Designing and building the Queensferry Crossing

  • The Queensferry Crossing took just a decade from the initial idea to opening the bridge and this included a nine-month delay due to weather conditions.
  • The cost of the project came in at more than 25% under budget with a £650 million saving.
  • The South Tower foundation required 16,000 m³ of concrete leading to a record-breaking 15 days of continuous pouring underwater.
  • Weather breaks on the Queensferry Crossing will eliminate the need to close during high winds.
  • Unlike the original Forth Road Bridge each of the cables supporting the structure can be replaced remotely without the need to close the bridge.

When officially opened by the Queen on 4 September 2017 the total duration of the Queensferry Crossing project was a decade from the initial idea to completion. It is officially the longest three tower cable-stayed bridge in the world and while the bridge itself is 1.7 miles in length when you include changes to the local road network the overall scheme covers an area of 13.7 miles. While the Queensferry Crossing will not be open to pedestrians there was a ballot resulting in 50,000 members of the public being able to walk over the bridge prior to its official opening. There is no access for pedestrians so the 50,000 people who pulled the winning tickets will take their unique place in the history of the Queensferry Crossing.

queensferry crossing

Mechanical engineering at its greatest

It is not very often we get the chance to discuss new structures, world breaking structures, which come in under budget. Well, in the initial stages of planning a total cost of £2 billion was discussed for the Queensferry Crossing project (there was talk of a cost of £4 billion in the very early stages although this did not materialise). By the time building began in 2011 the forecast cost had been reduced to a range of £1.45 billion up to £1.6 billion. Fast forward 24 months and the Scottish government announced a new forecast overall cost of between £1.4 billion and £1.45 billion. The final cost of the bridge was an even better-than-expected at £1.35 billion a full £650 million less than the initial forecast.

The only fly in the ointment was the fact that the project was nine months behind schedule because of the severe winds in the area which hampered installation of the breathtaking cable design.

Facts about the Queensferry Crossing

While the overall project took a decade to complete from start to finish, construction of the bridge only began in 2011 with preparation work taking nearly as long as the building of the bridge itself. It is also ironic that the construction of the Queensferry Crossing was delayed by nine months due to weather conditions because the bridge has windshields on either side which will ensure minimal, if any, future closures due to extreme weather conditions.

Those who have used the Forth Road Bridge will be aware that, on a regular basis, the bridge is closed due to “high winds”. We can only estimate the value of the new bridge to the region when you bear in mind the cost to the local economy and the additional travel expenses/time caused by closure of the old bridge.

Building the bridge

Many people will be unaware that while the consortium building the bridge was known as Forth Crossing Bridge Constructors it was actually a consortium of German, American, Spanish and Scottish companies. So, the idea that the bridge was built by Scottish materials and Scottish labour is unfortunately something of a myth. However, on the plus side it did create 15,000 local jobs!

queensferry crossing under construction

May 2016: Construction of northern tower of The Queensferry Crossing

Now that the project is finished it has been confirmed that the steel used to build the bridge totalled 35,000 tonnes with an astonishing 7,000 tonnes used on the North and South viaducts alone. The three towers are joined to the bridge via the cable network and are 207 m above high tide, 50m higher than the old bridge and utilised a staggering 23,000 miles of cable – nearly enough to travel the circumference of the globe (just under 25,000 miles). One of the more subtle marvels of the Queensferry Crossing is, unlike the original Forth Road Bridge, any damaged cables from the three towers can be replaced remotely with no need to close the bridge. Local drivers are well aware of the number of times the Forth Road Bridge was closed for “repairs”. This alone will have a massive impact on the local economy and that’s before you even begin to take into consideration the weather shields.

Aside from claiming the title of the world’s longest three tower cable-stayed bridge it is also worth mentioning the foundations required for the South Tower. While all towers are secured on the bedrock by circular steel structures known as caissons, it took 15 days continuous pouring of concrete to create the foundations for the South Tower (a staggering 16,000 m³ of concrete). This is the world’s longest continuous underwater pour and we can only imagine the challenges this brought about when you bear in mind the concrete had to be poured from barges on the water. One thing we can be certain of, the foundations should be there for many years to come!

The old Forth Road Bridge was eroding

It is only when you go over the bridge that you fully appreciate its size and many will be surprised at the relatively small width of the bridge – although it does still accommodate two lanes of traffic on each side and two hard shoulders. When you bear in mind that the old Forth Road Bridge was built to accommodate 11 million vehicles per year but hit a peak of 23 million vehicles in 2006, the need for a new bridge became obvious.

This excessive traffic volume lead to significant corrosion of the Forth Road Bridge cables and the initial 120 year life span, having been built in 1964, is now out of date. The old bridge will still accommodate cycles, pedestrians and in time buses. However, the new Queensferry Crossing will utilise the latest traffic management systems to vary the mandatory speed limits and incorporate bus lanes into the hard shoulder. It is interesting to learn that the forecast lifespan of the Queensferry Crossing has also been estimated at 120 years although the ability to maintain and replace elements of the bridge on an ongoing basis should not be underestimated.

More amazing facts about the Queensferry Crossing

It is very easy to dismiss the bridge as just another bridge but if you dig a little deeper there are yet more startling facts about the Queensferry Crossing. Unlike traditional bridges of its stature the exterior of the Queensferry Crossing is akin to a box in that it is a continuous structure. This reduces the chances of erosion and therefore ongoing maintenance costs. As we mentioned above, all the cables associated with the bridge can be replaced remotely without the need to close the bridge to traffic.

One fact which you will certainly appreciate when travelling over the crossing is the lack of bumps in the road. Cast your mind back, the last time you travelled over a long bridge you would have felt numerous bumps in the road which relate to the individual sectors that are slotted together. The Forth Road Bridge consists of sections which are 60 feet in length creating over 100 individual joins which are not only uncomfortable from a motorist’s point of view but also add to the wear and tear of the structure. This alone would have caused major erosion over the years especially when you bear in mind the increased vehicle capacity from its original blueprint. However, the new crossing only has two joins on the whole bridge deck with the huge sections built off-site and transported over.

Summary

The Queensferry Crossing project took just a decade from conception to opening, came in at £650 million under budget although weather delays did extend the project by nine months. It created a staggering 15,000 jobs, the largest three tower cable-stayed bridge in the world and a record for the longest continuous underwater pouring of concrete. Visually the bridge is stunning, from a maintenance point of view the ability to replace individual cables without closing the bridge is priceless and with just two sections completing the top deck, that constant pitter patter as you drive over traditional bridge joins has been removed. This lack of continuous, no matter how minute, movement as vehicles drive over the new bridge compares extremely favourably to the Forth Road Bridge, which has in excess of 100 joins – it doesn’t take a genius to appreciate the stress this creates.

It is not very often we hear of government managed/funded projects coming in anywhere near budget let alone under budget. At this moment in time there are still some traffic issues to address but there is no doubt that the Queensferry Crossing is an extremely positive development for the region.

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