InnoTrans 2018

••• 18••• Innovationen Schlank, aber resistent Erste Eisenbahnbrücke aus ultrahochfestem Beton Auf der Strecke der Tegern- see-Bahn bei Gmund ist die erste Eisenbahnbrücke in Deutschland aus ultrahochfestem Beton in Be- trieb genommen worden. Der neuartige Hochleistungsbeton er- möglichte eine besonders schlan- ke Bauweise. Ingenieure der Tech- nischen Universität München (TUM) haben das Projekt geplant und wissenschaftlich begleitet. „Es handelt sich um ein neues Ma- terial, das sich anders verhält als der herkömmliche Beton“, erklärt Prof. Oliver Fischer vom Lehrstuhl für Massivbau der TUM. Durch seine Zusammensetzung ist der Werkstoff besonders dicht, be- sitzt also kaum Hohlräume, in die Nässe oder Salze eindringen können, die das Material schä- digen. Auch hält es im Vergleich zum konventionellen Beton, der derzeit im Brückenbau verwen- det wird, dem vier- bis fünffachen Druck stand, ist also sehr viel „fes- ter“, dafür aber leichter. Die hohe Dichte und Festigkeit erhält der ultrahochfeste Beton durch ein genau abgestimmtes Verhältnis von Zementpartikeln, feinen Zusatzstoffen und abge- stuften Gesteinskörnungen. Ein weiterer wichtiger Bestandteil des ultrahochfesten Betons sind Mikrostahlfasern. Sie sorgen für eine höhere Zugfestigkeit. Denn wie beim Tauziehen auf das Seil wirken im Inneren der belasteten Brücke auch Zugkräfte, die sicher übertragen werden müssen. Tegernsee: erste Eisenbahn- brücke aus ultrahochfestem Beton in Deutschland Foto: Uli Benz / TUM T he city of Washington, D.C., is bound- ed on two sides by rivers and an un- told number of streams. Every morning the Orange Line, one of six train lines that serve the city, ferries 12 060 commuters – per hour. And this miracle occurs every day in Berlin, Tokyo, London, Amsterdam or Shanghai. In the United Kingdom alone there are more than 40000 railway bridges. Much has been written on how to maintain this infrastructure, particularly in the dif- ficult transition zones where trains leave land to ascend bridges over water. “All rail- way systems suffer rapid track deteriora- tion at the transition zones requiring high maintenance costs,” says Sakdirat Kaewun- ruen, Ph.D., Department of Civil Engineer- ing, University of Birmingham, United King- dom. “In the past decades, there have been so many ad hoc solutions provided, but there has been no work on evaluating its life cycle cost and sustainability.” New, daunting challenges created by cli- mate change – extreme heat, extreme cold, and severe flooding – require yet more rig- orous solutions. An unprecedented study titled “Lifecycle Assessments of Railway Bridge Transitions Exposed to Extreme Events”, benchmarks the costs and carbon emissions for the life cycle of eight mitiga- tion measures and reviews these methods for their effectiveness in three types of ex- treme environmental conditions. Railway systems are designed for a 50-year lifespan, which is calculated on the integri- ty of the materials used, and most railways are built along one of two common track systems: rails set on railway ties (U.S.A.) or sleepers (UK), which are then “ballasted” into beds of rock or gravel; or rails that are set onto concrete slabs. Sometimes both are used on one rail line with one transi- tion to the other. In either case, the engi- neering feat that must be solved is that as the train crosses the transition between ground and bridge, the relative stiffness of the bedrock, concrete, vs. metal bridge can impart intense vibrations that drastically impact the train rails and even make the ride uncomfortable to commuters. Transi- tion zones require four to eight times more maintenance than ordinary rail tracks. The study investigates mitigation measures for bridges that span 30 metres and 100 metres. The study reviews the eight most common techniques for bridge transitions, including: under ballast mats (UBMs), soft baseplates, under sleeper pads (USPs), rail pads, embankment treatments, transition slabs, ballast bonding, and wide sleepers. Overall, the study finds that elastic rail pads, soft baseplates, and UBMS are most suitable for short-span bridges, relying on a range of materials such as elastic materi- als, chloroprene rubber, or polymeric com- pounds to provide reduce railway stiffness. Unfortunately, the same materials that pro- vide elasticity deteriorate faster in extreme heat and extreme cold, conditions that have become more frequent with climate change. For reference, the materials tend to exhibit sensitivity at 20 degrees Celsius and severe problems in the dead of winter at -40 de- grees Celsius in the far northern latitudes. For long bridges the researchers recom- mend employing transition slabs, ballast bonding, and embankment treatments – methods that mitigate track stiffness gradually with longer transitions. These so- lutions tend to be greatly affected by flash flooding that can wash away embankments and ballast that supports the track struc- ture. In Norway, flooding has turned sedi- ments into mud causing train tracks to col- lapse. Solutions need to be developed on a case-by-case basis, taking into account cost over the life cycle and environmental fac- tors. Moreover, cost of materials and main- tenance can vary from country to country. Costs of maintenance Extreme weather events threaten railway bridges Railroad bridge in Stockholm, Sweden Photo: Wenni Zhou on Unsplash IN PERFEKTER HARMONIE Jetzt erleben: www.perfekte-harmonie.de und auf der InnoTrans · Halle 10.2 | Stand 103 vom 18.– 21. September 2018 in Berlin FLUIDTECHNIK-KOMPONENTEN, SYSTEME UND DIENSTLEISTUNGEN AUS EINER HAND