Section C2.4.3 (the commentary to Section 2.4.3) of ASCE 7-98 provides
a useful discussion of this topic. Essentially all materials display
strain-rate effects. Some materials (for instance, wood) have a
noticeably higher capacity for loads that last a few minutes, hours,
days, months, or even years.
For steel, strain-rate effects are neglible under wind and seismic
loading. You need to have VERY short duration loads (like blast
loading) to see noticeable changes in the capacity.
[By the way, what is the "Special Edition" of ASCE 7-98?]
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Michael Valley, P.E., S.E. E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc. Tel:(206)292-1200
1301 Fifth Ave, #3200, Seattle WA 98101-2699 Fax: -1201
> -----Original Message-----
> From: PEC - Lake City [mailto:pec(--nospam--at)isgroup.net]
> Sent: Wednesday, May 17, 2000 1:40 PM
> To: Seaint
> Subject: ASCE 7-98 and 1/3 Increase for Wind Load
> Section 2.4.3 of the Special Edition ASCE 7-98 (section 2.4
> deals with
> allowable stress design) reads in part:
> "Increases in allowable stress shall not be used with these
> loads or load
> combinations unless it can be demonstrated that such an increase is
> justified by structural behavior caused by rate or duration
> of load."
> Does wind load meet the 2.4.3 rate / duration criteria?
> In more simple terms, in steel design can I use a 1/3
> allowable stress
> increase for a DL + W combination if I am using ASCE 7-98
> wind loading?
> David Finley, P.E.
> PEC - Lake City