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Re: LRFD for SDI Diaphragm Design?

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The questions that you raised came up in the BSSC Case Studies Project, 
Building Case Study #4, which applied FEMA 273 Guidelines to this one-story 
building with reinforced concrete tilt-up walls and a steel metal deck 
diaphragm.  Copies of these BSSC case studies are on file in the PEER, 
Earthquake Engineering Research Center library at the Richmond Field Station, 
University of California, Berkeley.  Be sure to order your copy of FEMA 343 
(call 1-800-480-2520 for your free copy) which presents the results of the 
BSSC Case Studies Project involving over forty case studies applying FEMA 273 
to existing buildings.

In the BSSC Case Study Project, Building Case Study #4, the Design Firm had 
to make an assumption concerning the Flexibility Coefficient in order to 
calculate the deflection of the steel metal deck diaphragm to make a period 
calculation in accordance with FEMA 273, page 3-7, Section 3.3.1.2, Method 3, 
Equation (3-5).
The question raised was: Could one assume that the Flexibility Coefficient 
can be determined by assuming a linear relationship projecting the ASD 
Flexibility Coefficient values to the "yield state" steel diaphragm shearing 
values, which FEMA 273 requires?    You will recall that the Flexibility 
Coefficients given by the steel metal deck manufacturers are based on ASD 
level of steel metal deck diaphragm shear values.

Having no better data, the Design Firm assumed that one could use a linear 
relationship to obtain the Flexibility Coefficients for "yield state" steel 
diaphragm shear values.

As an aside, I would be very interested if someone could send me a copy of 
their calculations demonstrating how to calculate the period of building with 
a flexible diaphragm,  using FEMA 273, Method 3, Equation (3-5).  My Fax 
number is:
925-254-4602.   I have asked for over two years for someone to send me period 
 calculations following Method 3 and I have not received a response to my 
inquiry, even from the consulting engineering firms that wrote FEMA 273. 



Frank E. McClure   January 23, 2000