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Shimming Track For Bridge Abutments
Michael has HO scale and writes:
“I read abutments at the end of bridges serve to support the structure and foundations from the horizontal and vertical loads that get placed on them. I will need to determine the necessary heights and widths needed to support the bridge and track elevation, with my main concern being how to maintain level track over joins leading to and over the bridge. I am very much in the early planning stages so want to get my head around the process before I start out. Any help would be good. THX”
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Firstly I would suggest that you either visit or have a look at photos of prototype bridges that you are thinking of building & the situation they are spanning, your track plan will give you a start, are they spanning a road, is the road straight or skew, is it a river or another set of track’s, straight or skew.
Depending on the length of the bridge will determine where rail joints have to be placed, are you using scale length sections of track or meter flexible lengths of track or as in some prototypes longitudinal beams to which the track is placed in chairs directly onto the beam & kept in gauge by rods of steel crosswise at right angles to the beams & bolted either side of each beam so that they can be adjusted by the PW. Quite a good sound effect can be made if you use metal wheels on your stock and allow a little flexibility in the track at the joint and have the joint in the track in the middle of the bridge & make the joint a fraction wider than normal so that you get that lovely clickety clack each time a vehicle passes over the joint, some times a length of thin tin plate under the track will enhance the sound as it reverberates, steel plates riveted together formed the floor of a bridge in most case’s. I would strongly advice you not to have the rail joint at the beginning of the bridge as per the prototype the bridge should be just resting on the abutment plates to allow for temperature variations causing the bridge to expand or shrink.
I hope that I have managed to cover most of your query’s but if any other model engineer can add anything I have missed please let me know as I am now 80+yo & my memory is not as good as it used to be, Kindest regards John Cockburn.