Frequency Response Calculation of Multi-Span Simply Supported Bridge

Abstract

Since the railway bridge has many spans and long distance, it is complicated and time-consuming to model and analyze the random earthquake response of the structure with the finite element software. The dynamic frequency response equation of longitudinal vibration of simply supported girder bridge is established with the unit impulse as the input excitation, based on the motion equation of the MDF system and he transfer matrix principle. Finally, Taking seven cross-simply supported girder bridge as an example, the frequency response of the vertical displacement and axial force are computed with the Rayleigh damping. The result of the vertical displacement and axial force shows that: the mid-span displacement of spans in the middle of the bridge is slightly larger than that of the side spans while the difference between each value is small, but the mid-span axial force of spans in the ends of the bridge is significantly larger than that of the middle spans. And the corresponding Fourier amplitude spectrums under pulse loads are given. With this method, it is convenient to program and calculate the dynamic frequency response of the simply supported girder bridge by mathematical software, and it is available to provide a reference for the random seismic design of the structure.