Reliability-Based Service III Evaluation for Prestressed Girder Bridges Under Platoon Loads

Platooning may benefit heavy truck transportation through fuel savings, reduced congestion, enhanced safety, and lower emissions. In the future, platoons may be able to act as mobile-WIM stations, and their permit process and allowable load limits may differ from unregulated trucks in a convoy. Previous reliability-based studies have focused on the Strength I limit state and have shown that trucks can operate at weights exceeding standard legal load limits even with short headways at operating-level reliability. However, the Service III limit state often governs prestressed concrete bridges. The AASHTO Manual for Bridge Evaluation does not specify a target reliability index (β) nor reliability-based evaluation guidance for the Service III limit state. The work presented here performed reliability analyses to investigate implicit reliability indices (βImplicit) inferred from bridges designed according to current and past AASHTO criteria, as well as cracking probabilities. Design live loads were used to evaluate the Service III limit state for prestressed concrete NU I-girder bridges, optimally designed using LRFD and LFD/allowable stress design (ASD). Various span lengths, numbers, continuity conditions, prestress loss methods, and allowable tension stress levels were considered. Cracking probabilities ranged between 10% and 67%, which indicates that optimally designed bridges may crack during their service life. Although beyond the scope of the study, the present work suggests a reexamination of service behavior and performance is appropriate, using an alternate mechanistic approach to estimate potential cyclic damage and aid life-cycle assessment. Such assessments could provide a more rational framework for platoon operations while maintaining bridge health and safety.