Failure Analysis of Prestressed Concrete Girder Bridges Under Over-Height Truck Impacts

Accidental collisions between over-height trucks and bridge superstructures are a common threat to existing bridge infrastructure. These incidents often stem from illegal over-height vehicles or truck operators' unawareness of clearance limits, posing serious safety risks and causing substantial structural damage. This study presents a comprehensive numerical investigation of the dynamic response of prestressed concrete girder bridges subjected to over-height truck impacts. Large-scale finite element models were developed in LS-DYNA, with validation conducted against experimental results. The parametric study explored impact speeds ranging from 16 to 113 km/h (10 to 70 mph), impactor masses between 2 and 6 tons, impact locations, contact areas, and the presence and type of intermediate diaphragms (reinforced concrete and steel). The findings highlight that peak impact forces are strongly influenced by speed, mass, and contact area. For instance, at full-depth bottom flange impacts, the peak impact force increased by 80% as the speed rose from 16 km/h (10 mph) to 97 km/h (60 mph). In contrast, reducing the contact area by 85% in partial-depth impacts reduced peak forces by 70%–80%. Higher impact speeds and masses transitioned damage modes from global deformation to localized failure, with the impacted girder absorbing up to 93% of total energy, significantly reducing the contribution of the remaining girders and the overall bridge system in resisting the impact forces. Prestressing strands exhibited a range of responses, from remaining unaffected to experiencing rupture due to direct contact or yielding. The use of intermediate diaphragms proved effective in distributing lateral forces and mitigating damage.