OPTIMAL DESIGN OF REINFORCED CONCRETE FRAMES UNDER SEISMIC EXCITATION

The preliminary design of most buildings is based on equivalent static forces specified by the governing building code. The height wise distribution of these static forces seems to be based implicitly on the elastic vibration modes. Therefore, the employment of such a load pattern in seismic design of normal structures does not guarantee the optimum use of materials. In the present study, a method based on the concept of uniform distribution of deformation is implemented in optimization of dynamic response of reinforced concrete frames subjected to seismic excitation. This approach is based on an evolutionary optimization algorithm where structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform damage distribution is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. Steel reinforcement, as compared with concrete materials, appears to be the more cost-effective material, which can be effectively used to control drift beyond the occurrence of first yielding and to provide the required ductility of RC buildings. In this study, steel reinforcement ratios are taken as design variables during the design optimization process. 5,10 and 15 story reinforced concrete frame structures are used as a emonstration example to obtain the optimum design under the given earthquake excitations.