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Earthquake Engineering Sectional Committee, CED 39, , FOREWORD, This Indian Standard (Part 1) (Sixth Revision) was adopted by the Bureau of Indian Standards, after the draft, finalized by the Earthquake Engineering Sectional Committee had been approved by the Civil Engineering Division, Council., India is prone to strong earthquake shaking, and hence earthquake resistant design is essential. The Committee, has considered an earthquake zoning map based on the maximum intensities at each location as recorded from, damage surveys after past earthquakes, taking into account,, a), , known magnitudes and the known epicentres (see Annex A) assuming all other conditions as being, average; and, , b) tectonics (see Annex B) and lithology (see Annex C) of each region., The Seismic Zone Map (see Fig. 1) is broadly associated with 1964 MSK Intensity Scale (see Annex D) corresponding, to VI (or less), VII, VIII and IX (and above) for Seismic Zones II, III, IV and V, respectively. Seismic Zone Factors, for some important towns are given in Annex E., Structures designed as per this standard are expected to sustain damage during strong earthquake ground shaking., The provisions of this standard are intended for earthquake resistant design of only normal structures (without, energy dissipation devices or systems in-built). This standard provides the minimum design force for earthquake, resistant design of special structures (such as large and tall buildings, large and high dams, long-span bridges and, major industrial projects). Such projects require rigorous, site-specific investigation to arrive at more accurate, earthquake hazard assessment., To control loss of life and property, base isolation or other advanced techniques may be adopted. Currently, the, Indian Standard is under formulation for design of such buildings; until the standard becomes available, specialist, literature should be consulted for design, detail, installation and maintenance of such buildings., IS 1893 : 1962 ‘Recommendations for earthquake resistant design of structures’ was first published in 1962, and, revised in 1966, 1970, 1975 and 1984. Further, in 2002, the Committee decided to present the provisions for different, types of structures in separate parts, to keep abreast with rapid developments and extensive research carried out, in earthquake-resistant design of various structures. Thus, IS 1893 was split into five parts. The other parts in the, series are:, Part 1 General provisions and buildings, Part 2 Liquid retaining tanks — Elevated and ground supported, Part 3 Bridges and retaining walls, Part 4 Industrial structures, including stack-like structures, Part 5 Dams and embankments (to be formulated), This standard (Part 1) contains general provisions on earthquake hazard assessment applicable to all buildings, and structures covered in Parts 2 to 5. Also, Part 1 contains provisions specific to earthquake-resistant design of, buildings. Unless stated otherwise, the provisions in Parts 2 to 5 are to be read necessarily in conjunction with the, general provisions as laid down in Part 1., In this revision, the following changes have been included:, a), , Design spectra are defined for natural period up to 6 s;, , b) Same design response spectra are specified for all buildings, irrespective of the material of construction;

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c), , Bases of various load combinations to be considered have been made consistent for earthquake effects,, with those specified in the other codes;, , d) Temporary structures are brought under the purview of this standard;, e), , Importance factor provisions have been modified to introduce intermediate importance category of, buildings, to acknowledge the density of occupancy of buildings;, , f), , A provision is introduced to ensure that all buildings are designed for at least a minimum lateral force;, , g) Buildings with flat slabs are brought under the purview of this standard;, h) Additional clarity is brought in on how to handle different types of irregularity of structural system;, j), , Effect of masonry infill walls has been included in analysis and design of frame buildings;, , k), , Method is introduced for arriving at the approximate natural period of buildings with basements, step, back buildings and buildings on hill slopes;, , m) Provisions on torsion have been simplified; and, n) Simplified method is introduced for liquefaction potential analysis., In the formulation of this standard, effort has been made to coordinate with standards and practices prevailing in, different countries in addition to relating it to the practices in the field in this country. Assistance has particularly, been derived from the following publications:, 1), , IBC 2015, International Building Code, International Code Council, USA, 2015, , 2), , NEHRP 2009, NEHRP Recommended Seismic Provisions for New Buildings and Other Structures, Report No., FEMA P-750, Federal Emergency Management Agency, Washington, DC, USA, 2009, , 3), , ASCE/SEI 7-10, Minimum Design Loads for Buildings and Other Structures, American Society of Civil, Engineers, USA, 2010, , 4), , NZS 1170.5: 2004, Structural Design Actions, Part 5: Earthquake Actions – New Zealand, Standards New, Zealand, Wellington, New Zealand, 2004, , Also, considerable assistance has been given by Indian Institutes of Technology, Jodhpur, Madras, Bombay,, Roorkee and Kanpur; Geological Survey of India; India Meteorological Department, National Centre for Seismology, (Ministry of Earth Sciences, Govt of India) and several other organizations. Significant improvements have been, made to the standard based on findings of a project entitled, ‘Review of Building Codes and Preparation of, Commentary and Handbooks’ awarded to IIT Kanpur by the Gujarat State Disaster Management Authority, (GSDMA), Gandhinagar, through World Bank finances during 2003-2004., The units used with the items covered by the symbols shall be consistent throughout this standard, unless, specifically noted otherwise., The composition of the Committee responsible for the formulation of this standard is given in Annex G., For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960, ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded off, value should be the same as that of the specified value in this standard.

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IS 1893 (Part 1) : 2016, , Indian Standard, CRITERIA FOR EARTHQUAKE RESISTANT DESIGN, OF STRUCTURES, PART 1 GENERAL PROVISIONS AND BUILDINGS, , ( Sixth Revision ), 1 SCOPE, , IS No., 800 : 2007, , 1.1 This standard (Part 1) primarily deals with, earthquake hazard assessment for earthquake-resistant, design of (1) buildings, (2) liquid retaining structures,, (3) bridges, (4) embankments and retaining walls,, (5) industrial and stack-like structures, and (6) concrete,, masonry and earth dams. Also, this standard (Part 1), deals with earthquake-resistant design of buildings;, earthquake-resistant design of the other structures is, dealt with in Parts 2 to 5., , 875, (Part 1 : 1987), , (Part 2 : 1987), (Part 3 : 2015), (Part 4 : 1987), (Part 5 : 1987), , 1.2 All structures, like parking structures, security, cabins and ancillary structures need to be designed for, appropriate earthquake effects as per this standard., 1.3 Temporary elements, such as scaffolding and temporary, excavations, need to be designed as per this standard., , 1343 : 2012, , 1.4 This standard does not deal with construction, features relating to earthquake-resistant buildings and, other structures. For guidance on earthquake-resistant, construction of buildings, reference may be made to the, latest revisions of the following Indian Standards:, IS 4326, IS 13827, IS 13828, IS 13920, IS 13935 and, IS 15988., , 1498 : 1970, 1888 : 1982, 1893, (Part 2) : 2014, (Part 3) : 2014, (Part 4) : 2015, , 1.5 The provisions of this standard are applicable even, to critical and special structures, like nuclear power, plants, petroleum refinery plants and large dams. For, such structures, additional requirements may be, imposed based on special studies, such as site-specific, hazard assessment. In such cases, the earthquake, effects specified by this standard shall be taken as at, least the minimum., , 1905 : 1987, 2131 : 1981, 2809 : 1972, , 2 REFERENCES, , 2810 : 1979, , The standards listed below contain provisions, which,, through reference in this text, constitute provisions of, this standard. At the time of publication, the editions, indicated were valid. All standards are subject to, revision, and parties to agreements based on this, standard are encouraged to investigate the possibility, of applying the most recent editions of the standards, indicated below:, IS No., 456 : 2000, , 2974, (Part 1) : 1982, (Part 2) : 1980, (Part 3) : 1992, , Title, Code of practice for plain and, reinforced concrete (fourth revision), , (Part 4) : 1979, 1, , Title, Code of practice for general, construction in steel (second revision), Code of practice for design loads, (other than earthquake) for buildings, and structures:, Dead loads — Unit weights of, building, material and stored materials (second, revision), Imposed loads (second revision), Wind loads (third revision), Snow loads (second revision), Special loads and load combinations, (second revision), Code of practice for prestressed, concrete (second revision), Classification and identification of, soils for general engineering, purposes (first revision), Method of load test on soils (second, revision), Criteria for earthquake resistant design, of structures:, Liquid retaining tanks, Bridges and retaining walls, Industrial structures including stacklike structures (first revision), Code of practice for structural use of, unreinforced masonry (third revision), Method of standard penetration test, for soils (first revision), Glossary of terms and symbols relating, to soil engineering (first revision), Glossary of terms relating to soil, dynamics (first revision), Code of practice for design and construction of machine foundations:, Foundation for reciprocating type, machines, F o u n d a t i o n s f o r i m p a c t type, machines (Hammer foundations), Foundations for rotary type machines, (Medium and high frequency), Foundations for rotary type, machines of low frequency

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IS 1893 (Part 1) : 2016, IS No., (Part 5) : 1987, , 4326 : 2013, 6403 : 1981, 13827 : 1993, 13828 : 1993, 13920 : 2016, , 13935 : 1993, 15988 : 2013, SP 7 : 2016, (Part 6/Sec 4), , Title, Foundations for impact machines, other than hammer (Forging and, stamping press, pig breaker, drop, crusher and jolter), Earthquake resistant design and, construction of buildings—Code of, Practice (third revision), Code of practice for determination of, bearing capacity of shallow, foundations (first revision), Improving earthquake resistance of, earthen buildings — Guidelines, Improving earthquake resistance of, low strength masonry buildings —, Guidelines, Ductile design and detailing of, reinforced concrete structures, subjected to seismic forces — Code, of practice (first revision), Repair and seismic strengthening of, buildings — Guidelines, Seismic, evaluation, and, strengthening of existing reinforced, concrete building — Guidelines, National Building Code of India: Part 6, Structural Design, Section 4 Masonry, , 3.5 Design Horizontal Acceleration Coefficient (Ah) —, It is a horizontal acceleration coefficient that shall be, used for design of structures., 3.6 Design Horizontal Force — It is the horizontal, seismic force prescribed by this standard that shall be, used to design a structure., 3.7 Ductility — It is the capacity of a structure (or its, members) to undergo large inelastic deformations, without significant loss of strength or stiffness., 3.8 Epicentre — It is the geographical point on the, surface of earth vertically above the point of origin of, the earthquake., 3.9 Floor Response Spectrum — It is the response, spectrum (for a chosen material damping value) of the, time history of the shaking generated at a floor of a, structure, when the structure is subjected to a given, earthquake ground motion at its base., 3.10 Importance Factor (I) — It is a factor used to estimate, design seismic force depending on the functional use of, the structure, characterized by hazardous consequences, of its failure, post-earthquake functional needs, historical, value, or economic importance., 3.11 Intensity of Earthquake — It is the measure of the, strength of ground shaking manifested at a place during, the earthquake, and is indicated by a roman capital, numeral on the MSK scale of seismic intensity (see, Annex D)., , 3 TERMINOLOGY, For the purpose of this standard, definitions given, below shall apply to all structures, in general. For, definition of terms pertaining to soil mechanics and, soil dynamics, reference may be made to IS 2809 and, IS 2810, and for definition of terms pertaining to ‘loads’,, reference may be made to IS 875 (Parts 1 to 5)., , 3.12 Liquefaction — It is a state primarily in saturated, cohesionless soils wherein the effective shear strength is, reduced to negligible value for all engineering purposes,, when the pore pressure approaches the total confining, pressure during earthquake shaking. In this condition,, the soil tends to behave like a fluid mass (see Annex F)., , 3.1 Closely-Spaced Modes — Closely-spaced modes, of a structure are those of the natural modes of, oscillation of a structure, whose natural frequencies, differ from each other by 10 percent or less of the lower, frequency., , 3.13 Lithological Features — Features that reflect the, nature of the geological formation of the earth’s crust, above bed rock characterized on the basis of structure,, mineralogical composition and grain size., 3.14 Modal Mass (Mk) in Mode (k) of a Structure — It, is a part of the total seismic mass of the structure that, is effective in natural mode k of oscillation during, horizontal or vertical ground motion., , 3.2 Critical Damping — The damping beyond which, the free vibration motion will not be oscillatory., 3.3 Damping — The effect of internal friction,, inelasticity of materials, slipping, sliding, etc, in, reducing the amplitude of oscillation; it is expressed as, a fraction of critical damping (see 3.2)., , 3.15 Modal Participation Factor (Pk) in Mode (k) of a, Structure — The amount by which natural mode k, contributes to overall oscillation of the structure during, horizontal or vertical earthquake ground motion. Since, the amplitudes of mode shapes can be scaled arbitrarily,, the value of this factor depends on the scaling used, for defining mode shapes., , 3.4 Design Acceleration Spectrum — Design, acceleration spectrum refers to an average, smoothened graph of maximum acceleration as a, function of natural frequency or natural period of, oscillation for a specified damping ratio for the, expected earthquake excitations at the base of a, single degree of freedom system., , 3.16 Modes of Oscillation — See 3.19., 3.17 Mode Shape Coefficient (φik) — It is the spatial, 2

