Multiple Seismic Site Classes

[ArchiCam]

I am in the process of designing a LARGE U-shaped warehouse. After speaking to the Geotech it has been determined that the site conditions on one leg of the U are much more favorable than the other leg. If considered separately, we have at least site class C (maybe even B) on one leg and no better than site class D on the other. The warehouse consists of steel braced frames with tilt up walls along the perimeter. We typically separate the building into "bays" with expansion joints every 300-400 feet. My question is this: is there somewhere in the code that would allow us to consider the two legs of the building separate so as to design one with the more favorable conditions instead of taking the worst case over the whole site? If so, what constitutes "separate"? Is an expansion joint enough of a separation? I have begun researching this issue but thought I would put the question out there to see if anyone might know something I don't.

Thanks

 

[JAE]

I would say that an expansion joint would create two separate buildings and each could be designed for their specific site class.

That assumes that the expansion joint can directly align with the geotechnical line between the two areas....that might be difficult or impossible...especially if the line is not parallel with the natural column lines of the building.

 

[msquared48]

If the Geotech puts it in writing, I see no problem with that. Really no different than one portion of a foundation being on pile and the rest on spread/strip footing.

Just compute your deflections so the seismic joint is large enough so pounding will not occur.

Mike McCann
MMC Engineering