Long Span Bridge in Norway

Transcription

1 Long Span Bridge in Norway Børre Stensvold. Bridge Director, Norwegian Public Roads Administration, Directorate of Public Roads Arianna Minoretti. Senior Engineer, Norwegian Public Roads Administration, Directorate of Public Roads Abstract Because of Norway's distinctive topography, bridges have been necessary for mobility and accessibility for decades. This presentation gives a brief historical overview of the development of long-span bridges in Norway. From the 1950s, when the suspension bridges were designed with stiffening girder of trusses, until today, when we build even longer spans of modern aerodynamic steel box girder bridges. Also our two floating bridges built in the 1990s are described. In addition, this presentation provides an overview of our new Coastal Highway Route E39 Project. It is planned to replace seven different ferry connections with pioneering designs and constructions. Suspension bridges, cable stayed-bridges, floating bridges, submerged floating tube bridges or a combination of these bridge types. Here is presented the results of the feasibility study that shows alternative methods of crossing "extreme fjords", where the width varies from 2 to 7.7 km and depths up to 1,300 m. The project also includes evaluating whether to use the experiences of Norwegian oil and offshore technology to cross these fjords. The conclusion of this feasibility study shows that this is technically feasible, if our politicians allocate funds to both roads and these large and extreme structures. Introduction The Norwegian topography has promoted the development of bridge structures all around the country and especially near the coastal areas, which are also the ones that are more exposed to extreme weather conditions. This is due to the fact that the coastal development is full of deep fjords and bays, that alternate with mountains which reach heights up to meters. The coastal side is also the most populated area. The necessity to guarantee a functional public transport infrastructure has led to the construction of an impressive number of bridges: nowadays, we count more than , including about 360 ferry quays. Bridges are able to ensure the transport of the goods, the local necessities for move and the requirements of the touristic market. Undoubtedly the local environmental conditions, especially those related to the local climate, have required an effort from the economic and the technological point of view. By using new materials and new technologies, the Norwegian Public Road Administration (NPRA) reached the goals and now it is planning and realizing the maintenance for the existing structures as well as developing new solutions in order to afford some new challenging projects, like the Coastal Highway Route E39 Project. All this is achievable thanks to the work of approximatively 7,100 employees and a total annual budget of 48 billion NOK (7,8 billion USA dollars). In order to optimize the efficiency of the work, the Organisation is divided into two administrative levels: one Directorate and five Regional Offices. NPRA`s engineers and employees are responsible for the design, construction and maintenance of the bridges and the Offices are also provided of emergency teams that can set in place a temporary bridge rapidly, in case of a natural disaster.

2 Past and present in Norwegian transport It is mainly due to the extreme weather conditions and to the impressive landscapes that Norwegian public transport system is recognised as one of the most known worldwide. Furthermore, considering that the new structures cohabit with the historical paths, a lot of factors must be planned together. Their correct evaluation is careful weighted in order to obtain a well-balanced effect for achieving a spectacular final result for the visual impact. The NPRA, that has always a great attention to these topics, is enhancing the existing routes, with the creation of some of the most magnificent touristic viewpoints (Figure 1; Figure 2). Figure 1: Trollstigen Figure 2: Atlantic Road On the other hand, a great work has to be done every time there is the necessity to build a new structure, in order to maintain the global harmony in the landscape. That is why our design teams are working, for each structure, on different perspectives, such as the environmental impact, the study of the lighting, the structural design and so on. The complexity of the studies depends also on the size of the structure, because the bigger dimensions have a more relevant impact on the landscape.

3 Norway, due to the local topography, is one of the countries with more transport roads on bridges: the development of the total route, counting both coastline and the islands is of about Km. It is also one of the countries with the longest bridge`s span, as shown in the following table (Figure 3). Figure 3: World`s longest bridges span (2013) This goal has been achieved using the stiffening girder for the bridge deck. It consists of a truss girder, that became the dominant design structure for suspension bridges for decades in Norway. Varodd bridge (1956, main span of 337 m), Sotra bridge (1972, main span of 468 m), Kvalsund bridge (1977, main span of 525 m) and Nærøysund bridge (1981, main span of 325 m, Figure 4) are some examples of this type of structures. Figure 4: Nærøysund bridge After 1990, the fast technology development allowed NPRA to realize others different bridges, like Skarnsundet bridge (Figur 5), a concrete cable-stayed bridge finished in 1991 that was, on its completion, the longest bridge in the world of that type, for the length of the main span (530 m). At the same time, the structure of the suspension bridge was improved, using closed steel box girder for the deck, as in Askøy bridge (1992, Bergen, main span of 850 m, Figur 6) or in Osterøy bridge (1997, Bergen, main span of 595 m). The environmental actions and the attempt to optimize the structure have led to new challenges that have been faced and solved.

4 Figur 5: Skarnsundet bridge Figur 6: Askøy bridge This has also led to new structural concepts, like the first NPRA`s floating bridge without side/side anchoring, built in 1992, that has a total length of 931 m. It is composed by a steel superstructure made by trusses and pipes junctions, on seven concrete pontoons (Figure 7).

