A Study of Suspension Bridge Vibrations Induced by Heavy Vehicles
The Lysefjord suspension bridge (Norway) is instrumented with accelerometers, anemometers, weather station and a GPS monitoring system, making it a full-scale test bed for research on dynamic bridge behavior and wind characteristics in a complex terrain.
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A Study of Suspension Bridge Vibrations Induced by Heavy Vehicles Jonas Thor Snæbjörnsson, Thomas Ole Messelt Fadnes, Jasna Bogunovi´c Jakobsen, and Ove Tobias Gudmestad
Abstract The Lysefjord suspension bridge (Norway) is instrumented with accelerometers, anemometers, weather station and a GPS monitoring system, making it a full-scale test bed for research on dynamic bridge behavior and wind characteristics in a complex terrain. In this study we investigate bridge vibrations induced by heavy vehicles crossing the bridge. As the bridge is located on the outskirts of the urban environment, the traffic across the bridge is generally intermittent, allowing for investigating loading effects of individual heavy vehicles during days with low wind velocity. The findings suggest that heavy vehicles cause a considerable dynamic load effects, especially when entering and exiting the bridge, especially at higher modes of vibration with natural frequencies above 1 Hz. Spectral analysis of the traffic induced acceleration time series agree with results from previous studies showing that the acceleration bridge response to vehicles consists of a combination of both low and higher frequency modes. Truck induced excitation has been used to estimate the modal parameters of the bridge, such as critical damping ratios for the vertical modes of vibration assuming a viscous-equivalent damping and a logarithmic decay of the bridge motion as the trucks exit the bridge. The identified damping ratios as well as natural frequencies are found to be comparable to values obtained from general ambient vibration data. However, there are significant variations in the results depending on measurement location and the driving pattern of the truck along the bridge. Keywords Suspension bridge · Traffic · Vibrations · Acceleration · Damping
15.1 Introduction Norway’s coastline consists of long and deep fjords amongst mountainous terrain. This leads to challenges within road and transportation systems along the coast. Ferry transportation has been the solution for crossing the fjords which are up to 5 km wide and 1300 m deep. In 2012 the Norwegian Parliament presented a directive towards a ferry free coastline road (E39) between Kristiansand and Trondheim by 2030 [1]. In support of this goal, the Norwegian Public Roads Administration (NPRA) has been funding research work related to full scale monitoring of existing suspension bridges. The Lysefjord suspension bridge is instrumented with accelerometers, anemometers, weather station and a GPS system, making it a fullscale test bed for research on bridge dynamics and wind characteristics in a complex terrain [2]. A “full scale laboratory” of this kind provides the opportunity to study the characteristics and effects from wind in complex terrain on a suspension bridge, as well as allowing for an investigation into loading effects and response from the automobile traffic crossing the bridge. The focus of the present work is to study bridge vibrations induced by individual, heavy vehicles during days of lo
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