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Second Arc fault found

Bridge likely to be closed for at least six months as safety fears mount.

Glasgow's Clyde Arc bridge suffered its second setback in a month last Thursday when engineers discovered that a second tie bar connection was showing signs of stress .

The discovery has raised further questions about the safety of the bridge. It remains closed to road traffic and has also been closed to river traffic.

Following the failure of one of the hanger connections on 15 January (NCE 17 January), the remaining hangers have been inspected in detail.

The first tie rod and connector fell to the deck after a connection detail at the top of the arch failed.

At one end of the detail was a screw connection to fix to a Macalloy tie bar and at the other were two flattened lugs, which sat either side of a fin welded to the main arch structure.

A pin through the two lugs completed the connection.

Photographs taken after the failure showed that the lugs were fractured across the pin hole (News last week).

A crack was found in a second connection last Thursday afternoon.

"We are working on the basis that the crack was not visible prior to that point," said a Glasgow City Council spokesman.

"The cables are being inspected carefully and regularly and it had appeared on that day."

According to the spokesman, the second connection is showing similar signs to the first failure.

The council spokesman added: "Although the bridge is designed to allow for the removal of one support at a time for repair it is unclear at this stage what impact a second failure would have.

Work to replace the hanger which fell down on 15 January started on Tuesday with cranes operating from the banks to avoid loading the bridge. Remaining connections will be secured with steel wire bands, as an extra safety precaution.

Temporary steel support frames will also be installed on the bridge in the next few weeks.

These will secure the bridge deck during the work on the hangers by connecting the bridge deck outriggers to the arch.

Most of the inspection and repair work is to be carried out from the river with cherry pickers working from a pontoon, a 40t crane working from a barge and an 80t crane working from a jackup barge.

Glasgow City Council is in discussions with the design team including consultant Halcrow and contractor Nuttall and suppliers, examining options for replacing all the cable connection components.

The Clyde remains closed to river traffic until further notice. The bridge is likely to remain closed to road traffic for up to six months.

CLARIFICATION

In last week's issue, Halcrow was wrongly credited with designing the Clyde Arc's tie bar connections. While Halcrow is the main structural consultant on the bridge, the connections are in fact a bespoke system designed and manufactured by Macalloy.

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