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Two climbing systems optimally and safely combined
Lekki Ikoyi Bridge, Lagos, Nigeria
The striking, 90 m high pylon characterises the appearance of the 1357 m long Lekki Ikoyi Bridge. As the first cable-stayed bridge in Nigeria, it will connect two districts of the West African megacity, Lekki on Victoria Island and Ikoyi on Lagos Island, when it is completed at the end of 2012. The 722 m long approach bridge is supported on 37 piers and is being constructed using the so-called Full Span Launching Method with complete precast bridge sections. The 635 m long main bridge is realised using the segmental construction method and is suspended along a length of 225 m on a centrally-arranged individual pylon by means of stay cables.
Complex pylon geometry
Due to its special shape, the pylon has a markedly filigree appearance. Up to a height of 50 m it is A-shaped, then the pylon legs changes to the form of a fillet and, because of this, are inclined to the outside at the top. The legs are also not touching in the area of the cable anchorage but are subsequently connected with each other by means of crossbeams. In addition, the external dimensions of the shaft hollow sections continuously taper from 6.40 m x 4.80 m at the base to 4.10 m x 2.40 m at the narrowest point - in order to create a 3.00 m widening on the front side at the upper end. The top of the pylon head is constructed with prefabricated components.
The combined use of two PERI self-climbing formwork systems proved to be the ideal solution for forming the pylon. For the longitudinal surfaces with the forward and reverse inclinations, as well as the fillet with a continuously changing angle of inclination, the RCS rail climbing system (RCS = Rail Climbing System) provides the optimal basis. The internal formwork of the hollow cross-section climbs with help of the RCS on rails.
The RCS modular design allows the standard solution to be easily adapted to suit site-specific requirements. Thus, there is an articulated connection between the top and bottom climbing rails. As a result, the fillet section can also be climbed over at only a 77 m radius in generously-dimensioned sections with 3.60 m concreting cycle heights - without requiring any modification work to be carried out on the formwork and working platform. The one-off inclination correction was realised by means of adjustable spindles. With the help of mobile climbing hydraulics, moving to the next respective concreting section takes place without a crane.
The ACS self-climbing technology (ACS = Automatic Climbing System), however, has accelerated moving operations on the front sides. Even with the inclined surfaces with angles of up to 14 degrees, and along with likewise arranged climbing rails, the stable ACS system ensures that the high loads can be reliably carried. The two climbing technologies, optimally adapted to suit the respective construction tasks, have provided the site personnel with efficient and safe working procedures.
Access technology included
An important element of the PERI overall solution is the integration of the most appropriate access technology. For this project, the connecting bridge between the climbing platforms of the two pylon shafts in particular was the contributing factor. The so-called skywalk is joined to the inner platforms by means of an articulated connection. As a result, the bridge is climbed automatically and does not have to be separately pulled up on chain hoists and re-adjusted from cycle to cycle.
Ultimately, the connection of the elevator to the RCS working platform was also included in the concept developed by the PERI engineers. Safe access to the respective lower working scaffold level is provided by a telescopic platform. This compensates for the different spacings and inclinations found at each height - an important aspect for achieving the required high level of safety.
Julius Berger Nigeria PLC
Julius Berger International GmbH, Wiesbaden
PERI Frankfurt (Export Division Nigeria) and PERI Weissenhorn, Germany
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