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Watson Steel sues Macalloy over hanger failure
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Friday, 09 Jan 2009

It is reported that Watson Steel is suing its connection supplier Macalloy for GBP 1.8 million over the failure of 2 hanger connection on the troubled Glasgow Bridge in January 2008. Watson was forced to replace all 14 hangers on the GBP 20.3 million bowstring arch structure and now blames poor manufacturing of connection holes and faulty steel for the failures.

In legal papers obtained by the NCE, Watson claims Macalloy's connections did not meet specifications and failed to match supplied test certificates. The Clyde Arc had to close on January 14th 2008 after a connection on the 2 year old road bridge failed, causing a 35 meters 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. 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.

Watson claims that investigations show that the steel used o create the lugs did not match any grades of steel recognized by BS 3100:1991 Specification for steel castings for general engineering purposes.

Tests found that the steel had an elongation value over 10% below the 13% minimum specified and a Charpy impact value which was significantly below that specified. A Charpy impact value is a measure of brittleness.

Certificates supplied by Macalloy, which was responsible for the testing of components before delivery to ensure that they met the specification, failed to match results of tests on the steel in the bridge forks taken after the event, Watson claims.

The carbon content of the forks was 0.33% rather than between 0.18% and 0.28% as indicated in the certificate. Traces of other metals were found in the fork including 0.096% chromium, but these had not been mentioned in earlier certificates. Poor manufacture of the forks was also thought to have contributed to the failure. Watson Steel claims that the pin bores were neither concentric to each other nor perpendicular to the forks with the result that forces were distributed unevenly across the holes allowing stress concentrations to build up.

(Sourced from

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