SAP2000 Response Spectrum Problem
SAP2000 Response Spectrum Problem
(OP)
I´m having an issue with response spectrum analysis in SAP2000. I´ve defined a response spectrum with a constant value of 1g and am comparing to a linear acceleration of the structure of 1g. For the case of a frame of constant mass cantilevering from a support, these give the same answer. If I add a cantilever section to the frame, (think an upside down L with one fixed support), I get a base shear from the response spectrum that is less than the base shear from the linear case. Am I misunderstanding how a response spectrum functions?
Note I have 100% mass participation in all directions
Note I have 100% mass participation in all directions





RE: SAP2000 Response Spectrum Problem
Notice how the shear for the first mode all go in exactly the same direction (hence base shear matches). But, if you look at the higher modes, there is switch back based on the mode shape.... Hence, lower base shears.
Does this help?
RE: SAP2000 Response Spectrum Problem
RE: SAP2000 Response Spectrum Problem
Base shear is calculated for each mode and then modes are combined.