RELIABILITY-BASED OPTIMAL-DESIGN OF REINFORCED-CONCRETE FRAMES

Reliability based optimal design (RBOD) of structures aims at minimization of structural cost constrained by a specified allowable failure probability. A methodology has been developed for RBOD of reinforced concrete frames which considers the failure of structure, both at the component and system level simultaneously, under two different live load and wind load combinations. System failure probability is evaluated based on the generated stochastically dominant failure modes which consist of collapse mechanism failure modes and rotational failure modes (arising due to critical sections reaching their permissible inelastic rotation capacities). Optimal values of the moment capacities of critical sections are obtained based on the minimization of the total structural cost of the frame using the cost functions for member sections as a function of their moment capacities, which are derived by optimizing the member sections. It is observed that designs obtained using RBOD procedure give cost reduction for the chosen target reliability level, equal to that inherent reliability in the designs obtained as per the present Indian standard specifications.