Optimal seismic performance-based design of reinforced concrete buildings

Although the research on design optimization of structures under earthquake loads has been ongoing for the past few decades, there is still no effective method for optimizing buildings subject to seismic drift performance criteria. The control of drift performance, however, is one of the most challenging and difficult tasks in seismic design. In order to meet the emerging trend of the performance-based design approach, and to improve the design efficiency and to further extend the current optimization to seismic nonlinear performance-based design, this research aims to develop a systematic and comprehensive design optimization technique for seismic design of reinforced concrete (RC) buildings. The technique can minimize the construction cost or life-cycle cost during the life time of elastic and inelastic, fixed-base and base-isolated building structures subject to deterministic and indeterminstic seismic design constraints whilst simultaneously satisfying multiple levels of practical seismic performance requirements. The outcome of this research is an advanced computer-based design tool that is directly applicable to the optimal seismic performanced-based design of RC building structures. This thesis firstly introduces an elastic design optimization for RC buildings based on response spectrum and linear time history analysis methods. The design optimizaiton methodology is based on the rigorously derived Optimality Criteria approach due to its high computational efficiency. Secondly, the inelastic design optimization based on the nonlinear pushover analysis method is presented, which minimizes the construction cost of a RC building. Based on the consideration of the occurrence of reinforced concrete plasticity and the formation of plastic hinges, the explicit formulation of inelastic pushover interstory drift responses at the performance point is expressed by the Principle of the Virtual Work and the use of the second-order Taylor series approximation. To speed up the rate of convergence of this inelastic design optimization, an initial element sizing preprocessor is proposed based on the “closed form” results of a single drift optimization. This inelastic design optimization is further posed as a multi-objective optimization problem. The total life-cycle cost consisting of the construction cost and the expected future damage loss of a building system is formulated using the fuzzy theory. One of the multi-objective optimization algorithms, namely the ε-constraint method, is employed to produce a Pareto set of optimal solutions. The optimal seismic design problem is further broadened from fixed-base to base-isolated building structures under response spectrum loadings. For a base-isolated building, both the superstructure and the base isolation with linear and nonlinear isolators, as a whole, are simultaneously optimized to produce a well isolated optimal structure. Finally, the deterministic optimization is then extended to an indeterministic reliability-based optimization which takes into account of the uncertainties involved in designing structures under earthquake loadings. The First-Order Second-Moment method is used to estimate the reliability corresponding to the interstory drift responses of elastic or inelastic, fixed-base or base-isolated building structures under response spectrum loadings or pushover loadings. A number of illustrative examples are presented in relevant chapters to demonstrate the efficiency and applicability of the proposed automated optimization methods