The southern German City of Munich is investing heavily in its public tram sys-tem. Passenger levels are likely to exceed 110m people this year and to help improve operational running, a third-track expansion is underway on the busy section outside the main central station. Traditionally, the track support slabs would be reinforced with steel, however this can create a safety problem with the sensors on modern point-blocking circuits. These function by creating a resonant circuit in the area of the crossover. As a tram approaches, its large steel mass affects the resonant circuit, which is sensed by the track control system. If the carrier plate is reinforced using steel, this disturbs the resonant circuit in a similar way and may lead to interference in the point-blocking circuit – making it difficult for sensors to identify the presence of the tram, putting safety at risk. Any such risk is avoided by using Schöck Combar reinforcing bars, as the glass fibre reinforced polymer product is neither magnetic, nor elec-trically conductive.
Operational safety and vibration reduction too
In addition to the improved safety at crossovers, Combar also offers significant benefits in reducing noise and vibration. Mass-spring systems for these types of track typically consist of a rail carrier plate and a U-Trough shaped foundation of reinforced concrete. The two components being isolated to prevent mechanical vibration. However, because of the risk of local interference with the point-blocking sensors – and the fact that Combar has a tensile strength greater than steel – it was decided to incorporate the product in the mass-spring plates. Combar was installed in the area of the U-Trough and rail carrier plate and elastomer sheeting was used to completely isolate the carrier plate from its surroundings. The elastomer layer also served as lost formwork within the trough and as Combar units have no sharp detailing, there was no risk of them penetrating the layer and causing acoustic bridges.
Historically, steel has been used as the most common reinforcement material in concrete construction. However, the material properties of steel rebar make it unsuitable for many applications and Combar continues to gain ground in more and more markets. The unique physical characteristics of the product are achieved by bundling high-strength glass fibres tightly together, pulling them through a closed chamber and impregnating them with a synthetic resin before cutting. The resultant ribbed reinforcing bar of corrosion resistant glass fibre reinforced polymer is significantly lighter than steel and is neither electrically or thermally conductive.
Combar application examples include easy machinability in tunnel construction, where boring machines cannot drill through steel reinforced shaft walls. With Combar the machine can cut directly through the head wall. High voltage transformers and power plant reactors generate inductive currents within the reinforcing steel. The heat affects the rebar strength if too close to the coils, but Combar remains unaffected. And its corrosion resistance – even from salt – is unrivalled when building bridge and harbour constructions.