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RE: Drift Limits for Wind

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Generally stucco is much stiffer than the cantilevered steel columns.  For the system to work the stucco needs to be detailed with horizontal seismic joints so its stiffness matches the columns.  The signage needs to be detailed so it adds no stiffness to the wall system. This can be accomplished by using slotted or sliding connections.  It is more a detailing issue than a code issue.
Most of the time these details are not present and that is why stucco is demolished and signs drop to the ground with minor amounts of building drift.
Keep a eye on Houston this weekend and the building drifts caused by 140 mph winds.
James A. Sadler, SE
-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)]
Sent: Wednesday, September 21, 2005 4:14 PM
To: seaint(--nospam--at)
Subject: Drift Limits for Wind

I must be getting old cause I can’t seem to find this, so I ask all of you to refresh my memory….


I have a simple storefront renovation project and I am using cantilevered steel columns to resist the lateral wind load. The wind force governs over seismic by a factor of 2.


In UBC/CBC the Delta_M drift limit is 0.7*R*Delta_S …. Now that I know for sure is for seismic and is straight forward.


Since I have twice the load governed by wind, do I still need to meet this requirement?


I know technically there is no drift limit for 1 story steel construction and this is basically a false tower/covered entrance outside of an existing building but I’d still like to meet the drift limit since there are several illuminated signage type things and stucco finish that I’d rather not have bust all up under huge deflections.


Can I design it to meet L/240 for wind and the Delta_M for seismic and be okay?