Design and construction of a very lively bridge

Abstract

In recent years, an increasing number of light structures has been reported to exhibit substantial vertical vibrations when exposed to pedestrian-induced dynamic loading. It is believed that pedestrians interact with lively structures by altering their walking style and changing the dynamic properties of the vibrating system. As the existing vibration serviceability guidelines do not address these pedestrian-structure interaction effects, they cannot predict the structural dynamic response accurately. Fundamental understanding of the pedestrian-structure interaction is currently limited since most reported observations are of qualitative nature. To improve understanding and develop models of human interaction with lively structures, a purpose-built experimental facility that can be excited by human walking is required. This paper describes design and construction of a 19.9 m long, low-frequency and lightly damped experimental bridge for studying pedestrian-structure interaction. The challenge to design a relatively heavy and low-frequency footbridge in the limited space of the Structures Laboratory at the University of Warwick, UK, was met by adopting a traditional steel-concrete composite structural system. The experimental data collected on the "Warwick Bridge" during first six-months of structural life are presented to characterise both its static and dynamic behaviour. Dynamic testing of the bridge revealed that, with an achieved fundamental natural frequency of 2.4 Hz, the corresponding damping ratio of 0.5%, and an opportunity to tune the dynamic properties as required, the key design criteria were successfully met.