Final Phase of Truss End Link Replacement Begins
31 August 2016
The final phase of work to replace the Forth Road Bridge’s “truss end links” has begun, with Amey on behalf of Transport Scotland commencing work on site at the North East main span, where the original fracture occurred.
The truss end links are being replaced with a new permanent sliding bearing arrangement to be fixed to the tower beneath the existing end post (see schematic below). Structural health monitoring installed during the initial repairs will continue to be developed to provide engineers with ongoing live data.
(Above: Schematic showing completed truss end link replacement)
Thanks to the extra support provided by the temporary brackets installed on the main towers in February, this final phase to replace the links can be carried out below deck level with minimal disruption to road users. A small number of overnight contraflows will be required to allow works to progress at the North East main span link, however these have already been scheduled in parallel with other planned routine maintenance activities.
Once the new steelwork has been installed the load will be transferred from the temporary brackets onto the new sliding bearing arrangement. The temporary bracket will then be modified and re-located to the North East side span to allow future replacement works to be undertaken at that location.
An advanced trial has already been completed to investigate the buildability of the strengthening works that are required inside the main towers and to minimise the risks during the remainder of the project. Reinforcing steel must be assembled within a confined space, so a concrete replica of the tower and reinforcement was constructed to identify any difficulties that could arise without causing risk to the structure or to the safety of the workforce (see photo on right).
Work at the North East main span is expected to be complete by the end of the year, with the remaining seven links due to be replaced in a contract to be let in 2017.
Mark Arndt, Operating Company Representative for the Forth Bridges Unit, said: “We’re delighted to be commencing work on the full replacement of the truss end links with a completely new redesigned arrangement.
“The repairs carried out last winter were necessary to get the bridge back open to traffic as quickly and safely as possible. Since then we’ve been planning and preparing for this permanent replacement and it’s remarkable that the team has reached this point less than nine months since the original defect was discovered.
“We’ll press on now to get the job done with minimum disruption to bridge users.”