Field engineering; a handbook of the theory and practice of railway surveying, location, and construction : designed for the class-room, field and office, and containing a large nu by Searles William Henry 1837-1921 & Ives Howard Chapin 1878-1944

Author:Searles, William Henry, 1837-1921 & Ives, Howard Chapin, 1878-1944
Language: eng
Format: epub
Tags: Railroad engineering -- Handbooks, manuals, etc, Railroads -- Surveying
Publisher: New York, John Wiley & sons, inc.; [etc., etc.]
Published: 1910-03-25T05:00:00+00:00

Make BA' = AS and join FA' ; then by similar triangles, AA'FmdAFO,

AA : AF :: AF : FG whence

or (r + ft) = \g (1 -f 4n*) (215)

whence r = 2gn* = BF . n (216)

The chord of to the arc of the centre line is to AFas r is to ( r _j_ %g)t hence of = t ' — , and substituting values from sqs. (214) (215) we have

af= 2r (217)

4/1 -f ±n*

Issuming that, for small angles, the tangent offsets vary as «.he squares of their distances from the tangent point, which will lead to no material error in this case;

AB : DK :: BF* : AD* Whence AD=I

(218)

or AD = y4n* g . DK =

It is not necessary to determine the degree of curve in order to locate the turnout, for having fixed the position of BF, the position of af is found by laying off Ba, and F/, each equal to \g. Whatever be the length of the chord af, found by eq. (217) or (210), its middle ordinate is always ^g, and the orclin-nates at the quarter points, f . %g = T \#. 'Thus for the standard gauge of 4.708 the middle ordinate is 1.177, and the side ordinates 0.883.

By the preceding formulae Table XI. has been calculated, Which gives the required parts of a turnout for various frogs j When the gauge is 4 feet 8£ inches and the throw 5 inches; j also for a gauge of 3 feet and throw of 4 inches. For any other throw, onfy AD must be calculated. For a different gauge the engineer will do well to construct a similar table, I adapted to the frogs used on the road.

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