. Theory of structures and strength of materials. the stays, assuming them approximately straight. Assume that theproof load covers {a) a side span ; (d) two side spans; (c) the centre —(a) Pull on stays in centre span = 840,050 lbs. (d) • =: lonble that in (a), (c) side span = 948,466 lbs. EXAMPLES. 739 22. A floating landing-stage is held in position by a number of 4-in. steel-wire cables anchored to the shore, a shoreward movement beingprevented by rigid iron booms, pivoted at the ends and stretching fromshore to stage. The difference of level between the shore and stage at-tachmen
. Theory of structures and strength of materials. the stays, assuming them approximately straight. Assume that theproof load covers {a) a side span ; (d) two side spans; (c) the centre —(a) Pull on stays in centre span = 840,050 lbs. (d) • =: lonble that in (a), (c) side span = 948,466 lbs. EXAMPLES. 739 22. A floating landing-stage is held in position by a number of 4-in. steel-wire cables anchored to the shore, a shoreward movement beingprevented by rigid iron booms, pivoted at the ends and stretching fromshore to stage. The difference of level between the shore and stage at-tachments of the cables is 50 ft., and the horizontal distance betweenthese points is 150 ft. The horizontal pull upon each cable is 1360 the length of the cable, and the tensions at the points of attach-ment. (Weight of cable = 490 lbs. per cubic foot; form of cable a com-mon catenary.) Ans. ^ ft.; lbs. and 10,132 lbs. CHAPTER XTII. ARCHES AND ARCHED RIBS. I. An arch may be constructed of masonry, brickwork,timber, or Fig. 478. In the figure ABCD represents the profile of an arch. Theunder surface AD is called the soffit or intrados. The uppersurface BC is sometimes improperly called the extrados. Thehighest point K of the soffit is the crown or key of the springings or skewbacks are the surfaces AB, DC fromwhich the arch springs, and the haunches are the portions ofthe arch half-way between the springings and the each of the arch faces stands a spandril wall, and thespace between these two external spandrils may be occupiedby a series of internal spandrils spaced at definite distancesapart, or may be filled up to a certain level with masonry (,backing) and above that with ordinary ballast or other roughmaterial {, filling). A masonry arch consists of courses of wedge-shaped blockswith the bed-joints perpendicular, or nearly so, to the soffit. 740 EQUILIBRATED POLYGON AND LINE OF RESISTANCE. 74I The blocks are called vons
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