This is a pedestrian footbridge crossing a busy dual carriageway in Shropshire, UK, using an FRP deck suspended from steel cables. The bridge has a total length of 51.3m with a width of 2m. It is a popular route for pedestrians and cyclists to get between nearby towns. The deck was constructed with pultruded FRP Composolite sections, with additional concrete ballast inserted to increase the mass. It was installed in 2003 and its long, lightweight and flexible design results in quite a lively structure that is well-known to the locals. Figure 1 shows some photographs of the structure during testing.

Figure 1: Photos of the bridge

Modal testing

Due to the strong winds in the area, ambient conditions could be used to obtain the modal properties of the bridge. Accelerometers were placed at 26 points on the deck and six points on the cables to measure the vertical and lateral response. In total, nine modes were identified up to 5Hz (five vertical, three lateral and one torsional). Although natural frequencies in this range can be susceptible to resonance from human walking, the relatively high damping ratios of >1% helped ensure satisfactory serviceability performance.

 

Response measurements

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Finite element modelling

A finite element model of the structure was also created using the software package Abaqus. This model was tuned against the experimental results and then used to gain further insights into the behaviour of the bridge. Figure 2 shows a rendering of the entire structure and side views of the first four vertical bending modes.

Figure 2: Finite element modelling

Conclusions

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Gallery

The photos here show fun of the field work - including unpredictable microclimate.

Publications

• Zivanovic, S., Wei, X., Russell, J. and Mottram, J. T. (2017) Vibration Performance of Two FRP Footbridge Structures in the United Kingdom. Footbridge 2017, Berlin, Germany, 6 - 8 September.
• Wei, X., Russell, J., Zivanovic, S. and Mottram, J. T. (2017) Experimental Investigation of the Dynamic Characteristics of a Glass-FRP Suspension Footbridge. IMAC-XXXV, Garden Grove, California, 30 January - 2 February.