Seismic collapse prediction of frame structures by means of genetic algorithms

Abstract

This paper presents an automatic approach for the evaluation of the plastic loads and failure modes of planar frames. The method, based on the generation of elementary collapse mechanisms and on their linear combination aimed at minimizing the collapse load factor, is here originally extended to account for the contemporary presence of permanent and incremental loads. The presence of permanent distributed loads acting on beams, which affects the occurrence and the location of along-axis plastic hinges, is here evaluated by means of an exact formulation. Each elementary mechanism is built and studied through an original code developed in the agent-based programming language NetLogo, which is here employed for the first time with structural engineering purposes. The developed software interface is very user-friendly and has a great versatility. The minimization procedure is efficiently performed by means of genetic algorithms, which allow to compute both the collapse load factor and the correspondent failure mode with great accuracy and in a very short computing time. The possibility of taking into account both incremental horizontal load distributions at each floor level and permanent vertical loads on beams provides, for the first time, an automatic method which allows to obtain fast and reliable information on the resistance and collapse mechanisms of frame structures subjected to seismic loads. Many applications have been performed, either with reference to the classical plastic analysis approach, in which all the loads increase proportionally, or with seismic load scenarios. In the latter case, the numerical results have been compared to those obtained with pushover analysis, showing, in a shorter computing time, a very good correspondence even for large structures. Finally, a parametric study has also been performed, aiming at evaluating the influence of some geometric, mechanical and load distribution parameters on the ultimate collapse load of planar frames subjected to seismic loads.