. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . 420 2L = 2 X 175 = Difference in length = = Considering that this difference may be divided among 22joints (using 30-foot rails) no rail-cutting would be the difference is too large, a slight variation in the value ofthe new radius R will reduce the difference as much as neces-sary. A truer comparison of the lengths would be found bycomparing the lengths of the arcs. 52. Application of transition curves to compound compou
. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . 420 2L = 2 X 175 = Difference in length = = Considering that this difference may be divided among 22joints (using 30-foot rails) no rail-cutting would be the difference is too large, a slight variation in the value ofthe new radius R will reduce the difference as much as neces-sary. A truer comparison of the lengths would be found bycomparing the lengths of the arcs. 52. Application of transition curves to compound compound curves are only employed when the location islimited by local conditions, the elements of the compound curveshould be determined (as in §§38 and 39) regardless of the §52. ALIGNMENT. 57 transition curves, depending on the fact that the lateral shiftingof the curve when transition curves are introduced is very the limitations are very close, an estimated allowance may bemade for them. Methods have been devised for inserting transition curvesbetween the branches of a compound curve, but the device is. Fig. 35. complicated and usually needless, since when the train is onceon a curve the wheels press against the outer rail steadily anda change in curvature will not produce a serious jar even thoughthe superelevation is temporarily a little more or less than itshould be. 58 RAILROAD CONSTRUCTION. § 53. If the easier curve of the compound curve is less than 3° or4°, there may be no need for a transition curve off from thatbranch. This problem then has two cases according as transitioncurves are used at both ends or at one end only. a. With transition curves at both ends. Adopting the methodof § 49, calling ii = ^J, we may compute m^=MM^\ Similarly,calling J2 = ^^, we may compute m^=A/A/2- I^ut AI/ and Af/must be made to coincide. This may be done by moving thecurve Z^Mi and its transition curve parallel to Q^V a distanceM/M^j and ^the other curve parallel to QF a d
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