supported by foundations that, rest on ground. The system comprising of RC columns, and connecting beams is called a RC Frame. The RC, frame participates in resisting the earthquake forces., Earthquake shaking generates inertia forces in the, building, which are proportional to the building mass., Since most of the building mass is present at floor, levels, earthquake-induced inertia forces primarily, develop at the floor levels. These forces travel, downwards - through slab and beams to columns and, •walls, and then to the foundations from where they are, , dispersed to the ground. As inertia forces accumulate, downwards from the top of the building, the columns, and walls at lower storeys experience higher, earthquake-induced forces (Figure 1) and are therefore, designed to be stronger than those in storeys above., , (a) Out-of-plane, Vertical Movement, , (b) In-plane Horizontal Movement, , Figure 2: Floor bends with the beam but moves, all columns at that level together., , After columns and floors in a RC building are cast, and the concrete hardens, vertical spaces between, columns and floors are usually filled-in with masonry, walls to demarcate a floor area into functional spaces, (rooms). Normally, these masonry walls, also called, infill walls, are not connected to surrounding RC, columns and beams. When columns receive horizontal, , forces at floor levels, they by to move in the horizontal, direction, but masonry walls tend to resist this, movement. Due to their heavy weight and thickness,, these walls attract rather large horizontal forces, (Figure 3). However, since masonry is a brittle, material, these walls develop cracks once their ability, to carry horizontal load is exceeded. Thus, infill walls, act like sacrificial fuses in buildings; they develop, cracks under severe ground shaking but help share the, load of the beams and columns until cracking., Earthquake performance of infill walls is enhanced by, mortars of good strength, making proper masonry, courses, and proper packing of gaps between RC, frame and masonry infill walls. However, an infill wall, that is unduly tall or long in comparison to its, thickness can fall out-of-plane (i.e., along its thin, , direction), which can be life threatening. Also, placing, Total Force, , Figure 1: Total horizontal earthquake force in a, building increases downwards along its height., , infills irregularly in the building causes ill effects like, short-column effect and torsion (these will be discussed, in subsequent IITK-BMTPC Earthquake Tips)., , Roles of Floor Slabs and Masonry Walls, Floor slabs are horizontal plate-like elements,, which facilitate functional use of buildings. Usually,, beams and slabs at one storey level are cast together., In residential multi-storey buildings, thickness of slabs, is only about 110-150mm. When beams bend in the, vertical direction during earthquakes, these thin slabs, bend along with them (Figure 2a). And, when beams, move with columns in the horizontal direction, the, , slab usually forces the beams to move together with it., , Figure 3: Infill walls move together with the, columns under earthquake shaking., —, , 33

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IITK-BMTPC Earthquake Tip 17, How do Earthquakes Affect Reinforced Concrete Buildings?, /"W, (which receive forces from columns) should be, Horizontal Earthquake Effects are Different, stronger than columns. Further, connections between, Griwiti/ loading (due to self weight and contents) on, , buildings causes RC frames to bend resulting in, stretching and shortening at various locations. Tension, is generated at surfaces that stretch and compression, at those that shorten (Figure 4b). Under gravity loads,, tension in the beams is at the bottom surface of the, , beam in the central location and is at the top surface at, the ends. On the other hand, earthquake loading causes, tension, , on, , beam, , and, , column, , faces, , at, , locations, , different from those under gravity loading (Figure 4c);, the relative levels of this tension (in technical terms,, , bending moment) generated in members are shown in, Figure 4d. The level of bending moment due to, earthquake loading depends on severity of shaking, and can exceed that due to gravity loading. Thus,, under strong earthquake shaking, the beam ends can, develop tension on either of the top and bottom faces., Since concrete cannot carry this tension, steel bars are, required on both faces of beams to resist reversals of, bending moment. Similarly, steel bars are required on, all faces of columns too., , Strength Hierarchy, For a building to remain safe during earthquake, shaking, columns (which receive forces from beams), should be stronger than beams, and foundations, , beams & columns and columns & foundations should, , not fail so that beams can safely transfer forces to, columns and columns to foundations., , When this strategy is adopted in design, damage is, likely to occur first in beams (Figure 5a). When beams, are detailed properly to have large ductility, the, building as a whole can deform by large amounts, despite progressive damage caused due to consequent, yielding of beams. In contrast, if columns are made, weaker, they suffer severe local damage, at the top and, bottom of a particular storey (Figure 5b). This localized, damage can lead to collapse of a building, although, columns at storeys above remain almost undamaged., Damage^, y*t, , s^l, , 1 Large, , 1 Small, ^ displacement, , B sr collapse, , at collapse, , •, , •Damage, , f^^^^•distributed, , All damage, in one, slorev, , arJ, , _, , (a) Strong Columns, f, Weak Beams, , (b) Weak Column, , }p, , Strong Beam, , Figure 5: Two distinct designs of build ngs that, result in different earthquake perfornl a n c e s Gravity, , I Earthquake I, , columns should be stronger than beam s., Relevant Indian Standards, The Bureau of Indian Standards, New Delhi,, , Stretching of member, and locations of tension, , published the following Indian standards pertaining to, design of RC frame buildings: (a) Indian Seismic Code, (IS 1893 (Part 1), 2002) -for calculating earthquake forces,, (b) Indian Concrete Code (IS 456, 2000) - for design of, RC members, and (c) Ductile Detailing Code for RC, Structures (IS 13920,1993) -for detailing requirements in, seismic regions., Related IITK -HTilPi! Earthquake Tip, Tip 5: What are the seismic effects on structures?, Resource Material, , Englekirk,R.E.,(2003), "Seismic Design of Reinforced and Precast, Concrete Buildings", John Wiley & Sons, Inc., USA, , Penelis.G.C, and Kappos,A.J., (1997), "Earthquake Resistant Concrete, Structures," E&FN SPON, UK, , Next Upcoming Tip, How do Beams in RC Buildings Resist Earthquakes?, Authored, , C.V.R Murt), Indian Institute ol lechnolog) Kanpur, Kanpur, India, , Sponsored by:, Building Materials and Technologj Promotion, ( ouncil. New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, , Figure 4: Earthquake shaking reverses tension, and compression in members - reinforcement is, required on both faces of members., 34-, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceeiaiitk.ac.in Visit www.nioee.org or, , www.bmtpc.org, to see previous IITK-BMTPC Earthquake Tips., August 2003

