The new SR 520 floating bridge, located on Washington Lake in Seattle, was inaugurated on April 25, 2016 to replace the previous bridge built in 1963. It is the longest in the world in its category and has just won the National Award Engineering Association awarded by American Council of Engineering Companies | ACEC.
‘This is one of the great engineering works of our time’ – Roger Millar, Secretary of State of Washington Transportation.
It has a cost of about 4,000 million dollars, has a length of 2300 meters (only 40 meters longer than the previous bridge), has a depth of 65.2 meters, forms a path of 4750 meters and is built so that Remain unperturbed for 100 years.
Have you ever wondered why they have used a floating bridge and not a conventional suspension bridge?
The answer is simple. Lake Washington in its depths is filled with soft sediment and it would be risky and difficult to carry out other types of works other than that.
The engineers designed the new bridge to better withstand possible earthquakes, larger waves and withstand wind storms of up to 150 km / h. It has also expanded to include additional lanes, two lanes for public transportation and a bike / pedestrian lane on one of the banks. In the future, you could retrofit the light rail if required.
Building Description
The model structure consists of three substructures and two stability pontoons.
With the longitudinal pontoon, they form the substructure 1 and the substructure 2, composed of the frame of piles of the bridge, is connected by frames located in the bases of the piles to the substructure 1. Finally the substructure 3 represents the board of the bridge and joins to the piles of the substructure 2 through frames located in the heads of the piles.
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With regard to the mechanical properties of the structure, it should be noted that for the stacks and the panel a prestressed concrete of similar characteristics to the HP-40 has been used, whereas the pontoons are made of steel plates of thickness = 225 mm. For example, the standard pontoon has a length of 110 meters, a width of 23 meters and a height of 8.5 meters.
In the following figures is shown schematically the main section and the floor of the bridge.
With this geometry, dimensions and mechanical properties that the engineers have designed, the structure can float, being submerged under water 7.5 meters of the height of the pontoons. Then it uses a system of mooring with cables of steel of almost 8 centimeters of thickness.
The following images describe how the new floating bridge was built …
Below we leave a video where they provide an overview of the reasons why the new floating bridge SR 520 was built and some of the solutions that the project team developed efficiently to build the longest floating bridge in the world:
Finally, we leave you with this short documentary where tells the story of the new floating bridge across Washington Lake in Seattle, Washington:
AWARDS
- 2017 – Grand Conceptor Award, Engineering Excellence Awards, American Council of Engineering Companies.
- 2017 – Gold Award – Structural Systems, Engineering Excellence Awards, American Council of Engineering Companies of Washington.
- 2016 – VISION 2040 Award, Puget Sound Regional Council.
- 2016 – Excellence in Design (Engineering) Award from the Institute of Design and Construction of America.
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