Infrastructure protectionProtecting the world’s longest floating bridge from strong wind

Published 14 June 2017

The Bjørnafjord crossing in Norway will become the longest floating bridge in the world, that is, a bridge where the vertical load is supported by floating pontoons. In order to build the bridge, the engineers need to know exactly how the wind behaves on the bridge site. Scientists are working on a new method for wind measurements.

The Norwegian Public Roads Administration’s (NPRA) giant project Coastal Highway Route E39 (Ferjefri E39) includes finding solutions for seven fjord crossings along the 1,100 kilometer coastline between Kristiansand and Bergen.

To succeed in this ambitious road project, top expertise within road and bridge construction will be involved, and the engineers will be developing new knowledge and technology.

Three research groups are contributing to this endeavor: from the Norwegian University of Science and Technology (NTNU), Chalmers University of Technology in Gothenburg and the University of Stavanger (UiS).

Since 2013, the NPRA has been collaborating with a group of UiS researchers who have been investigating a new method for measuring wind. The method is being applied for the first time in relation to bridge design.

The longest bridge in the world
UiS says that the Bjørnafjord south of Bergen is one of the natural barriers that will be bridged in Ferjefri E39. With a water depth of up to 550 meters and a total length of around five kilometers, this is one of the three most difficult fjords to be crossed in this road project.

“It is the first time we develop a bridge of these dimensions. Gathering as accurate information as possible about waves, currents and wind conditions is therefore crucial”, says project manager Mathias Egeland Eidem from the NPRA

The Bjørnafjord crossing will become the longest floating bridge in the world, that is, a bridge where the vertical load is supported by floating pontoons.

“It is important that the scientists go the extra mile. We need as accurate information as possible, for example about the wind conditions above the sea surface”, explains Eidem.

Wind measurement on the Lysefjord bridge
Traditionally, wind in a fjord is measured by the anemometers installed on the measurement masts on land. Three years ago, wind researchers from UiS started using optical remote sensing to monitor wind conditions.

Lidar technology involves emitting invisible light pulses into the air and measuring the signals backscattered from particles that move with the wind. The difference between the frequencies of the emitted and the received pulses, the so-called Doppler effect, reflects the wind velocity in the direction of the light pulse.  

The UiS researchers were introduced to the lidar technology during their work in NORCOWE (Norwegian Center for Offshore Wind Energy). Inspired by the possibilities this technology offers, they started a pilot project on the optical wind sensing in the Lysefjord, in cooperation with the NPRA.