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In Bangkok, Thailand’s longest cable-stayed bridge is currently under construction – the Southern Bangkok Ring-Road Bridge. The erection of its 164 m tall towers presented a considerable formwork-technology challenge. Using Doka Automatic climbing formwork SKE 50 enabled the complex structure geometry, with its varying cross-sections and angles of inclination, to be tackled efficiently, swiftly and safely.
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The Thai capital Bangkok is on the verge of being swamped by the torrents of traffic that engulf it day by day. More than two million cars and around a million mopeds squeeze their way through the city every day, making private transportation one of the most pressing problems facing this megalopolis of six million people on the Chao Phraya River. In response, the Bangkok city authorities have made huge investments in transport infrastructure in recent years. The Outer Bangkok Ring Road is one of the city’s most important congestion-easing routes, and work is proceeding apace on closing the last gaps in this orbital motorway in southern Bangkok. The centrepiece of this 20 km long stretch of new road is a 941 m long cable-stayed bridge which will be the longest such bridge in Thailand. The cable-stayed bridge is itself only one part of an 8.5 km long bridge structure.
The bearer cables for this 8-lane motorway bridge are hung from two A-shaped, approx. 164 m tall towers between which there is a 500 m cable-stayed main span. To form the complex geometry of the structure members, Ch. Karnchang Public Comp. Ltd. opted for a climbing formwork solution from Doka. Slanting towards one another and tapering as they rise, the pylon legs made some very tough requirements indeed in terms of the flexibility and adaptability of the formwork systems used here – Doka automatic climbing formwork SKE 50 and Climbing formwork MF 240. Because of the fast, safe way in which the climbing formwork units could be adapted to the continually changing cross-section and inclination, an optimised construction workflow was assured. “Thanks to the Doka automatic climbing formwork we were able to form the complex structure geometry quickly and safely, and to make up for the delays we had had at the start of work”, notes Pornnarong Siriyothin, Construction Manager of Ch. Karnchang, summing up his satisfaction with the high efficiency of the SKE automatic climbing formwork. A total of 32 hydraulically operated automatic climbers were in service on each tower. The forming operations on the two towers were carried out in tandem.
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The complex structure geometry, with its continually varying cross-sections and angles of inclination of up to 10 degrees from the vertical, made it necessary to adapt the climbing formwork units after every one of the 43 casting sections. In particular, the fact that the Doka climbing formwork can be modified directly from the working platform made a crucial contribution towards shortening the construction times. In order to be adapted to the varying geometry of the structure, the climbing formwork does not have to be removed from the structure, but can be adjusted to the new cross-section immediately after the formwork has been struck. In this operation, the very maximum in workplace safety is provided by the wide working platforms, enclosed on all sides, by the fact that the climbing scaffolds are anchored in the concrete at all times, and by the automated climbing made possible by the automatic climbers. All these factors also combine to permit safe, fast working even at high wind speeds.
The statically complex construction of the pylon leg beneath the first cross-member was the central challenge for the contractors. To provide stiffening reinforcement, and a bearing surface for the cross-members, the towers were built with a hollow cross-section comprising two shafts. The main shaft measures 2.8 m by 8.44 m, and the second shaft 3.4 m by 4.02 m. At the height of the first cross-member, the twin-cell shaft changes to a single-cell cross-section. The system components needed for casting the small pylon shaft were modified for the middle part of the tower, as dictated by the changed cross-section, and re-used. From the 30th casting section upward, steel boxes with fixing sleeves were also integrated in the pylon legs, for fixing the post-tensioned cables. As it was not possible to place through-ties through the steel boxes, the formwork in this area had to be reinforced, and extra reinforcement anchors placed.
Another formwork-technology challenge was to form a hollow wall between the pylon legs above the second cross-member. This upwards tapering hollow wall was constructed using a combination of Automatic climbing formwork SKE 50 and Climbing formwork MF 240. This enabled the complex geometry to be formed with only a small number of different system components.
Thanks to the flexible way in which several automatic climbers can be combined, the Doka automatic climbing formwork SKE enables construction operations to proceed swiftly and efficiently – even when dealing with tough requirements such as inclined structure members and complicated cross-sections. The system’s numerous advantages – such as its high adaptability to the changing component geometry, and the fact that it allows all necessary modifications to be performed directly from the working platform while providing the very maximum in workplace safety – all kept construction moving ahead smoothly.
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| Doka automatic climbing formwork being used to build the two 164 m towers for Thailand’s longest cable-stayed bridge (941 m long). |
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| The 941 m long cable-stayed bridge is the centrepiece of an 8500 m long bridge structure forming part of Bangkok’s new southern motorway bypass. |
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| This upwards tapering hollow wall was constructed using a combination of Automatic climbing formwork SKE 50 and Climbing formwork MF 240. This enabled the complex geometry to be formed with only a small number of different system components. |
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