Assessment of reliability of EN 1992‐1‐1 variable strut inclination method of shear design provisions for stirrup failure

Abstract

AbstractThe best estimate shear strength predictions of the operational EN 1992‐1‐1 (EC2) variable strut inclination method (VSIM) have been shown to underestimate shear capacity at low stirrup quantities. Conversely, the model overestimates shear capacity at high stirrup quantities (Cladera and Mari, 2007; Olalusi and Viljoen, 2019). Sufficient safety performance of the design formulation should be confirmed at high levels of stirrup reinforcement, and over conservatism at low stirrup reinforcement is not ideal. This contribution assesses the consistency and uniformity of the reliability index of EC2 shear design formulation over the range of practical design situations. Prediction model uncertainty is an important parameter in the assessment (Olalusi and Viljoen, 2019). The principal reliability assessment was performed using as general probabilistic model (GPM), the probabilistic representation of the modified compression field theory (MCFT) as implemented in analysis program Response 2000 (R2k), which was shown to provide the most accurate estimates of shear capacity (Bentz, 2000). This was validated by means of a similar reliability analysis using the compression chord capacity model (CCC) as GPM. The outcome of EC2 reliability analysis indicated uneconomically high reliability at low levels of shear reinforcement, high concrete strength and large beam depth, and actively reducing reliability with increased levels of shear reinforcement, reduced concrete strength and reduced beam depth for both rectangular and I‐shaped beam cross‐sections. Reliability indices of all the test sections investigated meet the target reliability requirements for Reliability Class 2 structures prescribed by basis of design standards SANS 10160 and EN 1990, for the design range considered.