3 ms·

What about the materials and structure of a train car - can they sustain instantaneous force required to stop a speeding train? RRRIP! Oops, maybe not.

NamTaf 14y ago
They mention 300kN in the article, and in the design of trains that isn't a lot at all. For example, the AAR [1] standards require a railway vehicle to take up to 1.8x 1560kN longitudinal force - that is, the force imparted down the length of the train through the couplers in to the body structure - without causing bulk yield [2] of the body material. A second design requirement is for the body structure to take 4450kN 'collision' force without exceeding the ultimate strength of the body structure material. Other design criteria include, for example, crash protection of the driver's cabin if it's a locomotive where the drivers sit at the very front, so that part's often very strong and rigid as it needs to preserve a 'survivability space' for the drivers. For passenger cars, the body structure tends to have a lot of strength against longitudinal loads in order to combat the phenomenon of climbing. That is, in a railway collision with passenger cars, as the vehicles ride in to one another, there is the tendency for one to pop up/down and try to 'ride up/down' on top of/under the one in front. [3] This was demonstrated rather tragically in a particular accident (I can't find its name, sorry) where old wooden passenger vehicles did this. Their comparatively strong underframe simply sliced through the comparatively weak cabins like horizontal blades and caused huge fatalities. This is because old passenger cars used to basically be flat-top wooden vehicles with a cabin placed on top, so the body structure was very strong compared to the weak cabin. Since then, passenger vehicles must be specifically designed not to climb up on one another and do that. So really, in the sense of railway design, 300kN is minimal, especially when placed longitudinally down the length of the vehicle structure. They are far weaker against lateral collision so I guess if you ever want to cause a huge railway accident, hit a train side-on rather than end-on. [1]: Not the standards themselves, as they're not publically available - https://www.aar.org/Pages/Home.aspx https://www.aar.org/Pages/Home.aspx [2]: By 'bulk yield' I mean yielding over a significant portion of the structure. This is a legacy of the AAR standards originally being targeted towards hand calculations, where you couldn't easily inspect every particular section of every particular beam but rather you calculated it as a whole. With the advent of finite element analysis you can now do that, so it's permissible to see slight yield-levels of stress in certain small parts so long as the overall section as a whole remains under it. [3]: This will give a brief example of anti-climbers on rail vehicles: http://www.oleo.co.uk/products/rail/anti-climbers http://www.oleo.co.uk/products/rail/anti-climbers

NamTaf 14y ago

They mention 300kN in the article, and in the design of trains that isn't a lot at all. For example, the AAR [1] standards require a railway vehicle to take up to 1.8x 1560kN longitudinal force - that is, the force imparted down the length of the train through the couplers in to the body structure - without causing bulk yield [2] of the body material. A second design requirement is for the body structure to take 4450kN 'collision' force without exceeding the ultimate strength of the body structure material. Other design criteria include, for example, crash protection of the driver's cabin if it's a locomotive where the drivers sit at the very front, so that part's often very strong and rigid as it needs to preserve a 'survivability space' for the drivers. For passenger cars, the body structure tends to have a lot of strength against longitudinal loads in order to combat the phenomenon of climbing. That is, in a railway collision with passenger cars, as the vehicles ride in to one another, there is the tendency for one to pop up/down and try to 'ride up/down' on top of/under the one in front. [3] This was demonstrated rather tragically in a particular accident (I can't find its name, sorry) where old wooden passenger vehicles did this. Their comparatively strong underframe simply sliced through the comparatively weak cabins like horizontal blades and caused huge fatalities. This is because old passenger cars used to basically be flat-top wooden vehicles with a cabin placed on top, so the body structure was very strong compared to the weak cabin. Since then, passenger vehicles must be specifically designed not to climb up on one another and do that. So really, in the sense of railway design, 300kN is minimal, especially when placed longitudinally down the length of the vehicle structure. They are far weaker against lateral collision so I guess if you ever want to cause a huge railway accident, hit a train side-on rather than end-on. [1]: Not the standards themselves, as they're not publically available - https://www.aar.org/Pages/Home.aspx https://www.aar.org/Pages/Home.aspx [2]: By 'bulk yield' I mean yielding over a significant portion of the structure. This is a legacy of the AAR standards originally being targeted towards hand calculations, where you couldn't easily inspect every particular section of every particular beam but rather you calculated it as a whole. With the advent of finite element analysis you can now do that, so it's permissible to see slight yield-levels of stress in certain small parts so long as the overall section as a whole remains under it. [3]: This will give a brief example of anti-climbers on rail vehicles: http://www.oleo.co.uk/products/rail/anti-climbers http://www.oleo.co.uk/products/rail/anti-climbers