Forth crossing preliminary design

It is a nice slender design. I am not very convinced about the single line of stays (torsional resistance of the deck and tower stability are issues) or the stays from two towers crossing in the middle (difficult to detail and construct) but it is good to see the project moving on.



From the BBC:


The design for the Forth replacement crossing is being worked on by the same firm responsible for the 'Bird's Nest' stadium at the Beijing Olympics 2008.

Engineering firm Arup was also responsible for the world's second longest spanning cable-stayed bridge, Stonecutter's Bridge in Hong Kong. Jacob the other half of the joint venture, was responsible for the design of the Clackmannanshire Bridge. Public exhibitions for the Forth crossing are being held on Tuesday.

The new bridge design is expected to have the longest central spans in the world for a multi-span cable-stayed bridge. It will also be the only long span cable-stay bridge in the world to have central crossed cables. These provide enhanced stiffness to the bridge structure, minimising the size of the central tower and creating a slim, elegant appearance.

The cables will run along the centre of the bridge. Transport Scotland is taking the Forth crossing exhibition to 12 different venues over two weeks to allow members of the public to view the plans for the crossing. Engineers and specialists from Transport Scotland and its consultants Jacobs Arup will be on hand to explain the work undertaken during 2008 to develop the strategy for the new crossing over the Forth and answer questions. It follows the ministerial announcement in December which confirmed that the Forth Replacement Crossing strategy will make use of the existing Forth Road Bridge as a public transport corridor.

The project is to be progressed via a Parliamentary Bill to be introduced towards the end of 2009. John Howison, Forth crossing interim project director, said: "This is an exciting project and we and our world class consultants are delighted to be working on it to produce a lasting visual landmark for the Forth."

Sebastian Tombs, Architecture and Design Scotland chief executive said: "We are encouraged by the strong vision so far demonstrated by the project team and their aspiration for high design quality. "We have warmly welcomed the proposed 'mono-tower' design for the new bridge."

Tercer Milenio Bride in Zaragoza, Spain

Zaragoza just hosted the 2008 International Exposition, with Water and sustainable water use as the main theme. Since the city is on the south shore of the Ebro River, and the main Expo grounds were on the north shore, a couple of bridges were built before the event in order to improve communications. The Bridge Pavilion designed by Zaha Hadid was one of them, and I will reserve my opinion for a future post, the other one was the "Puente del Tercer Milenio" or Third Millennium Bridge (celebrating the city's ancient history).

This bridge is spectacular. It is a white concrete arch bridge with a 216 m main span. It has a beautiful shape and clean lines. The bridge was designed by Juan Jose Arenas, Spanish bridge designer (who incidentally was my Bridge I and Bridge II professor at university, but that is material for another blog). Mr. Arenas has designed several bridges, and I recommend a quick visit to the website of his company (do not worry, there is an English version).


I think that Mr. Arenas truly understands the arch shape and how to create some iconic bridges. One criticism is that this bridge is a scaled copy of one of his previous works, La Barqueta Bridge, for the 1992 World Exposition in Sevilla, Spain. I think that is a very valid comment. I would like to hear his opinion on it.

Apart of some photographs, I have included a couple of schematic drawings for the bridge, so that you can appreciate the scale and some of the details.

Strait of Gibraltar - Bridge or tunnel

The Gibraltar Strait is one of those remaining crossings anchored in legend for which a link has been discussed for centuries. For me, it is not a question of 'if' but of 'when' and 'how'.
A bridge crossing has been discussed several times. There is a particular article, by T.Y. Lin ("Gibraltar Straight Crossing - A challenge to bridge and structural engineers") that proposes a modified suspension bridge arrangement. This is probably the most famous scheme.



Although the article by T.Y. Lin says that the bridge is feasible with current bridge engineering knowledge and techniques, the truth is that it would be quite the undertaking, and probably not the best engineering solution.

The Spanish and Moroccan governments seem to agree with this. Following an agreement in 1979, in 1980 both governments established an agreement that saw the creation of twin organizations in Spain and Morocco to investigate the feasibility and progress in the construction of a permanent link between the two countries.

Although a bridge alternative was investigated, it was abandoned for a immersed tunnel alternative due to the following factors:

• Higher projected costs
• Technological uncertainty
• Interference with ship traffic and risk of impact
• Higher ecological impact
• Inability to phase the project in function of expected traffic increases

It seems that the project is moving forward and there are news that indicate May 2009 as the date in which a final decision will be taken about the project. If so, the tunnel construction could start in the near future.

Obviously I would prefer a bridge over a tunnel, but given the current technologies in both bridge and tunnel construction, and given the characteristics of the project, I have to agree that, at least by now, a tunnel solution seems to be the best.

Winning design unveiled for new Tarleton bridge

A WINNING design has been selected for a new bridge to cross the River Douglas through a local beauty spot.

The bridge will cross the river at the old railway bridge point between Hesketh Bank in West Lancashire and Much Hoole in South Ribble.

It will be a landmark feature of the Ribble Coast and Wetlands Regional Park the bridge will provide an alternative crossing point to the A59 at Tarleton.

The successful entry from London-based JDA Architects with Arup was chosen from 110 entries in an international competition organised by the Royal Institute of British Architects.

West Lancashire people had their say on which bridge was selected when the seven short-listed designs were displayed at public consultation meetings in September.

Lancashire County Council will now work with other organisations involved in the scheme to get funding for the bridge.

In total 271 consultation feedback forms were received, with considerable support for the winning design.

People’s views were taken into consideration by the jury panel, which included representatives from Lancashire County Council, West Lancashire District Council, South Ribble Borough Council and the North West Regional Development Agency.

Matthew Tomlinson, Cabinet Member for Sustainable Development said: "Although the proposal is still at a very early stage this crossing represents a great opportunity to develop sustainable transport links in the area by allowing people to visit this unique part of the region without using the car."

Once built the bridge will provide a link for people wishing to travel and explore West Lancashire and South Ribble on foot, by bicycle and on horseback.

Bob Allen from the Ribble Coast and Wetlands Regional Park said: "The River Douglas bridge will be a crucial gateway opening up sustainable access to the internationally recognised wildlife habitats within the Regional Park."

From the Southport Visitor

Beam Design formulas

One of the good things of Internet is the wealth of knowledge you can find available at your fingertips. The two bad things are first that this knowledge is difficult to find and second, you can not always trust what you find.

The American Wood Council has a very interesting site with good and useful information. Although not specifically related to bridges, one of the documents for free download has beam design formulas with shear and moment diagrams, as well as deflection calculations.

I have not used those tables for a few years now, but when I was doing some design and analysis, I found them very useful and very difficult to find. I always seemed to need the case they did not include.

I would recommend to download that document and browse the rest of the website, as I said, although not specifically related to bridges, still very interesting