SCBF Foundations

[kgengr]

Hello All,
I am designing an SCBF in SDC D. Per AISC Seismic Provisions (C8.5, 6.1-147) it seems clear that the connections of the column base to the foundation shall be designed for either the seismic loads with overstrength or loads based on member strengths, whichever were req'd/governed for the system connections. My question is with regard to the design of the foundation itself for overturning, bearing, and reinforcing. Should I be using the seismic design loads with overstrength or the same loads I used for my connection to the foundation - in my case, governed by loads based on member strengths? It seems to me this is not specifically addressed in any of the following codes: AISC, IBC, ASCE, or ACI.

Thanks for your help.

 

[SteelPE]

I don't know what code you are using but isn't this handled is section 12.13 and 12.1.5 of ASCE 7-05? I would guess from these sections that you would design the foundations for the forces imparted on the structure..... and then take any reductions allowed in section 12.13.4. Please keep in mind that I generally design using R=3.

 

[SethGuthrie]

You don't need to design the footing (or check soil stress) at the amplified overstrength seismic level (exception Battered piles). You should check the foundation for combinations including Ev the vertical component of the earthquake, however.

 

[kgengr]

This may be correct - but here's my line of thinking - if the SCBF is designed to dissipate energy by yielding at the foldline of the gusset plate, and all other detailing of members and connections has been done to "ensure" this will be the case, including anchorage to the foundation (for either overstrength or member capacity) - why then would the foundation itself be designed for the basic design level forces? It seems to fall short putting a massive connection and not the footings/foundations to support it...