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Learning, Earthquake Design, , HTK - bmliic, Earthquake Tip, , and, Construction, , How do Beams in RC Buildings Resist Earthquakes?, (b) Shear Failure: A beam may also fail due to shearing, , Reinforcement and Seismic Damage, In RC buildings, the vertical and horizontal, members (i.e., the beams and columns) are built, integrally with each other. Thus, under the action of, loads, they act together as a frame transferring forces, from one to another. This Tip is meant for beams that, are part of a building frame and carry earthquake-, , action. A, , shear crack is inclined at 45° to the, , horizontal; it develops at mid-depth near the, support and grows towards the top and bottom, faces (Figure 2b). Closed loop stirrups are provided, to avoid such shearing action. Shear damage occurs, when the area of these stirrups is insufficient., , induced forces., , Shear failure is brittle, and therefore, shear failure, , Beams in RC buildings have two sets of steel, reinforcement, namely: (a) long straight bars (called, longitudinal bars) placed along its length, and (b) closed, loops of small diameter steel bars (called stirrups), placed vertically at regular intervals along its full, length (Figure 1)., , must be avoided in the design of RC beams., , Vertical Stirrup, Smaller diameter steel, bars that are made into, , lleam, , Design Strategy, Designing a beam involves the selection of /7s, material properties (i.e, grades of steel bars and concrete), , and shape and size; these are usually selected as a part, of an overall design strategy of the whole building., And, the amount and distribution of steel to be provided, in the beam must be determined by performing design, calculations as per is:456-2000 and IS13920-1993., , closed loops and are, , placed at regular, intervals along the full, length of the beam, , Column, , Bottom face stretches in tension, , and vertical cracks develop, , (a), , Flexure Failure, , Inclined crack, , Longitudinal Bar, Larger diameter steel bars that, , go through the full length of the, beam, , Figure 1: Steel reinforcement in beams - stirrups, , Beam, , / \ <5-", , prevent longitudinal bars from bending outwards., (b), , Beams sustain two basic types of failures, namely:, (a)Flexural (or Bending) Failure: As the beam sags under, increased loading, it can fail in two possible ways., If relatively more steel is present on the tension, face, concrete crushes in compression; this is a brittle, failure and is therefore undesirable. If relatively, less steel is present on the tension face, the steel, yields first (it keeps elongating but does not snap, as, steel has ability to stretch large amounts before it, snaps; see IITK-BMTPC Earthquake Tip 9) and, redistribution occurs in the beam until eventually, , the concrete crushes in compression; this is a ductile, failure and hence is desirable. Thus, more steel on, , tension face is not necessarily desirable! The ductile, failure is characterized with many vertical cracks, , starting from the stretched beam face, and going, towards its mid-depth (Figure 2a)., , Shear Failure, , Figure 2: Two types of damage in a beam:, , flexure damage is preferred. Longitudinal bars, resist the tension forces due to bending while, vertical stirrups resist shear forces., 4, , Longitudinal bars are provided to resist flexural, cracking on the side of the beam that stretches. Since, both top and bottom faces stretch during strong, earthquake shaking (IITK-BMTPC Earthquake Tip 17),, longitudinal steel bars are required on both faces at the, , ends and on the bottom face at mid-length (Figure 3)., The Indian Ductile Detailing Code IS13920-1993, prescribes that:, (a) At least two bars go through the full length of the, beam at the top as well as the bottom of the beam., , (b) At the ends of beams, the amount of steel provided, at the bottom is at least half that at top., 35

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IITK-BMTPC Earthquake Tip 18, How do Beams in RC Buildings Resist Earthquakes?, Bon m steel at supports, , At leasl 2 bars should go, full length of beam, , at le> st half of that at top, , _Mge2, , bars are (a) made away from the face the column, and, (b) not made at locations where they are likely to, stretch by large amounts and yield (e.g., bottom bars at, mid-length of the beam). Moreover, at the locations of, laps, vertical stirrups should be provided at a closer, spacing (Figure 6)., Spacing of stirrups, , Spacing of stirrups, Column, , Column, , as calculated, , as calculated, , (but not more than d/4, , (but not more than d/4, , and 8 times beam bar, , Figure 3: Location and amount of longitudinal, , Spacing o( stirrups, l per calculations, , diameter), , and 8 times beam bar, , diameter), , steel bars in beams - these resist tension due to, flexjre., , Stirrups in RC beams help in three ways, namely, (i) they carry the vertical shear force and thereby resist, diagonal shear cracks (Figure 2b), (ii) they protect the, concrete from bulging outwards due to flexure, and, (iii) they prevent the buckling of the compressed, longitudinal bars due to flexure. In moderate to severe, seismic, , zones,, , the, , Indian, , Standard, , IS13920-1993, , prescribes the following requirements related to, stirrups in reinforced concrete beams:, (a) The diameter of stirrup must be at least 6mm; in, beams more than 5m long, it must be at least Smffl., (b) Both ends of the vertical stirrups should be bent, inl a 135° hook (Figure 4) and extended, , Column, , Column, , Figure 5: Location and amount of vertical stirrups, in beams - IS:13920-1993 limit on maximum, , spacing ensures good earthquake behaviour., , ummimMtrm, Spacing of stirrups, not more than 150mm, , sufficiently beyond this hook to ensure that the, stirrup does not open out in an earthquake., (b) The spacing of vertical stirrups in any portion of, the beam should be determined from calculations, , (c) The maximum spacing of stirrups is less than half, the depth of the beam (Figure 5)., (d) For a length of twice the depth of the beam from, the face of the column, an even more stringent, spacing of stirrups is specified, namely half the, spacing mentioned in (c) above (Figure 5)., The ends of stirrups, are bent at 135'., , Such stirrups do not, open during strong, earthquake shaking., , Column, , Lapping prohibited In, regions where, longitudinal bars can, , Column, , yield in tension, , Figure 6: Details of lapping steel reinforcement, in seismic beams - as per IS13920-1993., , Related IITK - bmlPC Earthquake Tip, Tip 9: How to Make Buildings Ductile for Cood Seismic, Performance?, , Tip 17: How do Earthquakes Affect Reinforced Concrete Buildings?, Resource Material, , IS 13920, (1993), "Indian Standard Code of Practice for Ductile Detailing, of Reinforced Concrete Structures Subjected lo Seismic Forces," Bureau, of Indian Standards, New Delhi, , Paulay.T., and Priestley.MJ.N., (1997), "Seismic Design of Masonry, , Preferred:, 135'hooks in, , Horizontal, , adjacent, , Spacing, , stirrups on, , > 10 times, , diameter of, stirruo, , alternate sides, , and Reinforced Concrete Buildings," John Wiley & Sons, USA, McGregorJ.M, (1997), "Reinforced Concrete Mechanics and Design,", Third Edition, Prentice Hall. USA, , Next Upcoming Tip, I low do Columns in RC Buildings Resist Earthquakes?, , Authored by:, C.V.R.Murtv, , Figure 4: Steel reinforcement in seismic beams, , - stirrups with 135 hooks at ends required as per, _ IS 13920-1993., , Steel reinforcement bars are available usually in, , lengths of 12-I4m. Thus, it becomes necessary to, overlap bars when beams of longer lengths are to be, , Indian Institute of livhnology Kanpur, Kanpur, India, , Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, , made. At the location of the lap, the bars transfer large, , Delhi. It may be reproduced without changing its contents, and ivith due acknowledgement. Suggestions/comments, , forces from one to another. Thus, the Indian Standard, , may be sent to: niceeiaiitk.ac.in Visit www.nicee.org or, www.bmtpc.ori;. tc> sec prci'ious IITK-BMTI'C Earthquake Tips, , IS:13^20-1993 prescribes that such laps of longitudinal, 36, , September 21X)3

