A practical methodology for optimum seismic design of RC frames for minimum damage and life-cycle cost

The design criteria in current seismic design codes are mainly to control lateral displacements and provide adequate strength to sustain expected design load combinations. However, to achieve the most economic design solutions, the life-cycle total cost (TLCC), which includes both initial structural cost and expected damage cost, should be also considered for the probable earthquakes during the lifetime of the structure. In the present study, the TLCC of the buildings is used as the main objective function for optimum seismic design of reinforced concrete (RC) frames. First, it is demonstrated that the blind increase of the reinforcement ratios does not necessarily reduce the displacement demands and the damage costs. Subsequently, a practical methodology is developed for the optimum seismic design of RC frames based on the concept of uniform damage distribution (UDD). Using an adaptive iterative procedure, the distribution of inter-storey drifts and TLCC of the floors is modified along the height of the structure. To demonstrate the efficiency of the method, 5, 8 and 12 storey RC frames are optimized using the proposed algorithm. The results indicate that, while all predefined performance targets are satisfied, the maximum inter-storey drift ratio and TLCC of the frames are considerably reduced (up to 56% and 45%, respectively) only after a few steps. The proposed method should prove useful for more efficient performance-based design of RC frames in practice.