Nonlinear stiffness design optimization of tall reinforced concrete buildings under service loads

Tall reinforced concrete (RC) building designs must satisfy serviceability stiffness criteria in terms of maximum lateral displacement and interstory drift. It is therefore important to assess accurately the effects of concrete cracking on lateral stiffness of such structures. This study integrates nonlinear cracking analysis methods with a powerful optimization technique and presents an effective numerical approach for the stiffness-based optimum design of tall RC buildings under service loads. A probability-based effective stiffness method is employed to identify cracked members and to modify their effective cracked stiffness. Iterative procedures are necessary for the serviceability analysis of tall RC buildings to determine their nonlinear stiffness characteristics due to concrete cracking. Design optimization based on a rigorously derived optimality criteria approach involves minimizing the cost of RC structures while satisfying the top and multiple interstory drifts constraints along with member sizing requirements. A framework example is presented to illustrate the applicability and efficiency of this proposed optimal design tool. Discussions about the effects of concrete cracking on the optimization results are also included.