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Learning, , IITK - bmfc, Earthquake Tip, , Earthquake Design, Construction, , How do Columns in RC Buildings Resist Earthquakes?, Possible Earthquake Damage, Columns, the vertical members in RC buildings,, contain two types of steel reinforcement, namely: (a), long straight bars (called longitudinal bars) placed, vertically along the length, and (b) closed loops of, , Vertical Bars tied together with Closed Ties, Closely spaced horizontal closed ties help in three, ways, namely (i) they carry the horizontal shear forces, , smaller diameter steel bars (called transverse ties), , induced by earthquakes, and thereby resist diagonal, shear cracks, (ii) they hold together the vertical bars, and prevent them from excessively bending outwards, , placed horizontally at regular intervals along its full, length (Figure 1). Columns can sustain two types of, damage, namely axial-flexural (or combined compressionbending) failure and shearfailure. Shear damage is brittle, and must be avoided in columns by providing, transverse ties at close spacing (Figure 2b)., , (in technical terms, this bending phenomenon is called, buckling), and (iii) they contain the concrete in the, column within the closed loops. The ends of the ties, must be bent as 135° hooks (Figure 2). Such hook ends, prevent opening of loops and consequently buckling, of concrete and buckling of vertical bars., , Vertical bars, , Larger diameter steel, bars that go through, the full height of the, column, , Closed Ties, Smaller diameter steel bars, that are made into closed, , loops and are placed at, , regular intervals along the, full height of the column, , The ends of ties are, bent at 135°. Such ties, , do not open during, strong earthquake, shaking., , w times, diameter, of tie, , Column, , Figure 1: Steel reinforcement in columns - closed[, , Shear Failure, , ties at close spacing improve the pen'onnance of, columns under strong earthquake shaking., , ties and lack of, , Large spacing of, 135° hook ends in, them causes brittle, , Design Strategy, Designing a column involves selection of materials, , to be used (i.e, grades of concrete and steel bars),, choosing shape and size of the cross-section, and, , calculating amount and distribution ofsteel reinforcement., The first two aspects are part of the overall design, strategy of the whole building. The Indian Ductile, Detailing Code IS:13920-1993 requires columns to be at, , least 300mm wide. A column width of up to 200mm is, allowed if unsupported length is less than 4m and, , beam length is less than 5m. Columns thatare required, to resist earthquake forces must be designed to, prevent sltear failure by a skillful selection of, reinforcement., , failure of during, 2001 Bhuj, earthquake, , (b), , Figure 2: Steel reinforcement in seismic columns, , - closed ties with 135 "hooksare required as per, Indian Ductile Detailing Code IS:13920-1993., , The Indian Standard IS13920-1993 prescribes, following details for earthquake-resistant columns:, (a)Closely spaced ties must be provided at the two, ends of the column over a length not less than, larger dimension of the column, one-sixth the, column height or 450mm., 37

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IITK-BMTPC Earthquake Tip 19, P'lge, , How do Columns in RC Buildings Resist Earthquakes?, , (b)Over the distance specified in item (a) above and, below a beam-column junction, the vertical spacing, Spacing of ties, , of ties in columns should not exceed D/4 for where, , D is the smallest dimension of the column (e.g., in a, , rectangular column, D is the length of the small, , not more wan D/4. but need, not be less than 75mm nor, , At least larger of, , mom than 100 mm, , D. no/6 and 450 mm, , side). This spacing need not be less than 75mm nor, more than 100mm. At other locations, ties are, , spaced as per calculationsbut not more than D/2., (c) The length of tie beyond the 135° bends must be at, , Ties required, , least 10 times diameter of steel bar used to make, , in joint region also, See Earthquake Tip 20, , the closed tie; this extension beyond the bend, should not be less than 75mm., , Spacing of ties, , Construction drawings with clear details of closed, ties are helpful in the effective implementation at, construction site. In columns where the spacing, , not more than D/2, , Spacing of ties in lap length, , between the corner bars exceeds 300mm, the Indian, , not more than smaller of, D/2 and 150 mm, , Standard prescribes additional links with 180" hook, ends for ties to be effective in holding the concrete in, , its place and to prevent the buckling of vertical bars., These links need to go around both vertical bars and, horizontal closed ties (Figure 3); special care is, required to implement this properly at site., , Spacing of ties, not more than D/2, , Ties required, , in joint region also, See Earthquake Tip 20, , Extra Links, , At least larger of, D. h</6 and 450 mm, , Spacing of ties, not more than D/4. but need, not be less than 75mm nor, more than 100 mm, , BOTH vertical bars, and 135 Ki, , Column, , Figure 4: Placing vertical bars and closed ties in, columns - column ends and lap lengths are to, be protected with closely spaced ties., , Related IITK -bmTPC Earthquake Tip, , Figure 3: Extra links are required to keep the, concrete in place - 180°links are necessary to, prevent the 135°tie from bulging outwards., , Ti>17: How do Earthquakes Affect Reinforced Concrete Buildings?, , TiplS: HowdoBeams inRC Buildings Resist Earthquakes?, Resource Material, IS 13920, (1993), "Indian Standard Code of Practice for Ductile Detailing, , ofReinforced Concrete Structures Subjected to Seismic Forces," Bureau, , Lapping Vertical Bars, , of Indian Standards, New Delhi, , In the construction of RC buildings, due to the, limitations in available length of bars and due to, constraints, , in, , construction,, , there, , are, , numerous, , PaulayT., and Priestley.M.J.N., (1992), "Seismic Design of Masonry, and Reinforced Concrete Buildings," John Wiley&Sons, USA, , Next Upcoming Tip, How do Beam-Column Joints in RC Buildings Resist Earthquakes?, , occasions when column bars have to be joined. A, , simple way of achieving this is by overlapping the two, bars over at least a minimum specified length, called, , lap length. The lap length depends on types of, reinforcement and concrete. For ordinary situations, it, is about 50 times bar diameter. Further, IS:13920-1993, , prescribes that the lap length be provided ONLY in the, middle half of column and not near its top or bottom, , ends (Figure 4). Also, only half the vertical bars in the, column are to be lapped at a time in any storey., , Further, when laps are provided, ties must be, provided along the length of the lap at a spacing not, more than 150mm., 38, , Authored by:, t \ R Murty, Indian Institute ol Technology Kanpur, Kanpur, India, Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of IIT Kanpur and BMTPC New, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceediitk.ac.in Visit www.nicee.org or, , www.bmtpc.org, to see previous IITK-BMTPC Earthquake Tips., October 2003:September 2005

