In a dynamic load case like Response Spectrum or Time History load case, you need to dine the mass by doing a mass modelling where you define the loading in the three orthogonal direction.
If you look into the clause-7.8.4.5 C of IS:1893 Part 1-2002, you would get a value of Ak (design horizontal acceleration ) which is (Z/2)X (I/R)*(Sa/g). The program is able to compute Sa/g value from the Response Spectrum curve for each mode and (Z/2)X (I/R) has to be provided in the direction factor.
In Response Spectrum Analysis as per the IS:1893-2002 code, the spectral data(Sa/g) is taken by the program from the equations provided in the code, against the specified Soil Type. After getting this value from the equations, STAAD internally multiplies that quantity with the value of "g" in the current input unit. In such a case, the SCALE Factor is given in the input as 1.
If you look into the clause-7.8.4.5 C of IS:1893 Part 1-2002, you would get a value of Ak (design horizontal acceleration ) which is (Z/2)X (I/R)*(Sa/g). The program is able to compute Sa/g value from the Response Spectrum curve for each mode and (Z/2)X (I/R) has to be provided in the direction factor.
In Response Spectrum Analysis as per the IS:1893-2002 code, the spectral data(Sa/g) is taken by the program from the equations provided in the code, against the specified Soil Type. After getting this value from the equations, STAAD internally multiplies that quantity with the value of "g" in the current input unit. In such a case, the SCALE Factor is given in the input as 1.