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[quote]QUOTE: Originally posted by beaulieu [quote]QUOTE: Originally posted by futuremodal <snipped> My understanding (and keep in mind I am not a lumber salesman) is that the heavier rail is needed primarily for the force of weight at the point of wheel/rail contact, and not the collective weight of the truck. The reason may have something to do with the fact that the spacing between axles is greater than the spacing between ties, so the weight of each axle is spaced at least three tie spacings between. All the rail and support components have to support at point of contact is that weight on the axle, thus less weight per axle allows for less vertically tall rail. Maybe lighter rail would need closer tie spacing of the collective weight of the truck was heavier? [/quote] Dave, think of the rail as a bridge beam spanning the ties. With the heavier rail the increase is partially in the head (more metal to wear before needing replacement) but also in the web (greater stiffness). If you noticed in the HAL article it said that the railroads discovered that you have to weld the rail on the ends of bridges to provide better support in the transition from roadbed to bridge deck. Also the trend is to ballasted deck bridges as a counter to the differences in stiffness on a bridge. Next time you pass under a highway overpass take a look at the bridge beams underneath, then take a look at those under a railroad overpass. You will see that those under a railroad bridge are at least twice the height of those under a road bridge. Also if you have seen a transition joint between two different weights of rail you will have seen a difference in height in the web. [/quote] Ballasted bridge decks - wasn't that a Milwaukee idea?[^] If you have ever been to Spokane WA, take a look at the RR bridges downtown. The NP apparently chose to go with thinner bridge beams compensated by more frequent support struts. I am sure thicker beams existed at this time, but it was probably cheaper to go with the thinner beams and increased struts. I would think this concept could be applied in other areas, aka if railroads could get away with it they would prefer their bridges over highways to have more strut support (and allowing thinner beams) rather than having to span the entire roadway. For bridges, the gross consist weight is more paramount than the point of contact weight. I also use this example for the thinner vs thicker rail debate.
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