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Learning, Earthquake Design, , HTK - hnilpc, Earthquake Tip, , and, Construction, , How do Beam-Column Joints in RC Buildings Resist Earthquakes?, Why Beam-Column Joints are Special, In RC buildings, portions of columns that are, common to beams at their intersections are called beam-, , column joints (Figure 1). Since their constituent, materials have limited strengths, the joints have limited, force carrying capacity. When forces larger than these, are applied during earthquakes, joints are severely, damaged. Repairing damaged joints is difficult, and so, damage must be avoided. Thus, beam-column joints, must be designed to resist earthquake effects., Beam-Coluinn Joint, , Overlap volume, common to beams, and columns, , Further, under the action of the above pull-push, forces at top and bottom ends, joints undergo, geometric distortion; one diagonal length of the joint, elongates and the other compresses (Figure 2b). If the, column cross-sectional size is insufficient, the concrete, , in the joint develops diagonal cracks., , Reinforcing the Beam-Column Joint, Diagonal cracking & crushing of concrete in joint, region should be prevented to ensure good earthquakeperformance of RC frame buildings. Using large column, sizes is the most effective way of achieving this. In, addition, closely spaced closed-loop steel ties are required, around column bars (Figure 3) to hold together, concrete in joint region and to resist shear forces., Intermediate column bars also are effective in confining, the joint concrete and resisting horizontal shear forces., -Closed ties, , 10 times, diameter of tie, Beam, , Figure 1: Beam-Column Joints are critical parts, of a building - they need to be designed., , 135, , Earthquake Behaviour of Joints, , Column, , Under earthquake shaking, the beams adjoining a, joint are subjected to moments in the same (clockwise, or counter-clockwise) direction (Figure 1). Under these, moments, the top bars in the beam-column joint are, pulled in one direction and the bottom ones in the, opposite direction (Figure 2a). These forces are, balanced by bond stress developed between concrete, and steel in the joint region. If the column is not wide, enough or if the strength of concrete in the joint is low,, there is insufficient grip of concrete on the steel bars., In such circumstances, the bar slips inside the joint, region, and beams loose their capacity to carry load., o, , <=> o, Gripping of, ar inside, , <=J, , /] //Compression, w, , joint region, , (a) Loss of grip on beam bars, , (b) Distortion of joint:, , W1, , Intermediate, Column Bars, , Figure 3: Closed loop steel ties in beam-column, joints - such ties with 135°hooks resist the ill, effects of distortion ofjoints., , Providing closed-loop ties in the joint requires, some, , extra, , effort., , Indian, , Standard, , IS:13920-1993, , recommends continuing the transverse loops around, the column bars through the joint region. In practice,, this is achieved by preparing the cage of the, reinforcement (both longitudinal bars and stirrups) of all, beams at a floor level to be prepared on top of the, beam formwork of that level and lowered into the cage, (Figures 4a and 4b). However, this may not always be, possible particularly when the beams are long and the, entire reinforcement cage becomes heavy., , Anchoring Beam Bars, The gripping of beam bars in the joint region is, improved first by using columns of reasonably large, cross-sectional size. As explained in Earthquake Tip 19,, the Indian Standard IS:13920-1993 requires building, , causes diagonal, cracking and cnishing, , columns in seismic zones III, IV and V to be at least, , Large column widthand good, concrete help in holding the, , of concrete, , when they support beams that are longer than 5m or, , in joint region:, , beam bars, , Figure 2: Pull-push forces on joints cause two, , problems - these result in irreparable damage in, joints under strong seismic shaking., , 300mm wide in each direction of the cross-section, , when these columns are taller than 4m between floors, , (or, , beams)., , The, , American, , Concrete, , Institute, , recommends a column width of at least 20 times the, , diameter oflargest longitudinal bar used in adjoining beam., 39

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IITK-BMTPC Earthquake Tip 20, How do Beam-Column loints in RC Buildings Resist Earthquakes?, JlQge2, beam top bar in position while casting the column up, to the soffit of the beam. Moreover, the vertical, , distance beyond the 90" bend in beam bars is not very, effective in providing anchorage. On the other hand, if, column width is large, beam bars may not extend, below soffit of the beam (Figure 5b). Thus, it is, preferable to have columns with sufficient width. Such, , an approach is used in many codes [e.g., ACI318, 2005],, In interior joints, the beam bars (both top and, , bottom) need to go through the joint without any cut, in the joint region. Also, these bars must be placed, within the column bars and with no bends(Figure 6)., •Seam bars bent injoint region overstress, the core concrete adjoining the bends, , c, , (a) Poor Practice, , Column, , Beam, , Stage II:, , Seam oars are within column, , Top bars of the beam, , bars and also straight, , are inserted in the, , beam stin~ups. and, , (b) Good Practice, , beam reinforcement, , cage is lowered into, , Shear failure of RC, , the formwork, , beam-column joint, during the 7985, , (C), , Mexico City, , Sfage ///:, , Earthquake,, , 77es in the joint region are, , when beam bars, are passed outside, , raised to their final locations,, , tied with binding wire, and, , the column crosssection, , column ties are continued, , Figure 4: Providing horizontal ties in the joints three-stage procedure is required., , (C), , In exterior joints where beams terminate at, columns (Figure 5), longitudinal beam bars need to be, , anchored into the column to ensure propergrippingof, bar in joint. The length of anchorage for a bar of grade, Fe415 (characteristic tensile strength of 415MPa) is, , about 50 times its diameter. This length is measured, , Figure 6: Anchorage of beam bars in interior, , joints - diagrams (a) and (b) show crosssectional views in plan of joint region., ., , Related IITK - bmlPC Earthquake Tip, Tipl7: How do Earthquakes Affect Reinforced Concrete Buildings?, Tipl8: How do Beams in RC Buildings Resist Earthquakes?, Tipl9:How do Columns in RC Buildings Resist Earthquakes?, , from the face of the column to the end of the bar, anchored in the column. In columns of small widths, , Resource Material, , and when beam bars are of large diameter (Figure 5a),, , ACI 318, (2005), "Building Code Requirements for Structural Concrete, , a portion of beam top bar is embedded in the column, , that is cast up to the soffit of the beam, and a part of it, overhangs. It is difficult to hold such an overhanging, , and Commentary," American Concrete Institute, USA, , IS13920, (1993), "Indian Standard Code ofPracticefor Ductile Detailing, of Reinforced Concrete Structures Subjected toSeismic Forces," Bureau, of Indian Standards, New Delhi, , SP 123, (1991), "Design of Beam-Column joints for Seismic Resistance,", Narrow Column, , WideC olumn, , c=, , £', , Why are Open-Cround Storey Buildings Dangerous in Earthquakes?, , L-shaped, bar ends, , Special Publication, American Concrete Institute, USA, , Next Upcoming Tip, ACI 318-2005, Practice, , Authored by:, C.V.R.Mui-tv, , Indian Institute of Technology Kanpur, Kanpur, India, , ored by:, Building Materials and Technology Promotion, , Portion of top beam, bar below soffit of the, beam, , Portion of column, , already cast, , (a) Poor, (b) Good, Figure 5: Anchorage of beam bars in exterior, , joints - diagrams show elevation of joint region., , Council, New Delhi, India, This release is a property of ITT Kanpur and BMTPC New, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceejaiitk.ac.in Visit www.nicee.org or, www.bmtpc.ors.,0 seeprevious IITK-BMTPC Earthquake Tips., November 2003:September 2005, , 40

