Tag Archives: scotland

Cost of Corrosion Increase – Forth Road Bridge

Significant inaccuracies in the as-built drawings for the Forth Road Bridge’s cable anchorages are to dramatically increase the cost of corrosion investigations, the “New Civil Engineer” publication learned this week.

Examination of the bridge’s southern anchorages – which hold the huge suspension cables in place – is taking much longer than anticipated because they are deeper and steeper than the on the original as-built drawings.

The Forth Estuary Transport Authority (Feta) is investigating the condition of the 48 year old anchorages after a resident engineer’s report raised concerns about the possibility of corrosion in the post tensioned strands within them.

In a capital update report to the bridge authority, Forth Road Bridge chief engineer and bridgemaster Barry Colford says the cost of the inspection is likely to be “significantly higher than the original estimate” of £3.5M.

“It’s a very resource driven contract,” Colford told NCE. “As the rockhead level was higher and there more was concrete [than anticipated] the contractor has had to spend more money.”


The anchorages are four concrete filled tunnels – 80m deep on the south side, 57m deep on the north side – and up to 14m in diameter.

The anchorages each transfer a load of 14,000t from the main suspensions cables into the bedrock.

Each anchorage consists of 114 ducts with four post-tensioned, galvanised, 32mm diameter high tensile steel strands made up of 19 wires in each.

With the original access chamber to the bottom of all four anchorages filled in, the only way to assess the condition of the strands is to dig down and open them up, said Colford.

Contractor Graham began the anchorage investigation on the southern bank in August 2011 under a New Engineering Contract (NEC) 3 Option C target cost contract with a target cost of £3.5M.

But after investigations began, engineers discovered that the ducts were 400mm deeper and were at an angle of 33˚, not 30˚ as recorded on the as-built drawings.

“It’s a significant change to what we expected and it is very disappointing the as-built drawings of a major structure were not correct,” added Colford.

Graham will begin exposing up to nine stands on each of the southern anchorages by the end of the year. Consultant Fairhurst will assess the strength of the anchorages by the end of 2013.

Colford is in discussions with Graham about the size of the compensation event – the cost of work unforeseen at tender stage – and £220,000 has already been agreed.

The extra funds for the anchorage investigation are contributing to an overall deficit of £3.5M in Feta’s capital budget for 2012/13.

Its capital funding was cut by 58% by Transport Scotland last year.

Colford said budget shortfall would be met by using some of Feta’s £5.8M reserve, as well as delaying or cancelling “non-committed” schemes on the bridge.

He was also seeking additional funds from Transport Scotland.

SOURCE: http://www.nce.co.uk/news/structures/forth-anchor-corrosion-probe-costs-pushed-up/8635624.article?blocktitle=Exclusive-news-from-NCE-magazine&contentID=204

Caissons a solid sign of progress on new Forth bridge

The new Forth crossing will be fitted with dehumidification equipment to cut the risk of the corrosion which has blighted the existing bridge.

At a briefing on the progress of the £1.4 billion project being built by the Forth Crossing Bridge Constructors, Transport Scotland project director David Climie said work was on schedule.

”We are still exactly where we want to be, on time and budget,” he said.

Only three months ago there were 384 people working from the Rosyth base but now that number has more than doubled, with 800 staff working on various parts of the site. At its peak 1,200 staff will be employed.

One of the most important milestones of the entire project has just been reached — the arrival of the first two caissons which will form the foundations of the north and south towers.

In a ”foundation” year for the project, Mr Climie said: ”We are extremely happy with the way things are progressing.”

Carlo Germani, the FCBC project director, said: ”We are into the real construction work now. We have done a lot of the preparation and what you see is work on the bridge itself starting with the arrival of the caissons.”

These are the huge cylinders ranging in height from 21.1m to 30m — around the same as an eight-storey building — with diameters of around 32m.

The largest weighs roughly 1,200 tonnes, making it one of the largest steel caissons ever sunk down to the seabed.

They will be used as moulds for the foundations, comprising underwater and reinforced structural concrete. More caissons are due to arrive in a few days.

FCBC’s Carson Carney explained the process of building the central tower, which will be constructed on site in 4m high increments, would start this year.

The deck sections are being built in China and Spain and will be shipped over and stored at Rosyth.

With corrosion affecting the existing bridge, Mr Carney explained the crossing’s cables are made up of strands containing galvanised steel wires, with a wax coating and covered in plastic.

”There is no way you can get water into the actual strands themselves. This is a state-of-the-art type system.”

Each strand is capable of being individually replaced if necessary without causing widespread disruption to traffic.

There is a dehumidification system at deck level and on the anchorage points.

SOURCE: http://www.thecourier.co.uk/News/National/article/23358/caissons-a-solid-sign-of-progress-on-new-forth-bridge.html

Corrosion report offers boost for future of Scotland’s Forth Road Bridge

A £1.6billion replacement for the Forth Road Bridge will still go ahead – despite experts stopping the crossing from rusting.

Engineers revealed they have halted corrosion of the bridge’s suspension cables.

But the Scottish Government insist a new crossing is still needed and will open by 2016.

A spokesman said: “The Forth replacement is vital to ensure Scotland’s economic wellbeing.”

Engineers had warned the bridge, which opened nearly 50 years ago, would have to close to heavy lorries by 2017.

But the new findings suggest restrictions could be delayed until much later.

Bridge chiefs are confident that an inspection of the cables, due to start in April, will show no further corrosion.

Green MSP Patrick Harvie said: “If correct, this willhighlight the poor decisionthe SNP made to plough ahead with the additional bridge.”


