Manual of military field engineering for the use of officers and troops of the line by unknow

Author:unknow
Language: eng
Format: epub, pdf
Tags: Military field engineering
Publisher: Kansas City, Mo., The Hudson-Kimberly publishing co.; [etc., etc.
Published: 1902-03-25T05:00:00+00:00

der, and others to the top pole, by means of which it is raised to a vertical position, when it is dropped to the bottom by slackening off on lower ropes. As soon as it is dropped,another raft is brought up, tied, and another trestle put into position, and so continued. Each trestle, as soon as it is in position, is then capped by nailing two boards horizontally on opposite sides of legs with tops in same plane. (Fig. 3, a.) Braces are then spiked on the legs. Saw oft the two inside posts even with the tops of boards. Spike a 2-in. plank across the top of posts and boards. Lay the balks, spike them, remove the raft, and move it into position to raise another trestle. If boards cannot be procured for capping, round sticks may be used as in Pig. 3, b, by cutting the two inside legs off 5 or 6 in. above the horizontal poles, then spiking two short pieces across the poles against the outside legs and one in center on which the cap piece or transom will rest. Advantages are—work can be commenced in any number of places at the same time; no accurate soundings required so long as poles are sufficiently long; capping and bracing do not retard work; different squads can be at work at same time, etc.

265.—The Two-legged Trestle. If only axes and rope are available, trestles may be made by lashing their parts together. (Fig. 4.) Having determined the height of the roadway above the bottom of the stream, mark this height from the butts on both legs, then mark the position of the transom on the legs, allowing for the thickness of the balks; also mark on the transom the width of roadway between side-rails plus 3 ft., for points of crossing of legs, the distance apart of legs depending on width of roadway. Give the legs a splay outwards at the bottom of 1-6 and mark on legs and ledger the points of lashing. All being ready, lay the transom on a couple of supports 3 or 4 in. high. Inside the position of the legs, lay on the legs In their proper positions, on the legs lay the ledger. With the square lashing fasten the four points of crossing. Next, lay on the braces, butts and one tip on same side as ledger and one tip on side of transom. Lash the butts with square lashings. Square the trestle by making the diagonals equal, measuring from the center of ledger lashing on one leg to the center of transom lashing on opposite leg. When these diagonals are made equal the tips are lashed with square lashings and the braces at the middle with a cross lash-

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lUg. Liedgtii' and braces can be of rather light timber* The trestles can be floated into position and raised as already described, or run out and down from the end of the bridge, which Is more dlfhcult. They are kept vertical by lashing the balks to the transoms, and longitudinal bracing Irom one to another.

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