As I remember, the C&C CGp values from Figure 6-5A and 6-5B are for wind in any
direction, therefore the number of required load combinations is significantly
smaller for C&C than MWFRS. I believe that the only components and cladding
load combinations are:
-external CGp positive on one side, negative on the other with positive internal
-external CGp positive on one side, negative on the other with negative internal
According to the top of page 149 in the commentary, "trusses should be designed
for loads associated with main wind-force resisting systems, and individual
memebers of trusses should ALSO be designed for component and cladding loads."
[emphesis added] This says to me that the individual members are designed for
MWFRS and C&C loads, while the overall truss is only designed for the MWFRS
loads. (Therefore, you also have to include the MWFRS combo's you listed in
your original question.)
Each truss member must be looked at for each load combination to find the
In the end, it seems like footnote 4 on Figure 6.5 says it all. "Each component
shall be designed for maximum positive and negative pressures."
My thesis steps through this calculation and shows my interpretation of the load
combinations. Let me know if you would like a faxed copy, but it is quite long
Just my 2 cents...
Mark J. Redlinger, PE
From: CDaniels <ced(--nospam--at)larsondesigngroup.com>
Subject: ASCE 7-95
I'm looking for some advice on the component and cladding loadings from
figure 6-5B in ASCE 7-95. How are the component and cladding values for a
gable roof applied? I have a heavy timber truss system (11:12 trusses @ 14'
O/C), purlins and common rafters. My question is, how are the values
applied to the truss? Is it the same as MWFRS, wind perp to ridge under
positive internal pressure, wind perp to ridge with negative internal
pressure, wind parallel to ridge windward edge and leeward edge with
positive and negative internal pressures. Or is the maximum positive and
negative pressures applied without considering windward and leeward effects?
Any input or references would be appreciated?
Larson Design Group