Comparative damage to roads, tram tracks and building foundations by trams and buses

The load under an LR55 tram track is half that of a bus wheel:

Dave,
I have attached as promised some loading graphs. These are all for main line railway loads (25tonne axles). Trams have 10 tonne axles loading and the pressure under a LR55 beam is under 100kN/m2. This compares to 140kN/m2 under the heal of an adult shoe.

LR55 reduces the pressure into the ground. Under the support beams, with 25tonne axle loads, the maximum pressure is 240kN/m2 (see attached graph). This has been determined both by FEA and from cyclic physical testing. Under railway sleepers the pressure is 334kN/m2. (40% greater), assuming the whole sleeper carries the axle load. With twin block sleepers the pressure is over 440kN/m2. Ballast has to be regularly tamped to maintain the right rail profile and train ride quality. Despite 150 years of research, the behaviour of ballast is still not understood. There were 10 more papers on the subject at the latest Railway Engineering Conference.

The reason that LR55 is more benign to the ground is that the wheel load is distributed over a bigger area, 2m ahead and behind  the wheel, and that the base of the beam is over 90% in contact with the ground, compared to less than 25% for sleepers on ballast.

The deflection of LR55 track under 25 tonne axle loads is also small, either from single axles or twin axle bogies, and the behaviour is damped and elastic.  LR55 has been tested to 80 tonne axle loading, and will carry a 25tonne axle over a 1 m void  ( that is a 0.5m region of no contact with the ground ahead and behind the wheel)  without failure. The maximum axle load globally is 48tonnes (Hamersley Line in Australia). Class One Railroads in the US are maintained to a 33 ton (30tonne) standard.

LR55 will soon complete 22 years of full line service without the need for maintenance. Thanks to its resilient mounting, rail wear and wheel squealing are reduced, and should be good for over 30 years, maintenance free service.

Hope this helps,
Lewis

 

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