Chap. VIII.
471
Six longitudinal walls rest on the back of the brick arch, which carry the platform on whichthe rails are fixed. Besides these two grand brick arches on each bank of the river are fourothers with semicircular heads; that on the abutments spans 21 feet, the six others areeach 28 feet.
Skew Bridges. — One on the London and Birmingham line carries the railway 23 feet7 inches above the level of the road, and the angle it makes is 32°, the square span of thearch being 21 feet, and the oblique span 39 feet 8 inches. The arch, 2 feet 6 inches thick,is the segment of a cylinder, the internal radius of which is 12 feet 6 inches, the versedsine 5 feet 8 inches. The angle at which the coursing joints of the soffite cross the axisof the cylinder is 53° 25', and that of the extrados is 58° 15'; the angle of the voussoirsconsequently is 4° 50'. The joints of the face of the arch all converge to a point, 32 feet6 inches below the axis of the cylinder, or 45 feet below the crown of the arch.
Midland Counties Railway , presents another variety of skewed brick bridge, the span ofwhich is 42 feet 6 inches, and versed sine 11 feet; the wdiole consists of six arches, 2 bricksin depth, and 4 feet in thickness: the total width of the bridge, measured through at rightangles with the face, being 24 feet.
Fig 472.
Another skew bridge on this line, over the Nottingham and Sawley Road, is of a differentconstruction; the whole depth of the bridge, measured square with the face, is 27 feet, andthe span 53 feet, with a versed sine of 7 feet.
Fig. 473.
BR1DGB OVER THE NOTTINGHAM AND SAWLEY ROAD.
A great variety of skew or oblique bridges has been erected in brick for several rail-ways, and by means of such arches the engineer has been enabled to avoid all awkwardand injurious turns in the lines of rails to be carried over them; the lines of pressure arc
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