The current expansion of the Krakow metropolitan railway network (KST) requires, among other things, crossing of the Krakow-Plaszow railway junction. Ensuring that daily rail operations remained unaffected during the construction of the 252 m long crossing was a prerequisite which meant the general contractor decided in favour of the cantilevered construction method for realizing the extradosed bridge with its hollow box cross-section. In addition, the compatibility with the PERI UP modular scaffolding provided safe working platforms and access means to all working areas.
Through the customized solution devised by PERI engineers, the construction team have been able to realize each 5.70 m long concreting section using 4 VARIOKIT cantilevered construction carriages. Thanks to the high degree of flexibility and easy alignment of the system, complicated pre-tensioning sequences have been implemented in the longitudinal and transverse directions of the viaduct. Among other things, the tendons as well as the anchorage points of the stay cables outside of the box girders had to be taken into account. Furthermore, carrying out construction work during daily train operations along with the allocated downtimes has complicated the ongoing completion of the cantilever above the tracks. Nevertheless, the respective segments can be constructed without any interruptions in 2-week cycles.
After closing the respective gap of the bridge span, the PERI VBC balanced cantilevered carriage automatically returns to its starting position although cable stays are positioned along the structural axis. As a result, dismantling the equipment is always efficient and safe.
PERI Poland took on the customized project planning and static calculations of the comprehensive solutions for the superstructure on PERI UP falsework as well as the cantilevered construction. All systems and processes were therefore optimally matched and allowed on-time completion according to plan. Through the close cooperation between the general contractor, planners and PERI engineers, the shape of the reinforcing ribs along the bridge superstructure, among other things, could be optimized during the planning phase in order to accelerate the execution times. The biggest challenge when realizing the formwork planning proved to be dealing with the significantly asymmetric shape of the superstructure cross-section as well as its varying width along the structural axis.
Fast implementation has been ensured by the provision of extensive technical documentation while a valuable contribution was made through the detailed preparation work on the basis of the very latest 3D formwork planning. This detailed visualization guaranteed cost-effective and efficient on-site forming operations. The construction team has been provided with support throughout the project which has also accelerated the building processes.
The compatibility of the cantilevered construction carriage with the PERI UP modular scaffolding has allowed, as part of the comprehensive PERI project solution, the creation of safe working areas. With a minimum of effort for the construction team, the scaffold could be connected to the VARIOKIT standard components by means of easy-to-use connecting devices in order to provide safe working platforms and access.
The PERI VARIOKIT solution for cantilevered construction is a combination of load-bearing frames consisting of hollow steel profiles for transferring loads and VARIOKIT standard components for the creation of formwork, working scaffolds and platforms as well as adapting the construction to match the geometry of the cross-section. The cantilever construction equipment transfers the fresh concrete load into the previously completed structure section and moves the formwork from section to section. In order to deal with the changes in the hollow box cross-section, a formwork solution consisting of VARIO girder wall formwork has been used.
With optimized components of the cantilevered construction carriage, up to 5.75 m long segments can be concreted. In addition, VARIOKIT system components are used. As a result, PERI achieves maximum adaptability for different bridge cross-sections.
In addition, the moving procedure to the next concreting section has an extremely practical focus. Thanks to the mechanical solution, all manual work required can be completed very quickly. The integrated, centrally-controlled mechanism with hydraulic cylinders as well as lifting and powering devices for moving, lowering and raising the carriage and formwork guarantees easy handling of the balanced cantilever equipment. The hydraulics also simplify the adjustment and levelling of the formwork from section to section.
All cantilevered construction carriage modules can be used again in future projects. In addition, virtually all the components are available from the PERI rental park. This not only ensures fast availability of all parts but it also increases the cost-effectiveness of the solutions for the construction company.