Simplistic Seismic Base Justification

[msquared48]

Anyone know a simple method (or thought process based on building geometry) of justifying a seismic base (wood over concrete parking as Multistory Condos or Apts) short of having to calculate the lateral deflection of the wood framing lateral system and comparing the two systems under the IBC code requirements?

Woodworks will not have lateral deflection calculations worked into their program for two years. RISA does the calcs for the concrete structure below, but does not do wood shear walls. There in lies the problem.

I'm reaching for the moon here trying to KISS.

Mike McCann
McCann Engineering

 

[haynewp]

I am not sure what you mean by seismic base. What are you trying to justify?

 

[msquared48]

In a multi wood story residential/retail structure sitting over say two to three stories of PT or CIP concrete (parking) construction, it is permissable, due to the difference in relative stiffnesses of the two types of construction, to consider the top of the concrete construction (podium slab level) as the "Seismic Base" for the wood portion. In other words, for the wood portion, the "H" starts at the top of the concrete portion.

The seismic reactions from the wood portion still have to be included in the design of the concrete portion.

Mike McCann
McCann Engineering