Proceedings of Bridge Engineering 2 Conference 2009 April 2009, University of Bath, Bath, UK CRITICAL ANALYSIS OF THE GREAT BELT EAST BRIDGE, DENMARK A. J. Weight1 1Undergraduate Student, University of Bath Abstract: This article provides an informative and critical analysis of The Great Belt East Bridge in Denmark. Not only is it one of the longest span bridges in the world but it was also part of the greatest engineering feat ever undertaken in Danish history. Its legacy is that the kingdom of Denmark is now fully linked up with mainland Europe, improving trade and transport. It paved the way for further bridging success between Denmark and Sweden with the Oresund Bridge. More than 10 years later, it is still regarded as one of the greatest bridges in the world as well as being a cultural and engineering icon for the people of Denmark. Keywords: Great Belt, East Bridge, Suspension, Denmark, Vortex induced oscillations Figure 1: The Great Belt East Bridge Construction of the link commenced in 1988 and, 1 Introduction although the link had been open to rail traffic for over a year, Queen Margethe II of Denmark finally declared the The Great Belt, or Storebaelt in Danish, is a 16-32km last part of the link the East Bridge open to road traffic on wide strait between two of the largest Danish islands, the 14th June 1998. It was declared as the largest Zealand and Funen/Fyn. For hundreds of years the ferry engineering project in Denmark, shrinking the size of the route between the two islands was regarded by the Danes country, linking the capital Copenhagen to the rest of as extremely important, but ferry services were often Denmark as well as mainland Europe. disrupted due to storms and particularly harsh winter The fixed link itself is broken up by the island of conditions. Sprogo and consists of a suspension bridge and a railway A link to replace the ferries became the source of tunnel between the islands of Sprogo and Zealand as well debate for a number of decades until 1987 when a fixed as a box girder bridge between the islands of Funen and link was finally approved by the Danish government. Sprogo (see Fig. 2). Figure 2: Plan and location of the Great Belt fixed link With Pylons reaching up to 254 metres the suspension bridge upset the simplicity of the bridge. The repetition of bridge on the east side of the great belt is without a doubt the cables gives the East Bridge good order, and due to the most visually impressive part of the whole project. their slender appearance they do not obstruct the view The completed East Bridge has a central span of 1624 through the bridge. One criticism could be that the lines metres, superseded at its completion in 1998 only by the of the abutments are too complex and clash with some of Akashi–Kaikyo Bridge in Japan which had just been the other column lines however this is negated by their completed 2 months previously. excellent fulfilment of function. As with all designs refinements improve the appearance of a bridge. The shape of the steel box girder 2 Aesthetics on the East Bridge ends with a thin edge giving the deck a Following the view of Fritz Leonhardt, in Ref. [1], slender smooth appearance. bridges can be assessed and analysed for aesthetics Another refinement is that the deck is suspended against ten sets of criteria or rules. This paper will now across the whole 2.7 kilometres of the bridge, rather than look at these criteria in the context of the East Bridge. supported at the towers, eliminating the need for bearings or suspension pendulum rods. This meant that the intermediate cross beam on the towers could be placed at mid-height which improves the proportions of the towers. The towers are also further refined by flaring the legs to allow for protection from ships rather than using stone islands. It is important that the style of bridge proposed fits in the location in which it is built. Due to its long central span the elegantly slim silhouette of the bridge deck hovers beautifully above the impossibly wide Great Belt strait and rises gently from the flat islands that the Great Belt divides. Figure 3: Form of Anchor block showing how the cables forces are transferred to the rear of the block. Most importantly a bridge should fulfil its function. It should be obvious even to non-engineers how the bridge works, inducing confidence in the user. The East Bridge is an excellent example of this, clearly showing off its strength in the form of a suspension bridge with large catenary cables and tall substantial pylons. Another exciting aspect of the function of this bridge is the way Figure 4: Light reflects off the water highlighting the the concrete pylons and anchor