The third bridge across the Bosporus is being built north of Istanbul. With a span of more than 1,400 m, it will be the longest cable-stayed suspension bridge in the world. Munich Re is supporting this ambitious project as the leading reinsurer.

Bridges

Relieving the bottleneck

The third bridge across the Bosporus is being built north of Istanbul. With a span of more than 1,400 m, it will be the longest cable-stayed suspension bridge in the world. Munich Re is supporting this ambitious project as the leading reinsurer.

09.05.2016

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Marmara is the smallest, but most densely populated region of Turkey and the country’s commercial centre. The region’s dynamic development has stretched the traffic network to the limit. The risk of traffic jams is especially great on the two existing bridges across the Bosporus in the multi-million metropolis of Istanbul. These structures have linked Europe and Asia since 1973 and 1988 respectively. According to the Turkish Ministry of Transport, an average of 400,000 vehicles cross these bridges every day, and the number is rising.

To ease the situation, the 118-km Northern Marmara Motorway is being built to take long-distance traffic in a wide arc around the centre of Istanbul. Due to the topography of the terrain, numerous tunnels and bridges will need to be built in the course of this mammoth project. More earth is being moved along the entire route than was excavated in the construction of the Panama Canal. The route runs north of the present west-east motorway and also includes a third bridge across the Bosporus. Near the Black Sea estuary, the Yavuz Sultan Selim Bridge will span the strait from Garipçe in Europe to Poyrazköy in Asia. Due to its size and complexity, this project calls for some formidable feats of engineering.

The Marmara motorway is being constructed on the basis of a Build Operate Transfer (BOT) model, which will see the project management, planning, construction, financing and operation being undertaken by a private franchisee. The contract was awarded to a joint venture between the Turkish construction firm İÇTAŞ and the Italian construction group Astaldi. The foundation stone was laid in May 2013 and the bridge is scheduled to open in summer 2016. The cost of this ambitious project is estimated at around US$ 4.5bn.

Munich Re is the leading reinsurer in this project

This public-private partnership is predominantly financed through bank loans, a scheme which was only made viable by appropriate risk hedging. When reinsuring these risks, Munich Re took the leading role, assuming a share of 40%. Experts from the engineering section of the Corporate Insurance Partner unit were not only responsible for negotiating the fundamental terms and conditions in the underwriting process, but also for monitoring the project’s progress and advising on risk management. Losses due to natural hazards (limited cover for earthquakes), bad workmanship, fire, defective design and statutory liability are covered through an all-risk policy. Liability is extended for a period of two years following completion. Losses due to acts of war and terrorism, as well as costs incurred as a result of delayed commissioning, are excluded.

The project can lay claim to a number of superlatives and presents particular challenges to underwriters. Firstly, there is the considerable earthquake risk to which this third Bosporus bridge is exposed. It is no more than some 35 km from the North Anatolian Fault, where the Anatolian continental plate meets the Eurasian plate. In the past, the whole region has been struck by a number of earthquakes, some with devastating effect.

With a span of more than 1,400 m, this will be the longest cable-stayed suspension bridge in the world

Wind loads are another significant risk for the bridge. With a span of more than 1,400 m, it will be the world’s longest cable-stayed suspension bridge and the deck width of 59 m is also unparalleled. As a result, a two-track railway line for high-speed trains can be accommodated in the middle of the bridge, with a four-lane motorway on either side. In order to prevent deformations, the design selected was that of a suspension bridge with cable stays for additional bracing strength. The entire structure is supported by two A-shaped towers of reinforced concrete standing more than 324 m high – the tallest of their kind in the world. The cross-section of the towers is also unique. Their inclined triangular structure, which tapers towards the top, placed special demands on the construction companies.

The middle section of the bridge consists of 59 steel segments in total, each measuring 59 x 24 m and weighing up to 923 tonnes. Their streamlined shape resembles an aircraft wing, increasing the bridge’s stability when exposed to strong winds. The stresses to which the bridge is exposed as a result of fluctuations in temperature is another factor not to be overlooked in a structure of this size. Expansion joints at both mainland ends ensure adequate movement of the roadway in high and low temperatures.

Provided that the waves are no more than a metre high, the segments – prefabricated in a steelworks some 50 km away – are transported to the site on pontoons. Since strong currents and frequent winds make navigation difficult, shipping on the Bosporus – one of the world’s busiest waterways – has to be briefly suspended each time these segments are moved.

The individual parts are raised to the level of the roadway by a special derrick crane which is anchored to the bridge and travels with the segments. The bridge is constructed using the cantilever method, i.e. by advancing the segments from the two towers; on average, around one week is needed to position and weld each segment. Protected by a special tent, the elements are joined together with millimetre precision. The welds then undergo radiographic testing as a quality assurance measure. The last 17 middle segments which are suspended from the main cable are positioned with the aid of a strand jack and then welded.

Pricing is a challenge

When underwriting the risks involved in such a complex infrastructure project as the Northern Marmara Motorway, pricing is an inherently tricky affair. After all, such fundamental factors as the geology, location or materials used and the technical processes make every project unique. The risks involved lack the typical features required for insurability. Although empirical values on losses incurred in bridge construction do exist, the unique nature of the project makes it impossible to determine the occurrence probability by conventional means. For the primary insurers and Munich Re, the leading reinsurer, the main challenge was to understand the risks as a whole before chopping them into “manageable” portions and assessing them appropriately.

For this purpose, Munich Re has developed special calculation models based on empirical loss data. Decades of experience have led to the development of MR Expert, a tool with which even peak risks can be modelled. The tool has already proved invaluable in other infrastructure projects supported by Munich Re, such as the enlargement of the Panama Canal or construction of the first road and rail tunnel under the Bosporus.

Our lean, flexible and highly innovative unit has shown itself to be a dependable partner, capable of delivering solutions that meet market needs. Its great advantage lies in the combination of our experts’ know-how and the strong financial security of Munich Re.

Construction of the Northern Marmara Motorway has proceeded without major problems to date. We are confident that the extremely tight three-year time frame can be adhered to and the project completed on schedule in 2016. This successful conclusion would be due in no small measure to the engineers and construction workers who have overcome unforeseen problems, showing great motivation, attention to detail and ingenuity.