A Practical Treatise on Suspension Bridges: Their Design, Construction and Erection

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Wiley, 1922 - Cantilever bridges - 204 pages
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Page 64 - ... this member will be in tension and the top chord will be in compression. If the curve of the bottom chord is made such that the equilibrium polygon will fall near the center of the truss or between the two chords under all conditions of loading, the stresses in both chords will always be tension. Figure 18 shows the three-hinged braced-chain type of suspension bridge provided with side spans (Type 3BS). The stresses in the main span trusses are not affected by the presence of the side spans,...
Page 20 - ... of suspension bridges with stiffening trusses is based on five assumptions, which are very near the actual conditions: (1) The cable is supposed perfectly flexible, freely assuming the form of the equilibrium polygon of the suspender forces. (2) The truss is considered a beam, initially straight and horizontal, of constant moment of inertia and tied to the cable throughout its length. (3) The dead load of truss and cable is assumed uniform per lineal unit, so that the initial curve of the cable...
Page 45 - Fig. 106; only a portion of the main span is loaded, the side spans being without load. There are no critical points in the side spans. For the greatest negative moment at any section x\ in one of the side spans, load the other two spans (Fig. lOc), giving Min. Ml - -#! . 1 ^3" . pi (102) Loading the span itself produces the greatest positive moments, which are obtained by the relation Max.
Page 19 - ... assume, as in all other rigid structures, that the lever arms of the applied forces are not altered by the deformations of the system. The resulting theory is the one ordinarily employed, and is sufficiently accurate for all practical purposes; any errors are generally small and on the side of safety. If the stiffening truss is not very stiff, or if the span is long, the deflections of truss and cable may be too large to neglect. To provide for such cases, there has been developed an exact method...
Page 18 - Assumptions Used. — In the theory that follows, we adopt the assumption that the truss is sufficiently stiff to render the deformations of the cable due to moving load practically negligible; in other words, we assume, as in all other rigid structures, that the lever arms of the applied forces are not altered by the deformations of the system. The resulting theory is the one ordinarily employed, and is sufficiently accurate for all practical purposes; any errors are generally small and on the side...
Page 145 - The maximum fiber stress in the tower columns will occur when the live load covers the main span and the farther side span at maximum temperature. Under this condition of loading, the top of the tower will be deflected toward the main span as a result of the following deformations: (1) The upward deflection (A/i) at the center of the unloaded side span. (2) The elongation of the cable between the anchorage and the tower due to the elastic strain produced by the applied loads. (3) The elongation of...
Page 173 - ... 31), and the loop thus formed is hung around a light grooved wheel (Fig. 30) which is fastened to the traveling rope. The traveling rope with its attached wheel, moving toward the other end of the bridge, thus draws two wires simultaneously across from one anchorage to. the other; one of these wires, having its end fixed to the shoe, is called the "standing wire"; while the other, having its end on the reel, is called the "running wire" and moves forward with twice the speed of the traveling...
Page 85 - Wire Rope Wire ropes are built up of strands made of wires twisted together, the numbers of wires commonly used being four, seven, twelve, nineteen and thirty-seven. Ordinarily the wires are twisted into strands in the opposite direction to the twist of the strands into rope. When wires and strands are twisted in the same direction, the rope is known as Lang lay rope. Standard wire rope is made of six wire strands and a hemp core. Wire strands are twisted around the core, either to the right or left,...
Page 47 - ... shears. Loading the main span from the given section x to the end of the span, we obtain the maximum positive shears by the formula: лл•> where the function and is given by Table 1 and the graph in Fig.
Page 64 - Figure 17 shows the single-span type, in which the backstays are straight (Type 3BF ). If the lower chord is made to coincide with the equilibrium polygon for dead load or full live load, the stresses in the top chord and the web members will be zero for such loading conditions. These members will then be stressed only by partial or non-uniform loading. Under partial loading, the equilibrium polygon will be displaced from coincidence with the lower chord : where it passes between the two chords,...

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