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Seismic Overstrength and Foundation Design Loads

Seismic Overstrength and Foundation Design Loads

Seismic Overstrength and Foundation Design Loads

I'm designing a 3 story, steel EBF structure in a high seismic area, it's design category D. The structure's columns will bear at various locations along grade beams which are in turn supported by precast piles. I'm designing everything with the 2005 code cycles per UFC (it's a military project) requirements.

I'm unclear on the required foundation design load. I know at least the following:
1. The steel beams, links, braces, columns, base plate, and anchorage of the base plate must be designed for the shear yield capacity of the links - per AISC 341-05.
2. ASCE 7-05, section - for Seismic Design Category D-F - allows you to design grade beams as regular reinforced beams IF you use load combinations with overstrength factor.
3. IF you don't use overstrength factor, ACI 318-05, section - requires you to design your beam as though it were part of Special Moment Frame.

Given all of this, I'm a little confused - Load combinations with overstrength will not produce the same loads as designing for shear yield of links. When designing an EBF supported on grade beams - what is the appropriate load for foundation design? I would go ahead and be conservative were I designing it all from scratch, but I'm stuck with foundating my EBF steel frame on someone else's grade beams..... Thanks in advance for your help.

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