Prince Street Bridge was built in 1879 and is a Grade 2 listed swing bridge, providing traffic access to the centre of Bristol and allowing boat traffic to pass into and out of the harbour.

It was originally constructed from three main wrought iron plate girders which are approximately 26 metres long and lift prior to rotating.  The original surface deck was timber.

Issues faced by Bristol Council engineers

In 2015, Bristol City Bridge Engineers determined that the bridge was in need of significant refurbishment.  Not only had the timber deck surface considerably deteriorated, but parts of the metal structure had also corroded significantly and needed either replacement or substantial repair.

Since the bridge was also a listed structure, the engineers, working alongside Historic England, were keen to ensure that all works retained as much of the original structure as possible and any replacement materials if modern, were as sympathetic as possible to the original design.

Working on a historic structure

When it came to replacing the surface decking, the council engineers were keen to use a GRP composite deck, because of its lightweight and non-rotting properties.  The objective of the engineers was to reduce the stress on the bridge’s ageing structure and hydraulic lifting system.  However, any GRP composite solution was required to look like the original timber beams from underneath and also be capable of supporting the heavy traffic loads including the occasional emergency service vehicle.

Polydeck’s solution

After meeting with the council, Polydeck were commissioned to develop a unique light-weight, composite decking plank, which had an aggregated top surface, the appearance of timber on its underside, but also matched the council’s loading requirements for the bridge’s 3 Tonne weight limit.

In collaboration with our external design experts, Polydeck produced a 170mm thick foam core filled plank which met all requirements and enabled the overall weight of the bridge to be reduced by approximately 20 tonnes.

Due to the layout of the bridge structure, each of the 260 composite decking planks were individually made in a bespoke mould.  There was a total of 52 bespoke moulds made, as some of the planks were also curved to accommodate the curved ends of the bridge.

Prince Street Plank in factory
Creating bespoke planks in our factory

Some of the planks were also moulded with an alloy fixing plate embedded within the foam to allow the panels to be bolted down.

Production of the planks took approximately two months, and after a two-year refurbishment programme, the bridge was opened in July 2017, just in time to celebrate the City’s Harbour Festival.

Prince Street Completed Bridge