What is the 'Strong Column-Weak Beam' requirement?

The sum of the moment capacities of columns framing into a joint must be at least 1.2 times the sum of the moment capacities of the beams framing into it (Clause 5.4.1).

Are all steel sections suitable for seismic design under this code?

No, only 'plastic' or 'compact' sections, as defined by the limiting width-to-thickness ratios in Table 2, should be used for members intended to undergo ductile yielding.

What is a 'protected zone' in a steel member?

It's a region at the ends of beams or other ductile members where plastic hinges are expected to form. No attachments, holes, or ancillary welding are permitted in this zone after fabrication (Clause 4.6).

What framing systems does this code cover?

It covers Moment Resisting Frames (MRFs), Concentrically Braced Frames (CBFs), and Eccentrically Braced Frames (EBFs) (Clauses 5, 6, and 7).

IS 15294

: 2003

Ductile Detailing of Steel Structures Subjected to Seismic Forces - Code of Practice

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This code of practice outlines the requirements for designing and detailing ductile steel structures to ensure they can withstand severe seismic shaking. It covers various structural systems like Moment Resisting Frames (MRFs) and Braced Frames (CBFs, EBFs), focusing on connection design and member proportions to achieve desired inelastic behavior without failure.

Lays down provisions for ductile detailing of steel structures to enhance their seismic performance.

Quick Reference Values

Strong Column-Weak Beam Moment Ratio≥ 1.2

Link Rotation Angle for EBF (not adjacent to column)≤ 0.02 rad

Link Rotation Angle for EBF (adjacent to column)≤ 0.08 rad

Flange width-thickness ratio limit for plastic sections (b/tf)8.4ε where ε = √(250/fy)

Web width-thickness ratio limit for plastic sections (d/tw)84.0ε where ε = √(250/fy)

Key Formulas

ΣMc* ≥ 1.2 ΣMb* — Strong Column-Weak Beam requirement for MRFs

Practical Notes

This code is a supplement to IS 800 and IS 1893, not a standalone document. Seismic loads are from IS 1893, and general steel design principles are from IS 800.

The 'Strong Column-Weak Beam' philosophy (Clause 5.4.1) is a critical concept to prevent a soft-storey mechanism and must be checked at all beam-column joints in MRFs.

Pay close attention to weld details and the designation of 'protected zones' (Clause 4.6), as connection integrity is paramount for seismic performance.