ABSTRACT
ABSTRACT: This paper describes the investigation work carried out to try to determine the remaining service life of the main cable anchorages at Forth Road Bridge. The anchorages on any suspension bridge are critical components and to be able to inspect these components to evaluate deterioration and remaining strength is vital. At Forth Road Bridge, the anchorages were constructed, on both the north and south sides, by forming tunnels within the rock formations. Concrete has been cast within these tunnels to form four large, individual, concrete plugs within the rock to which the cables are attached. The concrete in the tunnels is reinforced using pre-tensioned, galvanized, high tensile steel strands in grouted ducts. The strands are completely inaccessible and in a hostile environment. Concerns over the possible loss of galvanizing were expressed during construction and further evidence came to light in 2005 that the condition of the strands may be worse than previously reported. Given all the above, an investigation was carried out to try to determine with some certainty the long term structural integrity of the anchorages and also to establish that the risk of failure remains low and within acceptable levels. The investigation was considered to be a pro-active measure to ensure that all parts of the structure that can be reasonably accessed are inspected.
