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RE: WOOD RIGID DIAPHRAGM RESIDENTIAL UBC 1628.5[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: WOOD RIGID DIAPHRAGM RESIDENTIAL UBC 1628.5
- From: "Dennis S. Wish PE" <wish(--nospam--at)cwia.com>
- Date: Fri, 18 Dec 1998 17:02:40 -0800
Lots of questions here. The gist of the requirement is: 1. In most cases, the diaphragm deflection will be less than 2 times the story drift and the diaphragm is to be treated like a rigid diaphragm. 2. The code intended for diaphragms in rigid structures to be determined by analysis as blocked. However, this is not the case in all instances and diaphragms will be designed well within the unblocked requirements as is typical in residential construction. Again, the code does not omit unblocked diaphragms from rigid analysis since the deflection is still expected to be less than 2 times story drift. 3. I need to find the spreadsheet that was given to me by James Lord in Northern California - but this can be used for rigid diaphragm analysis and I will place it on the website as soon as I locate it (I have not done very much with rigid analysis in the past and this accounts for why I don't have it handy). 4. You still should compare the results of rigid and flexible diaphragms and design the line of shear for the worst case (also compare to wind). I'm not sure it is stated this way in the code, but the design examples from the SEAOSC Wood Seminar from February 1998 uses this approach. You might contact Bill Nelson at SEAOSC for his opinion (he is chair of the wood committee). Hope this helps Dennis Wish PE -----Original Message----- From: merrick group [mailto:merrickgroup(--nospam--at)compuserve.com] Sent: Friday, December 18, 1998 1:29 PM To: SEAonc seaint Subject: WOOD RIGID DIAPHRAGM RESIDENTIAL UBC 1628.5 RIGID WOOD DIAPHRAGM ANALYSIS FOR RESIDENTIAL. I have the following inquiry Comments please, SEND TO MERRICKGROUP(--nospam--at)COMPUSERVE.COM UBC 1997 section 1630.6 and UBC 1994 section 1628.5 requires a diaphragm to be analyzed as flexible when the deformation of the diaphragm is more than 2 times the average story drift of the associated story. If deformation was less than 2 times..., could it be analyzed as flexible? There is no wood house exclusion directly made in the code. Most residential wood frames have rigid diaphragms per code. For a wood diaphragm that is not blocked, the deflection equation is missing in the Standards. Does this mean that the rigid diaphragm rule excludes unblocked diaphragms? Many code sections require the use of equations that are not given. An adjustment factor could be made to the equations for the blocked diaphragm equations found in the Standards. Possible factors are.. ******Increase the deflection six times for loads parallel to unblocked edges. ***Increase the deflection three times for loads parallel to the joists. Code sections are given with deflection equations for some plywood diaphragm cases and not others. Does an excluded unblocked diaphragm equation of a family of included equations exclude the unblocked diaphragm case from the code section 1628.5? Does a building official have the power to add the exclusion of unblocked diaphragms for residential construction to the code section 1628.5? Does a popular vote of engineers create a Standard of Care over the legally accepted Standard of Care, the code? Legal cases exist where the answer is no. Are there wood analysis programs using the 1994 code with a rigid diaphragm option? Wood diaphragm force distributions have been treated as being flexible in shear and rigid in flexure. Another method uses the envelope of two combinations of shear or flexure and rigid or flexible. 1. Flexible shear, rigid flexure: This is the tributary area method 2. Rigid shear, flexible flexure: This is where interior shear walls are increased per the continuous beam model 3. The enveloping of case 1 and case 2: Enveloping case 1 and 2 is found in ATC-4 4. Rigid shear, rigid flexure: By demand of the code section of 1628.5. This is the method used for simple concrete structures, and seems to be the recommended approach per code. 5. Is an enveloping of all cases, or cases 1 and 4, reasonable?
- WOOD RIGID DIAPHRAGM RESIDENTIAL UBC 1628.5
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- WOOD RIGID DIAPHRAGM RESIDENTIAL UBC 1628.5
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