SOURCE: http://www.dailyrecord.co.uk/news/scottish-news/2012/02/26/rust-report-offers-boost-for-future-of-forth-road-bridge-86908-23765336/

Scotland’s Forth Bridge safety & corrosion tests to be less extensive

A £2.6 million ($4.1 million USD) contract awarded by the Forth Estuary Transport Authority yesterday will see eight sections of the suspension cables tested for corrosion to establish whether and when traffic restrictions may have to be imposed on the crossing.

The organization had originally planned to test twice the number of sections but said the cutbacks had been made after a 56% reduction in its capital budget over three years, which had nearly halved the contract’s value.

Previous tests conducted in 2004 and 2008 established that corrosion had caused a 10% reduction in strength in the cables, eventually leading the Scottish Government to go ahead with a £1.5 billion replacement crossing, due to be completed by 2016, in order to avoid any closure of the route.

Work on the third inspection will begin next spring, with data being available in early 2013.

Barry Colford, chief engineer and bridgemaster, said: “The condition of the main cables is the second-highest risk to the bridge after the condition of the main cable anchorages. We have already begun investigating the anchorages but this inspection of the main cables is also an essential project.

“Although the cost of the work has come down, the nature has not changed significantly and the inspection will still allow the cables’ strength to be evaluated.

But the cuts to the inspection program were criticized by opposition parties yesterday who warned that they could lead to further expenses.

SOURCE: http://www.heraldscotland.com/news/transport-environment/forth-bridge-safety-test-to-be-less-extensive-1.1131949

Doubts over management of Forth crossing could see bridge expertise lost

Vital specialist bridge engineering skills risk being lost to Scotland due to uncertainty over the future governance of the Forth Road Bridge, the convener of the Forth Estuary Transport Authority (FETA) has said.

The warning comes in advance of a decision by Transport Minister Keith Brown, due in October, on how the proposed new £2 billion Forth crossing is to be managed.

The main options are to manage the new structure along with the existing road bridge in a modified version of the existing governance structure, or to abolish FETA and allow Transport Scotland to manage both bridges.

Fife councillor Tony Martin, FETA’s convener, said: “Staff with unique long-term experience of managing long-span bridges are going to leave us if we can’t tell them what the future is going to be.

“To manage [the bridges] properly it is important that we retain that kind of expertise.”

Senior managers in Transport Scotland, who have a civil service rather than an engineering background, are known to favor a model where the maintenance contracts for the bridges is outsourced to private-sector firms, a system currently applied to Scotland’s trunk road system.

However, as the complex technical and safety requirements of large bridges are distinct from roads, and the current bridge has a reduced safety factor due to corrosion, engineering experts doubt whether Transport Scotland is sufficiently competent or accountable to assume responsibility for the day-to-day management of major long-span bridges.

The agency also has mixed record of negotiating best value for taxpayer with engineering multinationals, and may face criticism over its supervision of the construction contract for, and management of the Government grant to, the Edinburgh tram project.

Martin said: “Although the governance model would have to change, my view is that the bridges should be managed by the people who currently operate a system that employs local people, is flexible and has worked well for 40 years.”

FETA is currently preparing to award a contract to assess the impact of its four-year program of injecting air into its main cable to arrest the rust damage that has threatened to reduce the bridge’s safety factor below the level needed to allow Heavy Goods Vehicles (HGVs) within several years.

If the dehumidification process has been successful, the risk factor will stabilize, but the cables will still require a rolling program of maintenance.

In a separate operation, Northern Irish firm Graham Construction won a £3.5 million contract last month to open up and investigate the bridge’s main cable anchorage, to assess the impact of corrosion in the steel strands that hold the concrete together in the anchorage tunnels.

The excavation is expected to take 12 months and a further 12 months will be required to carry out the inspection and evaluate the findings.

Bridgemaster Barry Colford said: “This is a very important investigation into what are critical components of the suspension bridge… I would stress that there is no external evidence of any problem but it is our responsibility as a bridge authority to inspect every part of the structure in order to ensure there are no hidden issues.”

Transport Scotland successfully delivered the £120m Clackmannanshire Bridge over the Firth of Forth on time and on budget, which was opened by First Minister Alex Salmond in 2008.

However, the civil engineer John Carson, who led the team that built the new Skye Bridge, dismissed the precedent as irrelevant.

“Anyone who knows anything about bridges would know there is no meaningful connection between building a relatively simple short-span concrete bridge to maintaining one of the world’s largest suspension bridges, especially in its degraded form,” he said.

“Barry Colford is a hands-on engineer who has to take responsibility for the safety of the traffic on the bridge on a daily basis.

SOURCE: http://www.heraldscotland.com/business/analysis/doubts-over-management-of-forth-crossing-could-see-bridge-expertise-lost-1.1120249?96944

£3.5 contract awarded for Forth bridge cable corrosion probe

AN INVESTIGATION is to be launched into potential corrosion of the Forth Road Bridge’s main cable anchors.

A £3.5 million contract for the work was yesterday awarded by the Forth Estuary Transport Authority, which runs the bridge, to Graham Construction.This follows ongoing work to dry out the rest of the cable in an attempt to halt corrosion, which has already triggered the building of a new adjacent crossing costing up to £1.6 billion.

The anchorage work is expected to start in August, with 30ft deep excavations at the south end of the bridge taking a year. Inspection work and evaluation of the findings will take a further year.

Chief engineer and bridgemaster Barry Colford said there was no external evidence of any problem, but the work was a “very important investigation into what are critical components of the suspension bridge”.

He added: “It is our responsibility to inspect every part of the structure in order to ensure there are no hidden issues.”

The anchors are concrete-filled tunnels bored into the rock on either shore, where the bridge’s main suspension cables are attached to the ground.