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HTK - bniic, Earthquake Tip, Why are Open-Ground Storey Buildings Vulnerable in Earthquakes?, Basic Features, , Reinforced concrete (RC) frame buildings are, becoming increasingly common in urban India. Manv, such buildings constructed in recent times have a, special feature - the ground storey is left open for the, purpose of parking (Figure 1), i.e., columns in the, ground storey do not have any partition walls (of, either masonry or RC) between them. Such buildings, are often called open ground storey buildings or buildings, on stilts., , An open ground storey building, having only, columns in the ground storey and both partition walls, and columns in the upper storeys, have two distinct, characteristics, namely:, (a) It is relatively flexible in the ground storey, i.e., the, relative horizontal displacement it undergoes in the, ground storey is much larger than what each of the, storeys above it does. This flexible ground storey is, also called softstorey., (b) It is relatively weak in ground storey, i.e., the total, horizontal earthquake force it can carry in the, ground storey is significantly smaller than what, each of the storeys above it can carry. Thus, the, open ground storey may also be a weak storey., , Often, open ground storey buildings are called soft, storey buildings, even though their ground storey may, be soft and weak. Generally, the soft or weak storey, usually exists at the ground storey level, but it could, be at any other storey level too., Earthquake Behaviour, Open ground storey buildings have consistently, shown poor performance during past earthquakes, across the world (for example during 1999 Turkey, 1999, Taiwan and 2003 Algeria earthquakes); a significant, number of them have collapsed. A large number of, buildings with open ground storey have been built in, India in recent years. For instance, the city of, , Ahmedabad alone has about 25,000 five-storey, buildings and about 1,500 eleven-storey buildings;, majority of them have open ground storeys. Further, a, huge number of similarly designed and constructed, buildings exist in the various towns and cities situated, in moderate to severe seismic zones (namely III, IV, and V) of the country. The collapse of more than a, hundred RC frame buildings with open ground, storeys at Ahmedabad (~225km away from epicenter), during the 2001 Bhuj earthquake has emphasised that, such buildings are extremely vulnerable under, earthquake shaking., The presence of walls in upper storeys makes, them much stiffer than the open ground storev. Thus,, the upper storeys move almost together as a single, block, and most of the horizontal displacement of the, building occurs in the soft ground storey itself. In, common language, this type of buildings can be, explained as a building on chopsticks. Thus, such, buildings swing back-and-forth like inverted pendulums, during earthquake shaking (Figure 2a), and the, columns in the open ground storey are severely, stressed (Figure 2b). If the columns are weak (do not, have the required strength to resist these high stresses), or if they do not have adequate ductility (See IITBMTPC Earthquake Tip 9), they may be severely, damaged (Figure 3a) which may even lead to collapse, of the building (Figure 3b)., , Earthquake, oscillations, , «!<, , %, , (a), , Inverted, , Pendulum, , Stiff upper storeys:, Small displacement between, adjacent floors, Soft ground storey:, Large displacement between, foundation and first floor, , ' ', , Ground storey columns severely stressed, , Figure 2: Upper storeys of open ground storey, buildings move together as a single block such buildings are like invertedpendulums., 41

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IITK-BMTPC Earthquake Tip 21, Why are Open-Ground Storey Buildings Vulnerable in Earthquakes?, I"W ~, structure. The Code suggests that the forces in the, columns, beams and shear walls (if any) under the, action of seismic loads specified in the code, may be, obtained by considering the bare frame building, (without any infills) (Figure 4b). However, beams and, columns in the open ground storey are required to be, designed for 2.5 times the forces obtained from this, bare frame analysis., , For all new RCframe buildings, the best option is to, avoid such sudden and large decrease in stiffness, and/or strength in any storey; it would be ideal to, psy The EERIAnnotated Slide Set CD. Earthquake, mnng Research Institute Oakland (CAI. USA. 1998, , (a) 1971 San Fernando Earthquake, , build walls (either masonry or RC walls) in the ground, storey also (Figure 5). Designers can avoid dangerous, , effects of flexible and weak ground storeys by, ensuring that too many walls are not discontinued in, , the ground storey, i.e., the drop in stiffness and, strength in the ground storey level is not abrupt due to, the absence of infill walls., , The existing open ground storey buildings need to be, strengthened suitably so as to prevent them from, , collapsing during strong earthquake shaking. The, owners should seek the services of qualified structural, , engineers who are able to suggest appropriate, solutions to increase seismic safety of these buildings., (b) 2001 Bhuj Earthquake, , Figure 3: Consequences of open ground storeys, in RC frame buildings - severe damage to, ground storey columns and building collapses., • Direct flow of forces, , through walls, , The Problem, , Open ground storey buildings are inherently poor, systems with sudden drop in stiffness and strength in, the ground storey. In thecurrent practice, stiff masonry, walls (Figure4a) are neglected and only bare frames are, considered in design calculations (Figure 4b). Thus,, the inverted pendulumeffect is not captured in design., Infill walls not, considered in, , upper storeys, , Figure 5: Avoiding open ground storey problem continuity of walls in groundstorey is preferred., , Related IITK - bmlPC Earthquake Tip, Tip 6: Hon' Architectural Features Affect Buildings During, Earthquakes?, , Tip17: What aretheEarthquake Effects on Reinforced Concrete, Buildings?, Resource Material, , IS1893(Part 1) (2002), "Indian Standard Code of Practice for Criteria fur, Design of Earthquake Resistant Structures," Bureau of Indian, Standards, New Delhi, , (a) Actualbuilding, , (b) Building being assumed, in current design practice, , Figure 4: Open ground storey building assumptions made in current design practice, are not consistent with the actual structure., , Improved design strategies, After the collapses of RC buildings in 2001 Bhuj, earthquake, the Indian Seismic Code IS:1893 (Part 1) 2002 has included special design provisions related to, soft storey buildings. Firstly, it specifies when a, building should be considered as a soft and a weak, , storey building. Secondly, it specifies higher design, forces for the soft storey as compared to the rest of the, , Next Upcoming Tip, Why are short columns moredamaged duringearthquakes?, , Authored by:, C.V.R.Mum, , Indian Instituteof Technology Kanpur, Kanpur, India, , Sponsored by:, , Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of ITT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: nieceiautk.ac.in. Visit www.nicee.org or, www.bmtpc.org. to seeprevious IITK-BMTPC Earthquake Tips., December 2003, , 42

