Concrete tension stress at the Service III limit state is the governing condition for design and load rating of most prestressed concrete bridge members. The Service III limit state was first introduced in the AASHTO LRFD Bridge Design Specifications (BDS), 1st Edition, 1994, as an ad hoc adjustment to align design outcomes with those from the past practices of the AASHTO Standard Specifications for Highway Bridges. The Service III limit state was not calibrated with considerations of structural reliability. Over the years, as concrete and prestressing materials advanced, the method of estimating prestress losses prescribed in the AASHTO LRFD BDS became increasingly inaccurate for high-strength concrete, larger beam sections, larger diameter strands, and longer spans.

Stemming from confusion regarding the inclusion of elastic gains, concerns were raised by state departments of transportation (DOTs) that inclusion of elastic gains would result in designs requiring less prestressing than past practice. Subsequent research efforts attempted to recalibrate the live load factors and inadvertently created a two-tiered approach that can be interpreted to penalize more rigorous analytical methods that have been included in the 7th and subsequent editions of the AASHTO LRFD BDS. Additionally, the loss formulas were developed using a limited data pool, and there are new data that can be used to revise the loss estimates for greater consistency and accuracy. Many bridge owners have found that the current provisions give results that are inefficient in design and potentially cause challenges for load rating and permit evaluation during bridge operation. As a result, owners have developed their own methods that deviate from AASHTO and result in a patchwork of design methods across the United States.

Research is needed to develop clear and accurate design specifications for all types of prestressed concrete bridge members based on a proper calibration of the Service III limit state with a holistic view of the relevant variables. Additionally, research should provide state DOT bridge owners with a rational framework that addresses reliability, performance, and cost trade-offs and limits the need for state-specific deviations from the AASHTO LRFD BDS.

The objective of this research is to develop a revised set of Service III provisions that ensure consistent designs and cost-effective structures while maintaining operational flexibility. The goal is to provide owners with reliable guidelines that promote national consistency in bridge design.

Areas to consider as part of the holistic review include (1) load and resistance factors, (2) load combinations, (3) load distributions, (4) analysis methods, (5) prestress losses, and (6) reliability indices for design and rating.