On its own, the bridge represents US$51 million of the total investment and is actually two parallel, reinforced concrete structures 18.9m apart. Superstructure comprises three 110m long spans and a 55m span at each end. Four pairs of reinforced concrete piers with sliding bearings providing protection against expansion and contraction and earthquake movement support the superstructure. At the top of each prestressed concrete box girder is a 12.6m wide deck for two lanes of traffic. Clearance beneath the bridge will vary from approximately 69m to 80m, depending on the water level.

Main contractor Dong Bu started work on the project at the end of 1995. The scope of the foundation work included installation of 24, 1.5m diameter RCD piles to depths of 12m below the riverbed for each of the eight tallest piers. The 21m diameter by 17m high reinforced concrete cap for each set of piles was precast on shore and towed into position by boat.

Piles of the same diameter, but measuring 15m long, have also been used for the pier and abutment foundations on the north bank of the river. Steep gradients on the south bank, however, prevented the use of large piling equipment. Instead, Dong Bu installed 200mm diameter by 20m long micropiles.

The hollow piers taper from a cross section of 10m or 11m by 3.5m at the base to 7m by 3.5m at the top, with heights ranging from approximately 58m to 80m. To build the eight pairs of piers, Dong Bu is using two sets of Doka self-climbing formwork, made up of Doka's SKE50 automatic climbers and MF240 modular formwork panels. This allows the company to work simultaneously on two adjacent piers.

Each set has 17 climbers, providing a total load capacity of 85t. Overall dimensions vary from pier to pier, but the formwork climbs at regular intervals of 3.85m, apart from the initial section, where the pour height is adjusted according to the height of the pier. Adjustable end plates accommodate the changing profile.

After each pour, the formwork panels are retracted, and the climbing rod is hydraulically pushed upward and anchored in the next section. The climbing scaffold and formwork is then pulled up along the climbing rod and fixed in the new position. It takes two days to dismantle and re-erect the formwork for each pair of piers, followed by one day to install the rebar and one day to pour the 400kg/cm2 concrete from a 3m3 bucket attached to a tower crane.

During the project, four tower cranes, one serving each two pairs of piers, will help pour about 57,000m3 of concrete, place 15000t of 16-25mm diameter rebar and transport all the formwork.

Dong Bu is also relying on Doka formwork for the prestressed concrete box girder, which is being built in 4.75m long by 2.5m to 6m high hollow sections using the free cantilever method. Here the formwork is attached to a traveller, designed and manufactured by Doka's Korean representative company Kumkang Doka. Starting from the piers closest to the abutments, the traveller is bolted to a 13m section of the box girder, which is formed on the top of the first pair of piers.

A pump then places concrete for the next section. Once this has cured, the frame, carrier and formwork are launched forward by a hydraulic mechanism, and secured to the new section. The process continues in both directions until the girder has reached either the abutment or mid-span. The traveller is then moved to the next pier. Typical cycle time for the superstructure is 15 days.

High winds and water levels, fog and extremes of temperature are among the hazards facing Dong Bu. There are also environmental considerations, since the Namhan River is the main feed for Chungju Lake, a man-made reservoir that supplies drinking water for the region. Government inspectors and environmental groups carefully monitor the water quality around the site and further downstream.

Fortunately, none of this has affected the performance of the Doka formwork. However, the economic climate has had a big impact on the project. Temporary freezing of funds during the Asian financial crisis has put back the completion date by 12 months to the end of 2001.

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Eight cycles per week for Boemla Bridge builders

In a remote part of Norway, the number eight illuminated in light bulbs at the top of a 100m bridge tower can be seen for miles. It is the pride and joy of Norwegian contractor AS Beton which is building this structure as part of the Stord Triangle project some 70km south of Bergen. The number stands for eight climbing cycles - four on each leg of a twin tower in just five days.

This cycle time was accomplished by workers using the new SCF self-climbing formwork from Thyssen Hunnebeck. An average of 787m2 of shuttered and stripped surface was achieved per week.

The Boemla Bridge forms part of the new Triangle link to the island of Stord which started construction in summer last year. The scheme as a whole involves building two new bridges and a tunnel to replace the four ferries that currently provide the only link to the island. The scale of investment is quite considerable; the entire project will cost some US$260 million and will improve communications not only for the handful of island dwellers - around 40,000 - but also for local industries of mineral oil and shipbuilding.

This part of the link is a 990m long suspension bridge with a 44m clearance above the sea. Work on the two H-shaped towers was started in June last year by AS Beton. One tower stands on the shores of the North Sea while the other is founded on a small rocky island 100m from the mainland. Each set of towers measures 5.6m by 4.8m and will have a maximum height of 102m above sea level. When finished, the bridge will include 10,000m3 of concrete and 2000t of reinforcing steel.

