Time-history analysis of the roof slab of an underground garage under excitation of seimic waves

In order to investigate the seismic performance of the roof slab of an underground garage after it had been strengthened by superimposing 32cm thick concrete on the top of its roof slab, commercial software Sap2000 was used to model the structure. Four time functions were defined, together with the corresponding time-history analysis cases. In each case, the vertical displacement, bending moment, shear force and axial force at representative points of some typical structural members were plotted with respect to time; and the responses before and after strengthening were compared. The results indicate that the vertical displacement is quite small though it is reduced considerably after strengthening; the internal forces generally tend to change more uniformly with time and to become smaller after strengthening though there are some exceptions which attention should be paid. The method used in the study can be extended into the other similar situations.