It seems a bit of a stretch to apply rules for concrete columns to metal
stairs. Anyway, we are curious to know how you detail concrete stairs to
accommodate delta-M, and would welcome a sample detail at fax number (208)
From: Nicholas Blackburn [mailto:nblackburn(--nospam--at)fdgoak.com]
Sent: Wednesday, February 07, 2001 2:49 PM
Subject: RE: Metal stairs & story drift
Stairs are a life-safety item i.e: they are expected to be functional during
events that may render the elevators inoperable (fire, seismic).
The UBC (section 1921.7) requires that all frame members that are assumed
not to contribute to lateral resistance be detailed to accommodate Delta M.
This usually section applies to concrete columns and beams but I usually
extend it to any concrete stairs that we design for the above stated reason.
However, I would extend the analogy to steel design as it is desirable to
have the stairs function during/after an earthquake.
I hope this helps
Nick Blackburn, PE