This paper discusses possibility of increasing ultimate aseismic safety of steel buildings by utilizing PC curtain walls which have been non-structural members. Elastic-plastic seismic responses of the structures with and without walls are analyzed, and the results are compared to show aseismic effects of the walls. Moreover, allowable seismic accelerations of the structures are estimated on the assumption that they correspond to the beginning of strain-hardening of plastic hinges, and it is shown that the accelerations may be increased from less than about 800 cm/s^2 (without walls) to more than about 1000 cm/s^2 (with walls).