The code is suggesting to increase the allowable stresses induced for the seismic load combination by 33%. If we increase the factor of safety imposed on the load combination and use them in steel design, we would eventually design with higher loads. The stresses induced in the members for this load combination would be higher. But, by doing this we are not increasing the allowable stresses in the members. Our objective should be to increase the allowable stress in the member. By default, the ratio computed from the stresses induced from axial load and bi-axial bending to the allowable one for the same should be less than or equal to 1. This ratio has to be increased by 33%. This can be achieved in STAAD.Pro by using RATIO 1.33 parameter.
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