What is the maximum allowed storey drift?

0.004 times the storey height under unfactored design base shear (Clause 7.11.1).

What is the importance factor for a large residential building?

1.2 for buildings housing more than 200 persons, otherwise 1.0 (Table 8).

When is dynamic analysis mandatory?

For regular buildings > 40m in Zones IV/V or > 90m in Zones II/III, and for all irregular buildings taller than 12m (Clause 7.7.1).

How is the design base shear calculated?

Vb = Ah * W, where Ah is the design horizontal seismic coefficient and W is the total seismic weight of the building (Clause 7.2.6).

IS 1893 Part 1

: 2016

Criteria for Earthquake Resistant Design of Structures - General Provisions and Buildings

CurrentEssentialCode of PracticeBIMStructural Engineering · Structural Design and Loading

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This part of IS 1893 provides the general principles and criteria for earthquake-resistant design of structures, with a specific focus on buildings. It outlines methodologies for determining seismic base shear using equivalent static and dynamic analysis, its distribution along the building height, and the evaluation of storey drift to ensure life safety during seismic events.

Provides general criteria for earthquake resistant design of buildings and structures, including seismic zoning, importance factors, and design procedures.

Quick Reference Values

Seismic Zone Factor Z (Zone II)0.10

Seismic Zone Factor Z (Zone III)0.16

Seismic Zone Factor Z (Zone IV)0.24

Seismic Zone Factor Z (Zone V)0.36

Maximum allowable storey drift0.004 x storey height

Importance Factor for Hospitals/Schools1.5

Key Formulas

Ah = (Z/2) * (I/R) * (Sa/g) — Design horizontal seismic coefficient

Vb = Ah * W — Design seismic base shear

Ta = 0.075 * h^0.75 — Fundamental natural period for bare RC frame building

Ta = 0.09 * h / sqrt(d) — Fundamental natural period for building with masonry infill

Practical Notes

Base shear obtained from dynamic analysis must be scaled up to match the empirical base shear if it falls short of the calculated empirical value.

Ordinary Moment Resisting Frames (OMRF) are not permitted in high seismic zones (Zones IV and V). Special Moment Resisting Frames (SMRF) with ductile detailing as per IS 13920 must be used.

Storey drift checks must be evaluated using unfactored seismic loads (load factor = 1.0) and should not exceed 0.004 times the storey height.