Dynamic response of reinforced concrete bridges due to heavy vehicles

The paper presents results of a comprehensive study of structural responses of reinforced, prestressed concrete bridges loaded with moving, heavy trucks. Two-prong approach, consisting of computational mechanics and experimental testing, was used during this project. Several complete vehicle-bridge finite element (FE) models were developed for computational dynamics analysis using LS-DYNA computer code. Three heavy vehicles and three concrete bridges were considered for this study. The FE vehicle models included: a popular tractor-trailer, a moving crane, and a heavy truck with stiff suspension. The bridges with AASHTO type II, III, and IV prestressed reinforced concrete girders and concrete decks were chosen. Experimental testing was conducted on a selected bridge located in the northern part of Florida. The testing program also included a series of tests with permit vehicles traversing standard speed bumps. These tests were designed to verify and validate the vehicle suspension models. Comparison of results from both: computational mechanics and experimental methods allowed for validation and verification of the FE models of the bridges developed. Research output included time histories of accelerations, displacements and strains at selected points of the bridge superstructure. Data obtained allowed for studying a correlation between a vehicle mass, speed, road surface condition and other factors and a resulting dynamic impact factors for the bridges considered. AASHTO defined dynamic load allowance (DLA) were calculated based on strains and displacements data from experiments and from computational mechanics analyses. DLA = 33%, as recommended by AASHTO, was confirmed to be a conservative estimate. Although DLA for bridges depends on the vehicle speed, this relationship was not always directly proportional. It was also found that DLA significantly increased when abutment joints between asphalt pavement and the bridge deck were included in the model. DLA was further amplified when poorly secured truck cargo was modeled with bouncing load, which produced a hammering effect on the bridge. Results of ninety computer simulations with three bridges and three permit vehicles travelling at ten different velocities are shown in the paper.