MAXIMIZING THE COLLAPSE RESISTANCE OF COMPOSITE STEEL AND CONCRETE STRUCTURES

Abstract

The progress of research in combination with the evolution of the available construction technology has allowed the engineers to achieve a more effective use of the material properties, leading this way to the design of more economic, but also more safe structures. At the same time, it enabled the design codes to adjust in order to cover a wider spectrum of dangers, making them stricter in each generation. Various retrofit methods come to add to this lack of capacity of the existing structures; however it is inevitable that the total cost of the existing frame and the retrofit will be higher than the one of a structure designed originally with this capacity. The present work targets to give a perspective of the correlation between cost and performance of steel and concrete composite frame buildings, providing this way a decision making tool to the engineers who want to achieve the most cost effective design of a structure. For this purpose, the design of 3 composite buildings of different height was optimized for a spectrum of seismic performance levels. The minimization of the total material cost was achieved using the evolution strategies genetic algorithm, which was subject to the following constraints: (a) Eurocode 4 provisions for the composite column-members, (b) Eurocode 3 provisions for the steel beam-members (c) minimum targeted top displacement capacity determined by FEMA 440 and (d) the maximum interstorey drift for the life safety performance level. The results obtained show the effectiveness of the optimization method used, since there were determined feasible designs with up to 4 times the required capacity. Of particular interest is the comparison of the results obtained for the different building heights in a diagram of normalized cost versus capacity increase coefficient.