Reliability evaluation of reinforced concrete beams

The purpose of this paper is to evaluate the time-invariant reliability of reinforced concrete beams designed under the provisions of the ACI Building Code. A wide range of practical design situations is considered. The beams are subjected to bending, shear, and torsion. The interaction between shear and torsion is considered via an elliptical failure surface defined in the shear-torsion stress space. No interaction is assumed between flexural resistance and resistance in both shear and torsion. Representative statistics and appropriate probability distributions of the basic resistance and load variables are selected from previous related work. The reliability analysis is performed using modern reliability methods, in which the formulation of the limit-state functions is consistent with the underlying design criteria. Reliability indices for various failure modes are compared and a system reliability analysis is performed to include all failure modes. It is found that the reliability indices are most sensitive to live load, model uncertainties, and material strengths. For the failure modes considered, the reliability indices are found to be rather insensitive to design parameter values, indicating that the ACI Building Code achieves its desired objective of uniform reliability across a wide range of design situations.