Safety level assessment of the fib model code 2010 shear design provisions for beams with stirrups using a mechanics-based probabilistic model

Abstract

Stirrups are provided in reinforced concrete members to prevent sudden brittle shear failures. However, accurate prediction of the ultimate shear strength of stirrup reinforced concrete beams is still an involved process. Most of the available design codes of practice implements simplified ultimate strength methods for providing stirrups in design. The fib Model Code 2010 shear level of approximation III (MC-10 (III)) design procedure is based on the simplified codified version of the modified compression field theory (SMCFT). Previous studies pointed to the probable insufficient safety bias of MC-10 (III) shear capacity predictions for large beams. This trend of results for large beams leaves cause for concern. Adequate reliability performance of MC-10 (III) design model for large beams should be confirmed. Reliability evaluation informs on the level of safety of a structure. A practical reliability assessment of a shear design procedure for stirrup reinforced concrete beam requires the use of a suitable probabilistic model with corresponding model factor statistics. This contribution aimed at assessing the level of structural resistance reliability of the fib Model Code 2010 shear level of approximation III design provisions at parametric variations of beam depth. The reliability assessment was performed using the probabilistic representation of the mechanics-based compression chord capacity model (CCCM). The CCCM is shown to provide accurate estimates of shear capacity. Conclusions from the reliability investigation indicate that deep beams designed according to MC-10 (III) have consistently low reliabilities for the design range considered.