I define a SPECTRUM data as below
SPECTRUM CQC X 1 ACC SCALE 9.8 DAMP 0.030 0.072; 0.1 0.185; 0.4 0.185; 0.7 0.1092; 1.05 0.0746; 1.35 0.0588;1.7 0.0474; 2 0.0406; 2.35 0.0393; 2.7 0.038; 3 0.0368; 3.35 0.0355;3.65 0.0343; 4 0.033; 4.35 0.0316; 4.65 0.0305; 5 0.0291; 5.3 0.028;5.65 0.0266; 6 0.0253;
after staad finished the analysis,in its output anl file,i got the base shear result as below
CQC MODAL COMBINATION METHOD USED. DYNAMIC WEIGHT X Y Z 2.096803E+04 0.000000E+00 2.096803E+04 KN MISSING WEIGHT X Y Z -2.606766E+03 0.000000E+00 -2.542104E+03 KN MODAL WEIGHT X Y Z 1.836126E+04 0.000000E+00 1.842592E+04 KN
499 0.00 0.00 0.00 87.568 0.000 87.876 0.00 0.00 0.00 500 0.00 0.00 0.00 87.568 0.000 87.876 0.00 0.00 0.00 --------------------------- TOTAL SRSS SHEAR 1077.12 0.00 0.00 TOTAL 10PCT SHEAR 1277.83 0.00 0.00 TOTAL ABS SHEAR 2784.69 0.00 0.00 TOTAL CQC SHEAR 1264.07 0.00 0.00
there are 4 base shear data listed above,now i am puzzled which one will be the corrected one to be used to design the foudation area ?
anyone can help me? thanks
These are 4 different ways in which results from the modes are combined to arrive at the final response. Since you used CQC as your modal combination method when defining the spectrum input, I would suggest that you go with the CQC shear. The CQC is a good one to use specially when some of the modes are closely spaced and I always prefer using it.