blocks emphasize the load smooth finish of the steel deck path of the structure (see Fig. 3). Proportions give bridges balance in their geometry. Texture is often ignored in bridge design but on the The proportions of this bridge are aesthetically pleasing; East Bridge the contrast of the rough concrete towers and the deck has a relatively slim depth and contrasts well the smooth steel deck emphasize its proportions with the stockier towers. especially when viewed at sunset or when the light The order of the bridge should also be considered. reflects off the surface of the water (see Fig. 4). Too many disruptions along the edges and lines of the Figure 5: Main dimensions of the Great Belt East Bridge Colour can be used either in a quite obvious way or in Rasmussen and Ramboll & Hannemann. Danish a more subtle way to highlight elements of the bridge. On architects Dissing and Weitling provided all aesthetic the East Bridge it has been used in quite a subtle way, the contributions to the design. concrete is stone grey which when coupled with the bright The Great Belt is an international shipping route and blue backdrop of the strait and the sky evoke images of hence is subject to a large volume of ship traffic, about rocky cliffs. The bridge has dark grey cables that either 20,000 vessels per year. A study was completed involving contrast with the background or blend in, depending on theoretical ship-collision as well as simulations of actual the nature of the light, finally the shape the deck and the navigational conditions. These studies indicated that the piers which make the most of the contrast between main span should exceed 1.5 kilometres (see Ref. [2]). shadows and light. This meant that a suspension bridge was the only realistic Character can be quite hard to define and can depend solution to meet the main span requirements. By on individual opinion. It is perhaps not applicable to the optimizing the design, a 1624 metre main span with 535 East Bridge but should nevertheless be considered when metre side spans, carrying a four lane motorway plus assessing the aesthetic qualities of a particular bridge. emergency lanes was finally selected. The final Complexity can be stimulating if used appropriately, dimensions of the bridge can be seen in Fig. 5. however too much complexity can look chaotic. The simplicity of the East Bridge is what makes the bridge 3.1 Superstructure appear so stunningly elegant. The thin line of the deck curves gracefully and the geometrical shape of the closed 3.1.1 Girder section has also been kept very simple. The welded steel box girder is continuous between Some bridge designs take inspiration from nature or the anchor blocks over the whole suspension bridge even try to blend into the natural environment around length of 2700 metres. Hence there are expansion joints them. The East Bridge is more of a statement of the located at the anchor blocks but there are no expansion engineering achievements of which man is capable. joints at the towers. Vertical elastic support is exclusively Therefore it would be inappropriate for the East Bridge to provided by the hangers. This eliminated the need for incorporate nature into its design. bearings at the towers which would require maintenance. A beautiful bridge does not necessarily fulfil all ten The form of the box girder lends itself well to rules, just as an ugly bridge does not necessarily break all prefabrication and also helps with the bridges ten rules. The important thing is that when observing the aerodynamic performance. Transverse trusses inside the bridge it brings immediate pleasure to the eyes. In this deck improve the decks fatigue resistance. The inside of respect the East bride is a very aesthetically pleasing the deck is also protected from corrosion by bridge. dehumidification. 3.1.2 Cables 3 Structural Design A cable sag ratio of 1:9 was decided to be optimum to reduce sliding forces in the anchorages. The main The bridge design was led by a CBR joint venture of cables are 3079 metres long. Each cable consists of 37 COWI Consulting Engineers and Planners, B. Hojlund strands which in turn are made up of 504 high tensile To make matters worse Finland decided to seek an galvanized wires, which are 5.38 millimetres in diameter. injunction before the International Court of Justice at the The cables are also protected by wrapping a steel wire Hague to stop the East Bridge from going ahead. around the cables which is laid in a zinc paste. These were Although Denmark had notified other maritime nations of constructed using a modified version of the traditional the bridge earlier in 1977, in 1991 Finland requested a aerial method (see Fig.