Continuous span highway bridge vibrations

The objective of this investigation was to theoretically study the vibrations of a plate girder continuous four span highway bridge under vehicle loading. A three dimensional finite element analysis was utilized in the analysis of the bridge dynamic responses. Bridge damping has been considered and bridge surface roughness was simulated by the Fourier approximation of a real surface roughness. The mode superposition method was effectively utilized in the dynamic response calculations and the subspace iteration method was economically implemented for eigenvalue extractions.;Both two and three axle three dimensional vehicle models with true suspension systems with spring and damper, were developed for the bridge dynamic loadings. These models fully comply with the AASHTO vehicle standards. The Newmark-Wilson integration scheme was used for the step-by-step dynamic response calculations. The bridge analysis results are compared with the experimental tests.;A general purpose bridge vibration analysis computer program named DABS (Dynamic Analysis of Bridge Systems) was developed based on the mathematical model derived. DABS is a command-structured, STRUDL-like, bridge-problem-oriented language, in which the engineer can describe a bridge structure to the program and ask for results. It also has a post-processing program, which consists of the cubic-spline curve fitting and derivation routines and the Fast Fourier Transform (FFT) routine.;It has been found that three dimensional model must be used in the analysis of a continuous span highway bridge. Otherwise, it is not possible to incorporate the torsional response of the bridge which has a significant influence on the overall dynamic behavior.;Most of the parameters that affect bridge vibrations have been studied by using the DABS computer program. These include the bridge parameters, vehicle parameters, and bridge construction parameters. In the bridge parameters, the girder flexibility, the deck thickness, and the bridge damping ratio were studied. In the vehicle parameters, the vehicle transverse position, the vehicle speed, the vehicle initial suspension oscillation, and the vehicle weight of both the two and three axle vehicles were studied. In the bridge construction parameters, the bridge surface roughness and the elevation difference at the bridge entrance were studied.;In the bridge dynamic response study, the vehicle initial suspension oscillation was found to have the greatest effect on the maximum girder deflection and the maximum girder moment, and the vehicle speed was found to have the greatest effect on the maximum girder acceleration. The vehicle transverse position as well as the vehicle weight had a significant effect on the bridge dynamic responses. The bridge surface roughness was found to have sizable effect on the maximum girder acceleration, but it had only a negligible effect on the maximum girder deflection and the maximum girder moment.