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IS 1893 (Part 1) : 2016, deformation pattern of oscillation along degree of, freedom i, when the structure is oscillating in its natural, mode k. A structure with N degrees of freedom, possesses N natural periods and N associated natural, mode shapes. These natural mode shapes are together, presented in the form of a mode shape matrix [φ], in, which each column represents one natural mode shape., The element φik is called the mode shape coefficient, associated with degree of freedom i, when the structure, is oscillating in mode k., , design of structures subjected to earthquake ground, shaking; this value depends on the natural period of, oscillation of the structure and damping to be, considered in the design of the structure., , 3.18 Natural Period (Tk) in Mode (k) of Oscillation —, The time taken (in second) by the structure to complete, one cycle of oscillation in its natural mode k of, oscillation., , 3.26 Seismic Weight of a Floor (W) — It is the sum of, dead load of the floor, appropriate contributions of, weights of columns, walls and any other permanent, elements from the storeys above and below, finishes, and services, and appropriate amounts of specified, imposed load on the floor., , 3.24 Seismic Mass of a Floor — It is the seismic weight, of the floor divided by acceleration due to gravity., 3.25 Seismic Mass of a Structure — It is the seismic, weight of a structure divided by acceleration due to, gravity., , 3.18.1 Fundamental Lateral Translational Natural, Period (T1) — It is the longest time taken (in second), by the structure to complete one cycle of oscillation in, its lateral translational mode of oscillation in the, considered direction of earthquake shaking. This mode, of oscillation is called the fundamental lateral, translational natural mode of oscillation. A threedimensional model of a structure will have one such, fundamental lateral translational mode of oscillation, along each of the two orthogonal plan directions., , 3.27 Seismic Weight of a Structure (W) — It is the, sum of seismic weights of all floors., 3.28 Seismic Zone Factor (Z) — It is the value of peak, ground acceleration considered by this standard for, the design of structures located in each seismic zone., 3.29 Time History Analysis — It is an analysis of the, dynamic response of the structure at each instant of, time, when its base is subjected to a specific ground, motion time history., , 3.19 Normal Mode of Oscillation — The mode of, oscillation in which there are special undamped free, oscillations in which all points on the structure oscillate, harmonically at the same frequency (or period), such, that all these points reach their individual maximum, responses simultaneously., , 4 SPECIAL TERMINOLOGY FOR BUILDINGS, 4.1 The definitions given below shall apply for the, purpose of earthquake resistant design of buildings,, as enumerated in this standard., , 3.20 Peak Ground Acceleration — It is the maximum, acceleration of the ground in a given direction of ground, shaking. Here, the acceleration refers to that of the, horizontal motion, unless specified otherwise., , 4.2 Base — It is the level at which inertia forces, generated in the building are considered to be, transferred to the ground through the foundation. For, buildings with basements, it is considered at the, bottommost basement level. For buildings resting on,, , 3.21 Response Reduction Factor (R) — It is the factor, by which the base shear induced in a structure, if it, were to remain elastic, is reduced to obtain the design, base shear. It depends on the perceived seismic damage, performance of the structure, characterized by ductile, or brittle deformations, redundancy in the structure, or, overstrength inherent in the design process., , a), , pile foundations, it is considered to be at the, top of pile cap;, , b) raft, it is considered to be at the top of raft;, and, c), , 3.22 Response Spectrum — It is the representation of, maximum responses of a spectrum of idealized single, degree freedom systems of different natural periods, but having the same damping, under the action of the, same earthquake ground motion at their bases. The, response referred to here can be maximum absolute, acceleration, maximum relative velocity, or maximum, relative displacement., , footings, it is considered to be at the top of, the footing., , For buildings with combined types of foundation, the, base is considered as the bottom-most level of the bases, of the constituent individual foundations as per, definitions above., 4.3 Base Dimension (d) — It is the dimension (in metre), of the base of the building along a direction of shaking., , 3.23 Response Acceleration Coefficient of a Structure, (Sa/g) — It is a factor denoting the normalized design, acceleration spectrum value to be considered for the, , 4.4 Centre of Mass (CM) — The point in the floor of a, building through which the resultant of the inertia force, of the floor is considered to act during earthquake, 3

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IS 1893 (Part 1) : 2016, In step-back buildings, it shall be taken as the average, of heights of all steps from the base, weighted with, their corresponding floor areas. And, in buildings, founded on hill slopes, it shall be taken as the height of, the roof from the top of the highest footing level or pile, cap level., , shaking. Unless otherwise stated, the inertia force, considered is that associated with the horizontal, shaking of the building., 4.5 Centre of Resistance (CR), 4.5.1 For Single Storey Buildings — It is the point on, the roof of a building through which when the resultant, internal resistance acts, the building undergoes,, a), , 4.11 Horizontal Bracing System — It is a horizontal, truss system that serves the same function as a, diaphragm., , pure translation in the horizontal direction;, and, , 4.12 Joints — These are portions of columns that are, common to beams/braces and columns, which frame, into columns., , b) no twist about vertical axis passing through, the CR., , 4.13 Lateral Force Resisting System — It is part of, the structural system, and consists of all structural, members that resist lateral inertia forces induced in the, building during earthquake shaking., , 4.5.2 For Multi-Storey Buildings — It is the set of, points on the horizontal floors of a multi-storey building, through which, when the resultant incremental internal, resistances across those floors act, all floors of the, building undergo,, a), , 4.14 Moment-Resisting Frame — It is an assembly of, beams and columns that resist induced and externally, applied forces primarily by flexure., , pure translation in the horizontal direction;, and, , 4.14.1 Ordinary Moment-Resisting Frame (OMRF) —, It is a moment-resisting frame designed and detailed as, per IS 456 or IS 800, but not meeting special detailing, requirements for ductile behaviour as per IS 13920 or, IS 800, respectively., , b) no twist about vertical axis passing through, the CR., 4.6 Eccentricity, 4.6.1 Design Eccentricity (edi) — It is the value of, eccentricity to be used for floor i in calculations of, design torsion effects., , 4.14.2 Special Moment-Resisting Frame (SMRF) — It, is a moment-resisting frame designed and detailed as, per IS 456 or IS 800, and meeting special detailing, requirements for ductile behaviour as per IS 13920 or, IS 800, respectively., , 4.6.2 Static Eccentricity (e si) — It is the distance, between centre of mass (CM) and centre of resistance, (CR) of floor i., , 4.15 Number of Storeys (n) — It is the number of levels, of a building above the base at which mass is present, in substantive amounts. This,, , 4.7 Design Seismic Base Shear (VB) — It is the horizontal, lateral force in the considered direction of earthquake, shaking that the structure shall be designed for., , a), , 4.8 Diaphragm — It is a horizontal or nearly horizontal, structural system (for example, reinforced concrete, floors and horizontal bracing systems), which transmits, lateral forces to vertical elements connected to it., , b) includes the basement storeys, when they are, not so connected., , 4.9 Height of Floor (hi) — It is the difference in vertical, elevations (in metre) of the base of the building and, top of floor i of the building., , 4.16 Core Structural Walls, Perimeter Columns,, Outriggers and Belt Truss System — It is a structural, system comprising of a core of structural walls and, perimeter columns, resisting the vertical and lateral, loads, with, , 4.10 Height of Building (h) — It is the height of building, (in metre) from its base to top of roof level,, a), , excludes the basement storeys, where, basement walls are connected with the ground, floor deck or fitted between the building, columns; and, , excluding the height of basement storeys, if, basement walls are connected with the ground, floor slab or basement walls are fitted between, the building columns, but, , a), , the core structural walls connected to select, perimeter column element(s) (often termed, outrigged columns) by deep beam elements,, known as outriggers, at discrete locations, along the height of the building; and, b) the outrigged columns connected by deep, beam elements (often known as belt truss),, , b) including the height of basement storeys, if, basement walls are not connected with the, ground floor slab and basement walls are not, fitted between the building columns., 4

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IS 1893 (Part 1) : 2016, 4.23 Storey Lateral Shear Strength (Si) — It is the, total lateral strength of all lateral force resisting, elements in the storey considered in a principal plan, direction of the building., , typically at the same level as the outrigger, elements., A structure with this structural system has enhanced, lateral stiffness, wherein core structural walls and, perimeter columns are mobilized to act with each other, through the outriggers, and the perimeter columns, themselves through the belt truss. The global lateral, stiffness is sensitive to: flexural stiffness of the core, element, the flexural stiffness of the outrigger, element(s), the axial stiffness of the outrigged, column(s), and the flexural stiffness of the outrigger, elements connecting the core structural walls to the, perimeter columns., , 4.24 Storey Lateral Translational Stiffness (Ki) — It, is the total lateral translational stiffness of all lateral, force resisting elements in the storey considered in a, principal plan direction of the building., 4.25 RC Structural Wall Plan Density (ρsw) — It is, the ratio of the cross-sectional area at the plinth level, of RC structural walls resisting the lateral load and the, plinth of the building, expressed as a percentage., 5 SYMBOLS, , 4.17 Principal Plan Axes — These are two mutually, perpendicular horizontal directions in plan of a building, along which the geometry of the building is oriented., , The symbols and notations given below apply to the, provisions of this standard:, , ∆ Effect — It is the secondary effect on shear, 4.18 P-∆, forces and bending moments of lateral force resisting, elements generated under the action of the vertical, loads, interacting with the lateral displacement of, building resulting from seismic effects., , Ah, , Design horizontal earthquake acceleration, coefficient, , Ak, , Design horizontal earthquake acceleration, spectrum value for mode k of oscillation, Plan dimension of floor i of the building,, perpendicular to direction of earthquake, shaking, , bi, , 4.19 RC Structural Wall — It is a wall designed to, resist lateral forces acting in its own plane., 4.19.1 Ordinary RC Structural Wall — It is a reinforced, concrete (RC) structural wall designed and detailed as, per IS 456, but not meeting special detailing, requirements for ductile behaviour as per IS 13920., , C, d, , Index for the closely-spaced modes, Base dimension (in metre) of the building in, the direction in which the earthquake, shaking is considered, , 4.19.2 Special RC Structural Wall — It is a RC, structural wall designed and detailed as per IS 13920,, and meeting special detailing requirements for ductile, behaviour as per IS 13920., , DL, e di, , Response quantity due to dead load, Design eccentricity to be used at floor i, calculated as per 7.8.2, , e si, , Static eccentricity at floor i defined as the, distance between centre of mass and centre, of resistance, Response quantity due to earthquake load, for horizontal shaking along X-direction, , 4.20 Storey — It is the space between two adjacent, floors., , ELX, , 4.20.1 Soft Storey — It is one in which the lateral, stiffness is less than that in the storey above. The storey, lateral stiffness is the total stiffness of all seismic force, resisting elements resisting lateral earthquake shaking, effects in the considered direction., , ELY, ELZ, , 4.20.2 Weak Storey — It is one in which the storey, lateral strength [cumulative design shear strength of, all structural members other than that of unreinforced, masonry (URM) infills] is less than that in the storey, above. The storey lateral strength is the total strength, of all seismic force resisting elements sharing the lateral, storey shear in the considered direction., , Froof, Fi, , 4.21 Storey Drift — It is the relative displacement, between the floors above and/or below the storey under, consideration., 4.22 Storey Shear (Vi) — It is the sum of design lateral, forces at all levels above the storey i under, consideration., 5, , Response quantity due to earthquake load, for horizontal shaking along Y-direction, Response quantity due to earthquake load, for horizontal shaking along Z-direction, Design lateral forces at the roof due to all, modes considered, Design lateral forces at the floor i due to all, modes considered, , g, h, , Acceleration due to gravity, Height (in metre) of structure, , hi, I, , Height measured from the base of the, building to floor i, Importance factor, , IL, Ki, , Response quantity due to imposed load, Lateral translational stiffness of storey i

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IS 1893 (Part 1) : 2016, , Mk, , Dimension of a building in a considered, direction, Modal mass of mode k, , 6 GENERAL PRINCIPLES AND DESIGN, CRITERIA, 6.1 General Principles, , n, N, , Number of storeys or floors, Corrected SPT value for soil, , 6.1.1 Ground Motion, , Nm, , L, , Pk, , Number of modes to be considered as, per 7.7.5.2, Mode participation factor of mode k, , Qi, Qik, , Lateral force at floor i, Design lateral force at floor i in mode k, , R, Sa/g, , Response reduction factor, Design / Response acceleration coefficient, for rock or soil sites as given by Fig. 2, and 6.4.2 based on appropriate natural period, , Si, T, , Lateral shear strength of storey i, Undamped natural period of oscillation of, the structure (in second), , Ta, Tk, , Approximate fundamental period (in second), Undamped natural period of mode k of, oscillation (in second), , T1, , Fundamental natural period of oscillation (in, second), Design seismic base shear, , VB, VB, , Vi, , Shear force in storey i in mode k, Peak storey shear force in the top storey, due to all modes considered, , W, Wi, , Seismic weight of the building, Seismic weight of floor i, , Z, φik, , Seismic zone factor, Mode shape coefficient at floor i in mode k, , λ, , Peak response (for example, member forces,, displacements, storey forces, storey shears, or base reactions) due to all modes considered, Absolute value of maximum response in, mode k, , λc, λ*, ρ ji, ωi, , Effects of earthquake-induced vertical shaking can be, significant for overall stability analysis of structures,, especially in structures (a) with large spans, and, (b) those in which stability is a criterion for design., Reduction in gravity force due to vertical ground, motions can be detrimental particularly in prestressed, horizontal members, cantilevered members and gravity, structures. Hence, special attention shall be paid to, effects of vertical ground motion on prestressed or, cantilevered beams, girders and slabs., 6.1.2 The response of a structure to ground vibrations, depends on (a) type of foundation; (b) materials, form,, size and mode of construction of structures; and, (c) duration and characteristics of ground motion. This, standard specifies design forces for structures founded, on rocks or soils, which do not settle, liquefy or slide, due to loss of strength during earthquake ground, vibrations., , Design base shear calculated using the, approximate fundamental period Ta, Peak storey shear force in storey i due to all, modes considered, , Vik, Vroof, , λk, , The characteristics (intensity, duration, frequency, content, etc) of seismic ground vibrations expected at, any site depend on magnitude of earthquake, its focal, depth, epicentral distance, characteristics of the path, through which the seismic waves travel, and soil strata, on which the structure is founded. The random, earthquake ground motions, which cause the structure, to oscillate, can be resolved in any three mutually, perpendicular directions. The predominant direction of, ground vibration is usually horizontal., , 6.1.3 Actual forces that appear on structures during, earthquakes are much higher than the design forces, specified in the standard. Ductility arising from inelastic, material behaviour with appropriate design and, detailing, and overstrength resulting from the additional, reserve strength in structures over and above the, design strength are relied upon for the deficit in actual, and design lateral loads. In other words, earthquake, resistant design as per this standard relies on inelastic, behaviour of structures. But, the maximum ductility that, can be realized in structures is limited. Therefore,, structures shall be designed for at least the minimum, design lateral force specified in this standard., , Absolute value of maximum response in, mode c, where mode c is a closely-spaced, mode, Peak response due to the closely-spaced, modes only, , 6.1.4 Members and connections of reinforced and, prestressed concrete structures shall be designed (as, per IS 456 and IS 1343) such that premature failure does, not occur due to shear or bond. Some provisions for, appropriate ductile detailing of RC members are given, in IS 13920. Members and their connections of steel, structures should be so proportioned that high ductility, is obtained in the structure, avoiding premature failure, due to elastic or inelastic buckling of any type. Some, , Coefficient used in complete quadratic, combination (CQC) method while combining, responses of modes i and j, Circular frequency (in rad/s) in mode i, 6

