A two-step approach for reliability-based design optimization in power transmission line towers

Reliability-based design can be used to simultaneously take into account economic aspects as well as safety considerations for various failure probabilities of structures. Such problems have two categories of deterministic and probabilistic constraints. Evaluating the probabilistic constraints and calculating the reliability index, usually require a large number of evaluations of the limit state function. This increases the time and volume of computation; while there is no need to calculate the reliability index for all probable optimal solutions and this index should only be calculated for probable solutions in which deterministic constraints are met. Accordingly, in this study, a two-step approach for optimal design of reliability-based structures is proposed. In this approach, the probabilistic constraint is checked when the deterministic constraint is met; otherwise, the probabilistic constraint is not calculated and the reliability index of zero is considered as a probable solution penalty. In order to investigate the efficiency of this approach, four power transmission lines towers were studied with enhanced colliding bodies optimization (ECBO), water evaporation optimization (WEO), and enhanced vibrating particles system (EVPS). Deterministic and probabilistic constraints defined based on the members’ axial stress and nodal displacement, respectively. Monte-Carlo simulation method was used to evaluate the probabilistic constraints. The results show an appropriate safety margin than the allowable values for the probabilistic constraints.