Reliability-Based Assessment of Concrete Decks Designed Using Approximate Method at the Strength I Limit State

Abstract

The Approximate Method coupled with the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications (BDS) is applied for designing reinforced concrete bridge decks. Although the LRFD BDS has an intrinsic design return period of 75 years and a target reliability index of 3.5 at the Strength I Limit State, many concrete bridge decks exhibit much shorter service life. Besides the limitations of the crack control limit state at service, the inadequate nominal resistance at the Strength Limit State could contribute to the shortened service life. This paper presents a reliability-based assessment of the current concrete deck design provisions by utilizing actual truck load spectra collected from the national weigh-in-motion (WIM) data. Axle groups, including single axles, tandem axles, and tridem axles, were identified from the WIM data. The moment effects are obtained from influence surface analysis, formulating the live load statistics, particularly for the decks that are supported by girders. It was found that the current design load is not able to represent and envelop the actual traffic load. Additionally, the reliability indices are calculated for a series of reinforced concrete decks on account of both bending moment capacity and arching action moment capacity. The arching action was found to greatly enhance the reliability index for the positive moment region, providing satisfactory reliability indices. The negative moment region may or may not meet the target reliability index depending on the design criteria.