Siesmic Irregularities

[DTS419]

When I learned seismic design back in school, it was the old UBC... Regarding vertical and horizontal irregularities, if my memory serves me right, the code just assessed an increase penalty for irregularities. I'm trying to do my first seismic design in a long time using this new ASCE7-05 and this is anything but clear on how to handle irregularities with the ELF procedure. Tables 12.3-1 and 12.3-2 just jump you around to myriad other places but nothing seems to offer any definitive guidance. When can I and can't I use the ELF procedure if I have irregularities? What is a 3D representation mentioned in 12.7.3 and when must this be used?

 

[KBVT]

You can use equivalent lateral force method with CERTAIN irregularities but the ELF procedure makes certain assumptions about the vertical force distribution that does not hold true under certain circumstances. I would recommend you take a look at the 2006 IBC Structural/Seismic Design Manual published by the SEA & ICC as they break down the horizontal & vertical irregularities determination to relatively basic calculations.