| Bømla Bridge | |
|---|---|
| Official name | Bømlabrua |
| Carries | Two lanes of County Road 542 One pedestrian/bicycle path |
| Crosses | Spissøysundet |
| Locale | Stord and Bømlo, Norway |
| Maintained by | Norwegian Public Roads Administration |
| Design | Suspension bridge |
| Total length | 998 m (3,274 ft) |
| Width | 13 m (43 ft) |
| Longest span | 577 m (1,893 ft) |
| Clearance below | 36 m (118 ft) |
| Opened | 30 April 2001 |
| Toll | Yes |
The Bømla Bridge (Norwegian: Bømlabrua) is a suspension bridge which crosses Spissøysundet between the islands of Nautøy in Stord and Spissøy in Bømlo, Norway. The bridge is 998 meters (3,274 ft) long, has a main span of 577 meters (1,893 ft) and a clearance below of 36 meters (118 ft). It carries two lanes of County Road 542 (former National Road 542) and a combined pedestrian and bicycle pathway. It is part of the Triangle Link, a fixed link which connects Stord to Bømlo, and both to the mainland at Sveio. Plans for a crossing arose in the 1960s, and was until the 1990s planned as a pontoon bridge further north. The Bømla Bridge entered the plans after the decision to combine the crossing with the Bømlafjord Tunnel. Construction started in 1999; the bridge cost 342 million Norwegian krone (NOK) and was taken into use on 30 April 2001. The bridge and the link will remain a toll road until 2012 or 2013.
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The background for the Triangle Link was the desire to have a fixed link between the islands of Stord and Bømlo. The first documented proposals were made in the 1960s and involved building a pontoon bridge across Stokksundet, inspired by the plans to build what would become the Nordhordland Bridge north of Bergen. In 1973, the municipal councils of Bømlo, Stord and Fitjar decided to launch a planning process, which concluded that a pontoon bridge between Sørstokken and Foldrøyholmen would be optimal. The report also considered bridges across the Fitjar Archipelago, and across via Spissøy and Føyno. There were protests from the shipping industry, who wanted to continue to use the strait for ship traffic.[1]
In the early 1980s, plans for Stord Airport, Sørstokken were launched, and in 1982 the plans for a bridge crossing Stokksundet were again raised, this time from the industry on Bømlo, who would have to travel by ferry to reach the new airport. In May 1983, a committee was established, giving Engineer Harald Møyner the job to make a new report. He made three proposals: a pontoon or suspension bridge between Foldrøyhomen and Litlaneset; a suspension bridge between Setraneset and Sokkbleikjo, which would terminate just south of the new airport; and a combined fixed link between Spissøy and Digernes, without passing via the Fitjar Archipelago. The latter was the first time a fixed link to the mainland was proposed.[2] The Norwegian Civil Aviation Administration protested against a possible suspension bridge near the airport, but stated that one further away would be fine.[3]
Mapping of transport on Bømlo was performed by Hordaland Public Roads Administration in 1984, and based on this and other feedback, a pontoon bridge between Foldrøyholmen and Sørstokken became the most probable outcome. It was estimated to cost NOK 190 million, in addition to auxiliary roads for NOK 40 million. In 1982, plans were launched for a fixed link to the main land, which would include a bridge over Digernessundet, a causeway and low bridge across Spissøysundet and a low bridge over Gassasundet. In addition, a tunnel would have to be built from Føyno to Sveio.[3] In 1985, an all-tunnel proposal, following the same route, was proposed.[3] Hordaland Public Roads Administration stated that the proposals were unrealistic. The limited company Ytre Sunnhordland Bru- og Tunnelselskap AS (SBT) was founded in Ocotber 1986 by the municipalities of Bømlo, Stord, Fitjar and Sveio, Hordaland County Municipality and five banks.[4]
In December 1986, the Public Road Administration recommended a bridge solution.[5] SBT changed its name to Sunnhordland Bru- og Tunnelselskap, and a majority of the board shifted towards being in favor of a fixed link.[6] The Coastal Administration stated that they would not allow a pontoon bridge.[7] On 26 June 1987, SBT decided to work to get permission to collect advanced tolls on the ferry services.[8] On 16 September, they unanimously supported the triangular proposal, which was estimated to cost NOK 660 million.[9] This was criticized by Hordaland Public Roads Administration, who stated that it would take longer time to plan, and thus complete, the Triangle Link.[10]
From 1988, environmentalists started actively opposing the Triangle Link. The most active were the local chapter of the Norwegian Society for the Conservation of Nature and Nature and Youth, who stated that the road would have serious consequences for the local boat traffic to the recreational islands of Føyno and Nautøy. Instead, they recommended that the municipalities chose a pontoon bridge.[11] Another opponent to the project was the Action Committee Against a Hasty Construction of the Triangle Link, who wanted to delay the decision until after the 1991 municipal elections, to ensure that the municipal councils had backing in the public.[12] Gisle Tjong stated that the risk in the project was large and that it was uncertain how long the tolls would last: they could just as well be 60 as 15 years, and instead wanted to collect tolls in advance.[13]
