A Genetic algorithm aimed at optimising seismic retrofitting of existing RC frames

This paper presents a novel numerical procedure based on a dedicated genetic al-gorithm aimed at selecting the “optimal” retrofitting solution among the technically feasible ones obtained by combining structure- and member-level techniques. Specifically, both steel bracing systems, considered as structure-level intervention, and FRP-confinement of under-designed RC members, thought-out as member-level technique, are taken into account for achieving the retrofitting objectives within the conceptual framework of a multi-level Perfor-mance-Based approach. OpenSEES is one of the main “characters” of the numerical procedure, as it is intensively utilised for running the analyses that are needed for determining the seismic performance of the RC frame under consideration strengthened by means of a set of structure- and member-level interventions representing the generic “individual” of the current “genera-tion” of the genetic algorithm. The paper focusses on describing the interactions between Open-SEES and the aforementioned genetic algorithm implemented by the Authors in Matlab. Specifically, the main data structures and subroutines are outlined with the aim to show how input and output operations in/from OpenSEES are handled. Particularly, the paper describes how basic mechanisms inspired to the well-known Theory of Evolution by Charles Darwin are transposed to the problem under consideration. It is worth highlighting that executing the Non Linear Static (NLS) analyses requested for assessing the actual effect of seismic strengthening interventions represents the most computationally demanding and time consuming operation in the whole numerical procedure. Therefore, the paper gives some details about some specific measures taken in implementing the numerical procedure with the aim to enhance computa-tional efficiency without affecting simulation accuracy.