. 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 .. . posts in any panel. In panel No. 1, it will be 25 feet. 2, (( a 18 3, « a 17 4, « u 16 5, i( (( 16 and applying the formula 2240 bd^ = W WOODEN BRIDGES. 165 we get, in round numbers, the following dimensions, thebraces being bolted and blocked together: — For the 1st panel, 25 feet long, 8 X 10« 2(1 37 « 8 X 10« 3d « 49 « « 8 X 10 4th « 64 8 X 10 5th « 78 8 X 10. For
. 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 .. . posts in any panel. In panel No. 1, it will be 25 feet. 2, (( a 18 3, « a 17 4, « u 16 5, i( (( 16 and applying the formula 2240 bd^ = W WOODEN BRIDGES. 165 we get, in round numbers, the following dimensions, thebraces being bolted and blocked together: — For the 1st panel, 25 feet long, 8 X 10« 2(1 37 « 8 X 10« 3d « 49 « « 8 X 10 4th « 64 8 X 10 5th « 78 8 X 10. For the lattice-work, a double course on each side of eachtruss, in long spans, (150 to 200 feet) ; and a single coursein shorter spans, of 3 X 6 plank, treenailed at intersections,is ample. GENERAL TABLE OF DIMENSIONS FOR ARCH BRACE TRUSS. Span. Rise. Chords. Ties. Braces. Lattice. 50 75 100 150 200 1012152025 2 — 8 X 10 2 — 8 X 10 3 — 8 X 10 4 — 8 X 124 —8X 16 1—8 X 101—8 X 10 2 — 8 X 10 3 — 8 X 103 — 8 X 10 2 — 6 X 6 2 — 6 Xfi 3 — 6 X 6 4 — 6X84 —6X 9 2 X 9 or 3 X 62 X 9 or 3 X 62 X 9 or 3 X 62 X 9 or 3 X 62 X 9 or 3 X 6 166 HANDBOOK OF RAILROAD CONSTRUCTION. Fisr. nflK. Fie. no Fig. 69 A, shows themethod of bringing thearch braces to the find the dimensions ofthe cast-iron block, makea complete drawing of allof the braces, at theirproper angles, and thendraw in the block aroundthe feet, as shown in R A Note. — The centre of pressureof the braces in fig. 69 A, is not,as might seem, at C; because thevertical components of the forces,coming down the brace, are muchless in the braces at small anglesthan in those at the end of thespan. The load applied to eachbrace being the same, and the in-clines being found, we find the cen-tre of pressure, or the centre ofbridge seat as follows : — The length of the brace is to thevertical height, as the applied loadto the vertical pressure. In A, we have the following le
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