Opened in 1966, the M48 Severn Bridge has a main span of 988 m and represented a highly innovative and economic suspension bridge design. The cables were aerially spun and were protected in a traditional manner with red lead paste, wrapping wire and paint. Following intrusive inspections on other suspension bridges in the UK and US, the owners decided to carry out an internal inspection of the cables at a number of locations, which revealed unexpected poor results of corrosion, broken wires and a loss in strength. To provide data on the whole bridge, acoustic monitoring was installed to listen for wire breaks, with a system initially at mid-span, followed by a system covering the entire length of both cables. The deterioration process in the cables is driven by the presence of water leading to the corrosion of the cable wires, and followed by crack initiation, propagation and fracture. To arrest this process a cable dehumidification system has been installed. A two-stage procurement process was adopted to permit early drying of the most deteriorated sections of the cables at mid-span, with a second contract covering the remaining sections and integrating both systems. The complete dehumidification system was commissioned in late 2008.

Opened in 1961, Tamar Bridge in Plymouth, UK, is now approaching the mid-point of its original design life and has already undergone a significant modification during the strengthening and widening works of 2001. The 335 m span suspension bridge is owned and operated by the Tamar Bridge and Torpoint Ferry Joint Committee and raises virtually all of its operational and maintenance revenue from traffic tolls. The current decade has included some significant programmes of maintenance with further works planned through to 2020. Specific projects have included resurfacing, comprehensive improvements to access provisions, main-deck expansion joint replacements, truss steelwork recoating and suspension system remedial works. It is hoped that these will secure a continued high level of reliability of service for bridge users over the coming decades while minimising the requirements for raising additional maintenance funding in the form of toll increases.

No abstract

No abstract