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IS 1893 (Part 1) : 2016, provisions for appropriate ductile detailing of steel, members are given in IS 800., , irregular, consisting of several frequencies and, of varying amplitudes each lasting for a small, duration. Therefore, usually, resonance of the, type as visualized under steady-state, sinusoidal excitations will not occur, as it would, need time to build up such amplitudes. But,, there are exceptions where resonance-like, conditions have been seen to occur between, long distance waves and tall structures, founded on deep soft soils., , 6.1.5 The soil-structure interaction refers to effects of, the flexibility of supporting soil-foundation system on, the response of structure. Soil-structure interaction may, not be considered in the seismic analysis of structures, supported on rock or rock-like material at shallow depth., 6.1.6 Equipment and other systems, which are, supported at various floor levels of a structure, will be, subjected to different motions at their support points., In such cases, it may be necessary to obtain floor, response spectra for design of equipment and its, supports. For details, reference may be made to IS 1893, (Part 4)., , b) Earthquake is not likely to occur, simultaneously with high wind, maximum flood, or maximum sea waves., c), , 6.1.7 Additions to Existing Structures, Additions shall be made to existing structures only as, follows:, a), , The values of elastic modulus of materials,, wherever required, will be taken as for static, analysis, unless more definite values are, available for use in dynamic conditions [see, IS 456, IS 800, IS 1343, IS 1905 and IS 2974, (Parts 1 to 5)]., , An addition that is structurally independent, from an existing structure shall be designed, and constructed in accordance with the, seismic requirements for new structures., , 6.3 Load Combinations and Increase in Permissible, Stresses, , b) An addition that is structurally connected to, an existing structure shall be designed and, constructed such that the entire structure, conforms to the seismic force resistance, requirements for new structures, unless the, following three conditions are complied with:, , The load combinations shall be considered as specified, in respective standards due to all load effects mentioned, therein. In addition, those specified in this standard, shall be applicable, which include earthquake effects., , 1), 2), , 3), , 6.3.1 Load Combinations, , 6.3.1.1 Even when load combinations that do not, contain earthquake effects, indicate larger demands, than combinations including them, the provisions shall, be adopted related to design, ductile detailing and, construction relevant for earthquake conditions, which, are given in this standard, IS 13920 and IS 800., , Addition shall comply with the, requirements for new structures,, Addition shall not increase the seismic, forces in any structural element of the, existing structures by more than, 5 percent, unless the capacity of the, element subject to the increased force is, still in compliance with this standard, and, Addition shall not decrease the seismic, resistance of any structural element of the, existing structure unless reduced, resistance is equal to or greater than that, required for new structures., , 6.3.2 Design Horizontal Earthquake Load, 6.3.2.1 When lateral load resisting elements are oriented, along two mutually orthogonal horizontal directions,, structure shall be designed for effects due to full design, earthquake load in one horizontal direction at a time,, and not in both directions simultaneously., 6.3.2.2 When lateral load resisting elements are not, oriented along mutually orthogonal horizontal, directions [as per 7.1 and Table 5(e)], structure shall be, designed for the simultaneous effects due to full design, earthquake load in one horizontal direction plus, 30 percent of design earthquake load along the other, horizontal direction. Thus, structure should be designed, for the following sets of combinations of earthquake, effects:, , 6.1.8 Change in Occupancy, When a change of occupancy results in a structure being, re-classified to a higher importance factor (I), the structure, shall conform to seismic requirements laid down for new, structures with the higher importance factor., 6.2 Assumptions, The following assumptions shall be made in the, earthquake-resistant design of structures:, a), , a) ± ELX ± 0.3 ELY, and, b) ± 0.3 ELX ± ELY,, where X and Y are two orthogonal horizontal plan, , Earthquake ground motions are complex and, 7

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IS 1893 (Part 1) : 2016, 0.3 ELZ), (ELY ± 0.3 ELZ ± 0.3 ELX) or (ELZ ± 0.3 ELX ±, 0.3 ELY,). This implies that the sets of load combinations, involving earthquake effects to be considered shall be, as given below:, , directions. Thus, EL in the load combinations given in, 6.3.1 shall be replaced by (ELX ± 0.3 ELY) or (ELY ±, 0.3 ELX). Hence, the sets of load combinations to be, considered shall be as given below:, 1), , 1.2 [DL + IL ± (ELX ± 0.3 ELY)] and, 1.2 [DL + IL ± (ELY ± 0.3 ELX)];, , 2), , 1.5 [DL ± (ELX ± 0.3 ELY)] and, 1.5 [DL ± (ELY ± 0.3 ELX)]; and, , 3), , 0.9 DL ± 1.5 (ELX ± 0.3 ELY) and, 0.9 DL ± 1.5 (ELY ± 0.3 ELX)., , 1), , 1.2 [DL + IL ± (ELY ± 0.3 ELX ± 0.3 ELZ)];, 2), 3), , 6.3.4.2 As an alternative to the procedure in 6.3.4.1,, the net response (EL) due to the combined effect of the, three components can be obtained by:, , Structure is located in Seismic Zone IV or V;, , EL =, , b) Structure has vertical or plan irregularities;, d) Bridges;, Structure has long spans; or, , f), , Structure has large horizontal overhangs of, structural members or sub-systems., , 2, , 2, , 6.3.4.4 When components corresponding to only two, ground motion components (say one horizontal and, one vertical, or only two horizontal) are combined, the, equations in 6.3.4.1 and 6.3.4.2 should be modified by, deleting the term representing the response due to the, component of motion not being considered., , 6.3.3.3 Where both horizontal and vertical seismic, forces are taken into account, load combination, specified in 6.3.4 shall be considered., 6.3.4 Combinations to Account for Three Directional, Earthquake Ground Shaking, , 6.3.5 Increase in Net Pressure on Soils in Design of, Foundations, , 6.3.4.1 When responses from the three earthquake, components are to be considered, the responses due, to each component may be combined using the, assumption that when the maximum response from one, component occurs, the responses from the other two, components are 30 percent each of their maximum. All, possible combinations of three components (ELX, ELY, and ELZ) including variations in sign (plus or minus), shall be considered. Thus, the structure should be, designed for the following sets of combinations of, earthquake load effects:, , 6.3.5.1 In the design of foundations, unfactored loads, shall be combined in line with IS 2974, while assessing, the bearing pressure in soils., 6.3.5.2 When earthquake forces are included, net, bearing pressure in soils can be increased as per, Table 1, depending on type of foundation and type of, soil. For determining the type of soil for this purpose,, soils shall be classified in four types as given in Table, 2. In soft soils, no increase shall be applied in bearing, pressure, because settlements cannot be restricted by, increasing bearing pressure., , ± ELX ± 0.3 ELY ± 0.3 ELZ,, , b) ± ELY ± 0.3 ELZ ± 0.3 ELX, and, c), , 2, , 6.3.4.3 Procedure for combining shaking effects given, by 6.3.4.1 and 6.3.4.2 apply to the same response, quantity (say, bending moment in a column about its, major axis, or storey shear force in a frame) due to, different components of the ground motion., , 6.3.3.2 When effects due to vertical earthquake shaking, are to be considered, the design vertical force shall be, calculated for vertical ground motion as detailed in 6.4.6., , a), , ( ELX ) + ( ELY ) + ( ELZ ), , Caution may be exercised on loss of sign especially of, the axial force, shear force and bending moment, quantities, when this procedure is used; it can lead to, grossly uneconomical design of structures., , Structure is rested on soft soil;, , e), , 0.9 DL ± 1.5 (ELX ± 0.3 ELY ± 0.3 ELZ) and, 0.9 DL ± 1.5 (ELY ± 0.3 ELX ± 0.3 ELZ)., , 6.3.3.1 Effects due to vertical earthquake shaking shall, be considered when any of the following conditions, apply:, , c), , 1.5 [DL ± (ELX ± 0.3 ELY ± 0.3 ELZ)] and, 1.5 [DL ± (ELY ± 0.3 ELX ± 0.3 ELZ)]; and, , 6.3.3 Design Vertical Earthquake Effects, , a), , 1.2 [DL + IL ± (ELX ± 0.3 ELY ± 0.3 ELZ)] and, , 6.3.5.3 In soil deposits consisting of submerged loose, sands and soils falling under classification SP with, corrected standard penetration test values N, less than, 15 in Seismic Zones III, IV and V, and less than 10 in, Seismic Zone II, the shaking caused by earthquake, , ± ELZ ± 0.3 ELX ± 0.3 ELY,, , where X and Y are orthogonal plan directions and Z, vertical direction. Thus, EL in the above referred load, combinations shall be replaced by (ELX ± 0.3 ELY ±, 8

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IS 1893 (Part 1) : 2016, damping, given by expressions below:, a) For use in equivalent static method, [see Fig. 2(a)]:, , ground motion may cause liquefaction or excessive, total and differential settlements. Such sites should be, avoided preferably for locating new structures, and, should be avoided for locating structures of important, projects. Otherwise, settlements need to be, investigated, and appropriate methods adopted of, compaction or stabilization to achieve N values, indicated in Note 4 of Table 1. Alternatively, deep pile, foundations may be adopted and anchored at depths, well below the underlying soil layers, which are likely, to liquefy or undergo excessive settlements., , , 2.5 0 < T < 0.40 s, For rocky , or hard  1, 0.40 s < T < 4.00 s, soil sites  T, , 0.25 T > 4.00 s, , , 2.5 0 < T < 0.55 s, For med- , Sa , 1.36, 0.55 s < T < 4.00 s, = ium stiff , g soil sites  T, T > 4.00 s, 0.34, , , 2.5 0 < T < 0.67 s, , For soft 1.67, 0.67 s < T < 4.00 s, , , soil sites  T, , T > 4.00 s, 0.42, , b) For use in response spectrum method, [see Fig. 2(b)], , Also, marine clay layers and other sensitive clay layers, are known to liquefy, undergo excessive settlements or, even collapse, owing to low shear strength of the said, soil; such soils will need special treatment according, to site condition (see Table 2)., A simplified method is given in Annex F, for evaluation, of liquefaction potential., 6.4 Design Acceleration Spectrum, 6.4.1 For the purpose of determining design seismic, force, the country is classified into four seismic zones, as shown in Fig. 1., , , 1 + 15T T < 0.10 s, , , 0.10 s < T < 0.40 s, For rocky2.5, or hard  1, 0.40 s < T < 4.00 s, soil sites , , T, T > 4.00 s, , 0.25, , 1 + 15T T < 0.10 s, , For med- 2.5, 0.10 s < T < 0.55 s, , Sa , = ium stiff 1.36, g soil sites , 0.55 s < T < 4.00 s, ,  T, T > 4.00 s, 0.34, , , 1 + 15T T < 0.10 s, , 2.5, , 0.10 s < T < 0.67 s, For, soft, , , 1.67, , soil sites, 0.67 s < T < 4.00 s,  T, , , , T > 4.00 s, 0.42, , 6.4.2.1 For determining the correct spectrum to be used, in the estimate of (Sa/g), the type of soil on which the, structure is placed shall be identified by the, classification given in Table 4, as:, a) Soil type I — Rock or hard soils;, b) Soil type II — Medium or stiff soils; and, c) Soil type III — Soft soils., , 6.4.2 The design horizontal seismic coefficient Ah for a, structure shall be determined by:, , where, Z, I, ,  Z   Sa , 2  g ,    , Ah =, R,  , I, , = seismic zone factor given in Table 3;, = importance factor given in IS 1893 (Parts 1, to 5) for the corresponding structures; when, not specified, the minimum values of I shall, be,, a) 1.5 for critical and lifeline structures;, b) 1.2 for business continuity structures; and, , c) 1.0 for the rest., R = response reduction factor given in IS 1893, (Parts 1 to 5) for the corresponding, structures; and,  Sa ,  g  = design acceleration coefficient for different,  , soil types, normalized with peak ground, acceleration, corresponding to natural period, T of structure (considering soil-structure, interaction, if required). It shall be as given, in Parts 1 to 5 of IS 1893 for the corresponding, structures; when not specified, it shall be, taken as that corresponding to 5 percent, , In Table 4, the value of N to be used shall be the, weighted average of N of soil layers from the existing, ground level to 30 m below the existing ground level;, here, the N values of individual layers shall be the, corrected values., , 9

