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Re: Queries on ASD
[Subject Prev][Subject Next][Thread Prev][Thread Next]- To: seaint(--nospam--at)seaint.org
- Subject: Re: Queries on ASD
- From: Charlie Carter <carter(--nospam--at)aiscmail.com>
- Date: Tue, 22 Dec 1998 00:07:39 -0600
- Cc: rokach(--nospam--at)aiscmail.com
Check with Abe Rokach at AISC (rokach(--nospam--at)aiscmail.com). I think this limit was changed to 970/sqrt(Fy) to eliminate the confusion you are experiencing. Charlie Allen Adams wrote: > > 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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