The New VARIOKIT Cantilevered Construction Kit:
Through some additional, newly developed system components, the VARIOKIT engineering construction kit can now be also used for the balanced cantilever construction method. For the realization of a new bridge near the town of Tarnow in Poland, the new cantilevered construction equipment was used for the very first time. Thanks to the easy-to-use mechanical solution, the jobsite team achieved 4 to 5 day cycles for the up to 5 m long concrete sections. At the same time, meeting the high requirements concerning the very small tolerances for the variable bridge cross-sections could be comfortably met. The compatibility with the PERI UP modular scaffold furthermore ensured safe working platforms and access to all working areas.
Near Tarnow – about 80 km to the east of Krakow – a highway bridge with an overall length of 600 m is being constructed. Twelve pairs of piers support the two lanes of traffic, each of which is 13 m wide. Falsework carried the formwork for the hollow box superstructure of the foreland bridges – consisting of girder wall formwork elements together with the proven, high loadbearing GT 24 lattice girders. Depending on the support height and load, different PERI shoring solutions were used including ST 100 stacking towers as well as shoring towers on the basis of frameconnected MULTIPROP slab props.
The 210 m long section between the seventh and the tenth piers was realized in 48 casting segments using the balanced cantilevered method. For this, building contractors Dragados used four cantilever construction units based on the VARIOKIT engineering construction kit. This equipment carries the fresh concrete loads into the supporting structure and moves the formwork from section to section. In order to handle the cross-section variations of the hollow box cross-sections, a formwork solution comprised of girder wall formwork was used.
The aim of the development was to expand the application range of the proven VARIOKIT engineering construction kit with as few additional system components as possible. These new system components for the longitudinal direction of the cantilevering construction were optimized for 5 m long concreting sections; this length corresponds to current project requirements in general. In the transverse direction, the maxim was to use the existing system components of the engineering construction kit whilst simultaneously allowing maximum adaptability for a wide range of different bridge sections. The result: cantilevered construction equipment with a high degree of flexibility for the forming of the bridge crosssections that is also simple to use. In particular, the moving procedure to the next concreting section is extremely user-friendly as this is possible to carry out with very little additional manual work thanks to a newly-developed mechanism.
Apart from the ease of use, safety was very much the focus during the development. The compatibility achieved with the PERI UP modular scaffold ensured the provision of safe working areas with a minimum of effort for the construction team as the scaffolding can be connected to the VARIOKIT components by means of simple connection parts.
One particular advantage of this new type of cantilevered construction solution is that all the components can be reused in future projects without requiring any further modifications – most of these can even be used for the realization of other types of civil engineering structures (e.g. tunnels). As a result, the VARIOKIT engineer construction kit has a particularly broad field of applications with only a minimum of standard system components. In addition, nearly all components are available in PERI rental park stocks. This not only ensures fast availability of all components but it also increases the cost-effectiveness of the solutions for the construction company.
A total of four cantilevered construction units were used for the building of the bridge superstructure near Tarnow; the construction of the superstructure moved forward symmetrically in both directions from the starting point of two piers in each case. 3.50 m to 5.00 m long sections were concreted alternatively until the gap was finally closed.
The single-cell hollow box cross-section of the superstructure varies in height from around 2.50 m up to 6.10 m although the width remains constant throughout. The result is a continuous change in the angle between the outer side of the web and the cantilevers which meant the formwork had to be therefore readjusted for each concreting section. Regarding this standard requirement for bridge constructions, PERI has developed a simple and practical solution: a formable steel sheet connects the two girder formwork elements with the result that the angle between the web and carriageway formwork can be constantly changed by means of spindles. Following the change in the cross-section, the slab formwork of the web is fixed at its respective height whilst the element of external web formwork remains unchanged. With this construction, the required low dimensional tolerances for the bridge cross-section could be met without any problems.
The jobsite team achieved the best possible results for the entire span with this solution and each individual segment could be realized on a customized basis.
Furthermore, the crane-independent moving procedure was also optimized in terms of workload: after only a few simple steps, the frame could be moved forward to the next section through the use of hydraulic presses. For this process, the construction team needed only 2 hours on site. After the respective gap closure between two piers, the cantilevered construction units were moved back to the starting point on the pier head where they were dismantled.
PERI took on the responsibility for the customised planning and static calculations of the complete solutions for the falsework-supported superstructure as well as the cantilevered construction. As a result, all systems and processes were therefore optimally matched. The solution also included technical documentation along with providing constant back-office support for the construction team throughout the project. In addition, the on-site presence of the PERI supervisor accelerated building progress.
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