Vibrations of Bridge Structure under Kinematic Wave Excitations

Random vibrations of a bridge structure under propagating, seismic excitations are considered and joint effects of pseudostatic and dynamic vibrations are studied. Respective matrix equations of motion are derived. Detailed numerical analysis of a four-span bridge modeled as a three-dimensional (3D) frame under kinematic wave excitations with an oblique angle of propagation is carried out. Key parameters of seismic loads are identified and their effect on both displacement and force response is analyzed. The root-mean-square response is normalized with respect to uniform excitations. The normalized displacement response stays between 0 and 1 while the normalized force response may exceed 1, indicating additional spatial effects. These effects were identified to result from pseudostatic response, mostly for low apparent wave velocity with respect to support distances. A sensitivity, first passage, analysis is carried out to study the joint effect of propagation velocity and angle on the response.