Need a book? Engineering books recommendations...
[SEAOC] Re: [SEAOC] ASD/LRFD One More Time[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)power.net
- Subject: [SEAOC] Re: [SEAOC] ASD/LRFD One More Time
- From: Julie Mark Cohen <jmcohen(--nospam--at)emf.net>
- Date: Wed, 12 Jun 1996 10:27:57 -0700 (PDT)
- Cc: seaoc(--nospam--at)seaoc.org
Gentlemen: Please do not confuse global "efficiency" with local (member, connection) efficiency. 3-D structural framing system design and performance is a very different topic than examinging system components. Structural framing only performs as well as the "design" thinking that went into its creation. The overall framing (whether a true 3-D system or a collection of 2-D vertical and horiztonal planes) does not understand the difference between LRFD and ASD. _Nothing_ in any codes (past, present, or proposed) ensure that there will be a 3-D structural framing *system*. This comes from one's education, and, sadly, very sadly, this has not been a part of structural engineering education for decades. Check out "The Northridge Warning: Has 3-D Design Been Lost?", my ASCE Forum article published in Dec. 1994. Julie Cohen On Wed, 12 Jun 1996 BRBATES(--nospam--at)aol.com wrote: > In a message dated 96-06-12 10:18:23 EDT, you write: > > >I'd be real curious about which sorts of structures show the greatest > >efficiencies and whether there's a correlation between the degree to which > >lateral loading plays a part in the efficiencies. Was any comparison done > >to determine where the efficiencies come in? (Column, girder, connection > >economies? High rise vs small structures?) Are you implying simply lower > >allowable design margins based on more analysis or is there something > >inherently more reliable about LRFD that provides a better estimate of the > >margin? > > > >Christopher Wright P.E. |"They couldn't hit an elephant from > >chrisw(--nospam--at)skypoint.com | this dist--" (last words of Gen. > >Voice phone (612)933-6182 | John Sedgwick, Spotsylvania 1864) > > > > > >... > > Mr. Wright, > > The ASD/LRFD thread lives on! > > There's more to LRFD than just lowering allowable design margins. LRFD uses > load factors based on the predictability of the various loadings applied to > the model, for example when DL and LL are combined, you use a factor of 1.2 > for DL and 1.6 for LL. This reflects the fact that DL can be more accurately > predicted versus live load. This also is true for the resistance factors; > they are based on the predictability of the strengths of the members and > columns. For example, Phi for compression is .85, while Phi for tension is > .9, indicating that the tensile stength of a member can be predicted somewhat > more accurately than the compressive strength. > > I think the primary benefit of LRFD is that it puts the higher margins where > they belong, on those values you can't predict as accurately, while allowing > lower margins on those values that can be predicted more accurately. > > Bruce Bates > RISA Technologies > > ... > > ------------------------------------ | Dr. Julie Mark Cohen, P.E., | | Director and Principal | | Cladding Research Institute | | 6 Commodore Drive, Suite 330 | | Emeryville, CA 94608-1620 | | Tel (510) 654-7917 | | FAX (510) 4500-CRI | ------------------------------------ ...
- [SEAOC] ASD/LRFD One More Time
- From: BRBATES
- [SEAOC] ASD/LRFD One More Time
- Prev by Subject: [SEAOC] Re: [SEAOC] ASD vs. LRFD Survey Summary
- Next by Subject: [SEAOC] Re: [SEAOC] Basement wall with adjacent slab on grade - Help
- Previous by thread: [SEAOC] ASD/LRFD One More Time
- Next by thread: [SEAOC] Re: [SEAOC] Re: [SEAOC] ASD vs. LRFD Survey Summary