Harpe Bru – Norway's first extradosed cable-stayed bridge
In the course of the European Route E6 expansion in Norway, the plans include a 320 m long bridge which spans the Gudbrandsdalen Lågen river. For the bridge superstructure, PERI civil engineering technology experts developed a balanced cantilevered solution based on the VARIOKIT Engineering Construction Kit. In particular, the high degree of flexibility with regard to the geometrical adjustments to suit the superstructure cross-section has supported the rapid construction of the individual concreting sections while simultaneously ensuring optimized workloads.
The Norwegian administrative authority responsible for public road building, "Statens vegvesen", selected an extradosed cable-stayed bridge for the bridge construction. Thus, the Harpe Bru is the first bridge with this design technology in Norway. This technology combines the load-bearing behaviour of a cable-stayed bridge with that of a girder bridge whereby the tendons are positioned outside the bridge cross-section. As a result, the overall height of the superstructure as well as the height of the pylons can be kept at relatively low level. The slightly inclined stay cables support the superstructure and simultaneously tension it.
Altogether, the bridge is 320 m long with the largest section of around 100 m positioned over the middle of the river between the two pylons. On land, two additional piers along with the abutments have been arranged.
VARIOKIT cantilevered construction – a convincing case through its flexibility and fast assembly
The Polish subsidiary of the Porr Group was commissioned to undertake the construction of the bridge. This, in turn, developed a very cost-effective balanced cantilever solution for realizing the bridge superstructure in close cooperation with PERI engineers in Poland. The PERI Balanced Cantilever Equipment is based on standard components taken from the VARIOKIT Engineering Construction Kit. These are available in PERI rental parks – and thus all required quantities can be delivered at short notice as well as favourable terms and conditions.
The primary challenges for the implementation of balanced cantilever formwork are the geometric cross-sectional changes of the superstructure and the varying, in part, very high loads. In addition, the cross-section of Harpe Bru superstructure required the realization of transverse ribs between the lateral cantilever of the carriageway slab and the hollow box girders. Furthermore, the engineers had to take into consideration during the planning stage the cables used for the suspension by which the segments are attached to the pylons. At no time during the execution were they allowed to collide with the Balanced Cantilever Carriage. Last but not least, the planning of a balanced cantilever solution automatically involves high static requirements. As a result, constantly changing load conditions lead to varying stresses and deformations – these have to be taken into consideration regarding the dimensional accuracy of the concreting results.
The VARIOKIT solution for the cantilevered construction is a combination of heavy box girders for the load transfer and VARIOKIT standard components for forming formwork, working scaffolds and platforms. Due to the selected steel structure for the longitudinal direction of the PERI Balanced Cantilevered Carriage, up to 5.75 m long segments can be concreted.
For the Harpe Bru, a total of four Balanced Cantilever Carriages are in use with which 5.55 m long segments are constructed. In the process, the bottom slab with the side walls along with the outer ribs of the hollow box girders are concreted first. For this, compact DOMINO Panel Formwork Elements as well as project-specific VARIO GT 24 Formwork Elements have been used. The integrated formwork for the 1.30 m high transverse ribs is also based on the VARIO Girder Wall Formwork; spindling can take place very quickly and easily during striking. In a second concreting section for each segment, the carriageway slab is then concreted.
The PERI formwork solution ensures exact, dimensionally accurate concreting results. The high flexibility of the system facilitates fast adaptation of the formwork to match the geometric requirements. In addition, the independent moving procedure, in particular, results in optimized execution times thanks to the integrated hydraulics together with the fully hydraulically-operable aligning and adjusting. The PERI solution has thereby supported the construction team in keeping the required workloads for each bridge segment as low as possible. This has also had a measurable impact on the construction time.
The fact that the Balanced Cantilever Carriage can be combined with the PERI UP Modular Scaffolding has facilitated the realization of safe work spaces and access to all working areas. With a minimum of effort for the construction team, the scaffold could be connected with the VARIOKIT standard components using simple connecting means to form safe working platforms and access points.
Expansion of the European Route E6 in Norway
The European Route 6 (E6) stretches over 3,140 km from the southern Swedish town of Trelleborg through to Norway, and then runs through almost all of the country to Finnmark. It is therefore an important north-south connection in Norway, connecting the country with the west coast of Sweden. Currently, several projects for the expansion of the European Route are in planning or execution. This includes the route from Ostfold to the Swedish border at Svines being widened to form a four-lane road. In addition, several new bridges have been planned including the Harpe Bru bridge at Sør-Fron in the Oppland province.
Best PERI service
The balanced cantilever solution for the Harpe Bru bridge was developed in a close collaboration and partnership by PERI formwork engineers together with Porr work preparation experts. The comprehensive implementation plans, detailed designs and technical documentation ensure on-site formworking operations can be easily and efficiently carried out. With regard to the technical features of the Balanced Cantilever Carriage, the PERI solution has taken into account the customer's requirements with respect to a minimized workload. Last but not least, especially the high proportion of system components from the VARIOKIT Engineering Construction Kit as well as the high availability of materials in the PERI rental park ensure a high level of cost-effectiveness of the solution.