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Supplied Clyde Arc hangar forks met specification, claim Macalloy

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.

Readers' comments (2)

  • This is a shameful defence by Macalloy and one I suspect led by lawyers. Macalloy’s own website proudly claims "manufacturers since 1947", "experience, innovation, quality". To claim that only the yield stress was specified so this is all they supplied is disingenuous - as self proclaimed world leaders in supply of tension systems they would have known that ductility of material is just as important, as is manufacturing tolerances. To expect a customer such as Watson’s to have intimate knowledge of their proprietary product is unreasonable.

    If this is the main line of defence used by Macalloy I would be extremely worried as a client or owner of previous projects with product supplied by Macalloy. It also brings into question the effectiveness of certification systems such as Cares and European Technical Approvals if mistakes such as this can happen.

    It is very lucky that no injuries occurred when the connection failed, had there been so I suspect the HSE would have a very clear opinion about who was responsible for the steel properties.

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  • What was the bridge designer doing only specifying yield, I find this incredible. Whilst the first comment on this site seems to suggest that Macalloy should have known enough to sort out any inadequacies in the spec, this ignores the fact that there will have been a contract, under which Macalloy were presumably obligated to supply to spec only. Any other expertise they may have posessed is not relevant. In such a major component of such a major structure, was this really all that was specified!

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