Need a book? Engineering books recommendations...
perforated shearwalls[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: perforated shearwalls
- From: chuckuc <chuckuc(--nospam--at)dnai.com>
- Date: Sat, 25 Sep 1999 20:32:41 -0700
Dennis- No structural model is very trustworthy unless it has been validated by full scale testing. The UBC four term expression has been validated with phoney tie downs and at only one h/d ratio (1:1), so I wouldn't get too enamored with it just yet. A much more rigorous model is the one used by Richardo Foschi (at BC) and Dan Dolan (at VT). It has been tested over a wide range of h/d but it is very unfriendly to use. It models the deflection of each nail, the paneling, and the tie down. However, it is a good way to envision shearwall deflection. If the sheathing type, tie down, and height are constant in a wall line then deflection (and capacity) is proportional to the number of nails. If you want to give the framers an option (and I don't really think it is a good idea BTW) you can call for two, heavily nailed panels with four tie downs or a more lightly nailed wall with two tie downs and get the same stiffness. When you consider the waterproofing, the extra analysis and detailing, the likelihood ofconstruction screw ups, the extra construction supervision and inspection, and the splitting problems from close nailing, I think choosing the fully sheathed wall with modest nailing and tie downs is a no-brainer (despite what your architects/owners might think. You're the engineer, start educating them.) IMHO perforated walls without tiedowns don't contribute much stiffness. Without a tie down, the end studs pull the sill nails at the bottom corners of the wall at pretty low load. Ed Diekmann says about 600#(70 to 80 plf). You could include them in your analysis, but with reductions for door and window perforations, the wall typically isn't worth including. As for enveloping, it comes down to engineering judgment but unfortunately our judgment typically has minimal basis in fact (test results). What we do know from testing is that the typical floor diaphragm is pretty stiff compared to a typical shearwall. I run QLAT30 and a rigid diaphragm analysis and compare the numbers. The rigid diaphragm numbers have looked the most reasonable so far. Large tributary loading onto skinny walls can produce some pretty big numbers and I usually use the lower values that result from stiffness considerations. You may not be comfortable doing that, but it is not because you "know" how the structure actually behaves. Your knowledge has come from crunching numbers and seeing your designs built, not from observing lab tests or from a design level seismic event. That's not a personal criticism, it just our unhappy circumstances at present. Some of the "ivory tower" guys have a much better feel for the structures' behavior than the practicing engineers do-- because they've watched these diaphragms tested. Unfortunately, they don't have the benefit of analyzing actual structures or seeing the typical construction quality problems. The result is that they tend to get overly elaborate with their analytical tools. If you really want to help, perhaps there's a way to make some meaningful input into CUREe. It's goal is a practical piece of software (validated by adequate testing) that we can use for design work. Chuck Utzman, P.E.
- Prev by Subject: Re: Perforated shearwall analysis
- Next by Subject: Perforated sheawall -addendum
- Previous by thread: Re: Completly shearing a building (alsoanswertoperforatedshearwalls)
- Next by thread: UBC 1988 VS UBC 1997