. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 146 LECTURE to resist the direct crushing strain, but that it is sufficiently great, compared with their length, to avoid a sidewise flexure and conse- quent failure. Hodgkinson, in his elaborate experiments, has shown that, in practice, when the length of a post is less than thirty times its diameter it is not apt to break without it is absolutely crushed; but in such cases the ends should be square and'well fitted, and the strain should b
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 146 LECTURE to resist the direct crushing strain, but that it is sufficiently great, compared with their length, to avoid a sidewise flexure and conse- quent failure. Hodgkinson, in his elaborate experiments, has shown that, in practice, when the length of a post is less than thirty times its diameter it is not apt to break without it is absolutely crushed; but in such cases the ends should be square and'well fitted, and the strain should be central, and not on one side. Posts with rounded ends are much weaker than those with flat ones. When a post, subjected to an axial crushing strain, is inclined, as in the case of a main brace in a bridge truss, we must bear in mind that its deflection from its own weight will tend to weaken it as a strut, since it commences the flexure to the side which is the ultimate cause of the failure of a strut. For this reason, if the cross section of such a strut is not a square, and if the length is at all great, the greatest side of the cross section should be vertical, as in the case of a beam or joist. If a timber strut seems to be too flexible it may be much stiffened without adding much ,to its weight by spiking to the upper or lower side a fin of narrow plank, deep in the middle and tapering off towards the ends. Cast-iron struts should either be tubular or have a cruciform section, as in Fig. 36, so that the material being disposed at the greatest distance from the neutral axis may act with the preatest effect in preventing what we may call the initial Wrought iron may be used in both these forms with great economy of material, a piece of ordinary gas pipe forming the best of struts, and the cruciform section being readily got in the rolls of the mill. In fact these remarks apply to all pieces subjected to a com- pressive strain, such as posts, struts, and the upper chords of
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