IS 1893:2002 CRITERIA FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURES PART1 GENERAL PROVISIONS AND BUILDINGS The Code is now split into five parts Part Part Part Part Part 1 2 3 4 5 General provisions and buildings Liquid retaining tanks - Elevated and ground supported Bridges and retaining walls Industrial structures including stack like structures Dams and embankments

Part 1 contains provisions that are general in nature and applicable to all structures. Also, it contains provisions that are specific to buildings only. The important changes as compared to IS:1893-1984 are as follows: 1. Seismic zone map is revised with only four seismic zones. Zone I is upgraded to Zone II. Killari area is enhanced to Zone III. Bellary isolated zone is removed. East coast is enhanced to Zone III and connected with Zone III of Godavari Graben area.

2. Seismic zone factor is changed reflecting more realistic value of peak ground acceleration.

3. Response acceleration spectra are now specified for three types of founding strata viz. Hard, Medium and Soft. 4. The empirical formula for calculating fundamental natural period T=0.1n for moment resisting frames without bracing or shear walls is replaced with Ta=0.075h0.075 for RC framed buildings. This formula applies to bare frames e.g. in industrial plant buildings. The formula for framed buildings with in-filled masonry walls is Ta = 0.09h/d0.5 where h and d are the height and base dimension of the building along the considered direction of earthquake. 5. Revised procedure first calculates the actual force that may be experienced by the structure during the probable maximum earthquake, if it were to remain elastic. Then response reduction due to ductile deformation or frictional energy dissipation in the cracks is applied via `response reduction factor' R in place of the earlier performance factor K. The list of building systems and the corresponding values of R is more exhaustive. The code procedures for calculating base shear VB are summarized below: IS:1893-1984 -----------VB = K.C. h.W where K = Performance factor 1.0 for SMRF (IS:4326 detail) and 1.6 for OMRF (IS:456 detail) C = Fundamental time period dependant coefficient = 1.0 for T 0.35 sec h = .I. 0

= Soil-foundation system dependant coefficient = 1.2 for isolated footings without tie beams in medium soils, piles in soft soils, combined or isolated footings with tie beams in soft soils = 1.5 isolated footings without tie beams in soft soils I = Importance factor = 1.5 for hospitals, schools, cinema halls, monumental structures, telephone exchanges, radio, fire, railway power stations and 1.0 for others 0 = Zone dependant design seismic coefficient Zone 0 II 0.02 III 0.04 IV 0.05 V 0.08

W = Seismic weight of building = Dead load + appropriate amount of live load = Dead load + 25% for LL up to 3 kN/sq.m 50% for LL > 3 kN/sq.m

0% for LL on roof

IS:1893-2002 -----------VB = Ah.W [Z/2].[Sa/g] = -----------[R/I] = Zero period acceleration value for the Maximum Considered Earthquake II 0.10 III 0.16 IV 0.24 V 0.36 coefficient for Hard, Medium or Soft soil, 5% 1.00/T for T > 0.40 (Hard: GP,GW,SP,SW,SC with 1.36/T for T > 0.55 (Medium: All with 10 1.2*average storey drift ii) Re-entrant corners : if projection beyond re-entrant corner is > 15% of plan dimension in that direction iii) Diaphragm discontinuity: if open areas > 50% of gross enclosed area or change in effective diaphragm stiffness from one storey to next > 50% iv) Out-of-plane offsets: discontinuities in lateral load resisting paths v) Non-parallel systems In Elevation -----------i) Soft-storey: Lateral stiffness < 70% of that in in the storey above or < 80% of the average lateral stiffness of three storeys above ii) Mass: seismic weight of any storey except roof < 200% of adjacent storeys iii) Geometic: horizontal dimension of a lateral force resisting element > 150% of that in adjacent storey iv) In plane discontinuity: In plane offset of a lateral force resisting element > length of that element v) Weak-storey having lateral strength < 80% of that in the storey above Additional requirements for some of the irregularities are specified:

Soft Storey: The columns and beams of the soft storey are to be designed for 2.5 times the storey shears and moments calculated under seismic loads besides the columns designed and detailed for the calculated storey shears and moments, shear walls placed symmetrical in both directions of the building as far away from the center of the building as feasbible to be designed exclusively for 1.5 times the lateral storey shear force calculated as before. Non-Parallel Systems: Earthquake effects about the two orthogonal axes must be combined: a. Ex 0.3Ey b. Ey 0.3Ex 8. More load combinations are required: Basic Combination 1) 1.5(D+L) 2) 1.2(D+LE) 1.2(D+L+EXP), 1.2(D+L+EXN), 1.2(D+L-EXP), 1.2(D+L-EXN), 1.2(D+L+EYP), 1.2(D+L+EYN), 1.2(D+L-EYP), 1.2(D+L-EYN) 3) 1.5(DE) 1.5(D+EXP), 1.5(D+EYP), 4) 0.9D1.5E 0.9D+1.5EXP, 0.9D+1.5EYP, where D L E X Y P N : : : : : : : Dead Live Earthquake along X axis along Y axis Positive eccentricity Negative eccentricity 0.9D+1.5EXN, 0.9D+1.5EYN, 0.9D-1.5EXP, 0.9D-1.5EYP, 0.9D-1.5EXN, 0.9D-1.5EYN 1.5(D+EXN), 1.5(D+EYN), 1.5(D-EXP), 1.5(D-EYP), 1.5(D-EXN), 1.5(D-EYN) Expanded Combinations

This results in 25 actual combinations but can be reduced rationally. Limits of static analysis ------------------------Zone II Regular buildings