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IS 1893 (Part 1) : 2016, Table 1 Percentage Increase in Net Bearing, Pressure and Skin Friction of Soils, (Clause 6.3.5.2), Sl No. Soil Type, (1), (2), i), ii), iii), , Table 2 Classification of Types of Soils for, Determining Percentage Increase in Net, Bearing Pressure and Skin Friction, (Clause 6.3.5.2), , Percentage Increase Allowable, (3), , Type A: Rock or hard soils, Type B: Medium or stiff soils, Type C: Soft soils, , Sl No. Soil Type, (1), (2), , 50, 25, 0, , i), , Type A, Rock or, hard soils, , Well graded gravel (GW) or well graded sand, (SW) both with less than 5 percent passing, 75 mm sieve (Fines), Well graded gravel — sand mixtures with, or without fines (GW-SW), Poorly-graded sand (SP) or Clayey sand, (SC), all having N above 30, Stiff to hard clays having N above 30, where, N is corrected standard penetration test value, Type B, Poorly graded sands or poorly graded sands, Medium or with gravel (SP) with little or no fines having, stiff soils, N between 10 and 30, Stiff to medium stiff fine-grained soils,, like silts of low compressibility (ML) or, clays of low compressibility (CL) having, N between 10 and 30, Type C, All soft soils other than SP with N<10. The, Soft soils, various possible soils are:, Silts of intermediate compressibility (Ml);, Silts of high compressibility (MH);, Clays of intermediate compressibility (CI);, Clays of high compressibility (CH);, Silts and clays of intermediate to high, com-pressibility (MI-MH or CI-CH);, Silt with clay of intermediate compressibility, (MI-CI); and, Silt with clay of high compressibility, (MH-CH)., Type D, Requires site-specific study and special, Unstable, treatment according to site condition (see, collapsible, 6.3.5.3), liquefiable, soils, , NOTES, 1 The net bearing pressure shall be determined in, accordance with IS 6403 or IS 1888., 2 Only corrected values of N shall be used., 3 If any increase in net bearing pressure has already been, permitted for forces other than seismic forces, the, increase in allowable bearing pressure, when seismic force, is also included, shall not exceed the limits specified, above., 4 The desirable minimum corrected field values of N shall, be as specified below:, Seismic Depth (m) below N Values, Zone, Ground Level, III, IV, and V, , £5, ³10, , 15, 25, , II, , £5, ³10, , 10, 20, , ii), , Remarks, , iii), , For values of, depths between, 5 m and 10 m,, linear, interpolation is, recommended, , If soils of lower N values are encountered than those, specified in the table above, then suitable ground, improvement techniques shall be adopted to achieve, these values. Alternately, deep pile foundations should, be used, which are anchored in stronger strata, underlying, the soil layers that do not meet the requirement., 5 Piles should be designed for lateral loads neglecting lateral, resistance of those soil layers (if any), which are liable, to liquefy., 6 Indian Standards IS 1498 and IS 2131 may be referred, for soil notation, and corrected N values shall be, determined by applying correction factor CN for effective, overburden pressure σ, , Remarks, (3), , iv), , Table 3 Seismic Zone Factor Z, (Clause 6.4.2), , 'vo using relation N = C N N1 ,, , where CN = Pa σ ' vo ≤ 1.7 , P a is the atmospheric, pressure and N1 is the uncorrected SPT value for soil., 7 While using this table, the value of N to be considered, shall be determined as below:, a) Isolated footings — Weighted average of N of soil, layers from depth of founding, to depth of founding, plus twice the breadth of footing;, b) Raft foundations — Weighted average of N of soil, layers from depth of founding, to depth of founding, plus twice the breadth of raft;, c) Pile foundation — Weighted average of N of soil, layers from depth of bottom tip of pile, to depth of, bottom tip of pile plus twice the diameter of pile;, d) Group pile foundation — Weighted average of N of, soil layers from depth of bottom tip of pile group, to, depth of bottom tip of pile group plus twice the width, of pile group; and, e) Well foundation — Weighted average of N of soil, layers from depth of bottom tip of well, to depth of, bottom tip of well plus twice the width of well., , Seismic Zone Factor, (1), , II, (2), , III, (3), , IV, (4), , V, (5), , Z, , 0.10, , 0.16, , 0.24, , 0.36, , 6.4.3 Effects of design earthquake loads applied on, structures can be considered in two ways, namely:, a) Equivalent static method, and, b) Dynamic analysis method., In turn, dynamic analysis can be performed in three, ways, namely:, 1), , Response spectrum method,, , 2), , Modal time history method, and, , 3), , Time history method., , In this standard, Equivalent Static Method, Response, Spectrum Method and Time History Method are, 10

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IS 1893 (Part 1) : 2016, , FIG. 1 SEISMIC ZONES OF INDIA, , © Government of India Copyright, 2016, Based upon Survey of India Political map printed in 2002., The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate baseline., The interstate boundaries between Arunachal Pradesh, Assam and Meghalaya shown on this map are as interpreted from the North-Eastern Areas (Reorganization) Act, 1971, but have, yet to be verified., The state boundaries between Uttarakhand & Uttar Pradesh, Bihar & Jharkhand, and Chhattisgarh & Madhya Pradesh have not been verified by the Governments concerned., The administrative headquarters of Chandigarh, Haryana and Punjab are at Chandigarh., The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India., The responsibility for the correctness of internal details rests with the publisher., NOTE — Towns falling at the boundary of zones demarcation line between two zones shall be considered in higher zone., , FIG. 1 SEISMIC ZONES OF INDIA, , 11

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IS 1893 (Part 1) : 2016, , FIG. 2 DESIGN A CCELERATION COEFFICIENT (Sa /g) (CORRESPONDING TO 5 PERCENT D AMPING), Table 4 Classification of Types of Soils for Determining the Spectrum to be Used to, Estimate Design Earthquake Force, (Clause 6.4.2.1), Sl No., (1), i), , Soil Type, (2), I, Rock or, Hard soils, , ii), , II, Medium or, Stiff soils, , iii), , III, Soft soils, , Remarks, (3), a) Well graded gravel (GW) or well graded sand (SW) both with less than 5 percent passing 75 µm sieve, (Fines), b) Well graded gravel-sand mixtures with or without fines (GW-SW), c) Poorly graded sand (SP) or clayey sand (SC), all having N above 30, d) Stiff to hard clays having N above 30, where N is standard penetration test value, a) Poorly graded sands or poorly graded sands with gravel (SP) with little or no fines having N between 10 and 30, b) Stiff to medium stiff fine-grained soils, like silts of low compressibility (ML) or clays of low, compressibility (CL) having N between 10 and 30, All soft soils other than SP with N<10. The various possible soils are:, a) Silts of intermediate compressibility (Ml);, b) Silts of high compressibility (MH);, c) Clays of intermediate compressibility (CI);, d) Clays of high compressibility (CH);, e) Silts and clays of intermediate to high compressibility (MI-MH or CI-CH);, f) Silt with clay of intermediate compressibility (MI-CI); and, g) Silt with clay of high compressibility (MH-CH)., , 13

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IS 1893 (Part 1) : 2016, adopted. Equivalent static method may be used for, analysis of regular structures with approximate natural, period Ta less than 0.4 s., , 6.4.7 When design acceleration spectrum is developed, specific to a project site, the same may be used for, design of structures of the project. In such cases,, effects of the site-specific spectrum shall not be less, than those arising out of the design spectrum specified, in this standard., , 6.4.3.1 For structural analysis, the moment of inertia, shall be taken as:, a), , In RC and masonry structures: 70 percent of, Igross of columns, and 35 percent of Igross of, beams; and, , 7 BUILDINGS, The four main desirable attributes of an earthquake, resistant building are:, , b) In steel structures: Igross of both beams and, columns., , a), b), c), d), , 6.4.4 Where a number of modes are to be considered in, response spectrum method, Ah as defined in 6.4.2 for, each mode k shall be determined using natural period, Tk of oscillation of that mode., , 7.1 Regular and Irregular Configurations, , 6.4.5 For underground structures and buildings whose, base is located at depths of 30 m or more, Ah at the base, shall be taken as half the value obtained from 6.4.2., This reduced value shall be used only for estimating, inertia effects due to masses at the corresponding levels, below the ground; the inertia effects for the above, ground portion of the building shall be estimated based, on the unreduced value of Ah. For estimating inertia, effects due to masses of structures and foundations, placed between the ground level and 30 m depth, the, design horizontal acceleration spectrum value shall be, linearly interpolated between Ah and 0.5 Ah, where Ah, is as specified in 6.4.2., , Buildings with simple regular geometry and uniformly, distributed mass and stiffness in plan and in elevation,, suffer much less damage, than buildings with irregular, configurations. All efforts shall be made to eliminate, irregularities by modifying architectural planning and, structural configurations. A building shall be considered, to be irregular for the purposes of this standard, even, if any one of the conditions given in Tables 5 and 6 is, applicable. Limits on irregularities for Seismic Zones, III, IV and V and special requirements are laid out in, Tables 5 and 6., Table 5 Definitions of Irregular Buildings – Plan, Irregularities (see Fig. 3), (Clause 7.1), , 6.4.6 The design seismic acceleration spectral value Av, or vertical motions shall be taken as:, ,  2 Z ,   3 × 2  ( 2.5), ,  R, ,  I , , ,   2 Z  2.5,   3 × 2  ( ), ,  R, ,  I , , Av = ,   2 × Z   Sa ,   3 2   g , ,  R, ,  I , , ,   2 × Z   Sa ,   3 2   g , ,  R, ,  I , , , Robust structural configuration,, At least a minimum elastic lateral stiffness,, At least a minimum lateral strength, and, Adequate ductility., , Sl No., (1), , For buildings governed, by IS 1893 (Part 1), , i), , For liquid retaining tanks, governed by IS 1893, (Part 2), , For bridges governed, by IS 1893 (Part 3), , For industrial structures, governed by IS 1893, (Part 4), , Type of Plan Irregularity, (2), Torsional Irregularity, Usually, a well-proportioned building does not twist, about its vertical axis, when, a) the stiffness distribution of the vertical, elements resisting lateral loads is balanced in, plan according to the distribution of mass in, plan (at each storey level); and, b) the floor slabs are stiff in their own plane, (this happens when its plan aspect ratio is, less than 3), A building is said to be torsionally irregular, when,, 1 ) the maximum horizontal displacement of any, floor in the direction of the lateral force at, one end of the floor is more than 1.5 times its, minimum horizontal displacement at the far, end of the same floor in that direction; and, 2 ) the natural period corresponding to the, fundamental torsional mode of oscillation is, more than those of the first two translational, modes of oscillation along each principal plan, directions, In torsionally irregular buildings, when the ratio of, maximum horizontal displacement at one end and, the minimum horizontal displacement at the other, end is,, , The value of Sa/g shall be based on natural period T, corresponding to the first vertical mode of oscillation,, using 6.4.2., 14

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IS 1893 (Part 1) : 2016, , Dmax, Dmin, , Dmax > 1.5 Dmin, , PLAN, 3A TORSIONAL IRREGULARITY, , A/L1> 0.15, or, A/L2> 0.15, , A/L >0.15, , A, , A, L1, , L, A, A, , A, , A, , L, , L2, , PLAN, , PLAN, 3B RE-ENTRANT CORNERS, , Ao>0.5Atotal, , Ao>0.1Atotal, Ao, , Ao, , Atotal, , Atotal, , OPENING LOCATED ANYWHERE IN, THE SLAB, , OPENING LOCATED ALONG ANY, EDGE OF THE SLAB, , PLAN, , PLAN, , 3C FLOOR SLABS HAVING EXCESSIVE CUT-OUT AND OPENINGS, , ELEVATION, 3D OUT-OF-PLANE OFFSETS IN VERTICAL ELEMENTS, , PLAN, , PLAN, , (i), , (ii), , 3E NON-PARALLEL LATERAL FORCE SYSTEM:, (i) MOMENT FRAME BUILDING, and, (ii) MOMENT FRAME BUILDING WITH STRUCTURAL WALLS, , FIG. 3 DEFINITIONS OF IRREGULAR BUILDINGS — PLAN IRREGULARITIES, 15

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IS 1893 (Part 1) : 2016, Table 5 — (Concluded), , Table 6 Definition of Irregular Buildings – Vertical, Irregularities (see Fig. 4), (Clause 7.1), , i), , ii), , in the range 1.5 – 2.0, (a) the building, configuration shall be revised to ensure that, the natural period of the fundamental, torsional mode of oscillation shall be smaller, than those of the first two translational modes, along each of the principal plan directions,, and then (b) three dimensional dynamic, analysis method shall be adopted; and, ii) more than 2.0, the building configuration, shall be revised, Re-entrant Corners, , Sl No., (1), i), , A building is said to have a re-entrant corner in any, plan direction, when its structural configuration in, plan has a projection of size greater than 15 percent, of its overall plan dimension in that direction, In buildings with re-entrant corners, three-dimensional, dynamic analysis method shall be adopted., iii), , iv), , Floor Slabs having Excessive Cut-Outs or, Openings, Openings in slabs result in flexible diaphragm, behaviour, and hence the lateral shear force is not, shared by the frames and/or vertical members in, proportion to their lateral translational stiffness. The, problem is particularly accentuated when the opening, is close to the edge of the slab. A building is said to, have discontinuity in their in-plane stiffness, when, floor slabs have cut-outs or openings of area more, than 50 percent of the full area of the floor slab, , ii), , iii), , In buildings with discontinuity in their in-plane, stiffness, if the area of the geometric cut-out is,, a) less than or equal to 50 percent, the floor slab, shall be taken as rigid or flexible depending on, the location of and size of openings; and, b) more than 50 percent, the floor slab shall be, taken as flexible., Out-of-Plane Offsets in Vertical Elements, Out-of-plane offsets in vertical elements resisting, lateral loads cause discontinuities and detours in the, load path, which is known to be detrimental to the, earthquake safety of the building. A building is said to, have out-of-plane offset in vertical elements, when, structural walls or frames are moved out of plane in, any storey along the height of the building, , iv), , In a building with out-of-plane offsets in vertical elements,, a) specialist literature shall be referred for design, of such a building, if the building is located in, Seismic Zone II; and, b) the following two conditions shall be satisfied, if the, building is located in Seismic Zones III, IV and V:, 1 ) Lateral drift shall be less than 0.2 percent in, the storey having the offset and in the storeys, below; and, 2 ) Specialist literature shall be referred for, removing the irregularity arising due to outof-plane offsets in vertical elements., v), , v), , vi), , Non-Parallel Lateral Force System, Buildings undergo complex earthquake behaviour and, hence damage, when they do not have lateral force, resisting systems oriented along two plan directions, that are orthogonal to each other. A building is said, to have non-parallel system when the vertically, oriented structural systems resisting lateral forces, are not oriented along the two principal orthogonal, axes in plan, , vii), , Buildings with non-parallel lateral force resisting, system shall be analyzed for load combinations, mentioned in 6.3.2.2 or 6.3.4.1., , 16, , Type of Vertical Irregularity, (2), Stiffness Irregularity (Soft Storey), A soft storey is a storey whose lateral stiffness is less, than that of the storey above., The structural plan density (SPD) shall be estimated, when unreinforced masonry infills are used. When, SPD of masonry infills exceeds 20 percent, the effect, of URM infills shall be considered by explicitly, modelling the same in structural analysis (as per, 7.9). The design forces for RC members shall be, larger of that obtained from analysis of:, a) Bare frame, and, b) Frames with URM infills,using 3D modelling of the, structure. In buildings designed considering URM infills,, the inter-storey drift shall be limited to 0.2 percent in, the storey with stiffening and also in all storeys below., Mass Irregularity, Mass irregularity shall be considered to exist, when, the seismic weight (as per 7.7) of any floor is more, than 150 percent of that of the floors below., In buildings with mass irregularity and located in, Seismic Zones III, IV and V, the earthquake effects, shall be estimated by Dynamic Analysis Method (as, per 7.7)., Vertical Geometric Irregularity, Vertical geometric irregularity shall be considered to, exist, when the horizontal dimension of the lateral, force resisting system in any storey is more than, 125 percent of the storey below., In buildings with vertical geometric irregularity and, located in Seismic Zones III, IV and V, the earthquake, effects shall be estimated by Dynamic Analysis, Method (as per 7.7)., In-Plane Discontinuity in Vertical Elements, Resisting Lateral Force, In-plane discontinuity in vertical elements which, are resisting lateral force shall be considered to exist,, when in-plane offset of the lateral force resisting, elements is greater than 20 percent of the plan length, of those elements., In buildings with in-plane discontinuity and located, in Seismic Zones II, the lateral drift of the building, under the design lateral force shall be limited to, 0.2 percent of the building height; in Seismic Zones, III, IV and V, buildings with in-plane discontinuity, shall not be permitted., Strength Irregularity (Weak Storey), A weak storey is a storey whose lateral strength is, less than that of the storey above., In such a case, buildings in Seismic Zones III, IV, and V shall be designed such that safety of the, building is not jeopardized; also, provisions of 7.10, shall be followed., Floating or Stub Columns, Such columns are likely to cause concentrated, damage in the structure., This feature is undesirable, and hence should be, prohibited, if it is part of or supporting the primary, lateral load resisting system., Irregular Modes of Oscillation in Two Principal, Plan Directions, Stiffnesses of beams, columns, braces and structural, walls determine the lateral stiffness of a building in, each principal plan direction. A building is said to, have lateral storey irregularity in a principal plan, direction, if

