Reliability-Based Assessment of Doubly Reinforced Beams for Limit State of Collapse

This study examines the reliability levels of doubly reinforced beams designed according to the Indian standard code for plain and reinforced concrete (IS456:2000). Mathematical models were developed for limit state of collapse for flexure and shear according to IS456:2000. The resistance was expressed in the form of limit state of equations and the random variables identified were grade of concrete and grade of steel. The significant load variables considered were dead load and live load. Reliability indices were evaluated using first order reliability method. The analysis was carried out on beams designed for different live load intensities. The effect of reinforcement bar diameter and the effect of limit state equations on the reliability indices were evaluated. The results obtained were compared with international standards. This study evaluates the IS456:2000 provision for beam design from the probabilistic and risk-based analysis point of view. Accordingly, some suggestions have been made for setting the target reliability levels for IS456:2000. This analysis aims to initiate the basic application of reliability to design methodology of the code.