Innovative evaluation of precast, prestressed adjacent box beam bridges

Abstract

Load rating, the process of evaluating a bridge's safe live load capacity, is a critical aspect of bridge evaluation. Despite their prevalence, adjacent box beam bridges lack specialized methodologies and automated tools for their load rating. Engineers often resort to time-consuming, complex hand calculations or general-purpose tools that are not ideal for these unique bridges. This study addresses this challenge by developing a specialized computational methodology and an innovative computer tool for accurate, reliable, and rapid load rating of adjacent box beam bridges. The research accounts for diverse configurations, including skewed or non-skewed spans, composite and non-composite, and single or multicell beam sections; analyzes flexure and shear; assesses stresses at all critical locations for strength and service limit states; calculates capacities; and provides final load rating factors. A key innovation is its ability to identify the most critical location by precisely determining the exact maximum moment location, beyond conventional methods. It also evaluates shear at all potentially critical points, not just typical ones. The adopted shear flow approach enables the analysis of multicell box beam sections. To transfer these advancements to practice, the first specialized computer tool is developed for the load rating of adjacent box beam bridges. This tool is capable of rating 15 standard vehicles and custom vehicles with up to 35 axles. It also generates moment and shear envelopes for all vehicle types, assisting manual calculations or other analyses for various bridge types. Verification of the methodology and tool against 18 existing bridges using independent hand calculations and general-purpose software confirmed their high accuracy and reliability. A coefficient of determination of 0.974 or higher, a root mean square error (RMSE) of 0.251 or lower, a normalized RMSE of 7.43 % or lower and a bias close to zero are obtained.