Schöck Combar ensures safer tram system and reduced noise

A great deal of investment is being made in the continued expansion of the Munich tram network in southern Germany.   The latest construction work involves a third-track being added just outside Munich Central Station. The use of Combar, the electrically non-conductive glass fibre reinforced polymer (GFRP) from Schöck, greatly reduces noise levels at crossovers; and unlike steel solutions, poses no threat of interference to sensitive electronic track control systems

The Munich tram system is expected to transport in excess of 110m people this year and the rail section outside Munich Central Station is particularly busy.   During rush hour, up to six trams can run through this double-track section every ten minutes and a third-track expansion is underway to help make operational running smoother and more flexible.    Traditionally, the track support slabs involved would be reinforced with steel.   However, this can create a safety problem with the sensor system of modern point-blocking circuits, which work by creating a resonant circuit in the area of the crossover.     As a tram approaches the crossover, 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 much more difficult for sensors to identify the presence of the tram, thereby putting safety at risk.   Any such risk is avoided by using Schöck Combar reinforcing bars, as the glass fibre reinforced polymer solution is neither magnetic, nor electrically conductive.

Operational safety and vibration reduction too

In additon to the improved operational safety at crossovers, the use of Schöck Combar also offers significant benefits in reducing noise and vibration as well.   A welcome benefit, particularly for one of the largest department stores in Germany and also one of the most coveted large-scale properties in Munich’s city centre, which is located adjacent to this part of the track   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 possible risk of local interference with the point-blocking sensors at the crossovers – and the fact that Combar has a tensile strength greater than steel – it was decided to incorporate the product in the mass-spring plates.     Where Combar was installed in the area of the U-Trough and rail carrier plate, elastomer sheeting was used to completely isolate the carrier plate from its surroundings.     The elastomer layer also served as lost formwork within the trough, where the Combar elements were installed crosswise, using cable ties and concrete, strength class C30/37, being poured in the respective section.   Combar units have a smooth base and no sharp detailing, so there is no risk of them penetrating the elastomer layer and causing acoustic bridges.    After the trough had cured, the carrier plate, also reinforced by Combar, was then poured using concrete of the same strength class.  The construction section involved is around 1000 sq metres in total.

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Superior performance 

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.    Conversely, since its initial introduction around fifteen years ago, Schöck Combar  has gained ground in more and more markets, demonstrating its superiority as an alternative to steel.    The unique structural and physical characteristics of the product are achieved by bundling high-strength glass fibres tightly together and pulling them through a closed chamber where they are impregnated with a synthetic resin.   The lengths are then cut and the resultant product is a ribbed reinforcing bar made of corrosion resistant glass fibre reinforced polymer.    It is significantly lighter than steel and is neither electrically or thermally conductive.

Exceptional versatility

Combar application examples include its easy machinability in tunnel construction, where boring machines used in shaft walls of tunnels, cannot drill through steel reinforced walls.  With Combar the machine can cut directly through the head wall.    In high voltage transformers and power plant reactors, inductive currents are generated within the reinforcing steel.  The heat will affect 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, marine and harbour constructions.  Also, when it comes to onsite installation, handling Combar is effectively no different from conventional reinforcing steel, so no special user training is required.

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