Is it MWFRS or C&C? 1

[UcfSE]

Let's take our example as a column in the middle of a one-story building, say the size of a grocery store. It supports girders that support roof joists. It has assumed pinned ends and is not part of a moment frame, braced frame or shear wall. In other words it resists only gravity and uplift from the roof, no lateral forces. It's tributary area is, say, 400 square feet. Do you use MWFRS pressures or C&C? I say it is C&C but some in my office including my boss say to use MWFRS. It's tributary area is less than the 700 square feet that the ASCE 7 says is ok to use MWFRS pressures. What are your opinions on this, what pressures would you or do you use? This is purely a made up example though I have been in conflict with those in my office about this point before with similar set-ups. My logic is it does not provide stability to the structure as a whole by taking the main wind forces and therefore is not main wind. The opposing logic is it does not take wind forces directly but receives it from other members and therefore is main wind.

 

[haynewp]

The interior pressure coefficients don't cancel out for the interior column like they do for typical MWFRS columns, (like in a braced frame taking forces generated from a windward and leeward wall). To me it's counterintuitive to treat the column in question as MWFRS.

 

[ChuckerD]

The post by SmithJ piqued my interest so I dug up the ASCE7-02 to check the commentary. Section C6.2 Defintions (pg. 271) states the following:

COMPONENTS AND CLADDING. Components receive wind loads directly or from cladding and transfer the load to the main wind force-resisting system. Cladding receives wind loads directly.

The column in question certainly does not meet this definition.

 

[JAE]

Amen to ChuckerD.

 

[haynewp]

JAE,

I think ChuckerD is still saying that it should be treated as MWFRS and you are saying it should be C&C.

Does anybody have the Guide to the Wind Load Provisions for ASCE 7-98 or 7-02?

 

[ChuckerD]

I think it's pretty clear from the commentary cited above that the column does NOT fall within the definition of C&C. Thus use MWFRS wind loads.