Structural Safety of Post-Tensioned Concrete Slab Bridges With Unbonded Tendons

Abstract

The authors examine the structural safety of simply supported post-tensioned concrete slab bridges with unbonded tendons. Slab designs are in accordance with the American Association of State Highway and Transportation Officials (AASHTO) load factor design specifications, and service stresses and ultimate strength are both considered in the design. Probabilistic resistance models that consider variabilities in material properties and section dimensions are developed using simulation methods. Reliability for flexural capacity at ultimate limit state is measured in terms of the reliability index. Sensitivity analysis is conducted to study the effects of changes in span length and prestressing steel reinforcement ratio on stress in unbonded tendons, bending moment capacity, and reliability index. Results of the analysis revealed that statistical properties of bending moment capacity at ultimate are a function of the amount of prestressing steel. Furthermore, designs based on current AASHTO specifications result in considerable nonuniform safety for bridges having different span lengths and reinforcement indexes.