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Learning, Earthquake Design, , h t k - mm, Earthquake Tip, , and, Construction, , Why are Short Columns more Damaged During Earthquakes?, Which Columns are short?, , During past earthquakes, reinforced concrete (RC), , frame buildings that have columns of different heights, within one storey, suffered more damage in the, shorter columns as compared to taller columns in the, same storey. Two examples of buildings with short, columns are shown in Figure 1 - buildings on a, sloping ground and buildings with a mezzanine floor., , The Short Column Behaviour, Many situations with short column effect arise in, , buildings. When a building is rested on sloped ground, (Figure la), during earthquake shaking all columns, move horizontally by the same amount along with the, floor slab at a particular level (this is called rigid floor, diaphragm action; see IITK-BMTPC Earthquake Tip 17). If, short and tall columns exist within the same storey, level, then the short columns attract several times, , larger earthquake force and suffer more damage as, compared to taller ones., The short column effect also occurs in columns, , that support mezzanine floors or loft slabs that are, added in between two regular floors (Figures lb)., There is another special situation in buildings, when short-column effect occurs. Consider a wall, , (masonry or RC) of partial height built to fit a window, over the remaining height. The adjacent columns, , behave as short columns due to presence of these, walls. In many cases, other columns in the same storey, are of regular height, as there are no walls adjoining, them. When the floor slab moves horizontally during, , Tall, , Column, , Figure 1: Buildings with short columns - two, explicit examples of common occurrences., , an earthquake, the upper ends of these columns, -, , undergo the same displacement (Figure 3). However,, the stiff walls restrict horizontal movement of the, , Poor behaviour of short columns is due to the fact, , that in an earthquake, a tall column and a short, , column of same cross-section move horizontally by, same amount A (Figure 2). However, the short column, is stiffer as compared to the tall column, and it attracts, larger earthquake force. Stiffness of a column means, resistance to deformation - the larger is the stiffness,, larger is the force required to deform it. If a short, , column is not adequately designed for such a large, force, it can suffer significant damage during an, earthquake. This behaviour is called Short Column, , lower portion of a short column, and it deforms by the, full amount over the short height adjacent to the, window opening. On the other hand, regular columns, deform over the full height. Since the effective height, over which a short column can freely bend is small, it, offers more resistance to horizontal motion and, , thereby attracts a larger force as compared to the, regular column. As a result, short column sustains, , more damage. Figure 4 shows X-cracking in a column, adjacent to the walls of partial height., , Effect. The damage in these short columns is often in, , the form of X-shaped cracking - this type of damage of, columns is due to shear failure (see IITK-BMTPC, Earthquake Tip 19)., , \, , Partial, Short, <column, , Opening, , m, , Regular, , Height, Wall, , », , f, r, , r, , Column, , 5, , r1, , Portion of, column, , nastrained, , Tall Column:, , from, , Attracts smaller, horizontal force, , movina, , <3, , Short Column:, , Attracts larger, horizontal force, , Figure 2: Short columns are stiffer and attract, , larger forces during earthquakes - this must, be accounted for in design., , Figure 3: Short columns effect in RC buildings, when partial height walls adjoin columns the effect is implicit here because infill walls, are often treated as non-structural elements., 43

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IITK-BMTPC Earthquake Tip 22, Why are Short Columns more Damaged During Earthquakes?, , P"Se2, , •n, , LLJ, Length depends, on diameter of, , longitudinal bar, , Short column, between lintel, and sill of, window, , Figure 4: Effective height of column over which it, , can bend is restricted byadjacent walls - this \, short-column effect is most severe when, , opening height is small., , Short Column, , Regular Column, , Figure 5: Details of reinforcement in a building, with short column effect in some columns -, , The Solution, , additional special requirements are given in, , In new buildings, short column effect should be, avoided to the extent possible during arcltitectural, design stage itself. When it is not possible to avoid, , IS:13920-1993 for the short columns., , short columns, this effect must be addressed in, , structural design. The Indian Standard IS:13920-1993, for ductile detailing of RC structures requires special, confining reinforcement to be provided over the full, height of columns that are likely to sustain short, column effect. The special confining reinforcement (i.e.,, closely spaced closed ties) must extend beyond the, short column into the columns vertically above and, below by a certain distance as shown in Figure 5. See, ITTK-BMTPC Earthquake Tip 19 for details of the special, confinement reinforcement., , In existing buildings with short columns, different, retrofit solutions can be employed to avoid damage in, future earthquakes. Where walls of partial height are, present, the simplest solution is to close the openings, by building a wall of full height - this will eliminate, the short column effect. If that is not possible, short, columns need to be strengthened using one of the well, established retrofit techniques. The retrofit solution, should be designed by a qualified structural engineer, with requisite background., , Related IITK - bWpE Earthquake Tip, Tip 6:How Architectural Features Affect Buildings During, Earthquakes?, Tip17:How do Earthquakes Affect Reinforced Concrete Buildings?, Tip 19: How do Columns in RC Buildings Resist Earthquakes?, Resource Material, IS 13920, (1993), "Indian Standard Code of Practice for Ductile Detailing, , of Reinforced Concrete Structures Subjected lo Seismic Forces," Bureau, of Indian Standards, New Delhi, , Next Upcoming Tip, Why are buildings with shear walls preferred in seismic regions?, Autiwred, ( A lv\lml\, , Indian Institute ol rechnologj Kanpur, Kanpur, India, Sponsored by:, , Building Materials and rechnologj Promotion, l mini il, New I Villi, India, This release is a property of ITT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may be sent to: niceeiaiitk.ac.in Visit www.nicw.orK or, , www.bmtpc.orp. lo.«•<• previous IITK-BMTPC Earthquake Tips., January 2004, , 44

