Load Rating of Reinforced Concrete Box Culverts During Springtime Thaw Conditions

Abstract

As Minnesota’s bridge inventory continues to age and climate conditions become more extreme, it becomes increasingly important to characterize bridge strength under adverse conditions. Cast-in-place (CIP) reinforced concrete box culverts (RCBC) are some of the older bridge-classified structures in Minnesota, and their continued functioning under spring-thawing soil conditions is essential to many common transportation routes. Four cast-in-place reinforced concrete box culverts were selected for field testing out of a sample of ten box culverts representative of the Minnesota inventory. Using data from field testing, three-dimensional finite element models of the culverts were created and calibrated by changing material properties to match field deflections and strains. Calibrated models were modified to match two cases of spring-thawing soil conditions, and load rating factors were generated for normal and thawed soil conditions. Load rating factors calculated using calibrated models were compared with rating factors generated using AASHTO BrR 7.5. Results indicated that thawed soil conditions result in a lower load rating compared to normal soil conditions, and rating factors from BrR 7.5 were conservative compared to calibrated model rating factors.