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IS 1893 (Part 1) : 2016, Table 6 — (Concluded), a), b), , 7.2 Lateral Force, 7.2.1 Design Lateral Force, , the first three modes contribute less than, 65 percent mass participation factor in each, principal plan direction, and, the fundamental lateral natural periods of the, building in the two principal plan directions are, closer to each other by 10 percent of the larger, value., , Buildings shall be designed for the design lateral force, VB given by:, VB = AhW, where Ah shall be estimated as per 6.4.2, and W as per, 7.4., 7.2.2 Minimum Design Lateral Force, , In buildings located in Seismic Zones II and III, it, shall be ensured that the first three modes together, contribute at least 65 percent mass participation, factor in each principal plan direction. And, in, buildings located in Seismic Zones IV and V, it shall, be ensured that,, 1 ) the first three modes together contribute at least, 65 percent mass participation factor in each, principal plan direction, and, 2 ) the fundamental lateral natural periods of the, building in the two principal plan directions, are away from each other by at least 10 percent, of the larger value., , Buildings and portions there of shall be designed and, constructed to resist at least the effects of design, lateral force specified in 7.2.1. But, regardless of, design earthquake forces arrived at as per 7.3.1,, buildings shall have lateral load resisting systems, capable of resisting a horizontal force not less than, (VB)min given in Table 7., , Ki+1, Ki, Ki+1, , Ki+2, Ki+1, Ki, , Ki+1 > Ki+2, Ki+1 > Ki, , Ki+1, Ki, , ELEVATION, 4A STIFFNESS IRREGULARITY (SOFT STOREY), , HEAVY, MASS, , Wi+1, Wi, Wi -1, , ELEVATION, 4B MASS IRREGULARITY, , 17, , Wi > 1.5Wi+1, Wi > 1.5Wi-1

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IS 1893 (Part 1) : 2016, , 4C VERTICAL GEOMETRIC IRREGULARITY, , 4D IN-PLANE DISCONTINUITY IN VERTICAL, ELEMENTS RESISTING LATERAL FORCE, , 4E STRENGTH IRREGULARITY (WEAK STOREY), , FIG. 4 DEFINITIONS OF IRREGULAR BUILDINGS — V ERTICAL IRREGULARITIES, 18

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IS 1893 (Part 1) : 2016, critical damping for the purposes of estimating Ah in, the design lateral force VB of a building as per 7.2.1,, irrespective of the material of construction (namely, steel, reinforced concrete, masonry, or a combination, thereof of these three basic materials) of its lateral load, resisting system, considering that buildings experience, inelastic deformations under design level earthquake, effects, resulting in much higher energy dissipation, than that due to initial structural damping in buildings., This value of damping shall be used, irrespective of, the method of the structural analysis employed, namely, Equivalent Static Method (as per 7.6) or Dynamic, Analysis Method (as per 7.7)., , Table 7 Minimum Design Earthquake Horizontal, Lateral Force for Buildings, (Clause 7.2.2), Sl No., , Seismic Zone, , (1), , (2), , ρ, Percent, (3), , i), ii), iii), iv), , II, III, IV, V, , 0.7, 1.1, 1.6, 2.4, , 7.2.3 Importance Factor (I), In estimating design lateral force VB of buildings as, per 7.2.1, the importance factor I of buildings shall be, taken as per Table 8., , 7.2.5 Design Acceleration Spectrum, Design acceleration coefficient Sa/g corresponding to, 5 percent damping for different soil types, normalized to, peak ground acceleration, corresponding to natural period, T of structure considering soil-structure interaction,, irrespective of the material of construction of the structure., Sa/g shall be as given by expressions in 6.4.2., , Table 8 Importance Factor (I), (Clause 7.2.3), Sl No., (1), i), , ii), iii), , Structure, (2), , I, (3), , 7.2.6 Response Reduction Factor (R), , Important service and community build- 1.5, ings or structures (for example, critical, governance buildings, schools), signature, buildings, monument buildings, lifeline and, emergency buildings (for example,, hospital buildings, telephone exchange, buildings, television station buildings,, radio station buildings, bus station, buildings, metro rail buildings and metro, rail station buildings), railway stations,, airports, food storage buildings (such as, warehouses), fuel station buildings, power, station buildings, and fire station, buildings), and large community hall, buildings (for example, cinema halls,, shopping malls, assembly halls and subway, stations), Residential or commercial buildings [other 1.2, than those listed in Sl No. (i)] with, occupancy more than 200 persons, All other buildings, 1.0, , Response reduction factor, along with damping during, extreme shaking and redundancy: (a) influences the, nonlinear behaviour of buildings during strong, earthquake shaking, and (b) accounts for inherent, system ductility, redundancy and overstrength normally, available in buildings, if designed and detailed as per, this standard and the associated Indian Standards., For the purpose of design as per this standard,, response reduction factor R for different building, systems shall be as given in Table 9. The values of R, shall be used for design of buildings with lateral load, resisting elements, and NOT for just the lateral load, resisting elements, which are built in isolation., 7.2.7 Dual System, Buildings with dual system consist of moment resisting, frames and structural walls (or of moment resisting, frames and bracings) such that both of the following, conditions are valid:, , NOTES, 1 Owners and design engineers of buildings or structures, may choose values of importance factor I more than, those mentioned above., 2 Buildings or structures covered under Sl No. (iii) may be, designed for higher value of importance factor I,, depending on economy and strategy., 3 In Sl No. (ii), when a building is composed of more than, one structurally independent unit, the occupancy size, shall be for each of the structurally independent unit of, the building., 4 In buildings with mixed occupancies, wherein different I, factors are applicable for the respective occupancies,, larger of the importance factor I values shall be used for, estimating the design earthquake force of the building., , a), , Two systems are designed to resist total, design lateral force in proportion to their lateral, stiffness, considering interaction of two, systems at all floor levels; and, , b) Moment resisting frames are designed to, resist independently at least 25 percent of the, design base shear., 7.3 Design Imposed Loads for Earthquake Force, Calculation, , 7.2.4 Damping Ratio, , 7.3.1 For various loading classes specified in IS 875, (Part 2), design seismic force shall be estimated using, , The value of damping shall be taken as 5 percent of, 19

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IS 1893 (Part 1) : 2016, full dead load plus percentage of imposed load as given, in Table 10. The same shall be used in the threedimensional dynamic analysis of buildings also., , 2, 3, , Table 9 Response Reduction Factor R for Building, Systems, (Clause 7.2.6), 4, , Sl No., (1), , Lateral Load Resisting System, (2), , R, (3), , i), , Moment Frame Systems, a) RC buildings with ordinary moment resisting 3.0, frame (OMRF) (see Note 1), b) RC buildings with special moment resisting 5.0, frame (SMRF), c) Steel buildings with ordinary moment resisting 3.0, frame (OMRF) (see Note 1), d) Steel buildings with special moment resisting 5.0, frame (SMRF), ii), Braced Frame Systems (see Note 2), a) Buildings with ordinary braced frame (OBF) 4.0, having concentric braces, b) Buildings with special braced frame (SBF) 4.5, having concentric braces, c) Buildings with special braced frame (SBF) 5.0, having eccentric braces, iii), Structural Wall Systems (see Note 3), a) Load bearing masonry buildings, 1) Unreinforced masonry (designed as per, 1.5, IS 1905) without horizontal RC seismic, bands (see Note 1), 2) Unreinforced masonry (designed as per 2.0, IS 1905) with horizontal RC seismic, bands, 2.5, 3) Unreinforced masonry (designed as per, IS 1905) with horizontal RC seismic, bands and vertical reinforcing bars at, corners of rooms and jambs of openings, (with reinforcement as per IS 4326), 4) Reinforced masonry [see SP 7 (Part 6) 3.0, Section 4], 5) Confined masonry, 3.0, b) Buildings with ordinary RC structural walls 3.0, (see Note 1), c) Buildings with ductile RC structural walls, 4.0, iv), Dual Systems (see Note 3), a) Buildings with ordinary RC structural walls 3.0, and RC OMRFs (see Note 1), b) Buildings with ordinary RC structural walls 4.0, and RC SMRFs (see Note 1), c) Buildings with ductile RC structural walls 4.0, with RC OMRFs (see Note 1), d) Buildings with ductile RC structural walls 5.0, with RC SMRFs, v), Flat Slab – Structural Wall Systems, (see Note 4), RC building with the three features given below:, 3.0, a) Ductile RC structural walls (which are, designed to resist 100 percent of the, design lateral force),, b) Perimeter RC SMRFs (which are designed, to independently resist 25 percent of the, design lateral force), and preferably, c) An outrigger and belt truss system, connecting the core ductile RC, structural walls and the perimeter RC, SMRFs (see Note 1)., NOTES, 1 RC and steel structures in Seismic Zones III, IV and V, , shall be designed to be ductile. Hence, this system is not, allowed in these seismic zones., Eccentric braces shall be used only with SBFs., Buildings with structural walls also include buildings, having structural walls and moment frames, but where,, a) frames are not designed to carry design lateral, loads, or, b) frames are designed to carry design lateral loads,, but do not fulfill the requirements of ‘Dual Systems’., In these buildings, (a) punching shear failure shall be, avoided, and (b) lateral drift at the roof under design, lateral force shall not exceed 0.1 percent., , 7.3.2 For calculation of design seismic forces of, buildings, imposed load on roof need not be, considered. But, weights of equipment and other, permanently fixed facilities should be considered; in, such a case, the reductions of imposed loads, mentioned in Table 10 are not applicable to that part, of the load., Table 10 Percentage of Imposed Load to be, Considered in Calculation of Seismic Weight, (Clause 7.3.1), Sl No., (1), i), ii), , Imposed Uniformity, Distributed Floor Loads, kN/m2, (2), Up to and including 3.0, Above 3.0, , Percentage of, Imposed Load, (3), 25, 50, , 7.3.3 Imposed load values indicated in Table 10 for, calculating design earthquake lateral forces are, applicable to normal conditions. When loads during, earthquakes are more accurately assessed, designers, may alter imposed load values indicated or even replace, the entire imposed load given in Table 10 with actual, assessed load values, subject to the values given in, Table 7 as the minimum values. Where imposed load is, not assessed as per 7.3.1 and 7.3.2,, a), , only that part of imposed load, which, possesses mass, shall be considered; and, , b) lateral earthquake design force shall not be, calculated on contribution of impact effects, from imposed loads., 7.3.4 Loads other than those given above (for example,, snow and permanent equipment) shall be considered, appropriately., 7.3.5 In regions of severe snow loads and sand storms, exceeding intensity of 1.5 kN/m2, 20 percent of uniform, design snow load or sand load, respectively shall be, included in the estimation of seismic weight. In case, the minimum values of seismic weights corresponding, to these load effects given in IS 875 are higher, the, higher values shall be used., 20