5 Figure 7: Bergsøysundet bridge The structural concept has been developed by NPRA with the world`s longest floating bridge without side anchoring, of a total length of 1614 m (1246 m for the floating bridge). The structure, called Nordhordlands bridge (Figure 8), was finished in 1994 and was an interesting union of different type of bridges (floating bridge and cable-stayed bridge), in order to satisfy both the technical requirements and the local demand for a structure that allows the crossing by large ships. Figure 8: Nordhordlands bridge The importance of the vessel traffic on the Norwegian fjords, for the local activities related to fishing and the aquaculture, or for the great touristic attractiveness of places, has leaded to an effort in order to minimize the environmental impact and the interference with the vessels ` traffic. As a results, the longest Norwegian suspended bridge, Hardanger bridge, was built in 2013, with a main span of m. It also opened a new generation of long span suspended bridges, like Hålogaland bridge (that will be completed in 2017), with a main span of more than m (Figur 9, Figure 10).

6 Figur 9: Hålogaland bridge photomontage Figure 10: Hålogaland bridge - extracted from design project Despite the huge number of structures realized, for which NPRA is also planning and realizing the control and the maintenance, there are still some areas along the Norwegian coast that haven`t a permanent connection. This happens along the E39, a European coastal road (from Kristiansand to Trondheim, for Km) that till now is constituted by a combination of roads and ferries. NPRA wants to realize eight new connections, characterized by some of the most challenging crossing features.

7 The new challenges Halsafjorden, Moldefjorden, Storfjorden, Voldafjorden, Nordfjorden, Sognefjorden, Bjørnafjorden and Boknafjorden are the names of the fjords where NPRA is going to realize new connections characterized by peculiar characteristics. The fjords have depth from 300 to meters and the crossing will be from 2 to 7,5 kilometres. In addition, many fjords` areas are exposed to extreme natural loads, that have to be taken into account in the design phase. Furthermore, each fjord can have special requirements due to the vessels` traffic or to the local activities, such as fishing, aquaculture, navy military exercises and so on. All these aspects are evaluated in the design phase as in risk assessment, to find technical solutions, for example, for ship s collision on the structure or collisions with elements dragged by the passing ships. Normally the traffic volume on E39 is not so high, but it has to be underlined that such type of structure have a long service life and so a design phase with a long-term perspective is necessary. The challenging characteristics of these crossings require a careful evaluation of possible alternatives. Subsea rock tunnel, immersed tunnel, submerged floating bridge, floating bridge or suspension bridge have different features and the optimal solution must be evaluated for each crossing (Figure 11Figure 11). The high depth of the fjords drives the solution towards structures that are independent from the sea level. That is why new structures are being developed, also thanks to the recent advancements in offshore structures (Figure 12), such as tension legs structures or submerged floating tube bridges (SFTB). Many feasibility studies are being developed for the E39 crossings, carrying forward the structures that are able to reach the best solution from a structural, environmental and economical perspective. Sognefjord, Bjørnafjord and Boknafjord represent the most challenging crossings and, for their construction, innovative solutions have to be found. Figure 11: alternative methods for fjord crossing Figure 12: scheme of the development in offshore structures One of the most difficult aspects for these fjords is their width and the shores that are really steep. Therefore, it is difficult to cross them with some traditional solutions.

8 For Sognefjord, between Bergen and Førde, different solutions have been developed. The fjord has a width of approximately 4 Km and the sea depth is about m. In addition, this is an attractive fjord, so the navigation channel for large cruise ships must be guaranteed. These characteristics have brought to the development of interesting solutions, such as a one span suspension bridge (Figure 14), an endanchored floating bridge (Figure 15), a cablestayed bridge on floating pontoons (Figure 16) or a submerged floating tube bridge (Figure 17). Intermediate solutions have also been studied, as the end-anchored floating bridge combined with the submerged floating tube bridge. All these structures have been developed in a feasibility study carried out by NPRA together with external consultant and specific research projects are being developed, both in a national and international field. Figure 13: Sognefjord on E39 Figure 14: suspension bridge Figure 15: floating bridge Figure 16: cable-stayed bridge Figure 17: submerged floating tube bridge

9 Bjørnafjord, south of Bergen, will have a crossing of about 5 Km. The sea depth is smaller than in Sognefjord, but still high for ordinary structures (600 m). The structures that were evaluated for this crossing are: a floating bridge with tension legs platform (TLP, Figure 19), in combination with a suspension bridge; a side anchored floating bridge in combination with a cantilever bridge (Figure 20) or a submerged floating tube anchored with inclined tethers (Figure 21). But also others solutions are being investigated, such as curved floating bridge or submerged floating tube bridge with pontoons. Combined solutions, made by floating and submerged tube bridges, are also being studied. Figure 18: Bjørnafjord on E39 Figure 19: floating bridge on TLP Figure 20: side-anchored floating bridge Figure 21: submerged floating tube bridge

10 Boknafjord is on the north of Stavanger and has a depth of 550 m. The crossing will be approximatively 7,5 Km and one of the structure that is being evaluated for the project is a floating bridge with four towers on floating tension legs platforms (Figure 23, Figure 24). Figure 22: Boknafjord on E39 Figure 23: TLP Figure 24: floating bridge with TLP All these crossing will be a great opportunity to improve new technologies and give a considerable contribution to the international development of the long span bridges. Undoubtedly, the foresight and the economical long term planning of the national governments are essentials requirements in order to achieve these ambitious outcomes.