Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

GENERAL TABLE OF DIMENSIONS FOR ARCH BRACE TRUSS.
Span.	Rise.	Chords.	Ties.	Braces.	Lattice.
50	10	2–8 × 10	1–8 × 10	2–6 × 6	2 × 9 or 3 × 6
75	12	2–8 × 10	1–8 × 10	2–6 × 6	2 × 9 or 3 × 6
100	15	3–8 × 10	2–8 × 10	3–6 × 6	2 × 9 or 3 × 6
150	20	4–8 × 12	3–8 × 10	4–6 × 8	2 × 9 or 3 × 6
200	25	4–8 × 16	3–8 × 10	4–6 × 9	2 × 9 or 3 × 6

Fig. 69 K.

Fig. 69 A.

Fig. 69 A, shows the method of bringing the arch braces to the chord. To find the dimensions of the cast-iron block, make a complete drawing of all of the braces, at their proper angles, and then draw in the block around the feet, as shown in fig. 69 A.

Note.—The centre of pressure of the braces in fig. 69 A, is not, as might seem, at C; because the vertical components of the forces, coming down the brace, are much less in the braces at small angles than in those at the end of the span. The load applied to each brace being the same, and the inclines being found, we find the centre of pressure, or the centre of bridge seat as follows:—

The length of the brace is to the vertical height, as the applied load to the vertical pressure. In fig. 69 A, we have the following lengths of braces: a, 25; b, 37; c, 49; d, 64; e, 78; f, 92; and g, 106; and the weights corresponding thus,

a, 25 : 20 :: 6000 : 4800.

b, 37 : 20 :: 6000 : 3243.

c, 49 : 20 :: 6000 : 2450.