Stord Bridge - Construction

Construction

The construction of the Stord Bridge was undertaken as part of the same contract as the Bømla Bridge, which was awarded in December 1998 to Triangle Contractors, a joint venture between NCC and HBG Steel Structures. Most of the work was carried out by NCC with HBG having responsibility for the steel parts of the deck and the cables. HBG had previously built the steel for the Osterøy Bridge, which opened in 1997. The responsibility for the cables was given to Brown Beach Associates and Hordaland Mekaniske Verksted. Construction started on 20 February 1999. After the pylons were completed on 25 September 1999, two catwalks were erected between them, with the constructors choosing two continuous catwalks instead of three separate pairs. Extra stability to the catwalks was achieved by building connections between the two.

The cables were spun on-site using a reel because of the problems which had arisen using a bundle on the Great Belt Bridge in Denmark. This also allowed for cost savings, as the reels could be used two times. The cables were spun using air spinning with controlled tension, which allowed spinning with little space and with a crew with limited spinning experience. This involved installing a carrier which shuttles forward and back over the catwalk; it spins the upper side of the cable in the one direction and the lower side in the other direction. The system has two reel racks, each with four reels of wire. Each rack only uses one reel at a time, allowing for minimum down-time when changing reels. Wires were connected using pressure casing. The balance in the system is kept in place using a counterbalance tower. Spinning of the main cable started on 2 March 2000 and was concluded on 14 April. In all 11,600 kilometers (7,200 mi) of steel wire were used to create the cables. The two bridges were the first time that on-site spinning was chosen in Norway, and it gave a cost saving of NOK 10 to 11 million.

The cables consist of seven bundles which consist of 420 wires—each with a diameter of 5.35 millimeters (0.211 in). When compressed, this gives a diameter of 320 millimeters (13 in) and a quality of 1,570 megapascals. The fastening poles were delivered five weeks after schedule; a new mounting method was developed which allowed them to be installed in a quarter of the time, in part by using a helicopter, and the whole five-week delay was eradicated. This allowed the deck sections to be installed as scheduled. There arose problems with small holes being created in the coating; as these had also been found on the Great Belt Bridge, it was decided that nothing would be done with the issue.

The deck sections were produced by HBG in Schiedam, Netherlands, and transported by Barge to Stord. Each section is 36 meters (118 ft) long and consisted of two welded subsections. They were mounted using the crane ship Uglen, allowing up to nine and an average of four sections to be installed per day and completed in June 2000. The section of the bridge built as a beam bridge on the Føyno side was built by filling in the shallow fjord under the bridge with earthwork, building the bridge and then removing the earthwork again. Construction took 700,000 man-hours and cost NOK 442 million. The bridge was taken into use along with the Bømlafjord Tunnel on 27 December 2000. The bridge allowed, along with the rest of the Triangle Link, four ferry services to terminate.