UHPC Pedestrian Bridges and Measured Human Induced Vibrations

Abstract

The use of high strength materials in the design of pedestrian bridges leads to slender structures with decreased mass and low stiffness. The resulting low Eigen frequency makes the bridge more susceptible to human induced vibrations. As a consequence, user comfort may decrease significantly. In some designs it has been found that the geometry has been adapted to fulfil user comfort requirements (e.g. increased height, more mass, tuned mass damping), which has a negative effect on costs and use of resources but which is unnecessary from the point of view of ultimate limit states.

Today’s codes and backgrounds do not provide extensive knowledge of the vibration source and the effect of vibrations on human comfort, nor on dynamic analyses as common design philosophy for pedestrian bridges. The city of Rotterdam has currently built some very slender pedestrian bridges not only by use of concrete material but also fiber reinforced composites. Measurements have been carried out on site and in the factory with varying bridge support conditions (e.g. clamped, simply supported). The measurement devices are low-cost widely available cell phones and movie cameras. The measurement data gives results for accelerations, speeds and displacements. Test sets were created for heel tests, moving human impulses and intentional Eigen frequency excitation. Besides that the human awareness has been recorded. The data has been evaluated by use of advanced dynamic analyses and compared with findings in codes and literature. The comparison of dynamic behavior between concrete and fiber reinforced composites is very educative. The newly developed knowledge has been applied to the design of a new UHPC pedestrian bridge. This paper shows the interesting results of the measurements, analyses, modelling and comparison with the codes and how it affects the design of a UHPC pedestrian bridge. Conclusions and recommendations will be presented.