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IS 1893 (Part 1) : 2016, 7.3.6 In buildings that have interior partitions, the, weight of these partitions on floors shall be included, in the estimation of seismic weight; this value shall not, be less than 0.5 kN/m2. In case the minimum values of, seismic weights corresponding to partitions given in, parts of IS 875 are higher, the higher values shall be, used. It shall be ensured that the weights of these, partitions shall be considered only in estimating inertial, effects of the building., , where, h = height (in m) of building (see Fig. 5). This, excludes the basement storeys, where, basement storey, walls are connected, with the ground floor deck or fitted, between the building columns, but, includes the basement storeys, when, they are not so connected., b) Buildings with RC structural walls:, , 7.4 Seismic Weight, , Ta =, , 7.4.1 Seismic Weight of Floors, Seismic weight of each floor is its full dead load plus, appropriate amount of imposed load, as specified in 7.3., While computing the seismic weight of each floor, the weight, of columns and walls in any storey shall be appropriately, apportioned to the floors above and below the storey., , 0.09h, d, , 2, Nw , ,  L   , Aw = ∑  Awi 0.2 +  wi   ,  h   , i =1 , , , where, , h, , = height of building as defined in, 7.6.2(a), in m;, , Awi = effective cross-sectional area of wall i, in first storey of building, in m2;, L wi = length of structural wall i in first storey, in the considered direction of lateral, forces, in m;, , 7.6 Equivalent Static Method, As per this method, first, the design base shear VB shall, be computed for the building as a whole. Then, this VB, shall be distributed to the various floor levels at the, corresponding centres of mass. And, finally, this design, seismic force at each floor level shall be distributed to, individual lateral load resisting elements through, structural analysis considering the floor diaphragm, action. This method shall be applicable for regular, buildings with height less than 15 m in Seismic Zone II., , d, , Nw, , 7.6.1 The design base shear VB along any principal, direction of a building shall be determined by:, , = base dimension of the building at the, plinth level along the considered, direction of earthquake shaking, in m;, and, = number of walls in the considered, direction of earthquake shaking., , The value of Lwi/h to be used in this equation, shall not exceed 0.9., , VB = AhW, where, A h = design horizontal acceleration coefficient value, as per 6.4.2, using approximate fundamental, natural period T a as per 7.6.2 along the, considered direction of shaking; and, , c), , All other buildings:, , Ta =, , 0.09h, , d, where, h = height of building, as defined in 7.6.2(a),, in m; and, , W = seismic weight of the building as per 7.4., 7.6.2 The approximate fundamental translational natural, period Ta of oscillation, in second, shall be estimated, by the following expressions:, , d = base dimension of the building at the plinth, level along the considered direction of, earthquake shaking, in m., 7.6.3 The design base shear (VB) computed in 7.6.1, shall be distributed along the height of the building, and in plan at each floor level as below:, , Bare MRF buildings (without any masonry, infills):, , 0.075 0.75, h, , , , Ta = 0.080h0.75, , , 0.085h0.75, , , ≥, , where Aw is total effective area (m2) of walls in, the first storey of the building given by:, , 7.4.2 Any weight supported in between storeys shall, be distributed to floors above and below in inverse, proportion to its distance from the floors., , a), , 0.075h0.75, Aw, , (for RC MRF building), , a), , (for RC-Steel Composite, MRF building), (for steel MRF building), 21, , Vertical distribution of base shear to different, floor levels — The design base shear V B, computed in 7.6.1 shall be distributed along, the height of the building as per the following, expression:

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IS 1893 (Part 1) : 2016, , 5A, , 7.6.1, , 7.6.1, , 5B, , 5B, , 5E, , 5D, , FIG . 5 DEFINITIONS OF H EIGHT AND BASE WIDTH OF BUILDINGS, 22

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IS 1893 (Part 1) : 2016, ,  W h2, Qi =  n i i, , 2,  ∑ W j hj,  j =1, , Usually, reinforced concrete monolithic slab-beam, floors or those consisting of prefabricated or precast, elements with reasonable reinforced screed concrete, (at least a minimum of 50 mm on floors and of 75 mm on, roof, with at least a minimum reinforcement of 6 mm, bars spaced at 150 mm centres) as topping, and of plan, aspect ratio less than 3, can be considered to be, providing rigid diaphragm action., , , ,  VB, , , , , where, Qi = design lateral force at floor i;, Wi = seismic weight of floor i;, hi, n, , 7.7 Dynamic Analysis Method, , = height of floor i measured from base;, and, = number of storeys in building, that is,, number of levels at which masses are, located., , 7.7.1 Linear dynamic analysis shall be performed to, obtain the design lateral force (design seismic base, shear, and its distribution to different levels along the, height of the building, and to various lateral load, resisting elements) for all buildings, other than regular, buildings lower than 15 m in Seismic Zone II., , b) In-plan distribution of design lateral force, at floor i to different lateral force resisting, elements — The design storey shear in any, storey shall be calculated by summing the, design lateral forces at all floor above that, storey. In buildings whose floors are capable, of providing rigid horizontal diaphragm action, in their own plane, the design storey shear, shall be distributed to the various vertical, elements of lateral force resisting system in, proportion to the lateral stiffness of these, vertical elements., , 7.7.2 The analytical model for dynamic analysis of, buildings with unusual configuration should be such, that it adequately represents irregularities present in, the building configuration., 7.7.3 Dynamic analysis may be performed by either the, Time History Method or the Response Spectrum, Method. When either of the methods is used, the design, base shear VB estimated shall not be less than the design, base shear V B calculated using a fundamental period, Ta, where Ta is as per 7.6.2., , 7.6.4 Diaphragm, , When VB is less than V B , the force response quantities, (for example member stress resultants, storey shear, forces, and base reactions) shall be multiplied by, , In buildings whose floor diaphragms cannot provide, rigid horizontal diaphragm action in their own plane,, design storey shear shall be distributed to the various, vertical elements of lateral force resisting system, considering the in-plane flexibility of the diaphragms., , V B VB . For earthquake shaking considered along,, a), , A floor diaphragm shall be considered to be flexible, if it, deforms such that the maximum lateral displacement, measured from the chord of the deformed shape at any, point of the diaphragm is more than 1.2 times the average, displacement of the entire diaphragm (see Fig. 6)., , the two mutually perpendicular plan directions, X and Y, separate multiplying factors shall be, calculated, namely V BX VBX and V BY VBY ,, respectively; and, , b) the vertical Z direction, the multiplying factor, shall be taken as Max V BX VBX ;V BY VBY  ., 7.7.4 Time History Method, Time history method shall be based on an appropriate, ground motion (preferably compatible with the design, acceleration spectrum in the desired range of natural, periods) and shall be performed using accepted, principles of earthquake structural dynamics., 7.7.5 Response Spectrum Method, Response spectrum method may be performed for any, building using the design acceleration spectrum, specified in 6.4.2, or by a site-specific design, acceleration spectrum mentioned in 6.4.7., , FIG . 6 DEFINITION OF FLEXIBLE FLOOR DIAPHRAGM, 23

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IS 1893 (Part 1) : 2016, , ωi = circular natural frequency in mode i., b) Alternatively, the peak response quantities, may be combined as follows:, , 7.7.5.1 Natural modes of oscillation, Undamped free vibration analysis of the entire building, shall be performed as per established methods of, structural dynamics using appropriate mass and elastic, stiffness of the structural system, to obtain natural, periods Tk and mode shapes {φ}k of those of its Nm, modes of oscillation [k ∈(1,Nm)] that need to be, considered as per 7.7.5.2., , 1), , λ=, , 7.7.5.2 Number of modes to be considered, The number of modes Nm to be used in the analysis for, earthquake shaking along a considered direction,, should be such that the sum total of modal masses of, these modes considered is at least 90 percent of the, total seismic mass., , where, , 2), , c, , Peak response quantities (for example, member, forces, displacements, storey forces, storey, shears, and base reactions) may be combined, as per Complete Quadratic Combination (CQC), method, as given below:, λ =, , i =1, , j =1, , ∑∑, , 7.7.5.4 Simplified method of dynamic analysis of, buildings, Regular buildings may be analyzed as a system of, masses lumped at the floor levels with each mass, having one degree of freedom, that of lateral, displacement in the direction under consideration. In, such a case, the following expressions shall hold in the, computation of the various quantities:, , λ i ρij λ j, , where, λ = estimate of peak response quantity;, , a), , λi = response quantity in mode i (with sign);, λj = response quantity in mode j (with sign);, , ρij = cross-modal correlation co-efficient, =, , 8 ζ 2 (1 + β ) β1.5, , (1 − β ), , 2 2, , + 4 ζ 2β, , (1 + β )2, , If building has a few closely-spaced, modes, then net peak response quantity, λ∗ due to these closely space modes alone, shall be obtained as:, where, λc = peak response quantity in closely, spaced mode c. The summation is, for closely spaced modes only., Then, this peak response quantity, λ∗ due to closely spaced modes is, combined with those of remaining, well-separated modes by method, described above., , The responses of different modes considered shall be, combined by one of the two methods given below:, , Nm, , k =1, , 2, , k, , λ * = ∑ λc, , 7.7.5.3 Combination of modes, , Nm, , Nm, , ∑ (λ ), , λk = peak response quantity in mode k,, and, Nm = number of modes considered., , If modes with natural frequencies beyond 33 Hz are to, be considered, the modal combination shall be carried, out only for modes with natural frequency less than, 33 Hz; the effect of modes with natural frequencies more, than 33 Hz shall be included by the missing mass, correction procedure following established principles, of structural dynamics. If justified by rigorous analysis,, designers may use a cut off frequency other than 33 Hz., , a), , If building does not have closely-spaced, modes, then net peak response quantity, λ due to all modes considered shall be, estimated as:, , Modal mass — Modal mass Mk of mode k is, given by:, 2, ,  n, ,  ∑Wiφik , , M k =  in=1, 2, g∑Wi (φik ), , ;, , i =1, , where, g = acceleration due to gravity,, , Nm = number of modes considered;, , ζ = modal damping coefficient ratio which, , φik = mode shape coefficient at floor i in, mode k,, Wi = seismic weight of floor i of the structure,, and, n = number of floors of the structure., , shall be taken as 0.05;, , ωj, β = natural frequency ratio = ω ;, i, , ω j = circular natural frequency in mode j; and, 24

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IS 1893 (Part 1) : 2016, b) Mode participation factor — Mode, participation factor Pk of mode k is given by:, , where, e si = static eccentricity at floor i,, = distance between centre of mass and centre, of resistance, and, b i = floor plan dimension of floor i, perpendicular, to the direction of force., , n, , Pk =, , ∑W φ, n, , ∑ W (φ ), , 2, , i, , i =1, , c), , i ik, , i =1, , ik, , Design lateral force at each floor in each, mode — Peak lateral force Qik at floor i in mode, k is given by:, , The factor 1.5 represents dynamic amplification factor,, and 0.05b i represents the extent of accidental, eccentricity. The above amplification of 1.5 need not, be used, when performing structural analysis by the, Time History Method., , Qik = Akφik PkWi, where, A k = design horizontal acceleration spectrum, value as per 6.4.2 using natural period, of oscillation Tk of mode k obtained, from dynamic analysis., , 7.9 RC Frame Buildings with Unreinforced Masonry, Infill Walls, 7.9.1 In RC buildings with moment resisting frames, and unreinforced masonry (URM) infill walls, variation, of storey stiffness and storey strength shall be, examined along the height of the building considering, in-plane stiffness and strength of URM infill walls. If, storey stiffness and strength variations along the, height of the building render it to be irregular as per, Table 6, the irregularity shall be corrected especially in, Seismic Zones III, IV and V., , d) Storey shear forces in each mode — Peak, shear force Vik acting in storey i in mode k is, given by:, , Vik =, e), , f), , n, , ∑Q, , j = i +1, , ik, , Storey shear force due to all modes, considered — Peak storey shear force Vi in, storey i due to all modes considered, shall be, obtained by combining those due to each, mode in accordance with 7.7.5.3., , 7.9.2 The estimation of in-plane stiffness and strength, of URM infill walls shall be based on provisions given, hereunder., , Lateral forces at each storey due to all modes, considered — Design lateral forces Froof at roof, level and Fi at level of floor i shall be obtained, as:, , 7.9.2.1 The modulus of elasticity E m (in MPa) of, masonry infill wall shall be taken as:, , Froof = Vroof , and, , where fm is the compressive strength of masonry prism, (in MPa) obtained as per IS 1905 or given by expression:, , Em = 550 fm, , Fi = Vi – Vi+1., , 0.36, f m = 0.433 f b0.64 f mo, , 7.8 Torsion, where, , 7.8.1 Provision shall be made in all buildings for increase, in shear forces on the lateral force resisting elements, resulting from twisting about the vertical axis of the, building, arising due to eccentricity between the centre, of mass and centre of resistance at the floor levels. The, design forces calculated as in 7.6 and 7.7.5, shall be, applied at the displaced centre of mass so as to cause, design eccentricity (as given by 7.8.2) between the, displaced centre of mass and centre of resistance., , fb = compressive strength of brick, in MPa; and, fmo = compressive strength of mortar, in MPa., 7.9.2.2 URM infill walls shall be modeled by using, equivalent diagonal struts as below:, a), , Ends of diagonal struts shall be considered, to be pin-jointed to RC frame;, , b) For URM infill walls without any opening, width, wds of equivalent diagonal strut (see Fig. 7) shall, be taken as:, , 7.8.2 Design Eccentricity, While performing structural analysis by the Seismic, Coefficient Method or the Response Spectrum Method,, the design eccentricity edi to be used at floor i shall be, taken as:, 1.5esi + 0.05bi, edi = ,  esi − 0.05bi, , where, , wds = 0.175α h−0.4 Lds, ,  E t sin 2θ, α h = h  4 m,  4 Ef I c h, , whichever gives the more severe effect on lateral force, resisting elements;, 25, , , , 

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IS 1893 (Part 1) : 2016, c), , connected preferably to the moment resisting, frame of the building., , where Em and Ef are the modulii of elasticity, of the materials of the URM infill and RC, MRF, Ic the moment of inertia of the adjoining, column, t the thickness of the infill wall, and, θ the angle of the diagonal strut with the, horizontal;, For URM infill walls with openings, no, reduction in strut width is required; and, , 7.10.3 When the RC structural walls are provided, they, shall be designed such that the building does NOT, have:, , d) Thickness of the equivalent diagonal strut, shall be taken as thickness t of original URM, infill wall, provided h/t < 12 and l/t < 12, where, h is clear height of URM infill wall between, the top beam and bottom floor slab, and l clear, length of the URM infill wall between the, vertical RC elements (columns, walls or a, combination thereof) between which it spans., , b) Lateral stiffness in the open storey(s) is less, than 80 percent of that in the storey above;, and, , c), , a), , c), , Additional torsional irregularity in plan than, that already present in the building. In, assessing this, lateral stiffness shall be, included of all elements that resist lateral, actions at all levels of the building;, , Lateral strength in the open storey(s) is less, than 90 percent of that in the storey above., , 7.10.4 When the RC structural walls are provided, the, RC structural wall plan density ρsw of the building shall, be at least 2 percent along each principal direction in, Seismic Zones III, IV and V. These walls shall be well, distributed in the plan of the building along each plan, direction. RC structural walls of this measure can be, adopted even in regular buildings that do not have, open storey(s)., 7.10.5 RC structural walls in buildings located in, Seismic Zones III, IV and V shall be designed and, detailed to comply with all requirements of IS 13920., 7.11 Deformation, , FIG. 7 EQUIVALENT DIAGONAL STRUT OF URM, INFILL WALL, , Deformation of RC buildings shall be obtained from, structural analysis using a structural model based on, section properties given in 6.4.3., , 7.10 RC Frame Buildings with Open Storeys, 7.10.1 RC moment resisting frame buildings, which have, open storey(s) at any level, such as due to, discontinuation of unreinforced masonry (URM) infill, walls or of structural walls, are known to have flexible, and weak storeys as per Table 6. In such buildings,, suitable measures shall be adopted, which increase both, stiffness and strength to the required level in the open, storey and the storeys below. These measures shall be, taken along both plan directions as per requirements, laid down under 7.10.2 to 7.10.4. The said increase, may be achieved by providing measures, like:, a), , 7.11.1 Storey Drift Limitation, 7.11.1.1 Storey drift in any storey shall not exceed 0.004, times the storey height, under the action of design base, of shear VB with no load factors mentioned in 6.3, that, is, with partial safety factor for all loads taken as 1.0., 7.11.1.2 Displacement estimates obtained from dynamic, analysis methods shall not be scaled as given in 7.7.3., 7.11.2 Deformation Capability of Non-Seismic, Members, , RC structural walls, or, , For buildings located in Seismic Zones III, IV and V, it, shall be ensured that structural components, that are, not a part of seismic force resisting system in considered, direction of ground motion but are monolithically, connected, do not lose their vertical load-carrying, capacity under induced net stress resultants, including, additional bending moments and shear forces resulting, from storey deformations equal to R times storey, displacements calculated as per 7.11.1, where R is, specified in Table 9., , b) Braced frames, in select bays of the building., 7.10.2 When the RC structural walls are provided, they, shall be,, a), , founded on properly designed foundations;, , b) continuous preferably over the full height of, the building; and, , 26

