Pont King Morgan, Carmarthen

Pont King Morgan, Carmarthen

Structural Engineer

Gifford

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Carillion Regional Civil Engineering

Client

Carmarthenshire County Council

Carmarthen County Council’s new striking footbridge over the River Towy is a landmark structure fulfilling the client’s sustainable transport needs for the local community and the region. The bridge has a clear span over the river with foundations wholly out of the river channel and back spans clear of flood levels therefore providing minimal impact on river habitats.

The form of the bridge design is a twin masted cable stayed structure supporting a fabricated steel cycle/footwaydeck which is curved in elevation and S-shaped in plan. The vertical masts are formed from shaped steel pylons which perforate the deck on its centerline. The deck widens locally at the pylon positions to provide viewing platforms for bridge users to take in the vistas of the town and river. Lateral restraint to the pylons is provided by transverse stays, between the pylon tip and deck edge beams and is supplemented by tie-down stays connecting the deck to the reinforced concrete pylon supports immediately beneath the deck.

The S-shaped deck has spans of 28m over north car park, 78m over River Towy and 44m over flood relief channel, a total of 150m suspended. It has an effective skew over the river of 25o from bank to bank and is supported on cigar shaped steel pylons 20m in height via 14 pairs of stays – two pairs of which are high tensile steel bars providing lateral stability from the tips of the pylons to tie down stays connecting the deck edge beams to the concrete piers.

The eight deck sections and pylons were fabricated and fitted out with stainless steel parapets and anti skid surfacing at the factory. These items were delivered to site overnight due to their size (up to 21m long and 5.5m wide and ranging from 7T for the pylons and 11T to 29T for the deck sections) with widest sections around mast locations loaded on special type steel frames which were positioned structures at an angle to keep components within transport limits. The sections were lifted into place using 100T, 250T, 500T and 800T cranes, the larger cranes being used for the central deck section connecting the two arms of the bridge together. Deck sections over water were pre-fitted with access scaffold at joint connections prior to installation. These sections were then aligned and temporarily bolted together using sacrificial cruciform brackets to facilitate welding of the permanent joints. Final tensioning of the stays and plumbing of the pylons followed the welding operation.

All exposed steel deck and pylon surfaces received a 25 years to major maintenance paint protective system applied in the fabrication shop. Welded site joints were 100% NDT examined on completion and the full protective paint system applied to these locations.

Judges’ Comment

s:

This slender and light-weight footbridge over the River Towy provides vital pedestrian access between the historic Quay and the railway station.

The twin-masted cable-stayed structure sits well in the landscape of the floodplain.

High quality andthoughtful detailing are the hallmarks of the bridge, which provides a landmark for the town.