DYNAMIC BEHAVIOUR OF SLENDER CABLE SUPPORTED FOOTBRIDGES

摘要

In this conceptual study, a cable supported footbridge model with reverse profiled cables in both vertical andrnhorizontal planes is proposed to investigate the vibration behaviour of slender shallow suspension footbridgesrnunder human-induced dynamic loads. By introducing pre-tensions into the reverse profiled cables, the naturalrnfrequencies of the bridge model can be adjusted to cover the typical frequency range of human activities. Torninvestigate the effect of reverse profiled cables, two bridge models with different cable configurations arernconsidered. It is found that suspension footbridges with shallow cable profiles always have coupled vibrationrnmodes and this kind of coupled mode can be described by a "coupling coefficient" defined as the ratio of verticalrncomponent to the lateral one. The dynamic performance under human-induced loads is simulated by resonantrnvibration when the pacing rate of human activity matches one of the natural frequencies. The pedestrian loadsrncaused by walking activities are modelled as crowd walking dynamic load which has the three components:rnvertical dynamic force, lateral dynamic force and vertical static force. Numerical results show that slenderrnsuspension footbridges have different dynamic performance in lateral and vertical directions and the couplingrncoefficient has significant effect on the dynamic amplification factor (DAF) of lateral vibrations when a coupledrnvibration mode is excited by walking pedestrians. Larger DAF of lateral vibration is expected for footbridgesrnunder coupled vibration modes with small coupling coefficients.