Comparison of two FORM methodologies for reinforced concrete beams under flexure

Abstract The response of a reinforced concrete structure is influenced by the variability of design parameters such as materials strengths, geometry, and load intensity. One of the most rational ways to assess the safety level of a reinforced concrete structure is to employ a probabilistic approach. This paper aims to compare the reliability indexes for a set of reinforced concrete beams according to two different methodologies, based on the association of First Order Reliability Method (FORM) with the ANSYS software. In the first methodology, the reliability indexes were assessed through the direct coupling of the FORM to the Finite Element model. In the second methodology, a response surface was employed to fit a flexural resistance function, based on the FE results, being the reliability indexes assessed by an external FORM algorithm. The results showed that both methodologies led to equivalent reliability indexes and that the safety level of the beams, which were designed according to the Brazilian code NBR 6118:2014, is mainly influenced by the load combination, presenting unsatisfactory values when the live load increases.