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Re: RE: Special Moment-Resisting Truss Frames[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: RE: Special Moment-Resisting Truss Frames
- From: Eddie Gonzalez <Eagonzal(--nospam--at)ENG.CI.LA.CA.US>
- Date: Thu, 13 Aug 1998 17:04:16 -0700
The issue was ENR June 1, 1998. The project was an office building in Sacramento, California. Althought the article doesn't address it specifically, the picture seems to indicate that the ductility is provided by a sacrificial x-brace bay which is smaller than the rest of the chord elements. Can you specify what UBC restrictions you ran into when using it/ if your were to use it in the States, particularly, western states? Is it in reference to yielding of members or something else? The article notes that "Codes changed appreciably after the 1994 Northridge Earthquake, which exposed a tendency for brittle fractures in SMRF connections. Such changes included precursors to performance-base design, to allow owners to specify expected degrees of quake damage. Such a change in the 1996 supplement to the 1994 Uniform Building Code effectively permits the use of moment-resisting trusses with members that yield." Of course, as noted on the thread discussion regarding performance-base design, the owner's performance objectives must meet some be justified, particularly, to local building dept. The article indicates that the analysis had to be done by hand because of a "dearth of relevant software." I am assuming the analysis is iterative/nonlinear. If you know of any Research/Testing on this system, please let me know. Thanks again for your comments. Ed Gonzalez >>> Harold Sprague <hsprague(--nospam--at)aspen.klaalov.com> 08/13/98 02:55PM >>> What issue was it in? I have designed trusses to resist seismic and wind in frames all over the world where UBC does not dictate or limit designs. You basically must think in terms of nonlinear performance. Trusses in high seismic applications offer special challenges that were addressed by designing the truss for a controlled mode of failure. This was generally accomplished by using the "seismic fuse" top ductile connector plate and designing the truss for the applied ultimate strength / moment induced into the truss with an appropriate overstrength factor like the 1.25 used in concrete moment frame design. Harold Sprague, PE Krawinkler, Luth & Assoc.
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