Parametric Studies on Highway Bridge Impact

Traditionally, dynamic effects on bridge decks brought about by moving vehicle loads, are taken into account by increasing the static loads by an impact factor. Recent researchers have found that actual impact factors can be much higher than the recommendations given in various bridge design codes of practice and hence the subject needs investigation. In order to study the causes of high impact on highway bridges, a computer program BRVEAN for bridge-vehicle interaction model is developed. BREVEAN has its uniqueness of including most of the factors which would likely affect the impact factor and using the improved modelling of a bridge. The modelling of the bridge itself is using finite element formulation of quadrilateral flat shell elements with eccentric beam stiffeners. The vehicle is modelled as a rigid body with two-axle and four-wheel sprung load units. Because of the effect of interleaf friction in the suspension system of the vehicle, the load-deformation relationship for the spring is represented by a hysteretic bi-linear diagram. In addition, the surface roughness of the bridge pavement is considered as a stationary random process characterized by a power spectral density function. The possible factors which would likely affect the dynamic behaviour of a bridge are considered and dimensionless parameters are adopted in the parametric studies. The results demonstrate a clear picture of the effect of various parameters on the impact factors of bridges. Based on such results, the causes of high impact are addressed and it is concluded that the road roughness was considered as the main cause of high impact values. In addition, within the realistic range of vehicle considered in this study, the maximum impact factors could be 2.84, 1.57 and 1.35 for bridges with spans 10m, 20m, 30m respectively, and it concludes that most of the high impact factors occurs in short span bridges