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- One can notice that ETABS default combination including seismic load (E) is not completely match with basic load combinations at ASCE SEC.2.3.2 (1.2DL+1E +L +0.2S) & (0.9DL+E ).
- This is because ETABS create combinations mentioned at ASCE SEC.220.127.116.11 which include (vertical seismic load effect 0.2SDS) in addition to (horizontal seismic load effect ƿQ ) in lieu of the basic combinations and this is match with code requirement.
- The point is ETABS take default values for SDS=0.5 & ƿ=1.
- So we need to input the actual value for SDS & ƿ (to create correct seismic load combinations.
to adjust mentioned factors ( Design menu – concrete frame design – View\revise preferences )
- ƿ is redundancy factor defined in SEC.12.3.4
- SDS is response acceleration parameter defined in SEC.11.4.4
- Attached figures for illustration.