Porthill Bridge Refurbishment

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Suspension-Bridge-6024

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Client: Shropshire Council

Value: £489,000

Programme: 28 weeks

Completion Date: July 2012

McPhillips was appointed as Principal Contractor to undertake the refurbishment of Porthill Bridge on an NEC Option B contract for Shropshire Council in March 2012. The bridge is a main pedestrian route across the River Severn in Shrewsbury Town Centre.

The existing steel structure dates from the 1920’s and had last been refurbished during the 1980’s. The bridge consists of a 40m suspended span over the River Severn with two supported approach spans, one at each end. The river span is carried on four main cables, with vertical steel cable suspenders, supported on steel lattice towers at both riverbanks. The deck is constructed from lattice girders linked transversely through steel transoms which support the timber deck. The approach spans between masonry abutments and the support tower and the refurbishment works included:

  • Removal of the existing timber deck.
  • Removal of the existing bridge lighting
  • Grit Blast the steelwork
  • Repairs to the steelwork
  • Re-painting the steelwork
  • New timber deck
  • Installing new bridge lighting

A suitable method of providing safe working platforms and preventing any waste or materials entering the River Severn needed to be devised and McPhillips produced an innovative temporary works solution within the constraints of <789kn vertical loading and <180kn max wind loading with an 80m2 limit for encapsulation. Working with our scaffolding subcontractor McPhillips devised a temporary works design suspended from the bridge using low weight aluminium components and monoflex membrane which met these requirements and provided symmetrical loadings on the bridge.

Working systematically from both ends of the bridge McPhillips removed the existing 3m wide timber deck and performed class SA2 blasting on 300m2 of the structure with 10 tonnes of defective steelwork being cut out and replaced, replacement members were bolted and welded in-situ.

A 20 year guaranteed three coat paint system was sprayed and brush applied to the structure, the first coat being a high build aluminium epoxy two pack followed by the second coat of high build epoxy maintenance undercoat and finally an acrylic polyurethane gloss finish. A replacement hardwood timber deck was installed and coated with an Instagrip non slip surface. New lighting was installed consisting of floodlights to both towers and rope lighting to the steel cable suspender.

The bridge was closed to pedestrian traffic during the works but a water taxi was provided and advertised running between the river banks on demand.

Shropshire Council required completion in time for the Shrewsbury Flower Show in August 2012 and McPhillips was able to complete ahead of schedule on 24th July 2012.