Client: National Highways
Principal Contractor: Balfour Beatty
Design: Sweco
Works Commenced: November 2022
Works Completed: August 2023
The Myton Swing Bridge is an asymmetric cable-stayed structure featuring a steel twin box girder deck. It spans 55.6 metres at the front and 28.4 metres to the rear, with ballast incorporated into the shorter span to maintain balance during its swinging operation. The bridge rotates horizontally around a central tower to allow vessels to pass beneath.
The movable section of the bridge measures 32 metres in width and 82 metres in length, supporting two traffic lanes in each direction. It carries the A63 dual carriageway over the River Hull and is flanked by two reinforced concrete approach viaducts.
At the west abutment, the swing bridge deck is supported by two retractable pedestals, mounted on steel sliding units atop elastomeric bearings. The deck is lifted off the pedestals using nose jacking rams fixed within deck ends, unloading the bearings. The pedestals are then retracted into alcoves positioned outside the deck footprint via a sliding unit and hydraulic ram connected to the pedestal block and sliding unit.
Over the time, while both pedestals remained functional, excessive surface corrosion developed. Several holding-down bolts on the sliding base plates were either severely corroded or missing, making re-use impractical.
Additionally, the west expansion joint components were corroded, causing the joint plates to become loose. The joint gutter, clogged with road debris, failed to drain surface water effectively, leading to water ponding around the pedestals.
To restore the bridge functionality and safety, the following works were required:
- Replacement of bridge pedestals and bearings
- Replacement of west expansion joint
- Refurbishment of the east joint plates
- Installation of a new joint gutter
- Hydro-demolition of existing concrete
The west expansion joint was replaced in five phases between November 2022 and June 2023, minimizing disruption to traffic on one of the city’s busiest roads. A flexible, wall- mounted scaffold access platform was introduced to improve efficiency of joint replacement works.
Significant hydro-demolition of existing concrete was required to install the new joint. Due to the bridge’s unique structure, a custom joint levelling method was developed. The joint was secured to specially designed installation beams using threaded bars. The beams acted as the hangers, as one end could not rest on the moving bridge deck, ensuring the bridge remained operational for vessels passage. Typically, such beams rest on both ends to provide robust support for levelling and concreting, but in this case, concrete ballast blocks were specially designed and installed on the beams for stability.
Following joint installation, a new steel gutter was installed, consisting of hot-dip galvanized sections bolted together, supported by steel brackets welded to the bridge deck end. For enhanced protection, the gutter’s internal surface was coated with a high-performance waterproofing membrane.Before pedestal replacement, the existing elastomeric bearings required additional testing due to lack of as-built documentation. On-site testing was conducted alongside specific laboratory testing to verify mechanical properties and ensure like-for-like replacements.
The new pedestals consisted of a steel cast pedestal block and a fabricated sliding unit. Heavy-duty rollers fixed to the pedestal block facilitated movements along the sliding unit. This was achieved by lifting pedestal block by approximately 2mm in an unloaded condition (when the bridge deck was raised using nose jacking rams). The complex load transfer mechanism was controlled by elastomeric pads fixed to the roller bearings. When the bridge was loaded, the gap closed, transferring the load through the pedestal block to the elastomeric bearing.
To ensure reliability, a custom testing frame was constructed to evaluate the pedestal assembly and load transfer before installation. The pedestals replacement was carried out during two separate weekend closures between June and July 2023.
Following the successful pedestal replacement, the back-span bearings were replaced over two separate weekend closures, ensuring minimal disruption to traffic.