A Work on Bridge Building: Consisting of Two Essays, the One Elementary and General, the Other Giving Original Plans, and Practical Details for Iron and Wooden Bridges (Google eBook)

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H.H. Curtiss, printer, 1847 - Bridges - 120 pages
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Page 39 - Cast iron will resist a greater crushing force than any other substance whose cost will admit of its being used as a building material. Steel has a greater power of resistance, but its cost precludes its use as a material for building. Wrought iron resists nearly equally with cast iron, but its cost is twice as great, which gives cast iron entirely the advantage. On the other hand, wrought iron resists a tensile force nearly four times as well as cast iron, and twelve or fifteen times as well as...
Page 39 - ... cast iron, but its cost is twice as great, which gives cast iron entirely the advantage. On the other hand, wrought iron resists a tensile force nearly four times as well as cast iron, and twelve or fifteen times as well as wood, bulk for bulk. "Not only are these the strongest materials, but they are also the most durable. In fact with proper precautions they may be regarded as imperishable. "It would seem, then, that wrought iron for tension and cast iron for thrust, were the best materials...
Page 93 - ... arch. He suggested the use of a deep truss with the railroad track on top and the highway below the track between the trusses. In his words: "The passageway for carriages and common travel could be arranged underneath perfectly secure from all dangers except perhaps, that of frightening horses by the passage of trains overhead. It would probably be best, however, not to suffer horses to go on to the bridge when trains were in hearing.
Page 4 - Here, then, we have the elementary idea, the grand fundamental principal in bridge-building. Whatever form of structure be adopted, the elementary object to be accomplished is, to sustain a given weight in a given position, by a system of oblique forces whose resultant shall pass through the centre of gravity of the body, in a vertically upward direction, in circumstances where the weight cannot be conveniently met by a simple force in the same line with, and opposite to, that of gravity. To dwell...
Page 63 - There are few substances if any, and certainly wood and iron are not of the number, that fulfil this condition so nearly but that considerable discrepancies are found between the deductions of theory and the results of experiment. Indeed, in the case of cast iron, experiment shews the transverse strength to be fully twice as great as it is made to appear by the above formula.
Page 64 - ... contrary, that for a certain interval on each side of the maximum point, the power of resistance remains nearly stationary. But this stationary interval is reached on the positive, much sooner than on the negative side, and the inevitable consequence must be, that the neutral plane is transferred farther from the positive side, so as to preserve the equilibrium between the resistance to extension and the resistance to compression. Hence, the amount of resistance on the positive side is increased,...
Page 56 - ... subject, however, to correction whenever the facts and evidences shall be obtained, upon which the correction can be founded. In the mean time, since we know not the exact ratio between the greatest safe practical strength and 'he absolute strength of iron, and.
Page 62 - Now, it is manifest that the part below the neutral plane exerts exactly the same amount of resistance to rotation as the part above. Therefore the total resistance to rotation about c, in other words, the resistance to rupture, is equal to...
Page 62 - Now, to determine the amount of this resistance, we will first consider the upper portion; and it is obvious that at every part of the cross section, the resistance to rotation is as the resistance to extension, multiplied by the distance of the part above the neutral plane. But the resistance to extension is, by the law of elasticity, as the degree or amount of extension, which is determined by the distance from the neutral plane.

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