Development of applicable design models for concrete columns confined with aramid fiber reinforced polymer using Multi-Expression Programming

Abstract In this paper, a new series of applicable relations, including maximum confined stress and strain as well as the stress–strain relationship, for AFRP confined concrete are proposed based on the design-oriented approach. The main advantages of these new relations are their higher accuracy and unified nature for both circular and square cross sections as well as their ability to predict stress and strain of partially confined columns. For this purpose, a complete database of the available experimental results from the previous studies is collected. In order to achieve higher accuracy and reliability, only part of the collected experimental results that passes a series of deliberately considered criteria are used for derivation of the relations. In addition to the mentioned relations, a threshold for confinement pressure is defined which can be used as a beneficial tool by designers to specify sufficiency of their designed AFRP confinement. Furthermore, a simple relation to predict lateral hoop rupture strain of AFRP wraps is also provided. In order to make the suggested models utilizable for the cases that fibers are not placed perpendicular to the column axis, simple modification factors are also derived. The proposed models are formulated using an evolutionary algorithm named Multi-Expression Programming (MEP), which is an approach for predicting models in the cases of unknown mathematical structures. Accuracy of the proposed relations is compared with the other available models based on the collected experimental database. The obtained results showed that the suggested relations and especially the stress–strain model are capable to predict behavior of AFRP confined concretes with remarkable accuracy.