Sensitivity of the Vertical Response of Footbridges to the Frequency Variability of Crossing Pedestrians

Marta García-Diéguez,Jose Zapico-Valle

doi:10.3390/vibration1020020

Abstract

Contemporary design codes and guides for vibration serviceability assessment include some simplifications in load modelling. The same statistical distribution of the inter-pedestrian variability of the step interval (frequency) is proposed for all applications. Moreover, walking loads are considered to be periodic. The intra-pedestrian variability of the step interval is neglected. A more realistic load modelling trying to overcome the limitations of the codes is intended in this paper. Instead of a single mean value of the inter-pedestrian distribution of walking speed, a range of possible variation, which account for the real variations that occur in practice depending on the footbridge location and usage, is considered. An enhanced model is proposed in this paper to reproduce statistically both the intra- and inter-pedestrian variability of the step interval as a function of the walking speed distribution. This innovative model is then applied to study the sensitivity of the vertical response of footbridges to the variability of the step interval and to evaluate the influence of the aforementioned simplifications on the predicted characteristic responses. For this purpose, low-frequency footbridges excited by single-pedestrian crossings are chosen. The response is statistically characterized through Monte Carlo numerical simulations including 720 different configurations and 10,000 load cases in each configuration. Results of the study provide an overview of the influence of the footbridge and load parameters on the responses, which can be useful in practical applications where human–structure interactions are negligible. As for the simplifications of the codes, it is found that either using a single distribution to model the inter-pedestrian variability of the spatiotemporal parameters or neglecting the intra-pedestrian variability can lead to a significant underestimation of the characteristic response of footbridges.

Highlights

As for the simplifications of the codes, it is found that either using a single distribution to model the inter-pedestrian variability of the spatiotemporal parameters or neglecting the intra-pedestrian variability can lead to a significant underestimation of the characteristic response of footbridges
This study proved that the peak acceleration of the response corresponding to a certain level of exceedance is more informative than the deterministic maximum acceleration recommended by the contemporary design codes and guidelines for the assessment of vibration serviceability [19,20,21,22,23,24]
A statistical model describing the relationships between spatiotemporal parameters of human walking and their variability was developed and fitted to the experimental results

Summary

Introduction

With the use of new materials and innovative configurations, modern structures have become more slender and prone to vibrate. This is the case of footbridges and long-span floors under pedestrian loading. Due to the limitations of the contemporary codes for serviceability assessment [1], the number of structures that exhibit excessive vibration in service has grown exponentially in the last decades. This has motivated the research interest in walking-induced vibration [2]. This paper deals with the modelling of walking loads and their influence on the dynamic response of footbridges

Objectives

Results

Conclusion