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| PERI: space for inner-city restructuring  The Swiss are well-known for their tunnel constructions and have enhanced their reputation with the recent Gotthard Tunnel breakthrough which has created the world´s longest tunnel. In the city of Bern, a roundabout is currently being re-positioned almost 10 m under the ground which will transform a somewhat dismal road intersection into an attractive gateway to the country´s capital. PERI provided a comprehensive formwork solution for the realisation of the massive beams, reinforced concrete slab along with the conically-shaped roundabout walls which are to be formed in architectural concrete.Over 65.000 vehicles pass through the junction on a daily basis which is located close to the motorway - an intolerable situation with traffic reduced to a snail´s pace. This results in not only long waiting times for the drivers but also has a negative impact on the environment and badly affects the public transport system. The Wankdorfplatz is therefore being transformed into a two-storey structure – a project from an ideas competition is fast becoming a reality. From 2012 onwards, the underground roundabout with a 50 m diameter will accelerate the flow of traffic and, at the same time, create space for pedestrians and cyclists aboveground as well as greatly improving bus and tram connections. For the pre-stressed beams and reinforced concrete slab as well as for the conically-shaped walls in architectural concrete quality, PERI´s Swiss engineers developed various formwork solutions using mainly rentable system equipment which perfectly matched the requirements of the contractor. The customised wall formwork elements for the curved external walls of the roundabout area were prefabricated by PERI on the basis of the VARIO GT 24 girder wall formwork system. For this project, the radii range from 30 m to 45 m with a wall inclination of 10:1. Particularly advantageous, as it saved both time and money, was the combined use with TRIO panel formwork on the opposite side. For this, the tie points of the VARIO elements were matched to the TRIO tie arrangement. The construction of the 1.80 m wide, pre-stressed beams with varying heights of between 1.15 m and 2.70 m took place on a combined load-bearing and working level which angled upwards to the centre of the roundabout. This was formed using the flexible MULTIFLEX girder slab formwork system with the help of GT 24 lattice girders as very high load-bearing twin main beams and cost-efficient VT 20 cross beams – ideally combined for this application. The MULTIPROP system served as support with towers comprised of MRK frames connected to MULTIPROP aluminium slab props. Thanks to the free-running collar and the integrated measuring tape, these could be easily adjusted to suit the varying heights of between 5 m and 6 m. TRIO panel formwork also found use as the side formwork. By means of the double thickness formlining – screwed on from the rear – excellent concrete surfaces could be achieved. Following this, four slab segments were to be constructed and connected to the crosswise-arranged beams. The extremely tight construction schedule meant that sufficient formwork materials were to be available on site for the complete slab area – in the region of 1,400 m˛. The up to 1.20 m thick reinforced concrete slab runs in a truncated cone-shaped manner with an approximate 3 % gradient on the upper side. In addition, the underside of the slab features five height offsets and a number of different inclinations. In close cooperation with the contractor, PERI created a formwork concept for this which allowed safe and accurate positioning of the required additional special elements. MULTIPROP towers were once again used as shoring. The MULTIFLEX girder slab formwork system formed a level intermediate platform which covered the entire area. In contrast to the beam solution with VT 20 cross girders, the use of GT 24 girders as radially-positioned cross beams proved to be the more cost-effective variant in order to reliably transfer the loads via GT 24 double main beams and MULTIPROP props. From this working level, the construction crew were able to quickly install the pre-fabricated special elements which likewise had been put together in the PERI assembly hall and, in spite of the complicated geometry, achieve an accurately assembled form. The Wankdorfplatz has had to continue in its function as an important and heavily frequented road junction also during the construction period. This has, of course, affected site logistical operations: only limited storage space is available and all deliveries to the construction site must be precisely coordinated. As a result, PERI Switzerland delivered the formwork elements on a just-in-time basis. write your comments about the article :: © 2010 Construction News :: home page |