One large footprint RC bldg designed & built as 7 separate bldgs

[SIGrkr]

One large footprint RC bldg designed & built as 7 separate bldgs
In 25 years of engineering I have never seen a building designed and built as separate buildings. This mostly completed reinforced concrete (RC) building is in a seismic area (Ss=1.30, S1=50), has an 80000 SF footprint, has no irregularities and is 5 stories. The design build contractor designed it as 7 separate buildings (units) with separations varying in width from 7 to 10 inches. Separation looks ok per code if you have to have the separation, but I don't see why. All the "exterior" walls that were just extra work and materials. The contractor says they did it for seismic reasons but I don't see the benefit of having two RC shear walls adjacent to each other. Has anybody designed this way or seen designs or construction done this way?
Thanks, SIGrkr

 

[ztengguy]

I designed a multipurpose type building once, and we designed the entryway as a seperate building with expansion joints. Thay way, the main building didnt 'bang' into it during a EQ.

 

[dik]

In seismic area you have to make sure you have enough separation that the buildings don't 'hammer' into each other. Joints are a real issue.

Dik

 

[SIGrkr]

Thanks ztengguy. An entry like a porte-cochere, open with tall columns? That makes more sense because it may have been easier than tying in the roof diaphragm. Than designing for the appropriate separation per ASCE 7 sec. 12.12.3, for a more slender structure next to the stiffer main building.

 

[SIGrkr]

Thanks Dik. Seems like joints are a very good reason NOT to make a single building by putting 7 separate ones next to each other. Do you see some advantage? The building is almost square with rigid diaphragms and plenty of interior wall lines.

 

[ztengguy]

It was an all tilt up building, large span multipurpose type buiding with a small office/entryway with shorter height.