. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . simple circular curve AMB, having thecenter 0. Assume that the entire curve is moved in the direc-tion MO a distance 00=MM=BB=AA\ At some point TSon the tangent, the spiral begins and joins the circular curvetangentially at SC. The other spiral runs from CS to ST, Thesignificance of these symbols may be readily remembered fromthe letters; 7, S, and C signify tangent, spiral and circular curve;TS is the point of change from tangent to spiral, SCj the pointof change from spiral t
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . simple circular curve AMB, having thecenter 0. Assume that the entire curve is moved in the direc-tion MO a distance 00=MM=BB=AA\ At some point TSon the tangent, the spiral begins and joins the circular curvetangentially at SC. The other spiral runs from CS to ST, Thesignificance of these symbols may be readily remembered fromthe letters; 7, S, and C signify tangent, spiral and circular curve;TS is the point of change from tangent to spiral, SCj the pointof change from spiral to curve, etc. At the other end of thecircular curve the letters are in reverse order, the station numbersincreasing from A to B. The meaning of the various symbols is 88 RAILROAD CONSTRUCTION. §76. indicated in Fig. 36. The student should appreciate the fact ofthe necessary distortion of the figure in order to make it on the figures of the following numerical problem, thedistance MM^ is about fourteen times its proper amount. Anothereffect of the distortion is that the dimension U, instead of being. Fig. 36. nearly twice V, which is usual, as given in Table IV, Part B, isonly a little longer than V. 76. Proper length of spiral. This can only be computed onthe basis of certain assumptions as to the desired rate of tippingthe car, so as to avoid discomfort to passengers, and, of course,this depends on the expected velocity. There is also a maximumlimitation, since the sum of the two spiral angles cannot exceedthe total central angle of the curve. The minimum lengthsrecommended are as follows: § 77. ALINEMENT. 89 On curves which limit the speed: 6° and over, 240 feet; Less than 6% SJXspeed in for elevation of 8 curves which do not limit the speed: 30 times elevation in inches, or f Xultimate speed in Xelevation in inches. For example. (1) 5° curve which Hmits speed; speed limit48 by interpolation in table, § 41; 48X5| = 256 feetminim
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