Nonlinear Design Optimization of Reinforced Concrete Structures Using Genetic Algorithms

The aim of this study is to identify the optimal cross sections and reinforcement area of the beams and the columns in a frame structure in order to improve their seismic response. A six-storey reinforced concrete structure, modelled using fibre finite elements to represent the nonlinear behaviour, was studied. The structure was first designed according to existing codes (the equivalent static load method) and the total quantity of material computed (concrete and reinforcement). Secondly, a genetic algorithm was used in order to determine the optimized beam and column cross section dimensions along with the longitudinal reinforcement area for both types of elements. The optimization process aims to minimize the cost of the reinforced concrete structure while at the same time improving or at least maintaining the seismic response of the structure. A set of constraints was imposed for the optimization process: the minimum reinforcement area, the ratio between the beam height and width and the maximum drift of the structure at both the ultimate and service state, according to design codes. Dynamic time history analysis is used to determine the maximum drift of the structure. The analyses are carried out for three ground motion records which represent the seismic conditions given by the Vrancea source in Bucharest.