High strength concrete prestressed bridges: Exposure conditions, mechanical properties, modified design equations, parametric study, and structural reliability

Abstract

The majority of the current requirements for prestressed concrete were established based on the mechanical properties of normal strength concrete. However, with the more common use of High Strength Concretes (HSC) for bridges and structures, some of these requirements become conservative and require re-evaluation. The main objective of this research study was to modify the allowable stresses for HSC prestressed members and evaluate their impact on both structural design and reliability. An experimental program was developed and a statistical analysis was conducted to determine the effects of various field exposure conditions on the mechanical properties of HSC. Accordingly, property relationships and prediction formulas were proposed and compared to the current codes and standards. A parametric study was conducted to evaluate the economic impact of the modified stress limit formula on the design of typical HSC prestressed bridges, in terms of the maximum span lengths that can be achieved. Results revealed that the proposed modified design equation resulted in longer maximum spans in comparison with the current standards specifications, which would lead to cost reduction. Results also revealed that the majority of the prediction formulas used by codes and standards and suggested by various researchers overestimated the results obtained from this study and only the AASHTO LRFD Specifications and ACI 318 formulas provided conservative estimates. Furthermore, the safety of the proposed modified stress limit was evaluated by applying structural reliability theory and utilizing Monte-Carlo simulations..