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Re: Diaphragm Calculations

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>As Chuck Greenlaw pointed 
>out, the test of our liability will occur in court an will most likely be 
>decided upon the qualifications and confidence of the expert witness and the 
I'll stick my nose into a residential construction issue with which I thankfully have nothing to do and suggest that other people may have been looking at lateral load resistance. The lawyering, if any, may go further than just the particular hired gun involved. I got the following from the Florida Board of Professional Engineers <>. One of the Board's recent actions was accepting a full report from James Powers P.E. and issuing the following as a bulletin:

It has recently been brought to the attention of the Florida Board of Professional Engineers that current practice in the design and construction of residential gable end wall does not, in some cases, provide the degree of wind resistance mandated by the Standard Building Code. The problem is particularly severe in the case of relatively long walls and relatively steep roof pitches and is further complicated when a vaulted ceiling abuts the gable end wall.
This deficiency stems from a failure to provide effective lateral support at the interface of the gable wall and the gable truss. Designers are cautioned to be alert to recognize the problem when it exists.
If a ceiling is utilized to provide effective lateral support it should be noted that the 1997?Standard Building Code assigns no value to gypsum board as a horizontal diaphram [sic]. If gypsum board is to be used as permitted under the prescriptive requirements of SSTD-10 or the provisions of AF & PA Wood Frame Construction Manual for One and Two Family Dwellings?1995 Standard Building Code High Wind Edition, it is essential that the characteristics mandated by those documents (attachment to the gable wall and to the perpendicular shear wall) be clearly specified.
If bracing members are utilized to provide effective lateral support, it must be demonstrated that there will be no conflict between bracing members and truss diagonals. Further it must be demonstrated that consideration has been given to the effect on the trusses of loads imposed by the bracing, most particularly in the case of loads applied at locations other than panel points.
Engineers practicing in the structural field should be cognizant of the referenced deficiencies and take due caution in designing gable end walls.
The Florida Board of Professional Engineers
June 10, 1999

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)