Forth Road Bridge “truss end links”.

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We know the Forth Road Bridge is closed due to a “north east tower truss end link” defect.  This is a pain for me as I live in Edinburgh, but my wife and I have family in Fife…. and Christmas is coming.

Like most people in Scotland I have crossed the bridge many times. I have also walked and cycled across it a few times.

As part of my job, I have been to the top of the bridge’s north tower, visited the anchor chambers and also walked on the truss under the truss deck (no problems spotted!).  These visits took place over the period where the tolls were scrapped by the SNP (meaning the Scot Gov had to fund maintenance directly), the main cable dehumidification (ground breaking stuff) and the privatisation of bridge maintenance by the Scottish Government.

All this means I know the bridge well, but I still don’t know what a truss end link is! However I do know that as bridge maintenance was publicly run lots of details are in the public domain. What did I find?

February 2009: It is recognised that work on the truss is needed, but this is (correctly) deferred until the main cable dehumidification is complete:
The assessment work has now been completed and an independent check is being commissioned. Strengthening work on the truss has also been put back until there is confirmation on the outcome of the de-humidification scheme. However, work on the truss end links is scheduled to start in 2010/11 following completion of the independent check

May 2010: A tender for work on the truss end links is cancelled.

October 2012: Audit Scotland say of Forth Road Bridge funding from the SNP Government: “The budget for capital expenditure was cut significantly and a report highlighting the impact on the Capital Plan was noted by Board Members.

August 2013: Work on the truss is planned on the truss ends:
As reported in June 2013, the Chief Engineer and Bridgemaster will bring three projects to tender during 2013/14. The projects that have been selected on the basis of criticality and affordability are; Main Cable Acoustic Monitoring, Truss End Linkages and Suspended Span Gantry Improvements. It is currently estimated that these three projects will cost £2.270m based on the current Capital Plan. This will represent the majority of the funds available for non-committed schemes and therefore it is recommended that a full risk assessment of all projects on site is carried out before the tenders are approved.

February 2014: Planned work “deferred”  due to Scottish Government budget cuts: During this second round of deferrals, the four projects detailed below were identified as having the highest estimated cost.  Therefore, these projects had to be considered in part or full for deferral in order to produce a significant reduction in the predicted deficit.  These projects were:

  1. The Upgrading of the Main Cable Acoustic Monitoring Project 
  2. Improvements to the Suspended Span Underdeck Gantries
  3. Truss End Linkages Work
  4. Improvements to the Suspended Span Underdeck Access System

Later:
Upgrading of the Main Cable Acoustic Monitoring Project and the Truss End Links Project were both considered vital to maintain the operational capacity of the bridge and were *retained in the programme*.

and importantly:
There is always a residual risk when maintenance works are deferred and it was noted that deferral of part or all of these projects does increase the risk to the long term structural integrity of the bridge and is likely to increase the actual cost of the works when they are eventually carried out.  

May 2015: Work is further delayed: The intention of the Authority was to carry out a trial repair on one tower leg and if successful, this repair would be carried out on the other three tower legs. However, due to issues with the quality of the existing tower steelwork; the difficulties of access and the existence of red lead paint, coupled with the loss of key management staff, the focus changed during the year to completing the trial on one tower leg before the end of May 2015.  If the trial is successful, a recommendation would be made to Transport Scotland that this work be continued post abolition of the Authority. If the repair trial is unsuccessful then full replacement will have to be considered by Transport Scotland.

 

 

 

 

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12 thoughts on “Forth Road Bridge “truss end links”.

  1. Alec says:

    I hadn’t made the link between cancellation of tolls. Another populist move by the SNP without any consideration for where the shortfall was going to come from.

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    • Mark says:

      I think you will find this decision was taken in 2007 when SNP in minority government & was voted through 120-0 other parties had no problem with decision then

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      • Jack Wardell says:

        The decision to cancel the tolls is not the issue; it is the failure to provide FETA with an alternative source of maintenance funding.

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  2. Andy Hodge Jnr says:

    the dogs called snp were to busy being traitors to queen and country with the so called yes vote spending money trying to get their hands on our country the snp party should be devolved never to be a political party ever again more jobs more homeless more pensioners dying from lack of money to pay for food and bills in years I hope they are happy but what other cuts have they hide from our people in scotland

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  3. Dotty says:

    thanks for the further info I have been watching this for a while and suspected the failure was avoidable I have been unable to find a before picture of the failed link (links) and am interested in the pin itself as its shown as oval and well off the retainer does anyone have any construction pictures for the Facebook group Bridges and other engineering marvels

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    • Jack Wardell says:

      The likelihood of failure was predicted though not the specific timing. It was reported as overstressed over 5 years ago. This means the stress in the steel was higher than allowed for in the design for one or more reasons; e.g. corrosion greater that allowed for, dead load or dynamic load greater, relaxation of other load bearing systems putting more load on the link. If the load continued to increase the time to failure would become shorter. It is possible that other components, such as the pins and their respective bearings/bushes could also be overloaded. However the repair proposed does not strengthen these so the engineers must be satisfied these are ok. I think the oval appearance of the pin is simply because the photo is taken from above it is being viewed at an angle.

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