Macalloy has this week defended itself against claims by Watson Steel that it supplied faulty tension bars on the Clyde Arc Bridge in Glasgow
Clyde Arc fabricator Watson Steel launched legal proceedings in January this year against its connection supplier Macalloy for £1.8M over the failure of two hanger connections on the troubled Glasgow bridge in January 2008.
The Clyde Arc had to close on 14 January last year after a connection on the two year old road bridge failed, causing a 35m long Macalloy bar to fall onto the carriageway below. The bar was one of 14 tension bars which suspend the deck from the bridge’s bowstring arch.
A second crack in another connection was found 10 days later, prompting a decision to replace all the existing connections.
Watson was forced to replace all 14 hangers on the £20.3M bowstring arch structure, and blamed poor manufacturing of connection holes and faulty steel for the failures. Watson claimed Macalloy’s connections did not meet specifications and failed to match supplied test certificates.
However Macalloy claim that only the minimum yield stress was specified for the forks, which the fork material achieved.
The connection had two flattened lugs sitting either side of a fin welded onto the main arch structure. A pin through the two lugs and the fin connected the two. The connection failed in a brittle fracture in the lugs across the holes for the pin.
The Clyde Arc was designed by consultant Halcrow and built by contractor Nuttall for Glasgow City Council. It opened to traffic in September 2006 but was closed in January 2008 due to the connection failures.
Repair works, undertaken by Nuttall and supported by Halcrow and fabricators Watson Steel, resulted in the cast steel connection components replaced by milled steel. The bridge reopened in June 2008.