Danish engineers build the world’s longest bridge

BRIDGE DESIGN: The world’s longest road bridge is being built across the Gulf of Thailand. It is being constructed on the principles used for the Great Belt Bridge in Denmark – by the same experts who invented the method: Denmark’s COWI

There are many ways to build a bridge.

     But – project for project –only one is the right way when all the variables are taken into account: time, environment, land or seabed conditions, plus many others – not least of which is price. And there is one company that stands out from all the others for its skill and expertise in building the right bridge at the right price: Danish consulting engineers COWI.

Thailand’s Department of Highways was well aware of that fact, when they sent an express mail to COWI in late December 2003: “We have a feasibility study for a bridge project which will connect Bangkok with Phet Buri across the north western corner of the Gulf of Thailand. The bridge will become the world’s longest road bridge crossing water. 47 kilometres, and a further 50 kilometres of connection over land. A project of almost 100 kilometres. Can you help us make the study into a project which can be implemented in practice? Please respond immediately, if not sooner.”

Conceptual thinking
“Naturally we could do so, although we used a few days for it,” says head of department Ejgil Martin Veje of COWI, which has thus added yet another spectacular bridge project to the extensive portfolio which carries COWI’s seal: Qatar-Bahrain Causeway, Subiyah Causeway in Kuwait, SuTong Bridge in China, The Great Belt Bridge in Denmark, The Normandy Bridge in France and Stonecutters Bridge in Hong Kong. And a vast number of others which all have required, in one way or another, the special competencies of COWI.

Assembly line production
The Gulf of Thailand project is a shining example. Based on COWI’s experience from the Great Belt Bridge and the Øresund Bridge in Denmark, where for the first time in history a gigantic floating crane was constructed for mounting prefabricated bridge elements between the bearing constructions, COWI proposed a similar model in Thailand, adjusted to Thai conditions. The method results in dramatic time saving compared to the more traditional method where the elements are cast on the bridge itself.

     “Above all it is a major logistical task to work out at sea, where there is often a strong swell and windy weather. Not least in Thailand, where we also have to consider the monsoon season,” says Jesper Rasmussen, COWI’s project manager on the task. “If you are sailing 20 kilometres out to the middle of the bridge each day, it takes almost three hours. For that reason we suggest that nearly all constructions are done on land and shipped out for installation. It also provides a far more durable construction to make concrete elements on land where they are produced on an assembly line.”

Completion in 2007
“It is crucial that the construction method is already thought through at design level,” says Veje. “When we were presented with the Thailand project, there was only an overall layout available, and a feasibility study which obviously does not go into details regarding the design itself, and construction methods from a university in Bangkok. Since it is a “Design-and-Build” project, it was our task, in addition to planning the bridge, to advise the Chulalongkorn University in Bangkok together with our local collaboration partner Arun Chaiseri Ltd, on possible construction methods for building the bridge.

Whereas the focus with traditional bridge building on land is often on material costs, on water it is about finding the best construction method. An inappropriate solution can become unbelievably expensive.” The time schedule for the world’s longest road bridge is two to three years. It requires that an average 50 metres is added each day. The aim is for the bridge to be completed before the King of Thailand’s birthday in 2007.