. 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 . he tangents and the long3hord are obstructed. The above methods are but samplesjf a large number of similar methods which have been choice of the particular method to be adopted must be determined by the local conditions. 62. Obstacles to location. In this section will be given onlya few of the principles involved in thiiclass of problems, with illustrations. Theengineer must decide, in each case, whichis
. 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 . he tangents and the long3hord are obstructed. The above methods are but samplesjf a large number of similar methods which have been choice of the particular method to be adopted must be determined by the local conditions. 62. Obstacles to location. In this section will be given onlya few of the principles involved in thiiclass of problems, with illustrations. Theengineer must decide, in each case, whichis the best method to use. It is frequentlyadvisable to devise a special solution forsome particular case. a. When the vertex is inaccessible. Asshown in § 56, it is not absolutely essentialthat the vertex of a curve should belocated on the ground. But it is very evi-dent that the angle between the terminaltangents is determined with far less prob-able error if it is measured by a singlemeasurement at the vertex: rather than asthe result of numerous angle measurementsFig. 22. along the curve, involving several posi- ;tions of the transit and comparatively short sights Some-. 70 RAILROAD CONSTRUCTION. § 62! times the location of the tangents is already determined oithe ground (as by hn and am, Fig. 22), and it is required t(join the tangents by a curve of given radius. Method. Measureab and the angles Vba and baV. A is the sum of these anglesiThe distances bV and aV are computable from the above data;Given A and R, the tangent distances are computable, and thenBb and a A are found by subtracting bV and aV from the tan-gent distances. The curve may then be run from A, and theT/ork may be checked by noting whether the curve as run endsat B—previously located from b. Example. Assume o6=546 82; angle a = 15° 18; angleh = 18° 22; D =3° 40; required aA and bB. J = 15° 18 +18° 22=33° 40 Eq. (4) R (3° 40) tan ^A =tan 16° 50 r= v= 7. sin 18° 22 ab
Size: 1074px × 2327px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorwebbwalt, bookcentury1900, bookdecade1920, bookyear1922
