Reliability assessment of prestressed concrete beams

Second-moment structural reliability analysis methods are used to assess the reliability levels implied by the current (1989) American Concrete Institute (ACI) code for 73 single-span prestressed concrete beams commonly used in the construction industry for offices and retail buildings. The analysis is limited to only flexural load effects. Several limit states are considered, including permissible compressive and tensile stresses at both initial and final stages, flexural cracking, and ultimate strength. The loads, material and geometrical properties, pre-stressing force levels, and the models used to predict structural behavior at initial, final, and ultimate stages are all treated as random variables. The statistical parameters selected for these variables are believed to represent the present state of knowledge on uncertainties associated with prestressed concrete beams. The reliability levels are shown to be nonuniform over various ranges of live load levels, span lengths, and limit states. Information is also provided on the effects of secondary moments, cable eccentricities, and prestressing area on the reliability of a continuous three-span prestressed concrete beam.