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Irish rail bridge collapse triggers network-wide inspections

HUNDREDS OF rail bridges across southern Ireland are to be urgently inspected after initial investigations into the collapse of the Cahir Viaduct in County Tipperary last month pointed to a widespread problem.

The collapse happened as a goods train with 22 bulk cement wagons derailed. Thirteen wagons plunged 15m from the bridge to the River Suir below.

Investigators now believe the derailment could have been caused by outward movement or spreading of the rails.

An interim report into the accident carried out by the Irish Department of Transport's Interim Railway Safety Commission (IRSC) states that timber supporting the rails was rotting.

Railway engineers said this would make it more vulnerable to spread.

The IRSC confirmed that there are 'hundreds' of similar bridges across southern Ireland.

It has told Irish Rail that all must be inspected immediately to prevent further collapses.

The three-span bridge, opened in 1852, comprises two outer wrought iron plated box girders carried on masonry abutments and connected with a series of iron transverse members.

The rails are carried on a pair of timber way beams with timber wheel guards to prevent derailment. More timber beams were placed transversely between the way beams to maintain the 1,600mm gauge.

The initial investigation found that the condition of these timbers varies significantly. Some had only recently been replaced, some showed some signs of rotting and/or distress, and some were in 'poor' condition.

This deterioration could have allowed the rails to spread, but the report concludes that the extent of damage in the area of the derailment may make it impossible to determine the exact cause.

Other possible causes such as a broken rail, speeding, an obstruction on the tracks or structural failure of the viaduct are all ruled out by the report.

However, engineers said that such severe failure was partially due to fact that there was no base plate to spread the load among the connections.

As the wagons hit the cross members they were torn straight out of the box girder leaving gaping holes where the beams used to sit.

'The entire strength of the structure seems to rely on the connections between the cross beams and the box girder, ' said Railway Civil Engineers Association past chairman Graeme Montieth.

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