Should I use IS 1893 Part 1 or Part 4 for a factory building?

Part 4 is used for process and industrial plant structures, whereas standard administrative buildings within the same facility follow Part 1.

What is the Importance Factor (I) for a hazardous chemical storage tank?

1.5, as it falls under Category 1 (Hazardous structures) per Table 1.

What is the response reduction factor (R) for an unlined steel chimney?

The factor varies based on the detailed structural system, but stack-like structures generally have lower R values (often 2.0 or 2.5) as given in Table 2.

What is the recommended damping for an RC cooling tower?

5% for reinforced concrete structures as per Table 3.

IS 1893 Part 4

: 2015

Criteria for Earthquake Resistant Design of Structures - Industrial Structures Including Stack-Like Structures

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This code establishes the criteria for the earthquake-resistant design of industrial structures, encompassing plant buildings, elevated structures, and stack-like structures such as chimneys, silos, and cooling towers. It provides specialized design parameters including importance factors, response reduction factors, and damping ratios tailored to the unique dynamic characteristics and hazard levels of industrial facilities.

Specifies criteria for earthquake resistant design of various industrial structures and stack-like structures.

Quick Reference Values

Importance Factor for Hazardous Structures (Category 1)1.5

Importance Factor for Lifeline/Important Structures (Category 2)1.5

Importance Factor for General Industrial Structures (Category 3)1.0

Damping ratio for welded steel structures2%

Damping ratio for bolted steel structures5%

Damping ratio for reinforced concrete structures5%

Key Formulas

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

VB = Ah * W — Design seismic base shear

T = C * sqrt(W * h / (E * A * g)) — Fundamental natural period of uniform stack-like structures

Practical Notes

Must be used in conjunction with IS 1893 (Part 1) for general seismic parameters like the Zone Factor (Z) and basic response spectra.

Response Reduction Factors (R) for industrial structures are typically lower than those for standard commercial buildings due to a lack of structural redundancy.

Carefully classify the industrial structure into Categories 1 to 4 based on toxicity, flammability, and post-earthquake functional requirements to determine the correct Importance Factor (I).