Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering


Moving loads have great effect on dynamic stresses in structures and cause them to vibrate extensively, especially at high velocities. A peculiar feature of moving loads is that they are variable in both space and time. This is why the dynamic analysis of bridges under moving forces has attracted researchers worldwide. When a moving load is traveling on a bridge, different factors play an important role in the vibration of the bridge. Road surface profile, vehicle dynamics, weight and speed of the moving vehicle and the geometry of the bridge all play an important roles in the analysis. The main objective of this research work is to study the collective effect of all these factors over the impact factor.

Road surface roughness is generated by using a Power Spectral Density function which represents different classes of roads. A 12 Degree Of Freedom model of an HS20- 44 truck is modeled and an interactive function of this model with the road surface roughness is developed to find an increased load which is applied on the bridge decks to find the dynamic response. The bridge deck is analyzed by using analytical and numerical methods. An orthotropic plate theory is used to solve the bridge deck analytically and the finite element analysis method is used to solve the bridge numerically. The increased load calculated from the interaction function of road surface roughness and vehicle model is simulated as a train of moving loads by using Dirac-delta function in the orthotropic plate theory. The same train of moving loads is simulated in finite element analysis by using arrival time and time function data for the nodal points along the moving path of the truck load.

Dynamic response is calculated in terms of the vertical deflection at the center of the bridge deck and compared with the static deflection where the load is considered to be steady. For the bridge deck under investigation, the impact factor given by AASHTO underestimates the dynamic effect under the moving loads. This might be because of the inability o f the impact factor formula given by AASHTO, which is a function of span length of the bridge deck, to take into account the effect of road surface roughness, vehicle dynamics, vehicle weight, and vehicle speeds. Its is suggested that it is necessary to do the detailed dynamic analysis of bridges by considering road surface roughess, vehicle dynamics, vehicle weight, and vehicle speed.