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IS 1893 (Part 1) : 2016, 7.11.3 Separation between Adjacent Units, , moments due to fixity to pile cap., , Two adjacent buildings, or two adjacent units of the, same building with separation joint between them,, shall be separated by a distance equal to R times sum, of storey displacements ∆1 and ∆2 calculated as per, 7.11.1 of the two buildings or two units of the same, building, to avoid pounding as the two buildings or, two units of the same building oscillate towards each, other., , 7.12.2 Cantilever Projections, 7.12.2.1 Vertical projections, Small-sized facilities (like towers, tanks, parapets, smoke, stacks/chimneys) and other vertical cantilever, projections attached to buildings and projecting, vertically above the roof, but not a part of the structural, system of the building, shall be designed and checked, for stability for five times the design horizontal seismic, coefficient Ah specified in 6.4.2 for that building. In the, analysis of the building, weights of these projecting, elements shall be lumped with the roof weight., , When floor levels of the adjacent units of a building or, buildings are at the same level, the separation distance, shall be calculated as (R1∆1 + R2∆2), where R1 and ∆1, correspond to building 1, and R2 and ∆2 to building 2., , 7.12.2.2 Horizontal projections, , 7.12 Miscellaneous, , All horizontal projections of buildings (like cantilever, structural members at the porch level or higher) or, attached to buildings (like brackets, cornices and, balconies) shall be designed for five times the design, vertical coefficient Av specified in 6.4.6 for that building., , 7.12.1 Foundations, Isolated RC footings without tie beams or unreinforced, strip foundations, shall not be adopted in buildings, rested on soft soils (with corrected N < 10) in any, Seismic Zone. Use of foundations vulnerable to, significant differential settlement due to ground shaking, shall be avoided in buildings located in Seismic Zones, III, IV and V., , 7.12.2.3 The increased design forces specified, in 7.12.2.1 and 7.12.2.2 are only for designing the, projecting parts and their connections with the main, structures, and NOT for the design of the main, structure., , Individual spread footings or pile caps shall be, interconnected with ties (see 5.3.4.1 of IS 4326), except, when individual spread footings are directly supported, on rock, in buildings located in Seismic Zones IV and V., All ties shall be capable of carrying, in tension and in, compression, an axial force equal to Ah/4 times the larger, of the column or pile cap load, in addition to the, otherwise computed forces, subject to a minimum of, 5 percent of larger of column or pile cap loads. Here,, Ah is as per 6.4.2., , 7.12.3 Compound Walls, Compound walls shall be designed for the design, horizontal coefficient Ah of 1.25Z, that is, Ah calculated, using 6.4.2 with I = 1, R = 1 and Sa/g = 2.5., 7.12.4 Connections between Parts, All small items and objects of a building shall be tied to, the building or to each other to act as single unit, except, those between the separation joints and seismic joints., These connections shall be made capable of, transmitting the forces induced in them, but not less, than 0.05 times weight of total dead and imposed load, reactions; frictional resistance shall not be relied upon, in these calculations., , Pile shall be designed and constructed to withstand, maximum curvature imposed (structural response) by, earthquake ground shaking. Design of anchorage of, piles into the pile cap shall consider combined effects,, including that of axial forces due to uplift and bending, , 27

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IS 1893 (Part 1) : 2016, , ANNEX A, (Foreword), MAP OF INDIA SHOWING EPICENTRES OF PAST EARTHQUAKES IN INDIA, (From Catalog of 2015), , © Government of India Copyright, 2016, Based upon Survey of India Political map printed in 2002., The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate baseline., The interstate boundaries between Arunachal Pradesh, Assam and Meghalaya shown on this map are as interpreted from the North-Eastern Areas (Reorganization) Act, 1971, but have, yet to be verified., The state boundaries between Uttarakhand & Uttar Pradesh, Bihar & Jharkhand, and Chhattisgarh & Madhya Pradesh have not been verified by the Governments concerned., The administrative headquarters of Chandigarh, Haryana and Punjab are at Chandigarh., The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India., The responsibility for the correctness of internal details rests with the publisher., , NOTE — For details regarding the up-to-date seismic activity (plotted on the Map of India), please visit the online portal of the National Centre for Seismology (NCS),, Ministry of Earth Sciences, New Delhi., , 28

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IS 1893 (Part 1) : 2016, , ANNEX B, (Foreword), MAP OF INDIASHOWING PRINCIPALTECTONIC FEATURES IN INDIA, (From Catalog of 2001), , © Government of India Copyright, 2016, , Based upon Survey of India Political map printed in 2002., The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate baseline., The interstate boundaries between Arunachal Pradesh, Assam and Meghalaya shown on this map are as interpreted from the North-Eastern Areas (Reorganization) Act, 1971, but have, yet to be verified., The state boundaries between Uttarakhand & Uttar Pradesh, Bihar & Jharkhand, and Chhattisgarh & Madhya Pradesh have not been verified by the Governments concerned., The administrative headquarters of Chandigarh, Haryana and Punjab are at Chandigarh., The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India., The responsibility for the correctness of internal details rests with the publisher., , 30

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IS 1893 (Part 1) : 2016, , ANNEX C, (Foreword), MAP OF INDIA SHOWING PRINCIPAL LITHOLOGICAL GROUPS, , © Government of India Copyright, 2016, Based upon Survey of India Political map printed in 2002., The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate baseline., The interstate boundaries between Arunachal Pradesh, Assam and Meghalaya shown on this map are as interpreted from the North-Eastern Areas (Reorganization) Act, 1971, but have, yet to be verified., The state boundaries between Uttarakhand & Uttar Pradesh, Bihar & Jharkhand, and Chhattisgarh & Madhya Pradesh have not been verified by the Governments concerned., The administrative headquarters of Chandigarh, Haryana and Punjab are at Chandigarh., The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India., The responsibility for the correctness of internal details rests with the publisher., , 32

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IS 1893 (Part 1) : 2016, , ANNEX D, (Foreword and Clause 3.11), MSK 1964 INTENSITY SCALE, D-1 The following description shall be applicable., a), , limits of sensibility; the tremor is detected and, recorded by seismograph only., , Type of Structures (Buildings), ii), , Type A — Building in field-stone, rural, structures, un-burnt brick houses,, clay houses, , iii) —, II Scarcely Noticeable (Very Slight), , Type B — Ordinary brick buildings, buildings, of large block and prefabricated, type, half timbered structures,, buildings in natural hewn stone, Type C — Reinforced buildings, well built, wooden structures, , c), , :, :, :, , Vibration is felt only by individual people at, rest in houses, especially on upper floors of, buildings., , ii), , —, , III Weak, Partially Observed, , About 5 percent, About 50 percent, About 75 percent, , i), , The earthquake is felt indoors by a few people,, outdoors only in favourable circumstances., The vibration is like that due to the passing of, a light truck. Attentive observers notice a, slight swinging of hanging objects., , ii), , —, , Classification of Damage to Buildings, , Classification Damage, Grade 1, Grade 2, , Grade 3, , Slight, damage, Moderate, damage, , Grade 4, , Heavy, damage, Destruction, , Grade 5, , Total damage, , Description, Fine cracks in plaster; fall, of small pieces of plaster, Small cracks in walls; fall, of fairly larger pieces of, plaster; pantiles slip off;, cracks in chimneys parts, of chimney fall down, Large and deep cracks in, walls; fall of chimneys, Gaps in walls; parts of, buildings may collapse;, separate parts of the, buildings lose their, cohesion; and inner, walls collapse, Total collapse of the, building, , iii) —, IV Largely Observed, , Persons and surroundings,, , ii), , Structures of all kinds, and, , The earthquake is felt indoors by many, people, outdoors by few. Here and there, people awake, but no one is frightened. The, vibration is like that due to the passing of a, heavily loaded truck. Windows, doors, and, dishes rattle. Floors and walls crack., Furniture begins to shake. Hanging objects, swing slightly. Liquid in open vessels are, slightly disturbed. In standing motor cars the, shock is noticeable., , ii), , —, , V Awakening, , D-2.1 The following introductory letters (i), (ii) and, (iii) have been used throughout the intensity scales, (I to XII), describing the following:, i), , i), , iii) —, , D-2 MSK INTENSITY SCALE, , i), , iii) Nature., I Not Noticeable, i), , i), , iii) —, , b) Definition of Quantity, Single, few, Many, Most, , —, , The intensity of the vibration is below the, 34, , The earthquake is felt indoors by all, outdoors, by many. Many people awake. A few run, outdoors. Animals become uneasy. Buildings, tremble throughout. Hanging objects swing, considerably. Pictures knock against walls or, swing out of place. Occasionally pendulum, clocks stop. Unstable objects overturn or, shift. Open doors and windows are thrust, open and slam back again. Liquids spill in small, amounts from well-filled open containers. The

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IS 1893 (Part 1) : 2016, sensation of vibration is like that due to heavy, objects falling inside the buildings., ii), , ii), , Slight damages in buildings of Type A are, possible., , iii) Slight waves on standing water. Sometimes, changes in flow of springs., , iii) Small landslips in hollows and on banked, roads on steep slopes; cracks in ground up to, widths of several centimetres. Water in lakes, become turbid. New reservoirs come into, existence. Dry wells refill and existing wells, become dry. In many cases, change in flow, and level of water is observed., , VI Frightening, i), , ii), , Felt by most indoors and outdoors. Many, people in buildings are frightened and run, outdoors. A few persons loose their balance., Domestic animals run out of their stalls. In, few instances, dishes and glassware may, break, and books fall down, pictures move,, and unstable objects overturn. Heavy, furniture may possibly move and small steeple, bells may ring., , IX General Damage of Buildings, , Damage of Grade 1 is sustained in single, buildings of Type B and in many of Type A., Damage in some buildings of Type A is of, Grade 2., , i), , General panic; considerable damage to, furniture. Animals run to and fro in confusion, and cry., , ii), , Many buildings of Type C suffer damage of, Grade 3, and a few of Grade 4. Many buildings, of Type B show a damage of Grade 4 and a, few of Grade 5. Many buildings of Type A, suffer damage of Grade 5. Monuments and, columns fall. Considerable damage to, reservoirs; underground pipes partly broken., In individual cases, railway lines are bent and, roadway damaged., , iii) Cracks up to widths of 10 mm possible in wet, ground; in mountains occasional landslips:, change in flow of springs and in level of well, water are observed., VII Damage of Buildings, i), , Most people are frightened and run outdoors., Many find it difficult to stand. The vibration, is noticed by persons driving motor cars., Large bells ring., , ii), , In many buildings of Type C damage of Grade 1, is caused; in many buildings of Type B damage, is of Grade 2. Most buildings of Type A suffer, damage of Grade 3, few of Grade 4. In single, instances, landslides of roadway on steep, slopes: crack in roads; seams of pipelines, damaged; cracks in stone walls., , iii) On flat land overflow of water, sand and mud, is often observed. Ground cracks to widths of, up to 10 cm, on slopes and river banks more, than 10 cm. Furthermore, a large number of, slight cracks in ground; falls of rock, many, land slides and earth flows; large waves in, water. Dry wells renew their flow and existing, wells dry up., X General Destruction of Buildings, , iii) Waves are formed on water, and water is made, turbid by mud stirred up. Water levels in wells, change, and the flow of springs changes., Sometimes dry springs have their flow, restored and existing springs stop flowing. In, isolated instances parts of sand and gravelly, banks slip off., VIII Destruction of Buildings, i), , 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. Most, buildings of Type A suffer damage of Grade 4., Occasional breaking of pipe seams. Memorials, and monuments move and twist. Tombstones, overturn. Stone walls collapse., , i), , —, , ii), , Many buildings of Type C suffer damage of, Grade 4, and a few of Grade 5. Many buildings, of Type B show damage of Grade 5. Most of, Type A has destruction of Grade 5. Critical, damage to dykes and dams. Severe damage, to bridges. Railway lines are bent slightly., Underground pipes are bent or broken. Road, paving and asphalt show waves., , iii) In ground, cracks up to widths of several, centimetres, sometimes up to 1 m, parallel to, water courses occur broad fissures. Loose, ground slides from steep slopes. From river, banks and steep coasts, considerable, landslides are possible. In coastal areas,, , Fright and panic; also persons driving motor, cars are disturbed. Here and there branches, of trees break off. Even heavy furniture moves, and partly overturns. Hanging lamps are, damaged in part., 35

