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Queries on ASD
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- Subject: Queries on ASD
- From: Allen Adams <aadams(--nospam--at)ramint.com>
- Date: Tue, 22 Dec 1998 09:09:00 -0800
Regarding the use of Fb in the Noncompactness equation for Webs: It is common to use Fb = 0.60Fy in that equation (760/sqrt(Fb)). It is conservative to do so, although not unreasonably so. However, it is simple enough to be more precise if you deem it necessary: If the section does not qualify as compact, assume the web qualifies as noncompact. Then calculate the allowable Fb from the appropriate equations from Section F1. Then use this value in the equation 760/sqrt(Fb) and determine if your assumption of noncompactness was correct. If the section is now determined to be noncompact, you can use the value of Fb that you calculated for the design of the member. If the section is slender, you should either select a larger size (which is normally what is done) or you must follow the requirements for slender members found in Appendix B. (Note that if the section's h/tw is less than 760/sqrt(0.60Fy), then the web is definitely not slender, and it is not necessary to re-check it against 760/sqrt(Fb) after the actual Fb is calculated.) Allen Adams RAM International >From: John Smith <smith_john_1(--nospam--at)yahoo.com> >Subject: Queries on ASD >To: seaint(--nospam--at)seaint.org > > >I am an Australian Engineer and have a project requiring a design >conforming to ASD. > >I have a query regarding the interpretation of the use of Fb in Table >B5.1 - Limiting Width-Thickness Ratios for Compression elements page >5-36. > >In rows 10 & 11 of the table, regarding the use of webs in flexural >and axial compression, the table requires the use of an Fb in the >NonCompact limit of 760/Sqrt(Fb). > >My inquiry is: >Is it common practice to use an Fb = 0.60Fy ?? >(from equation F1-5) > >Note: >I notice that in the LRFD that this limit is now 970/Sqrt(Fy) which >corresponds to an equivalent Fb = 0.614Fy > >JS
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