Abstract Summary
The dynamic effects caused by circulating vehicles on bridges are one of the main concerns on the design, monitoring and maintenance of the roadway infrastructure. In the case of modular steel bridges, which are truss structures composed by regular prefabricated units, this regard is critical, as despite presenting numerous advantages, such as a rapid and easy deployment, high adaptability to the terrain and reduced construction costs, they usually face operational restrictions for span lengths larger than 60 m. In the recent years, new efforts are in search of developing long-span modular steel bridges that may be able to overcome these limitations, for which it is essential to fully understand the dynamic effect of vehicles on such bridges. To this aim, this contribution provides a detailed study on two modular steel bridge typologies, considering span lengths from 120 to 140 m. A 3D coupled vehicle-bridge model is used to represent the vehicle-bridge interaction and to evaluate the dynamic load allowance of the structures. The vehicle is represented as a multi-body truck system and the bridges are modelled with the finite-element method. To reduce the computational cost, the modal superposition method is used to calculate the bridge response, assuming that the vehicle does not significantly alter the dynamic behaviour of the structures. The vehicle-bridge coupled system is solved using a fourth-order Runge-Kutta method in the time domain. As part of the analyses, different randomly-generated road surface profiles are considered on the bridge deck, accounting for typical defects and irregularities found on the deck of modular steel bridges. The results reveal the notable influence of defects that involve abrupt vertical displacements that excite bouncing modes of the vehicle. The effect of the velocity of the passing vehicle is also studied, concluding that dynamic load allowance indices tend to decrease as the velocity increases, except when a resonance is produced. Finally, inconsistencies are found when comparing calculated and predicted dynamic load allowance indices with the expressions given in several design codes, as they do not take into account the characteristics of the bridges nor the effect of road irregularities or resonance situations.
