## Vertical distribution for base shear determined by response spectrum

## Vertical distribution for base shear determined by response spectrum

(OP)

Hey. I’m doing a response spectrum analysis as per section 12.9 of ASCE7-05. It does not address how to distribute the seismic base shear (like the equivalent lateral force procedure does). As I recall, there is some formula to use (i.e. F(level)=participation factor x mode shape vector x acceleration x etc.,etc.). Does anyone have an opinion on this? Does STAAD perform this for you?

## RE: Vertical distribution for base shear determined by response spectrum

Be aware that STAAD gives all the forces (support reactions, member forces, etc etc) ignoring their sign...meas for a horizontal seismic force on a portal frame it gives both the support reactions +ve (insted of one +ve & other -ve).