. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . s at Z, the forward alinement may be obtained by sightsing back at Q (or at any other point) with the proper deflectionfor that point from the station occupied. Then when the platesread 0° the telescope will be tangent to the spiral and to thesucceeding curve. All rear points should be checked from Z,If it is necessary to occupy an intermediate station, use the de-flections given for that station, orie
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . s at Z, the forward alinement may be obtained by sightsing back at Q (or at any other point) with the proper deflectionfor that point from the station occupied. Then when the platesread 0° the telescope will be tangent to the spiral and to thesucceeding curve. All rear points should be checked from Z,If it is necessary to occupy an intermediate station, use the de-flections given for that station, orienting as just explained for Z,checking the back points and locating all forward points up to Zif possible. After the center curve has been located and Z- is reached, the M RAILROAD CONSTRUCTION. §81. other spiral must be located but in reverse order, , the sharpcurvature of the spiral is at Z and the curvature decreasestoward Q. 8i. To replace a simple curve by a curve with spirals. Thisjmay be done by the method of § 79, but it involves shifting thewhole track a distance m, which in the given example feet. Besides this the track is appreciably shortened,. Fig. 37. which would require rail-cutting. But the track may be keptat^practically the same length and the lateral deviation from theold track may be made very small by slightly sharpening theieurvature of the old track, moving the new curve so that it iswholly or partially outside oi the old curve, the remainder of itwith ike spirals being inside of the old curve. It is found byexperience that a decrease in radius of from 5% to 10% willanswer the purpose. The larger the central angle the less thechange. The solution is as indicated in Fig. 37. ON^R cos -\-Y. 0F = 0iV sec |A % =R cos sec lA+F sec ^A. i § 81. ALINEMENT. 95 mm = MM=MV-MV ir =RexsecU-{0V-R) = R exsec ^A—R cos ^ sec |A —7 sec lA+JK. , (38)AQ=QK-KN+NV-VA =X-R sin 0 + (/2 cos + Y) tan ^A -E tan |A=Z-/2sin0+/2cos0tan|A-(i2-7) tan^A. . (39) ATh
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Keywords: ., bookauthorwebbwalt, bookcentury1900, bookdecade1920, bookyear1922
