Underground Garage Design under Seismic 1

[onetimedeal]

I have a building in Maryland with the following information:

1. Three levels underground parking garage
2. Street level is a retail space
3. Second floor is a 14" thick concrete transfer floor
4. Four levels wood apartment building above the transfer floor.

I am using RAM RSS and Concept to design the concrete structure. This RAM model can only show concrete portion of the building which the wood building will only transfer DL and LL to the transfer floor.

The question I have is how to model this structure for seismic? If I take the entire building for seismic design, how do I specify the underground portion of the structure? Can I only model the one elevated slab plus the LL and DL of the wood struture for seismic design?

Please help.

 

[msquared48]

Best to model as two separate structures - one for the wood and one for the concrete. In a year or two, RISA will be able to model both together for both vertical and lateral loads, but not now.

The vertical, lateral, and uplift loads from the wood portion can be applied to the podium slab, and the concrete portion designed separately.

The top of the podium slab can be taken as the seismic base for the wood portion, but this will have to be justified per calculations and code requirements.

Mike McCann
MMC Engineering

 

[haynewp]

Mike, I know you have mentioned this before, regarding how you are allowed to model a wood building being supported by a concrete structure as if the top of concrete is the base for the wood building. Can you point me to where this allowance is stated in the ASCE/IBC?

 

[OldPaperMaker]

haynewp,
I think that section 12.2.31 of ASCE 7-05 outlines the procedure for a two stage equivalent lateral force procedure.

 

[msquared48]

That's 12.3.2.1 - you missed a period OldPaperMaker. I hope you're not pregnant!

By the way, thanks for bailing me out.

Mike McCann
MMC Engineering

 

[onetimedeal]

Thank for the comments about the wood structure.

How about the underground portion of the building? Shall I only model the podium slab with wood structure for seismic? How about the underground portion of the building? Thanks.

 

[MarkAJohn]

This may answer your question, check out the NEHRP Commentary Section 7.5 (free on line) for the most definitive write up on yielding and nonyielding walls:

http://www.bssconline.org/NEHRP2003/comments/

HTH

 

[msquared48]

The podium slab has to distribute all the vertical and horizontal forces of the wood structure to the concrete structure below, columns, beam, other PT slabs, walls and footings. The concrete system also has to carry it's own lateral and vertical loads too.

Mike McCann
MMC Engineering

 

[VoyageofDiscovery]

To account for seismic you must do a RSA and model the soil as a pseudostatic pressure for non-yielding walls on top of the existing lateral soil pressure.

HTH

VOD