. The trackman's helper, a handbook for track foremen, supervisors and engineers . d would probably bethirty per cent or more of the weight upon the tie,not to mention the grip of the spikes, etc. It is ob-vious that while depressed under a wheel load thebase of the rail is on the circumference of an arc ofgreater radius than the neutral axis. Since the basecannot slip the neutral axis must move forward thedifference between lengths of the arcs. As there is adifference between the length of the neutral axis whenhorizontal and when on the curve, in the rolling ofthe wheel load there must be an
. The trackman's helper, a handbook for track foremen, supervisors and engineers . d would probably bethirty per cent or more of the weight upon the tie,not to mention the grip of the spikes, etc. It is ob-vious that while depressed under a wheel load thebase of the rail is on the circumference of an arc ofgreater radius than the neutral axis. Since the basecannot slip the neutral axis must move forward thedifference between lengths of the arcs. As there is adifference between the length of the neutral axis whenhorizontal and when on the curve, in the rolling ofthe wheel load there must be an elongation or a move-ment. If there were no wave motion beneath thetrain and the depression were uniform, the depressedcurved track would evidently be longer than the orig-inal horizontal track since the straight line is shorterthan a curve. It would appear, therefore, that the 168 THE TRACKMANS HELPER advance wave and depression, together with the resil-ience wave in the rear are the causes of the horizontalmotion of the rail. On the basis of the above theory, it follows that,. Figure Fig. 30. Wave Motion, Cause of Creeping should the rail be supported in some manner from thetop, it would move in the opposite direction. Thisit has been shown actually to do upon a model con-structed for the purpose. This model was prepared EFFECTS OF WAVE MOTION OF RAIL 169 with a wooden rail mounted on springs and free tomove. A rolling weight was moved around a circulartrack causing deep depressions. A forward motionwas very apparent when the rail was supported atthe base and a similar backward motion when the railwas supported from the top. A practical demonstra-tion of this action has also appeared in bridges whichshow a marked tendency to move on their supportsunless held by rigid connections. Through spans arethus forced forward and deck spans backward. Many contradictions appear among the observationsof creeping rails; some observers declare that the outerrail on curves creeps more than
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