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American Wood Council

I noticed that MWFRS coefficients are used. That's ok for walls, but I typically use C&C coefficients for truss anchorages. How does WFCM address this?


From the WFCM Commentary: Uplift for design of rafters, roof cladding, and roof sheathing attachment is calculated using Components and Cladding (C&C) loads. Uplift connections for roof assemblies are calculated using enveloped Main Wind Force-Resisting System (MWFRS) loads. The rationale for using MWFRS loads for computing the uplift of roof assemblies recognizes that the spatial and temporal pressure fluctuations that cause the higher coefficients for components and cladding are effectively averaged by wind effects on different roof surfaces consistent with the definitions of C&C and MWFRS loads in ASCE 7. Also note that C&C loads are used to calculate wall bending loads whereas MWFRS loads are used to calculate combined bending and axial loads. Within the scope of the WFCM, C&C bending loads control. See the following paper for more details:
Considerations in Wind Design of Wood Structures 

 
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