Probabilistic Safety Analysis of Prestressed Concrete Beams Failing Due to Web-crushing

Web-crushing failure in beams is a brittle failure mode as it typically occurs suddenly without warning. In order to ensure ductile shear behaviour, shear strength is limited by the maximum strut capacity equation (web-crushing equation) to prevent the crushing of concrete before the yielding of shear reinforcement. The accurate prediction of the web-crushing strength of beams is an involved process. Consequently, many codes of practices have resorted to implementing simplified methods for predicting web-crushing failure in beams. Eurocode 2 uses the Variable Strut Inclination Method. This paper aims to assess the model uncertainty and bias (model error) related to the web-crushing strength of prestressed concrete beams. The characteristics of the model error were obtained by comparing experimental web-crushing strengths to predicted web-crushing strengths. Effects of shear parameters on the model error realisations were analysed. The model error was treated as a random variable and used as input in the reliability and safety performance assessment of prestressed concrete beams designed according to Eurocode (EC2) design provisions and failing due to web-crushing. The reliability analysis was conducted using the First Order Reliability Method (FORM). The assessment revealed that the reliability levels implied by the operational EC2 code for web-crushing failure in beams are not consistent over the parametric variation of shear reinforcement (ρwfywm) investigated. The results indicated an increase in estimated reliability index (β) values as ρwfywm increases and a decrease in reliability as concrete strength fcm increases. Low strength beams with ρwfywm ≤ 12.5 MPa and medium strength beams with ρwfywm ≤ 17 MPa generally failed to meet the resistance safety requirement as recommended by EN 1990. The research has contributed to existing studies on the effective application of reliability methods in deriving structural design guidelines.