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IS 1893 (Part 1) : 2016, displacement of sand and mud; change of, water level in wells; water from canals, lakes,, rivers, etc, thrown on land. New lakes occur., , requires to be investigated specifically., XII Landscape Changes, , XI Destruction, i), , —, , ii), , Severe damage even to well built buildings,, bridges, water dams and railway lines., Highways become useless. Underground, pipes destroyed., , i), , —, , ii), , Practically all structures above and below, ground are greatly damaged or destroyed., , iii) The surface of the ground is radically, changed. Considerable ground cracks with, extensive vertical and horizontal movements, are observed. Falling of rock and slumping of, river banks over wide areas, lakes are dammed;, waterfalls appear and rivers are deflected. The, intensity of the earthquake requires to be, investigated specially., , iii) Ground considerably distorted by broad cracks, and fissures, as well as movement in horizontal, and vertical directions. Numerous landslips and, falls of rocks. The intensity of the earthquake, , ANNEX E, (Foreword), LIST OF SOME TOWNS WITH POPULATION MORE THAN 3 LAKHS (as per CENSUS 2011), AND THEIR SEISMIC ZONE FACTOR Z, Town, Agra, Ahmedabad, Ajmer, Allahabad, Almora, Ambala, Amritsar, Asansol, Aurangabad, Bahraich, Bangalore (Bengaluru), Barauni, Bareilly, Belgaum, Bhatinda, Bhilai, Bhopal, Bhubaneswar, Bhuj, Bijapur, Bikaner, Bokaro, Bulandshahr, Burdwan, , Zone, III, III, II, II, IV, IV, IV, III, II, IV, II, IV, III, III, III, II, II, III, V, III, III, III, IV, III, , Town, Calicut (Kozhikode), Chandigarh, Chennai, Chitradurga, Coimbatore, Cuddalore, Cuttack, Darbhanga, Darjeeling, Dharwad, Dehra Dun, Dharampuri, Delhi, Durgapur, Gangtok, Guwahati, Gulbarga, Gaya, Gorakhpur, Hyderabad, Imphal, Jabalpur, Jaipur, Jamshedpur, , Z, 0.16, 0.16, 0.10, 0.10, 0.24, 0.24, 0.24, 0.16, 0.10, 0.24, 0.10, 0.24, 0.16, 0.16, 0.16, 0.10, 0.10, 0.16, 0.36, 0.16, 0.16, 0.16, 0.24, 0.16, 36, , Zone, III, IV, III, II, III, II, III, V, IV, III, IV, III, IV, III, IV, V, II, III, IV, II, V, III, II, II, , Z, 0.16, 0.24, 0.16, 0.10, 0.16, 0.10, 0.16, 0.36, 0.24, 0.16, 0.24, 0.16, 0.24, 0.16, 0.24, 0.36, 0.10, 0.16, 0.24, 0.10, 0.36, 0.16, 0.10, 0.10

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IS 1893 (Part 1) : 2016, Town, Jhansi, Jodhpur, Jorhat, Kakrapara, Kalpakkam, Kanchipuram, Kanpur, Karwar, Kochi, Kohima, Kolkata, Kota, Kurnool, Lucknow, Ludhiana, Madurai, Mandi, Mangaluru, Mungher, Moradabad, Mumbai, Mysuru, Nagpur, Nagarjunasagar, Nainital, Nashik, Nellore, Osmanabad, Panjim, Patiala, , Zone, II, II, V, III, III, III, III, III, III, V, III, II, II, III, IV, II, V, III, IV, IV, III, II, II, II, IV, III, III, III, III, III, , Z, 0.10, 0.10, 0.36, 0.16, 0.16, 0.16, 0.16, 0.16, 0.16, 0.36, 0.16, 0.10, 0.10, 0.16, 0.24, 0.10, 0.36, 0.16, 0.24, 0.24, 0.16, 0.10, 0.10, 0.10, 0.24, 0.16, 0.16, 0.16, 0.16, 0.16, , Town, Zone, Patna, IV, Pilibhit, IV, Pondicherry (Puducherry) II, Pune, III, Raipur, II, Rajkot, III, Ranchi, II, Roorkee, IV, Rourkela, II, Sadiya, V, Salem, III, Shillong, V, Shimla, IV, Sironj, II, Solapur, III, Srinagar, V, Surat, III, Tarapur, III, Tezpur, V, Thane, III, Thanjavur, II, Thiruvananthapuram, III, Tiruchirappalli, II, Tiruvannamalai, III, Udaipur, II, Vadodara, III, Varanasi, III, Vellore, III, Vijayawada, III, Vishakhapatnam, II, , 37, , Z, 0.24, 0.24, 0.10, 0.16, 0.10, 0.16, 0.10, 0.24, 0.10, 0.36, 0.16, 0.36, 0.24, 0.10, 0.16, 0.36, 0.16, 0.16, 0.36, 0.16, 0.10, 0.16, 0.10, 0.16, 0.10, 0.16, 0.16, 0.16, 0.16, 0.10

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IS 1893 (Part 1) : 2016, , ANNEX F, (Clauses 3.12 and 6.3.5.3), SIMPLIFIED PROCEDURE FOR EVALUATION OF LIQUEFACTION POTENTIAL, F-1 Due to the difficulties in obtaining and testing, undisturbed representative samples from potentially, liquefiable sites, in-situ testing is the approach, preferred widely for evaluating the liquefaction, potential of a soil deposit. Liquefaction potential, assessment procedures involving both the SPT and, CPT are widely used in practice. The most common, procedure used in engineering practice for the, assessment of liquefaction potential of sands and silts, is the simplified procedure. The procedure may be, used with either standard penetration test (SPT) blow, count or cone penetration test (CPT) tip resistance or, shear wave velocity Vs measured within the deposit, as described below:, , and high initial static shear stress using:, , CRR7.5= standard cyclic resistance ratio for a 7.5, magnitude earthquake obtained using, values of SPT or CPT or shear wave, velocity (as per Step 6), and, MSF = magnitude scaling factor given by, following equation:, MSF = 102.24 M W2.56, , This factor is required when the magnitude is different, than 7.5. The correction for high overburden stresses, Kσ is required when overburden pressure is high, (depth > 15 m) and can be found using following, equation:, , Step 1 — The subsurface data used to assess, liquefaction susceptibility should include the location, of the water table, either SPT blow count N or tip, resistance qc of a CPT cone or shear wave velocity Vs,, unit weight, and fines content of the soil (percent by, weight passing the IS Standard Sieve No. 75 µ)., , (, K ó = (σ vo, ′ Pa ), , Step 3 — Evaluate stress reduction factor rd using:, 0 < z ≤ 9.15 m, 1 − 0.00765 z, rd = , 1.174 − 0.0267 z 9.15 m < z ≤ 23.0 m, , For assessing liquefaction susceptibility using:, , where z is the depth (in metre) below the ground surface., , a), , Step 4 — Calculate cyclic stress ratio CSR induced by, the earthquake using:, , SPT, go to Step 6(a) or, , b) CPT, go to Step 6(b) or, c), , ,  rd ,, , , Shear wave velocity, go to Step 6(c)., , Step 6 — Obtain cyclic resistance ratio CRR7.5,, 6(a) Using values of SPT, , where, amax = peak ground acceleration (PGA) preferably, in terms of g,, g, rd, , f −1), , where σ 'vo effective overburden pressure and Pa, atmospheric pressure are measured in the same units, and f is an exponent and its value depends on the, relative density Dr. For Dr = 40 percent ~ 60 percent,, f = 0.8 ~ 0.7 and for Dr = 60 percent ~ 80 percent,, f = 0.7 ~ 0.6. The correction for static shear stresses Kα, is required only for sloping ground and is not required, in routine engineering practice. Therefore, in the scope, of this standard, value of Kα shall be assumed unity., , Step 2 — Evaluate total vertical overburden stress σvo, and effective vertical overburden stress σ 'vo at, different depths for all potentially liquefiable layers, within the deposit., ,  a  σ, CSR = 0.65  max   vo,  g   σ 'vo, , CRR = CRR7.5 ( MSF ) K ó K á ,, , where, , Evaluate the SPT (standard penetration test), blow count N60, for a hammer efficiency of, 60 percent. Specifications for standardized, equipment are given in Table 11. If equipment, used is of non-standard type, N60 shall be, obtained using measured value (N):, , = acceleration due to gravity, and, = stress reduction factor., , If value of PGA is not available, the ratio (amax/g) may, be taken equal to seismic zone factor Z (as per Table 3)., Step 5 — Obtain cyclic resistance ratio CRR by, correcting standard cyclic resistance ratio CRR7.5 for, earthquake magnitude, high overburden stress level, , where, , N 60 = NC60 ,, , C60 = CHT CHW CSSCRL CBD ., 38

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IS 1893 (Part 1) : 2016, (qC1N)CS = kC qC1N, , 6(b) Using values of CPT, The CPT procedure requires normalization of, measured cone tip resistance q c using, atmospheric pressure Pa and correction for, overburden pressure CQ as follows:, , qC1N, , where, kC = Correction factor to account for grain, characteristics, 1.0 (for I ≤ 1.64), , c, = , 4, 3, 2, −0.403 I c + 5.581I c − 21.63 I c + 33.75 I c −17.88, , q , = CQ  c  ,, P , , (for Ic > 1.64), and, , a, , where qCIN is normalized dimensionless cone, penetration resistance, and,  P , CQ =  a ,  σ 'vo , , 0.5, n=, 1, , Ic =, , 2, ,  q − σ vo   Pa , Q= c,  , , ′ ,  Pa   σ vo, , n, , 2, , (3.47 − log Q ) + (1.22 − log F ), n, , , fs , F = 100 ,  percent , and,  qc − σ vo , , for sand, for clay, , where fs = measured sleeve friction., , The normalized penetration resistance qC1N, for silty sands is corrected to an equivalent, clean sand value (qC1N)CS by the following, relation:, , Using (qC1N)CS find the value of CRR7.5 using Fig. 9., Alternatively, the CRR 7.5 can be found using, following equations:, , FIG. 9 R ELATION BETWEEN CRR AND (qC1N)CS FOR MW7.5 EARTHQUAKES, 40

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IS 1893 (Part 1) : 2016, where Vs1* is limiting upper value of Vs1 for, liquefaction occurrence; a and b are curve, fitting parameters. The values of a and b in, , ,  ( q C1N )CS , 0.833,  + 0.05, 0 < (q C1N )CS < 50,  1 000 , , CRR7.5 = , 3,   ( q C1N )CS , 93,  ,  + 0.08, 50 ≤ ( q C1N )CS < 160,   1 000 , , Fig. 10 are 0.022 and 2.8, respectively. Vs1* can, be assumed to vary linearly from 200 m/s for, soils with fine content of 35 percent, to 215 m/s, for soils with fine contents of 5 percent or less., , 6(c) Using shear wave velocity:, Apply correction for overburden stress to, shear wave velocity Vs for clean sands using:,  P , Vs1 =  a , ′ ,  σ vo, , Step 7 — Calculate the factor of safety FS against initial, liquefaction using:, , 0.25, , Vs, , FS =, , where (V s1) is overburden stress corrected, shear wave velocity. Using Vs1 find the value, of CRR7.5 using Fig. 10. Alternatively, the, CRR7.5 can be found using following equation:, , CRR, ,, CSR, , where CSR is as estimated in Step 4 and CRR in Step 5., When the design ground motion is conservative,, earthquake related permanent ground deformation is, generally small, if FS ≥ 1.2 ., , 2, ,  1, 1 , V , CRR7.5 = a  s1  + b  *, − *, −, V, V, V, 100, , ,  s1, s1, s1 , , Step 8 — If FS < 1, then the soil is assumed to liquefy., , FIG. 10 RELATION BETWEEN CRR AND VS1 FOR MW7.5 EARTHQUAKES, , 41

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IS 1893 (Part 1) : 2016, Table 11 Recommended Standardized SPT Equipment (see IS 2131), [Clause F-1, Step: 6(a)], Sl No., (1), , Element, (2), , i), , Sampler, , ii), iii), , Drill rods, Hammer, , iv), v), , Rope, Borehole, , vi), vii), viii), , Drill bit, Blow count rate, Penetration, resistant count, , Standard Specification, (3), Standard split-spoon sampler with, outside diameter, OD = 51 mm; and inside diameter, ID = 35 mm, (constant, that is, no room for liners in the barrel), A or AW type for depths less than 15.2 m; N or NW type for greater depths, Standard (safety) hammer with,, a) weight = 63.5 kg; and, b) drop height = 762 mm (delivers 60 percent of theoretical free fall energy), Two wraps of rope around the pulley, 100-130 mm diameter rotary borehole with bentonite mud for borehole stability (hollow stem augers, where SPT is taken through the stem), Upward deflection of drilling mud (tricone or baffled drag bit), 30 to 40 blows per minute, Measured over range of 150 mm – 450 mm of penetration into the ground, , Table 12 Correction Factors for Non-Standard SPT Procedures and Equipment, [Clause F-1, Step: 6(a)], Sl No., (1), i), , Non-standard hammer weight or height of fall, , ii), , iii), iv), , v), vi), , Correction for, (2), , Correction Factor, (3), CHT =, , 0.75 (for Donut hammer with rope and pulley), 1.33 (for Donut hammer with trip/auto), , and, Energy ratio = 80 percent, HW, Non-standard hammer weight or height of fall, CHW =, 48387, where, H = height of fall (mm), and, W = hammer weight (kg), Non-standard sampler setup (standard samples with, 1.1 (for loose sand), CSS =, room for liners, but used without liners), 1.2 (for dense sand), Non-standard sampler setup (standard samples with, 0.9 (for loose sand), CSS =, room for liners, but liners are used), 0.8 (for dense sand), = 0.75 (for rod length 0-3 m), = 0.80 (for rod length 3-4 m), Short rod length, CRL =, = 0.85 (for rod length 4-6 m), = 0.95 (for rod length 6-10 m), = 1.0 (for rod length 10-30 m), Nonstandard borehole diameter, 1.00 (for bore hole diameter of 65-115 mm), CBD =, = 1.05 (for bore hole diameter of 150 mm), = 1.15 (for bore hole diameter of 200 mm), , NOTES, 1 N = Uncorrected SPT blow count., 2 C60 = CHT CHW CSSCRL CBD, 3 N 60 = NC60, 4 CN = Correction factor for overburden pressure, , ( N1 )60 = CN C60 N, , 42, , .

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