G) The latest revised earthquake code, IS 1893 (Part 1): 2002 ‘Criteria for earthquake resistant design of structures: Part 1 General provisions and buildings’, has been incorporated, due implementation of the provisions of which in applicable seismic zone of the country, needs to be duly adhered to. Examples on IS 1893(Part 1) IITK-GSDMA-EQ21-V2.0 Example 1/Page 6 Table 1.1 – Lateral Load Distribution with Height by the Static Method Lateral Force at ith Level for EL in.

This Indian Standard. ( Fourth Revision) was adopted by the Indian Standards Institution on 16 November 1981, after the draft finalized by the Earthquake Engineering Sectional Committee had been approved by the Civil Engineering Division Council. Himalayan-Nagalushai region, Indo-Gangetic plain, Western India, Kutch and Kathiawar regions are geologically unstable parts of the country and some devastating earthquakes of the world have occurred there. A major part of the peninsular India has also been visited by strong earthquakes, but these were relatively few in number and had considerably lesser intensity. The earthquake resistant design of structures taking into account seismic data from studies of these Indian earthquakes has become very essential,. particularly in view of the heavy construction programme at present all over the country. It is to serve this purpose that IS : 1893-1962 ‘Recommendations for earthquake resistant design of structures’ was published and subsequently revised in 1966. As a result of additional seismic data collected in India and further knowledge and experience gained since the publication of the first revision of this standard, the Sectional Committee felt the need to revise the standard again incorporating many changes, such as revision of maps showing seismic zones and epicentres, adding a more rational approach for design of buildings and substructure of bridges, etc. These were covered in the second revision of IS : 1893 brought out in 1970. As a result of the increased use of the standard, considerable amount of suggestions were received for modifying some of the provisions of the standard and, therefore, third revision of the standard was brought out in 1975. The following changes were incorporated in the third revision:
a) The standard incorporated seismic zone factors ( previously given as multiplying factors in the second revision ) on a more rational basis.
b) Importance factors were introduced to account for the varying degrees of importance for various structures.
c) In the clauses for design of multi-storeyed building the coefficient of flexibility was given in the form of a curve with respect to period of buildings.
d) A more rational formula was used to combine modal shears.
e) New clauses were introduced for determination of hydrodynamic pressures in elevated tanks.
f) Clauses on concrete and masonry dams were modified, taking into account their dynamic behaviour during earthquakes. Simplified formulae for design forces were introduced based on results of extensive studies carried out since second revision of the standard was published. The fourth revision has been prepared to modify some of the provisions of the standard as a result of experience gained with the use of this standard. In this revision a number of Important basic modifications with respect to load factors, field values of N, base shear and modal analysis have been introduced. A new concept of performance factor depending on the structural framing system and brittleness or ductility of construction has been incorporated. Figure 2 for average acceleration spectra has also been modified and a curve for zero percent damping has been incorporated. It is not intended in this standard to lay down regulations so that no structure shall suffer any damage during earthquake of all magnitudes. It has been endeavoured to ensure that, as far as possible, structures are able to respond, without structural damage to shocks of moderate intensities and without total collapse to shocks of heavy intensities. While this standard is intended for earthquake resistant design of normal structures, it has to be emphasized that in the case of special structures detailed investigation should be undertaken, unless otherwise specified in the relevant clauses. Though the basis for the design of different types of structures is covered in this standard, it is not implied that detailed dynamic analysis should be made in every case. There might be cases of less importance and relatively small structures for which no analysis need be made, provided certain simple precautions are taken in the construction. For example, suitably proportioned diagonal bracings in the vertical panels of steel and concrete structures add to the resistance of frames to withstand earthquake forces. Similarly in highly seismic areas, construction of a type which entails heavy debris and consequent loss of life and property, such as masonry, particularly mud masonry and rubble masonry, should be avoided in preference to construction of a type which is known to withstand seismic eflects better, such as construction in light weight materials and well braced timber-framed structures. For guidance on piecautions to be observed in the construction of buildings, reference may be made to IS : 4326-1976*. Attention is particularly drawn to