Live-Load Effect in Reinforced Concrete Box Culverts under Soil Fill

Abstract

The effects of live load in box culverts may be nearly negligible compared with the effects of dead loads when significant fill is placed above the crown of the culvert. The objective of this study was to determine the effects of live load (truck loads) on reinforced concrete box culverts classified as bridges [spans greater than 6 m (20 ft)] under soil fills of different thicknesses. The study considered the field testing of 10 existing reinforced concrete box culverts with fill depths ranging from 0.76 m (2.5 ft) to 4.1 m (13.5 ft). Instrumentation of the culverts consisted of 12 reusable strain transducers and 12 linear variable displacement transducers. The instrumentation was designed to be applied, used, and removed in one day of testing. Loaded trucks were driven over the culvert to provide live load. The results of the testing show that the live-load effect does diminish with increasing fill depth. The 2012 AASHTO LRFD bridge design specifications are overly conservative in predicting strains and displacements compared with the field data for fill depths less than 2.4 m (8 ft). At fill depths beyond about 1.82 m (6 ft), the live-load pressures are less than 10% of the dead-load pressures, and this fill depth may be considered as a point at which live-load effects may be neglected.