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Re: Unblocked Plywood Diaphragm Deflection Calculation
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- Subject: Re: Unblocked Plywood Diaphragm Deflection Calculation
- From: FEMCCLURE(--nospam--at)aol.com
- Date: Wed, 19 May 1999 14:41:17 EDT
- Cc: FEMCCLURE(--nospam--at)aol.com, DLM(--nospam--at)eqe.com
Niaz A. Nazir, You wrote: "I am trying to compare the FEMA 273 equations for the deflection computation of blocked and unblocked plywood diaphragms" The unblocked diaphragm deflection is given in FEMA 273, Section 8.5.7.1, page 8-27, bottom of right hand column, "The deflection for unblocked diaphragms may be calculated using Equation 8-5, with diaphragm shear stiffness, Gd as follows: Unblocked, chorded diaphragms: Gd = 800,000 lb/in., Unblocked, unchorded disphragms: Gd = 400,000 lb/in." Note: Equation 8-5 is presented on page 8-25, FEMA 273, for calculating the deflection of straight sheathed diaphragms. Apparently, the authors of FEMA 273 felt that Equation 8-5 could be used for wood structural panel unblocked sheathed diaphragms with the proper Gd values greater than Gd value = 200,000 lb/in. for straight sheatheed diaphragms. You wrote: " The blocked diphragm stiffness is given by equation 8-6 & 8-7 (FEMA 273). Using these equations will yield unblocked diaphragm stiffer than blocked one.." Since Equation (8-5) is so different from Equations (8-6) and (8-7) which have many more and different terms than Equation (8-5), it is difficult for me, without seeing your detailed calculations, using these three equation, to agree with your conclusion, "Using these equations will yield unblocked diaphragm stiffer than the blocked one." You wrote: "Using ATC-7-1 one could compute unblocked diaphragm stiffness which calcs out to be much less than FEMA 273." I did not pull out ATC-7-1 to review what you wrote, but could you be a bit more specific, using mathematical examples to illustrate your point. I am not agreeing or disagreeing with your conclusions. I need more information using mathematical substitutions in the above three equations to better understand what you are saying. There are other problems with Equations (8-6) and (8-7) which will be the subject of another email message by me to the SEAOSC List Server. Keep up the good work and an open mind in questioning the provisions of FEMA 273. Frank E. McClure FEMCCLURE(--nospam--at)aol.com May 19,1999 File:FEMA273diaphragmdeflections.doc
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