the fact that the intensity of shock due to an earthquake could greatly vary locally at any ~given place due to variation in the soil conditions. Earthquake forces would be affected by different types of foundation system in addition to variation of ground motion due to various types of soils. Considering the effects in a gross manner, the standard gives guidelines for arriving at design seismic coefficients based on type of soil and foundation system. Earthquakes can cause damage not only on account of the shaking which results from them but also due to other chain effects like landslides, floods, fires and disruption to communication. It is, therefore, important to take necessary precautions in the design of structures so that they are safe against such secondary effects also. It is important to note that the seismic coeficient, used in ihe design of any structure, is dependent on many variable factors and it is an extremely dificult task to determine the exact seismic coefficient in each given case. Tt is, therefore, necessary to indicate broadly the seismic coeficients that could generally be adopted in different parts or zones or the country though, of course, a rigorous analysis considering all the factors involved has got to be made in the case of all important projects in order to arrive at suitable seismic coefficients for design. The Sectional Committee responsible for the formulation of this standard has attempted to include a seismic zoning map ( see Fig. 1 ) for this purpose. The object of this map is to classify the area of the country into a number of zones in which one may reasonably expect earthquake shock of more or less same intensity in future. The Modified Mercalli Intensity ( see 2.7 ) broadly associated with the various zones is V or less, VI, VII, VIII and 1X and above for zones I, II, III, IV and V respectively. The maximum seismic ground acceleration in each zone cannot be presently predicted with accuracy either on a deterministic or on a probabilistic basis. The design value chosen for a particular structure is obtained by multiplying the basic horizontal seismic coefficient for that zone, given in Table 2, by an appropriate Importance Factor as suggested in Table 4. Higher value of importance factor is usually adopted for those structures, consequences of failure of which, are serious. However, even with an importance factor of unity, the probability is that *Code of practice for earthquake resistant design and construction of buildings (Jr& revision ). a structure which is properly designed and detailed according to good construction practice, will not suffer serious damage. It is pointed out that structures will normally experience more severe ground motion than the one envisaged in the seismic coefficient specified in this standard. However, in view of the energy absorbing capacity available in inelastic range, ductile structures will be able to resist such shocks without much damage. It is, therefore, necessary that ductility must be built into the structures since brittle structures will be damaged more extensively. The Sectional Committee has appreciated that there cannot be. an entirely scientific basis for zoning in view of the scanty data available. Though the magnitudes of different earthquakes which have occurred in the past are known to a reasonabIe amount of accuracy, the intensities of the shocks caused by these earthquakes have so far been mostly estimated by damage surveys and there is little instrumental evidence to corroborate the conclusions arrived at. Maximum intensity at different places can be fixed on a scale only on the basis of the observations made and recorded after the earthquake and thus a zoning map which is based on the maximum intensities arrived at, is likely to lead in some cases to an incorrect conclusion in the view of (a) incorrectness in the assessment of intensities, ib) human error in judgement during the damage survey, and (c) variation in quality and design of structures causing variation in type and extent of damage to the structures for the same intensity of shock. The Sectional Committee has, therefore, considered that a rational approach to the problem would be to arrive at a zoning map based on known magnitudes and’ the known epicentres (see Appendix A) assuming all other conditions as being average, and to modify such an average idealized isoseismal map in the light of tectonics ( see Appendix B ), lithology ( see Appendix C) and the maximum intensities as recorded from damage surveys, etc. The Committee has also reviewed such a map in the light of past history and future possibilities and also attempted to draw the lines demarcating the different zones so as to be clear of important towns, cities and industrial areas, after making special examination of such cases, as a little modification in the zonal demarcations may mean considerable difference to the economics of a project in that area. Maps shown in Fig. 1 and Appendices A, B and C are prepared based on information available up to 1986. In the formulation of this standard due weightage has been given to international coordination among the standards and practices prevailing in different countries in addition to relating it to the practices in the field in this country.

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