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Learning, Earthquake Design, , HTK - bnflpc, Earthquake Tip, , and, , Construction, , Why are Buildings with Shear Walls Preferred in Seismic Regions?, What is a Shear Wall Building, , structural elements (like glass windows and building, , Reinforced concrete (RC) buildings often have, vertical jdate-like RC walls called Shear Walls (Figure 1), , contents)., , Architectural Aspects of Shear Walls, , in addition to slabs, beams and columns. These walls, , Most RC buildings with shear walls also have, , generally start at foundation level and are continuous, throughout the building height. Their thickness can be, , columns; these columns primarily carry gravity loads, (i.e., those due to self-weight and contents of building)., Shear walls provide large strength and stiffness to, , as low as 150mm, or as high as 400mm in high rise, buildings. Shear walls are usually provided along both, length and width of buildings (Figure 1). Shear walls, are like vertically-oriented wide beams that carry, earthquake loads downwards to the foundation., , buildings in the direction of their orientation, which, significantly reduces lateral sway of the building and, thereby reduces damage to structure and its contents., Since shear walls carry large horizontal earthquake, forces, the overturning effects on them are large. Thus,, design of their foundations requires special attention., Shear walls should be provided along preferably both, length and width. However, if they are provided along, only one direction, a proper grid of beams and, columns in the vertical plane (called a moment-resistant, frame) must be provided along the other direction to, resist strong earthquake effects., Door or window openings can be provided in, shear walls, but their size must be small to ensure least, , Foundation, , Shear, Wall, , Figure 1: Reinforced concrete shear walls in, , buildings - an excellent structural system for, earthquake resistance., , Advantages of Shear Walls in RC Buildings, Properly designed and detailed buildings with, , shear walls have shown very good performance in past, earthquakes. The overwhelming success of buildings, with shear walls in resisting strong earthquakes is, , interruption to force flow through walls. Moreover,, openings should be symmetrically located. Special, design checks are required to ensure that the net crosssectional area of a wall at an opening is sufficient to, carry the horizontal earthquake force., Shear walls in buildings must be symmetrically, , located in plan to reduce ill-effects of twist in buildings, (Figure 2). They could be placed symmetrically along, one or both directions in plan. Shear walls are more, effective when located along exterior perimeter of the, building - such a layout increases resistance of the, building to twisting., , summarised in the quote:, , "We cannot afford tobuild concrete buildings meant, to resist severeearthquakes withoutshearwalls.", :: Mark Fintel, a noted consulting engineer in USA, , 0, , shear walls, , not desirable, , Shear walls in high seismic regions require special, detailing. However, in past earthquakes, even, , Symmetry of buildingin, plan about both axes, , buildings with sufficient amount of walls that were, , not specially detailed for seismic performance (but had, enough well-distributed reinforcement) were saved, , from collapse. Shear wall buildings are a popular, choice in many earthquake prone countries, like Chile,, , Unsymmetric, location of, , shear walls along the, perimeter of, building Is desli, , New Zealand and USA. Shear walls are easy to, construct, because reinforcement detailing of walls is, , relatively straight-forward and therefore easily, implemented at site. Shear walls are efficient, both in, terms of, , construction cost and, , effectiveness in, , minimizing earthquake damage in structural and non, , Figure 2: Shear walls must be symmetric in plan, layout - twistin buildings can be avoided., , =f

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IITK-BMTPC Earthquake Tip 23, page2, Why are Buildings with Shear Walls Preferred in Seismic Regions?, increased., RC, walls, with, boundary, elements, have, Ductile Design of Shear Walls, substantially, higher, bending, strength, and, horizontal, Just like reinforced concrete (RC) beams and, shear force carrying capacity, and are therefore less, columns, RC shear walls also perform much better if, susceptible, to earthquake damage than walls without, designed to be ductile. Overall geometric proportions, boundary, elements., of the wall, types and amount of reinforcement, and, connection with remaining elements in the building, help in improving the ductility of walls. The Indian, Tension, Compression, Standard Ductile Detailing Code for RC members, (IS:13920-1993) provides special design guidelines for, ductile detailing of shear walls., Overall Geometry of Walls: Shear walls are, , ... f . ... f . f . s . . . . .•, , oblong in cross-section, i.e., one dimension of the, , Closely spaced confining, reinforcement in boundary, , cross-section is much larger than the other. While, , elements, , rectangular cross-section is common, L- and U-shaped, sections are also used (Figure 3). Thin-walled hollow, RC shafts around the elevator core of buildings also, act as shear walls, and should be taken advantage of to, resist earthquake forces., C-Shaped, , Proper anchoring of vertical, reinforcement into foundation, , (a), Boundary, , L-Shaped, , Element, , Boundary Elements, without increased thickness, , -m, , LH, Boundary, , Boundary Elements, , Element, , e, , RC Hollow, , Core around, Elevators, , 0, , Confining reinforcement in, , -*C ,, , Anchoring of wall, , boundary elements:, , reinforcement in, , 1351 hooks, closely spaced ties, Rectangular, , Figure 3: Shear walls in RC Buildings - different, geometries are possible., Reinforcement, , Bars, , in, , RC, , Walls:, , boundary element, , (b), , Figure 4: Layout of main reinforcement in shear, walls as per IS:13920-1993 - detailing is the, key to good seismic performance., ', , Steel, , reinforcing bars are to be provided in walls in, regularly spaced vertical and horizontal grids (Figure, 4a). The vertical and horizontal reinforcement in the, wall can be placed in one or two parallel layers called, curtains. Horizontal reinforcement needs to be, anchored at the ends of walls. The minimum area of, , reinforcing steel to be provided is 0.0025 times the, cross-sectional area, along each of the horizontal and, vertical directions. This vertical reinforcement should, , be distributed uniformly across the wall cross-section., Boundary Elements: Under the large overturning, , effects caused by horizontal earthquake forces, edges, of shear walls experience high compressive and tensile, stresses. To ensure that shear walls behave in a ductile, , wav, concrete in the wall end regions must be, , reinforced in a special manner to sustain these load, reversals without loosing strength (Figure 4b). End, , regions ofa wall with increased confinement arecalled, boundary elements. This special confining transverse, reinforcement in boundary elements is similar to that, , provided in columns of RC frames (See IITK-BMTPC, Earthquake Tip 19). Sometimes, the thickness of the, shear wall in these boundary elements is also, 46, , a, , 9, , Related IITK - timTPC Earthquake Tip, Tip6:How Architectural Features Affect Buildings During, Earthquakes?, Tip19: How do Columns in RC Buildings ResistEarthquakes?, Resource Material, IS 13920, (1993), "Indian Standard Code of Practice for Ductile DetmUng, of Reinforced Concrete Structures Subjected toSeismic Forces," Bureau, of Indian Standards, New Delhi, , Paulay.T., and Priestley.M.J.N., (1992), "Seismic Design of Reinforced, Concrete andMasonry Buildings," John Wiley StSons, USA, , Next Upcoming Tip, How to Reduce Earthquake Effects on Buildings?, , Authored by., C.V.R.Murry, Indian Institute of Technology Kanpur, Kanpur, India, Sj'onsored by:, , Building Materials and Technology Promotion, Council, New Delhi, India, 77iis release is a property of IIT Kanpur and BMTPC New, , Delhi. It may be reproduced without changing its contents, and with due acknowledgement. Suggestions/comments, , may he sent to: niceeiaiitk.ac.in Visit www.nicee.org or, , www.bmtpc.org, to see previous IITK-BMTPC Eartliquake Tips., February 2004

