Design of slender steel pedestrian bridges

Abstract

Developments in structural engineering give rise to the ability of increasing the slenderness within the design of footbridges. However, this often results in a fundamental eigenfrequency which coincides with the step frequency range of humans on the bridge. This can lead to uncomfortable vibrations of the structure. In order to maintain the comfortability, the Dutch national annex of the Eurocode prescribes to consider a dynamic jogger load case, which is often governing for the slenderness of a design. In this thesis, a moving model for the dynamic jogger load case with the addition of human­-structure interaction (HSI) in vertical direction is considered in order to reduce conservatism. Using a simplified 1-dimensional Finite Element representation of a footbridge consisting of 4 HEA320 pro­files, a comparison is made between a moving force (MF) and a moving mass­-spring-­dashpot (MSD) model representing the jogger. Different analyses of a single jogger case are made to investigate the influence of the following simplifications: 1) applying a stationary instead of a moving dynamic load, 2) applying a load model neglecting the separation between jogger and bridge and 3) neglecting the subject variability. The Dutch national annex prescribes the use of multiple joggers during the load case. Therefore, an initial research is done on the effect of HSI on a multiple jogger case. It is found that the HSI results in a decrease of the maximum accelerations for all load cases. The effect increases when the joggers-­to-­bridge mass ratio increases. The same holds for the influence of separation. The results show that reduction of the maximum acceleration due to the addition of the HSI is generally not large enough to result in an increase of the maximum slenderness.