building separation for seismic design category C

[kgr85]

Hi,

IBC specified that the building shall be separated by:
1) delta,MT = sqrt( (delta,M1)^2 + (delta,M2)^2 ) for buildings in the same property
2) set back by delta,M if the building adjoins a property line

But, exceptions are buildings in SDC A,B or C.

Then, how much of separation should be provided in SDC A,B and C. I guess it should be the same as D or worse. Why the code has this exception???

Lastly, what if there is a builidng adjoining the property line in the next site? Should the new building in our site consider the deflection of the existing building and add it to the set back amount??

Thanks in advance,

 

[ishvaaag]

Have not the paragraph at sight but sites classed as exposed to lesser intensity earthquakes will be being also thought to experience less effective lateral displacement, and so the space allowed to forfeit hammering action by some structure closeby can be reduced.

 

[RockEngineer]

Last week I attended the on-line web seminar 2009 IBC Boot Camp by SK Ghosh Associates and they stated that the idea behind the two different requirements was that two structures on the same property were usually owned by the same person and could lightly bump each other and the owner absorb that risk, thus sqrt of sum of squares. Two structures with a property line in between each must be back from the property line by the maximum deflection at the height of the shorter building so they could not bump under any circumstance.

If an existing building isn't back from the property line by it's required maximum deflection I would make sure my structure was far enough away from the other structure that they would never collide.