During shuttering work with the Thyssen Hunnebeck SCF, the contractor used a new formwork concept. This involved fastening self-climbing platforms on only two sides of the tower and suspending the other sides crab-like from the projecting steel girders of the two climbing platforms. "This innovation makes AS Beton that decisive bit quicker," explains Armin Bochen, head of the special formwork construction and construction methods department at Thyssen Hunnebeck. Initial assembly, shuttering and concreting was accomplished in four days, thus enabling stripping to be carried out on the fifth. This was followed by the first climbing cycle, propelling the formwork upwards. To complete each tower will require 48 lifts of this kind, each 4.09m height - a total of 96 concreting stages.

The SCF Self-Climbing Formwork was just what AS Beton was looking for - a quick, cost-effective solution to enable competitive tendering while still offering a high degree of safety. At this location the formwork must be extremely stable, especially when working at heights of over 100m, and every square metre of working space is appreciated. The 77m2 working platform provides a previously unavailable degree of rigidity and safety during the climbing process, claims Thyssen Hunnebeck.

In this respect the manufacturer believes that the SCF beats all the self-climbing systems on the market. AS Beton project manager Stig Giesdal says: "The extra working space yields not only a greater feeling of safety, but also more room in which to manoeuvre during work, and this in turn increases productivity.

The platform is designed for a traffic load of 600kg per m2 which means that there is plenty in reserve at all times. After five months' work with the SCF, Giesdal is suitably satisfied, as the work is right on schedule. In the early stages, up to the tenth lift at a height of about 45m, the form ran unevenly due to the geometry of the towers. One side tilted back while the other three sides were curved. This affected the position of the SCF climbing shoes. In addition, the contractor had to alter the pitch for Thyssen Hunnebeck's R24 formwork on each lift.

Above this height, however, the system exceeded expectations and the changes in cross section were easily negotiated. The rounded corners were shaped with special formwork. The gap between the two tower legs is 16m at the base and tapers to only 8.2m towards the top. At a height of 26.5m, a 14m long by 6m high cross beam of reinforced concrete joins the two legs. Above the height of 45m, the cross section of the tower legs stays the same. The bridge towers are then finally joined by a compact bar of concrete at a height of 96m.

The inner and outer formwork were precisely adapted to one another for AS Beton. Whilst the inner formwork is raised by crane, the outer formwork is propelled upwards by the self-climbing platforms. The structure consists of the reinforcing level, a main working level and two trailing platforms. After stripping, the climbing shoes are shifted. The entire structure then ascends hydraulically on climbing rails.

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All-weather climbing aids Storda Bridge progress

Once complete, the Storda Bridge will be Norway's second longest suspension bridge with a total length of 1076m. The structure is being built as part of the Triangle project to link three islands in the Hardanger Fjord not far from Bergen. The scheme also involves construction of a shorter bridge and a tunnel. Two towers, 86.5m and 91.5m high support the suspension bridge; these concrete structures had to be shuttered 667m apart.

Contractor NCC Eeg-Henriksen awarded the formwork planning and supply contract to German specialist Peri. The Norwegian contractor had already achieved accuracy at remarkable speed, high quality concrete finishes and a high degree of safety with the Peri ACS Automatic Climbing System when building the 114m high pylons of the Kvisti Bridge which links the Island of Osreroy to the Norwegian mainland.

Peri's Automatic Climbing System was first used ten years ago on Frankfurt's BGF building. It allows all-weather climbing without reliance on a crane. Work can continue even at high wind speeds and great heights, since the units always remain firmly connected to the structure, says Peri. The very flexible climbing bracket arrangement easily accommodates structural details.

The pylons of the Storda Bridge consist of double box piers with 500mm thick walls. The piers taper in height on the outside longitudinal face, whereas the opposite face runs straight up at a constant inclination of just over 2degrees to the vertical. The end faces of the structure have a uniform taper from an initial width of 5.6m to 3.5m at a height of 42.2m after which they remain constant.

The outside formwork - Peri Vario girder wall formwork - was erected on four automatic climbing units, each with two brackets. These were adjusted to suit the tapering pier sections by cutting back the formwork panels for successive lifts. Four work levels; concreting platform, shuttering and striking level, platform for hydraulics and control system, and finishing platform for removing the climbing hinges and anchor cones, ensured that personnel could carry out all operations safely and at any time. All of the levels could be raised together hydraulically from one cycle to the next. The climbing mechanism's generous stroke of 0.5m/min lent smoothness and speed to the operation.

The inside formwork was supported on the inside platform fitted with gravity pivot plates. On the two end faces of the piers it was possible to cut the two-part Vario panels back to suit the tapering geometry from cycle one to eleven. The Vario panels on the longitudinal face only had to be adjusted on one side over the eleven lifts.

Peri engineers developed a bridge to connect together the formwork units on the pylon bases, and this proved to be particularly cost-effective and safe for the site. This solution saved the contractor having to stock a complete passenger lift and allowed the gang to switch from one side of the pylon to the other in safety. The bridge's electric chain block makes it easy to level, even when climbing has progressed further on one side of the tower than the other.

Using the crane-independent ACS system in conjunction with Vario girder wall formwork, Peri came up with a formwork concept that allowed for fast construction. Daily concreting allowed six lifts with a standard height of 4.07m to be completed each and every week.

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