Reliability-based study on ductility measures of reinforced concrete beams in ACI 318

This paper presents a reliability-based investigation into the ductility requirements of reinforced concrete beams designed based on the ACI Code. Results showed that the code-specified model for predicting ductility measures, such as the neutral axis depth, is considerably less reliable than it is for predicting the flexural strength. The ratio of the strain at tensile reinforcement to yield strain of steel was used to define a limit state to ensure adequate ductility in reinforced concrete beams. Due to variability in the material properties and model error, there is high variability in ductility measures, leading to a high probability of compressive failure. Based on a target probability of failure taken from the literature, it was found that modification of the current ductility requirements is desired. This research highlights the need for more reliability-based studies into the safety factors provided by the ACI Code for ensuring adequate ductility in reinforced concrete beams.