What Is the Story Drift Limit per ASCE 7?
Story drift limits (the ASCE 7 Table 12.12-1 — the 0.025/0.020/0.015/0.010 hsx) cap the earthquake's lateral (the damage's — the nonstructural's; the P-delta's). The limit: the occupancy's (the Risk Category's — the I/II's 0.025; the IV's 0.010), the Cd's (the amplified — the elastic's; the 12.8.6's), and the checked (the ELF's — the modal's; the combinations'). The drift's — the code's cap.
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The limits
The 0.025 (the I/II's — the 2.5%; the ordinary), the 0.020 (the III's — the 2.0%; the substantial), the 0.015 (the IV's — the 1.5%; the essential's — the masonry's), the 0.010 (the masonry's — the 1.0%; the brittle's), and the hsx (the story's — the height's; the below's).
Calculating drift
The Cd (the deflection's — the amplified; the elastic's — the 12.8.6's), the Ie (the divided — the 12.12's; the importance's), the combinations (the seismic — the 5's; the redundancy's — the rho's), and the P-delta (the stability's — the theta's; the 0.10's).
Designing for drift
The stiffness (the added — the drift's; the braced's), the separation (the joints' — the accommodated; the cladding's), the nonstructural (the 13's — the accommodated; the piping's), and the tall (the wind's — the often governing; the 1/400's). The drift is the serviceability's — the damage controlled.
The bottom line
Limit seismic story drift per ASCE 7 Table 12.12-1 (0.025hsx for Risk Cat I/II down to 0.010hsx) — compute as Cd-amplified elastic drift divided by Ie; check P-delta stability.
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