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| PERI: construction time shortened and high quality ensured  Currently, a new bridge is being constructed for the crossing of the Vistula River. For the foreland bridge from south-east direction, a so called incremental launching method is being used. The prefabrication of the individual repetitive bridge sections is being carried out with a stationary formwork. A temporary protection roof on the basis of the PERI UP modular scaffold spans the working area and allows weather-independent construction of the individual sections for the superstructure. This is one of the factors that contributed to the fact, that the Skanska-NDI Joint Venture has been able to shorten the construction period by three months. Thanks to the rental concept for the weather protection roof, this solution is also particularly cost-effective.Two lanes, each around 556 m long, are being constructed in 25 concreting cycles with standard lengths of 24 m. The formwork has a length of 25 m and is positioned behind the bridge abutments. The individual sections of the superstructure are concreted directly together here and connected by means of tensioning cables. Subsequently, the hardened bridge section is raised a few millimetres and moved forward together with the other finished segments by one cycle length in the direction of the bridge´s longitudinal axis. For the concreting work of the hollow box profile, a construction time of altogether twelve months was originally planned. As work started in November 2009, minimum temperatures of up to minus 25°C were expected during the winter. In order to provide protection against the effects of all types of weather, and especially the extremely low temperatures in winter, the contractor planned the erection of a temporary protection roof for the construction phase. The technical concept of PERI easily convinced the construction company. In addition, the possibility of renting the LGS protection roof for the period of use provided an economical solution. Altogether, the jobsite team is using four roof structures: two smaller, permanently installed tents are used for reinforcement work preparations; two movable protection roofs on basis of the LGS lattice girder system span the formwork and concreting areas. In order to ensure unhindered material and concrete installation, the design allows the protection roofs to be moved. The girder supports are also equipped with rails and extend over a length of 55.50 m – they are therefore more than twice as long as the protection roofs. The wheel facilitates the moving of the roofs in a longitudinal direction. At the level of the girder, the static system of a single-span beam with one stationary and one movable support can be realized without any problems by means of system components. The spatial arrangement of the two sets of incremental launching equipment gave the position of the weather protection roofs – the available space between the formwork for both lanes was very limited. Load transfer of the support construction of both weather protection roofs had to be guaranteed via a common central support. A challenge for the planning – as the high loads can cause large deflections to the construction which could make moving the roofs on the rails difficult. It therefore meant ensuring that resulting loads and deformations were to be accurately calculated during the planning phase and to be taken into consideration in the execution. The wind loads could be transferred through serial components. In order to secure the protection roofs against lifting, the support plates were provided with ballast and, in part, anchored in the bottom slab. With Keder track and sheeting, the scaffold constructions result in very light and translucent roofs. The solution in Grudziądz also includes a side and gable covering. Overlapping of the sheeting at all joints ensures a tightly-fitting enclosure which at the same time can easily be opened. With extremely low outside temperatures, the temporary tents were also heated. Thanks to this protective roof construction, the building site team have been able to continue all working operations without any stoppages – in spite of the very low outside temperatures during the past winter. This has resulted in enormous time savings. An additional positive effect of the enclosure is the consistently high concrete quality achieved throughout due to the constantly good setting process. The improved working conditions for site personnel are an important factor here, too. For reinforcement installation and concreting work, the LGS protective roofs are moved into position over the reinforcement tents. A problem free operation due to the smooth running wheels from the PERI UP standard product programme. Despite the high loads and complex boundary conditions, a protective roof is easily moved by two to four persons - without the need of any additional equipment. This fact confirms the high degree of stability and dimensional accuracy of the scaffold construction. In addition to the technical solution, the contractor also considers the rental concept and constructive co-operation with PERI to be very positive. The sum of all points leads to an extremely cost-effective solution which has contributed to the success of the project. write your comments about the article :: © 2010 Construction News :: home page |