DYNAMIC RESPONSE OF HlGHW AY BRIDGES TO MOVING VEHlCLES CONSIDERING HIGHER MODES

The impact factor included in the design code formula to account for the dynamic effect of traffic is a function of only the span length with no reference to other factors affecting the bridge response. In this paper the dynamic response of highway bridges is studied to evaluate the various parameters affecting the bridge dynamics. The bridge is modeled as a one dimensional beam element. The vehicle model is ranged from moving force, moving mass and lumped mass supported by springs and damping elements. Closed form expressions to the bridge vibration modes and dynamic response to moving loads are obtained using Galerkin s approach. This gives more insight into the nature of the problem and helps identify the significant parameters affecting the bridge response. The developed approach allows for the consideration of higher modes of vibrations in the dynamic response of bridges to moving vehicles. Different bridge models are analyzed for different vehicle speed and different vehicle weight considering the contribution of the various individual modes. The important effect of higher modes on the bridge response is highlighted. Depending on the dynamic characteristics of the bridge and the speed of the vehicle higher modes contribution can become too significant to be neglected.