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Live Load Reduction

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I am designing a 4-story cold-formed steel structure. 

The gravity system consists of composite metal deck w/ LWC topping

supported by cold-formed steel stud walls. 

 

What is the appropriate method for reducing the live load for the load bearing wall studs?

 

If I design the wall studs individually,

Trib Area   =   Stud Spacing   x   Trib. Width over the Wall   x   # of Floor Levels Supported

This approach means that I will not be able to reduce the live load because the trib area is not great enough.

This approach seems overly conservative to me because we are talking about

vertical load path down thru a 4-story structure.

 

However, if I consider each load-bearing wall as a complete assembly,

Trib Area   =   Wall Length   x   Trib. Width over the Wall   x   # of Floor Levels Supported

This way I will be able to fully reduce my live load to 40% of the total live load.

This approach seems like it could be non-conservative because the top track probably does not provide

capacity that would warrant considering the wall as a complete assembly (i.e. I could envision a

single stud within a wall failing while studs on each side do not fail)

 

An appropriate method would seem to be somewhere in the middle. 

I have not, however, been able to find any specific guidance in the building codes for this situation. 

Any input or recommendations would be greatly appreciated. 

 

Evan Mizue

For Baldridge & Associates Structural Engineering