Porthill Bridge

A safe means of working over the river — without allowing any waste or materials to enter it — had to be devised within tight limits (under 789kN vertical and 180kN maximum wind loading, with an 80m² encapsulation limit). Working with our scaffolding sub-contractor, McPhillips designed a temporary-works solution suspended from the bridge using lightweight aluminium components and a monoflex membrane, giving symmetrical loadings on the structure.

Working systematically from both ends, we removed the existing 3m-wide timber deck and carried out class SA2 blasting on 300m² of the structure, cutting out and replacing 10 tonnes of defective steelwork bolted and welded in situ. A 20-year guaranteed three-coat paint system was then applied — a high-build aluminium epoxy primer, a high-build epoxy undercoat and an acrylic polyurethane gloss finish.

A replacement hardwood timber deck was installed with an Instagrip non-slip surface, and new lighting added — floodlights to both towers and rope lighting to the cable suspenders. The bridge was closed during the works, with a water taxi provided on demand between the riverbanks.