Pedestrian load models of footbridges

Jiří Máca,Jan Štěpánek,J Melcer,K Kotrasova

doi:10.1051/matecconf/201710700009

Jiří Máca, Jan Štěpánek + Show 2 more

Open Access

https://doi.org/10.1051/matecconf/201710700009

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Abstract

The increase of vibration problems in modern footbridges shows that footbridges should no longer be designed for static loads only. Not only natural frequencies but also damping properties and pedestrian loading determine the dynamic response of footbridges and design tools should consider all of these factors. In this paper the pedestrian load models for serviceability verification of footbridges, which are missing in the current European codes, are presented. For simplicity reasons the proposed pedestrian load models are based on stationary pulsating loads instead of moving pulsating loads. It is shown that simplified procedure can be used in verification of the serviceability limit state related to vibration due to pedestrians. Footbridge vibrations don’t cause usually structural problems, but if the vibration behaviour does not satisfy the comfort criteria, changes in the design or damping devices could be considered. The most popular external damping devices are viscous dampers and tuned mass dampers (TMD). The efficiency of TMD is demonstrated on the example of a footbridge prone to vibrations induced by pedestrians. It is shown that if the TMD is tuned quite precisely the reduction of accelerations can be very significant.

Highlights

Modern footbridges are very often lightweight and flexible structures, where the first natural frequencies of vibration may fall close to dominant frequencies of the dynamic excitation due to walking or running
Pedestrian loading was modelled using Eq (6) and Eq (7) for three principal load cases – a) horizontal excitation with pacing frequency corresponding to the fundamental lateral frequency; b) vertical excitation with pacing frequency corresponding to the fundamental vertical frequency; c) vertical excitation with pacing frequency corresponding to the commonly adopted mean value frequency for walking 2.0 Hz
In this paper the pedestrian load models for serviceability verification of footbridges, which are missing in the current European codes, are presented

Summary

Introduction

Modern footbridges are very often lightweight and flexible structures, where the first natural frequencies of vibration may fall close to dominant frequencies of the dynamic excitation due to walking or running. Such bridges are susceptible to vertical as well as to horizontal vibrations leading to a resonant response characterized by high levels of vibration and a dynamic design is necessary. Provided that the vibration behaviour due to expected pedestrian traffic is checked with dynamic calculations and satisfies the required comfort, any type of footbridge can be designed and constructed. If the vibration behaviour does not satisfy some comfort criteria, changes in the design or damping devices could be considered

Pedestrian loads

Proposed load models

Example - Footbridge in Čelákovice

Results

Footbridge with TMD

Conclusions