Investigating the Increase in Load Rating and Reliability of a Prestressed Concrete Bridge When Utilizing Field-Derived Distribution and Impact Factors

Abstract

When the load rating of a bridge is less than 1.0 for AASHTO HL-93 live load and state-specific legal trucks, the bridge is posted. Posting a bridge causes an inconvenience to the public and may result in trucks taking longer routes. Thus, this paper investigated the effects of field-derived distribution factor (DF) and impact factor (IM) from static and dynamic load tests using computer vision and deflection measurements, instead of AASHTO factors, on the bridge load rating and component as well as system reliability for posting avoidance. The reliability approach used Monte Carlo simulations to account for uncertainties in calculating the flexural strength limit state (Strength I). Both Flexural strength I and serviceability (Service III) limit states were investigated. The bridge’s superstructure was studied in as-built, repaired, and damaged condition scenarios. For that, AASHTO HL-93, Florida legal trucks, and emergency vehicles were considered. In this regard, load rating distributions and component and system reliability indices were computed using both AASHTO and field-derived DF and IM. The increase in load rating and reliability was investigated. By using field-derived factors, a load rating increase of up to 17% was achieved. The component reliability also increased significantly. For example, the damaged case’s component reliability increased by 1.0 when replacing DF and IM, which indicates a major reduction in the probability of failure. The increase in system reliability was most significant because using the field-derived DF increased the capacity contribution from other girders. A 2.12 increase in system reliability was achieved in the damaged condition when only substituting DF, providing even higher system reliability as a result of a reduction in the system probability of failure.