hvac screen - mwfrs or cc
 

hvac screen - mwfrs or c&c?
would you consider an eight foot tall x 21' x 13' hvac screen on top of a pre-eng metal building roof, under 30' high, to be a structure required to resist wind loads calculated for mwfrs or c&c?
i'm seeing this as a c&c element considering other adjacent, geometries of the building.
please advise ...
c&c for me.
both.
you would use the screen mwfrs load to design the overall wind resistant system of the building, tracking though the entire load path from the screen, down through its supports, into the roof diaphragm, into the collectors, into the x-bracing and then to the footing.
then, for the screen design itself, you'd use the c&c as a check on the component design.
adding a large screen affects the overall wind resistant system and it requires a localized wind for its own design.
jae is right on target. let me add a couple of simplifications:
1. any structural member that receives wind directly, i consider it as c&c.
2. in case of cmu wall, as an example, it is c&c when designed in resisting windward or leeward wind loads. however, the same cmu wall is mwfrs if designed as shear wall.
i recommend that you get a copy of the asce 7 design guide published by asce. the back end has many q&a and they address your question in more than on place.
hope this helps.
regards,
lutfi