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RE: Deflection

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I was working backwards to determine the maximum elastic drift under strength level design seismic loads. 


1/(0.02/4) = 200


Although, even that is not an apples-to-apples comparison as that value would need to be divided by 0.7 for service level.


200/0.7 = 286


The commentary in ASCE 7-02 gives a range of H/400 to H/600, which is for serviceability, but then goes on to say that this is excessively conservative.  It recommends using 0.7*W to determine service load deflection for frames, which would be:


400*0.7 = 280


That might be the source of the 0.7 factor for wind deflection limits in IBC/CBC Table 1604.3, footnote f.  Anyway, these wind and seismic drift limitations seem comparable.  Thanks for all the help.


Doug Mayer, SE


From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)]
Sent: Wednesday, November 04, 2009 12:42 PM
To: seaint(--nospam--at)
Subject: Re: Deflection


Those are inelastic limits.

On Wed, Nov 4, 2009 at 12:30 PM, Doug Mayer <doug.mayer(--nospam--at)> wrote:

David, Matthew:

Seismic drift limitations are often in the realm of H/200 (using 0.020*hx and a Cd=4)…why so much more stringent for wind?


Doug Mayer, SE


From: Stuart, Matthew [mailto:mStuart(--nospam--at)]
Sent: Wednesday, November 04, 2009 12:18 PM
To: seaint(--nospam--at)
Subject: RE: Deflection




D. Matthew Stuart, P.E., S.E., F.ASCE, SECB

Senior Project Manager

Structural Department


Engineers and Consultants - CMX

200 Route 9

Manalapan, NJ 07726

732-577-9000 (Ext. 308)

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From: Doug Mayer [mailto:doug.mayer(--nospam--at)]
Sent: Wednesday, November 04, 2009 3:15 PM
To: seaint(--nospam--at)
Subject: Deflection


When wind governs in your lateral system design, what is the building drift limitation?  There doesn’t seem to be any specified building drift limitation for wind loads (that I can find) in the code.  What do you wind country folks do?




Doug Mayer, SE