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Learning, Earthquake Design, , IITK - hmlpc, Earthquake Tip, , and, Construction, , How to Reduce Earthquake Effects on Buildings?, Why Earthquake Effects are to be Reduced, Conventional seismic design attempts to make, buildings that do not collapse under strong earthquake, shaking, but may sustain damage to non-structural, elements (like glass facades) and to some structural, members in the building. This may render the building, non-functional after the earthquake, which may be, problematic in some structures, like hospitals, which, need to remain functional in the aftermath of the, , earthquake. Special techniques are required to design, buildings such that they remain practically, undamaged even in a severe earthquake. Buildings, with such improved seismic performance usually cost, more than normal buildings do. However, this cost is, justified through improved earthquake performance., Two basic technologies are used to protect, buildings from damaging earthquake effects. These are, Base Isolation Devices and Seismic Dampers. The idea, , behind base isolation is to detach (isolate) the building, from the ground in such a way that earthquake, motions are not transmitted up through the building,, or at least greatly reduced. Seismic dampers are special, devices introduced in the building to absorb the, energy provided by the ground motion to the building, (much like the way shock absorbers in motor vehicles, absorb the impacts due to undulations of the road)., , them look like large rubber pads, although there are, other types that are based on sliding of one part of the, building relative to the other. A careful study is, required to identify the most suitable type of device, for a particular building. Also, base isolation is not, suitable for all buildings. Most suitable candidates for, base-isolation are low to medium-rise buildings rested, on hard soil underneath; high-rise buildings or, buildings rested on soft soil are not suitable for base, isolation., If the gap between the, building and vertical wall of, the foundation pit is small,, , the vertical wall of the pit, may hit the building, when, , Rollers, , the ground moves under, , the building., , Hypothetical, , Building, Building on rollers without any friction, , - building willnot move with ground, Forces induced can be up to, 5-6 times smaller than those, , in a regular building resting, , Small, , <£, , movement, , of building, , directly on ground., , Large, movement, , Flexible pads, , in isolators, , Base Isolation, , The concept of base isolation is explained through, an example building resting on frictionless rollers, (Figure la). When the ground shakes, the rollers freely, roll, but the building above does not move. Thus, no, force is transferred to the building due to shaking of, the ground; simply, the building does not experience the, earthquake. Now, if the same building is rested on, flexible pads that offer resistance against lateral, movements (Figure lb), then some effect of the ground, shaking will be transferred to the building above. If, the flexible pads are properly chosen, the forces, induced by ground shaking can be a few times smaller, , than that experienced by the building built directly on, ground, namely afixed base building (Figure lc)., The flexible pads are called base-isolators, whereas, the structures protected by means of these devices are, called base-isolated buildings. Ilie main feature ol the, base isolation technology is that it introduces, , Original, , Lead plug-, , Isolator, -Flexible, Material, , Stainless, , ' steel plates, Base Isolated, , Building, , Forces induced are large, , of building, , Fixed-Base, , Building, , response of the building. Several commercial brands of, , base isolators are available in the market, and many of, , Large, movement, , medium-rise masonry or reinforced concrete building, becomes extremely flexible. The isolators are often, , Isolator during Earthquake, , Building on flexible pads connected to building, and foundation - building willshake less, , flexibility in the structure. As a result, a robust, , designed to absorb energy and thus add damping to, the system. This helps in further reducing the seismic, , wmmmm, , Building resting directly on ground, - building willshake violently, , Figure 1: Building on flexible supports shakes, lesser - this technique is called Base Isolation, •47

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IITK-BMTPC Earthquake Tip 24, How to Reduce Earthquake Effects on Buildings?, , Base Isolation in Real Buildings, Seismic isolation is a relatively recentand evolving, , P<W 2, provided in a 18-storey RC frame structure in Gurgaon, (SeehttfJ^/www.palldynamics.com/main.htm)., , technology It has been in increased use since the, 1980s, and has been well evaluated and reviewed, , internationally. Base isolation has now been used in, numerous buildings in countries like Italy, Japan, New, Zealand, and USA. Base isolation is also useful for, , retrofitting important buildings (like hospitals and, historic buildings). By now, over 1000 buildings across, the world have been equipped with seismic base, isolation. In India, base isolation technique was first, demonstrated after the 1993 Killari (Maharashtra), Earthquake [EERI, 1999]. Two single storey buildings, (one school building and another shopping complex, building) in newly relocated Killari town were built, with rubber base isolators resting on hard ground. Both, were brick masonry buildings with concrete roof. After the, 2001 Bhuj (Gujarat) earthquake, the four-storey Bhuj, Hospital building was built with base isolation, technique (Figure 2)., , (c) Yielding Dampers, , Basement columns, , supporting base isolators, , Figure 2: View of Basement in Bhuj Hospital, building - built with base isolators after the, original District Hospital building at Bhuj, collapsed during the 2001 Bhuj earthquake., , Seismic Dampers, Another approach for controlling seismic damage, in buildings and improving their seismic performance, is by installing seismic dampers in place of structural, elements, such as diagonal braces. These dampers act, like the hydraulic shock absorbers in cars - much of, the sudden jerks are absorbed in the hydraulic fluids, and only little is transmitted above to the chassis of the, car. When seismic energy is transmitted through them,, dampers absorb part of it, and thus damp the motion of, the building. Dampers were used since 1960s to, protect tall buildings against wind effects. However, it, was only since 1990s, that they were used to protect, buildings against earthquake effects. Commonly used, types of seismic dampers include viscous dampers, (energy is absorbed by silicone-based fluid passing, between piston-cylinder arrangement), friction dampers, (energy is absorbed by surfaces with friction between, them rubbing against each other), and yielding dampers, (energy is absorbed by metallic components that yield), (Figure 3). In India, friction dampers have been, , Figure 3: Seismic Energy Dissipation Devices each device is suitable for a certain building., , Related IITK - bTfilPC Earthquake Tip, Tip 5: What are the Seismic Effects on Structures?, , Tip 8: What is the Seismic Design Philosophyfor Buildings?, Resource Material, , EERI, (1999), "Lessons Learnt Oi'er Time - Learning from Earthquakes, Series: Volume II Innovative Recovery in India," Earthquake, Engineering, , Research, , Institute, Oakland, , (CA), USA; also, , available at http//wwu'.nicee.org/readings/EERI_Report.htm., Hanson,R.D., and Soong,T.T., (2001), "Seismic Design, , with, Supplemental Energy Dissipation Devices," Earthquake Engineering, Research Institute, Oakland (CA), USA, , Skinner.R.I., Robinson.W.H., and McVerry.G.H., (1999),, Introduction lo Seismic Isolation," John Wiley & Sons, USA, , "An, , Authored hi/:, C.V.R.Murtv, , Indian Institute of Technology Kanpur, Kanpur, India, , Sponsored by:, Building Materials and Technology Promotion, Council, New Delhi, India, This release is a property of UT Kanpur and BMTPC New, Delhi. It may be reproduced without changing its contents, , and with due acknowledgement. Suggestions/comments, may be sent to: nteec milk.ac.in Visit www.nicee.org or, , www.bmtpc.org, toseeprevious IITK-BMTPC Earthquake Tips., March 2004, , 48

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Strong, Sh iking, , ., , j45£s3, W«', , "1, , For more information, please contact:, Coordinator, , National Information Center of Earthquake Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Phone: (0512) 259 7866; Fax: (0512) 259 7794, Email: [email protected]; Web: unvw.nicee.org