Project Description

With a total length of 182 m, the Aare Footbridge is the longest stressed ribbon bridge in Switzerland. The ultra slender four-span bridge was built for local pedestrian and cycle traffic access to the new Mülimatt sports training centre, south of the River Aare in the municipalities of Brugg and Windisch in Northern Switzerland, plus to connect these facilities with car parking and the existing Au Stadium to the north.

 

This unusual design is really a simple suspension structure, stressed from abutment to abutment in a cantenary arc and more or less similar to a tightrope. The steel suspension cables or tendons are located within the 20 cm thick concrete deck, and these were progressively post-tensioned as the structure was built. In this design the concrete is effectively stressed in compression, which acts to stiffen the structure and prevent swaying movement. Substantial abutments were required because the structure is subject almost entirely too longitudinal forces, but its lightweight design allowed for large spans with relatively low materials consumption. The slenderness of this bridge design therefore has a low visual impact in this natural setting and blends very discreetly into the environment.

Project Requirements

High specifications were demanded for the concrete due to this special design, particularly since the main carriageway slab with a concrete volume of 100 m3 was to be installed within just two hours in a single operation. Three concrete pumps and two cranes were made available to ensure continuous concrete placement was assured. Preliminary tests by Sika Technical Services Department were used to define the specific high performance concrete requirements, with strict shrinkage limits and strength levels required.

 

The concrete deck surface also required the application of a crackbridging waterproofing system to protect the embedded steel reinforcement and prestressing cables; this also had to provide slip and skid resistance to safely accommodate the slopes of up to 6%.

 

Additional protection against water ingress was specified to be applied on the rest of the exposed concrete surfaces.

Sika Solutions

The combination of a Sika® ViscoCrete®-3082 ultra-superplasticiser and Sika® Control-40 shrinkage reducer ensured that the water/cement ratio could be limited to 0.42, whilst still maintaining the ideal consistency for placement in the deck; with the shrinkage after 28 days limited to only 0.22 ‰.

 

Sikafloor®-161/350 Elastic, a polyurethane resin based deck coating system, was then applied as a highly mechanically resistant and crack-bridging wearing surface; with increased slip and skid resistance for the sloping concrete carriageway surfaces, being obtained by broadcasting with selected granular aggregates.

 

The parapet edges and other exposed concrete surfaces of the bridge were given additional protection by the application of Sikagard®-706 Thixo, a colourless, hydrophobic water repellent impregnation.

 

The new footbridge and the Mülimatt sports training centre were opened to the public in autumn 2010. The Aare bridge now gives sports enthusiasts, residents and visitors to the region, an attractive link route which blends beautifully into the natural river landscape.

Sika Products

In addition the following Sika products were used in the project

  • Sika® ViscoCrete®-3082
  • Sika® Control-40
  • Fro-V10
  • Sika® Retarder
  • Sikafloor®-161/350 Elastic/359
  • Sikagard®-706 Thixo

Project Participants

Client: Municipality of Brugg
Owner: Municipality of Windisch
Design and Project Management: Conzett Bronzini Gartmann AG, Chur
Contractor: Implenia Bau AG, Zurich
Concrete Producer: Beton Baden-Brugg AG, Wettingen, Siggenthal Plant
Deck Waterproofing Contractor: Tecton Spezialbau AG, Emmenbrücke