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Truss-MWFRS or C & C

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Title: Truss-MWFRS or C & C

WTCA has developed a Load Guide (v1.02) in Excel format that has commentary on this subject excerpted from Tab C6-Wind as follows:

"Structural members that spans from eave to ridge or eave to eave will typically include more than one C&C pressure zone. Structural members must be designed for use in either the lower (interior area) or for the higher (end zone). This design information is typically indicated as part of the design notes.

Uplift values are included on the truss design drawing and are typically based upon the accepted engineering practice of using MWFRS pressure values. They typically may be used to determine the appropriate connector to resist uplift.

Where tributary areas are greater than 700 ft2 (6.5.12.1.3, p.32) Components and cladding elements with tributary areas greater than 700 ft2 shall be permitted to be designed using the provisions for main wind force resisting systems.

MWFRS values are used to determine uplift values, unless the use of C&C design values for uplift are required by the AHJ.

Overhangs are designed for a positive pressure on the bottom surface of the windward overhang (Cp = 0.8) in combination with the appropriate MWFRS pressure (per ASCE 7, 6.5.11.4.1) determined from Figures 6-6 and 6-10."

The Load Guide is free to download from the WTCA website: http://www.sbcindustry.com/loads.php#tlg

HTH

Buddy

John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791
http://www.awc.org

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

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The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.

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From: Ramesh Savaliya <savaliyaramesh(--nospam--at)yahoo.ca>
Subject: Truss-MWFRS or C & C
To: seaint(--nospam--at)seaint.org

I always design trusses for C & C loading. In which situation it should be designed for MWFRS load?
Aegis software have selection for both.
Thanks
Ramesh Savaliya, P. Eng.