Large-spanned trusses with high load-bearing capacity and low deadweight

The building of the Mur Bridge near Frohnleiten is the centrepiece of the S 35 motorway modernization project between the Bruck/Mur and Graz intersections. After completion at the end of 2015, the new structure will completely replace the existing 60-year-old bridge which runs alongside.

Including the foreshore areas, the total length of all 11 spans is 406 m. The pre-stressed concrete superstructure has been designed as a 11.75 m wide T-beam cross-section complete with 2.50 m web heights. In spite of every respective 40 m spans of the two main bridge sections over the Mur, the construction of the superstructure on heavy-duty falsework by means of framework units is the most cost-effective solution.

Premiere in Austria

Xervon Austria GmbH, which has been commissioned by the Strabag/Habau consortium for carrying out the shoring operations, is using here the new VARIOKIT heavy-duty truss girder from PERI – for the first time in Austria. A German-Austrian team of PERI engineers designed a customised project solution on the basis of standardized, rentable system components from the VARIOKIT engineering construction kit. As a result, the truss arrangement and spacings can be flexibly determined in accordance with static requirements – the truss spacings in Frohnleiten are 50 cm and 150 cm.

In addition to the benefits of the project-specific planning and verifiable static calculations, the rapid availability of materials along with the briefing of the scaffold team on-site by a PERI supervisor ensured short assembly times from the beginning onwards. Despite the difficult conditions – the assembly and storage areas were extremely limited – this still allowed the construction schedule to be maintained. Furthermore, the lifting of the over 37 m long coupled trusses by means of a mobile crane parallel to the existing bridge required maximum concentration and perfectly coordinated working steps. A big advantage here was the low weight of the VARIOKIT truss which resulted in time and cost savings especially during the lifting procedure.

VARIOKIT heavy-duty truss

The modular VARIOKIT framework unit system can be used for spans of up to 40 m and is characterized by a very high load-bearing capacity – the permissible load of a truss can be up to 2.5 t per linear metre according to the respective type calculations for a 30 m span. Through the combination of perfectly matched frame lengths and the compensatory function of the support frame, all spans have been realised inch perfect without any gaps as well as compensating for the assembly tolerances of the supporting structure. In addition, the calotte bearing allows easy and simple adaptation to suit the respective longitudinal and transverse inclinations of the superstructure. Standard connections are provided by bolts and cotter pins whilst site-compliant alignment and lateral bracing has been carried out using DW 15/20 tie rods.

With the introduction of the VARIOKIT heavy-duty truss, PERI has once again significantly expanded its product portfolio in the field of civil engineering. During the development phase, PERI engineers took into consideration – as was the case with the VARIOKIT heavy-duty shoring tower – all the requirements of day-to-day activities on the construction site regarding heavy-duty shoring operations. The truss was impressively presented to industry professionals at bauma 2013 in Munich in the PERI exhibition hall.

VARIOKIT engineering construction kit

With standardized, rentable system components and site-compliant connecting means of the VARIOKIT engineering construction kit, bridge and tunnel projects can be cost-effectively realised and optimally adapted to suit the respective construction site requirements. In addition, the modular concept allows customised, load-optimized truss solutions to be developed for virtually every geometry.