A question for the structural engineering community: The ASCE/IBC load combinations include a combination under the ASD Basic Load Combinations for D+(W or E)+L+(Lr or S or R). When two or more transient loads are combined in this section a 0.75 factor on the live loads may be used. Now here is the question, how many engineers use this load combination for C&C design of say a rafter or bar joist?
Here is an example that would be typical for my part of the country. Assume a roof snow load of 20 psf (unreducible) and the wind load minimum inward pressure of 10 psf.
S = 20 psf
W = 10 psf
0.75(20 psf + 10 psf) = 22.5 psf > 20 psf for snow
However, I don't know personally of any engineers who would design for 22.5 psf in this case as nobody combines the roof live load with wind.
The typical interpretation I hear is that this load combination is intended for design of elements such as columns where axial load results from the lateral loads.
Do you agree or disagree???
Here is an example that would be typical for my part of the country. Assume a roof snow load of 20 psf (unreducible) and the wind load minimum inward pressure of 10 psf.
S = 20 psf
W = 10 psf
0.75(20 psf + 10 psf) = 22.5 psf > 20 psf for snow
However, I don't know personally of any engineers who would design for 22.5 psf in this case as nobody combines the roof live load with wind.
The typical interpretation I hear is that this load combination is intended for design of elements such as columns where axial load results from the lateral loads.
Do you agree or disagree???