Impact Factors for Highway Bridges Using Road Surface Roughness and Vehicle Dynamics

The cumulative effect of road surface roughness, vehicle dynamics, vehicle weight and speed is considered to find the impact factor for highway bridges. The roads and their surface roughness are classified in three classes which are further divided into various categories given in the literature. The power spectral density function is used to find the roughness of a road surface profile. The AASHTO HS20-44 vehicle is modelled as 12 degrees of freedom system and is assumed to be running on a very good road surface to consider the vehicle dynamics. The AASHTO truck is modelled to contain five rigid masses of tractor, trailer, and three masses of steer, tractor, and trailer wheel axles. The equations of motion are formulated consisting of the masses, the damping and spring forces in the suspension systems of the axles and in the tires. The equations of motion are solved using the road surface roughness to give the tire forces that are coming on the bridge deck. The tire forces are higher than the static tire forces due to the weight of the truck only. The tire forces are used to find the maximum vertical deflection in the centre of a T-beam bridge deck when the AASHTO vehicle is moving at different speeds. The maximum vertical deflection is compared with the static deflection at the corresponding point due to the weight of the truck to find the impact factor. T