Response Spectrum

I want to analyse my model for a response spectrum in X, Y and Z directions. I am specifying all the 3 direction factors as 1.0. SPECTRUM SRSS X 1 Y 1 Z 1 ACC SCALE 32.2 DAMP 0.05 0 0.375; 0.881 0.375; 0.9 0.3375; 1 0.328; 1.1 0.3; 1.2 0.27; 1.3 0.2475 1.4 0.24; 1.5 0.2325; 1.592 0.2175 Is my correct approach correct? If the direction factors for X, Y and z are all specified as 1, it indicates an earthquake of full intensity in all 3 directions simultaneously. This is an unlikely scenario. An earthquake which is occuring at its full intensity along X cannot act with full intensity in Y and Z also at the same time. Instead, you ought to have 3 separate load cases, with the spectrum applied in each of those 3, and the direction factors being X=1,Y=0,Z=0 for the first case, X=0,Y=1,Z=0 for the second case, and X=0,Y=0 and Z=1 for the third case, as shown below. LOAD 4 SPECTRUM IN X-DIRECTION SELFWEIGHT X 1.0 SELFWEIGHT Y 1.0 SELFWEIGHT Z 1.0 JOINT LOAD 10 FX 17.5 10 FY 17.5 10 FZ 17.5 SPECTRUM SRSS X 1.0 ACC SCALE 32.2 0 0.375; 0.881 0.375; 0.9 0.3375; 1 0.328; 1.1 0.3; 1.2 0.27; 1.3 0.2475 1.4 0.24; 1.5 0.2325; 1.592 0.2175 LOAD 5 SPECTRUM IN Y-DIRECTION SPECTRUM SRSS Y 1.0 ACC SCALE 32.2 0 0.375; 0.881 0.375; 0.9 0.3375; 1 0.328; 1.1 0.3; 1.2 0.27; 1.3 0.2475 1.4 0.24; 1.5 0.2325; 1.592 0.2175 LOAD 6 SPECTRUM IN Y-DIRECTION SPECTRUM SRSS Y 1.0 ACC SCALE 32.2 0 0.375; 0.881 0.375; 0.9 0.3375; 1 0.328; 1.1 0.3; 1.2 0.27; 1.3 0.2475 1.4 0.24; 1.5 0.2325; 1.592 0.2175