The Triangle Link was passed by the various municipal councils in February and March 1988.[14][15] Hordaland Public Roads Administration still supported a pontoon bridge, and stated that two and a half years of work on a master plan had been wasted. A new master plan for the Triangle Link was published in early 1989.[16] During late 1989, advance tolls on the ferries was approved by the municipal councils and the county council, who recommended that collection start from 1 July 1990, but this was not immediately supported by the government.[17]
In July 1991, the master plan was passed by the Council of State.[18] On 10 December 1992, Parliament approved advanced payment of tolls on the ferry, which were made effective from 1 January 1993. Ticket prices increased with between NOK 10 and 12. This resulted in protests from the ferry employees who stated that they would have to collect the tolls which would remove their jobs.[19] Work on the development plan started in 1992. It included safety and environmental improvements which increased the project's cost by NOK 200 million.[19] In May 1994, it was made subject to consultative statements.[18] In May, SBT proposed building a culvert on Digernes as a compromise to avoid a new plan which could have postponed the project several years. On 11 June 1996, Parliament decided with 144 against 20 votes to build the Triangel Link.[20] The original name proposal for the bridge was Bømlobrua; this was later changed to Bømlabrua after input from the municipal councils and name committees.[21]
The construction of the Bømla Bridge was done under the same contract as the Stord Brige, which in December 1998 was awarded to Triangle Contractors, a joint venture between NCC and HBG Steel Structures. Most of the work was performed 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 (HMV).[22] Construction started on 25 March 1999. After the pylons were completed on 20 December 1999,[23] two catwalks were erected between them, with the constructors choosing a continual catwalk instead of three separate ones. Extra stability to the catwalk was achieved by building connections between the two.[22]
The cables were spun on-site using a reel, based on the problems which had arisen using a bundle on the Great Belt Bridge. This also allowed for cost savings, as the reels could be used two times. The cables were spun using the air spinning with controlled tension, which allowed spinning with little place and with a crew with limited experience with spinning.[24] This involved installing a cable car and connecting two double loops with a spinning wheel each, with one loop doing the outward spinning the other the inward spinning. The system has two reel racks, each with four reels, with two reels on one rack at any given 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 counter-weight tower.[25] Spinning of the main cable started on 24 May 2000 and was concluded on 13 July.[23] In all 11,600 kilometers (7,200 mi) of steel wire were used to create the cables for both bridges. It was the first time that on-site spinning was chosen in Norway, and it gave a cost saving of NOK 10 to 11 million.[26]
The cables consist of seven bundles of cables, each consisting 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.[25] 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 helicoper, 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.[27]
The deck sections were produced by HBG in Cimolais, Italy, and transported first by truck from the plant to the port, and then by Barge to Stord. Each section is 48 meters (157 ft) long and consisted of subsections 6 by 12 meters (20 by 39 ft) to allow for transport to the port.[28] They were mounted using the crane ship Uglen, allowing an average of four sections to be installed per day.[29] and completed in September 2000.[30] Construction took 550,000 man-hours and cost NOK 342 million. The bridge was taken into use on 30 April 2001, after the E39-section of the Triangle Link had opened on 27 December 2000.[26] The bridge allowed two ferry services to terminate.[23]
The Stord Bridge is a 998 meters (3,274 ft) long suspension bridge with a 577 meters (1,893 ft) long main span. It carries two lanes of County Road 542 (former National Road 542) and a combined pedestrian and bicycle path across Spissøysundet, connecting the islands of Nautøy and Spissøy. The bridge has a width of 13 meters (43 ft) and a clearance below of 36 meters (118 ft). It has two concrete pylons, each 105 meters (344 ft) tall,[26] one on Brumsholmen on Stord, the other on a on the extreme east of Spissøy in Bømlo.[30] The pylons consist of 2,780 cubic meters (98,000 cu ft) of concrete and 830 tonnes (820 long tons; 910 short tons) of steel.[23] The deck between the towers consists pre-built steel sections, each 48 meters (157 ft) long and 2.5 meters (8 ft 2 in) tall. They are connected to the main suspended cable, which is 360 millimeters (14 in) thick,[31] and 944 meters (3,097 ft) and weighs 860 tonnes (850 long tons; 950 short tons),[23] by vertical cables every 12 meters (39 ft). The bridge's vertical curvature has a radius of 5,206 meters (17,080 ft). The bridge weighs 2,168 tonnes (2,134 long tons; 2,390 short tons).[31] In 2010, the bridge had an average 2,506 vehicles per day.[32]It is estimated that the bridge will be paid off and the tolls removed in 2012 or 2013.[33]
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