. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature. to shear ofif the loaded from the unloaded part of the frame A, is forced down below the frame A3 by &shearing stress resisted by the india-rubber in a .-;y 290 BRIDGES [be A MB. imperfect manner. To mate the frame into a true beam,this tendency of the loaded frame to slip through betweenthe others must be counteracted by tongues, T, Tj, T,,projecting from one frame and working in a groove in theneighbouring frame (vide § 19). Each tongue should bemade so that it does not abut against the bottom
. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature. to shear ofif the loaded from the unloaded part of the frame A, is forced down below the frame A3 by &shearing stress resisted by the india-rubber in a .-;y 290 BRIDGES [be A MB. imperfect manner. To mate the frame into a true beam,this tendency of the loaded frame to slip through betweenthe others must be counteracted by tongues, T, Tj, T,,projecting from one frame and working in a groove in theneighbouring frame (vide § 19). Each tongue should bemade so that it does not abut against the bottom of thegroove, and is thus incapable of resisting any horizontalforce—it must neither prevent-the whole beam nor anypart of it from being extended or compressed longitudi-nally. The structure •will now be found capable of carryingweights as a beam. It deflects or bends as in £g. 11. Fig. 11. under the action of a load on Aj; all the pieces ofindia-rubber above the centre of the beam are then com-pressed ; aU those below the centre are then extended; andat the sections between the frames the horizontal internalforces are wholly met by the elastic reaction due to thesehorizontal extensions and compressions. At any one section, say at a distance x^ from the supportQ, the pieces Cj and d^ are just as much compressed as thepieces 6j Oj are extended; the equal and opposite parallelresultants of these forces consequently constitute a couple,and the moment of this couple must be equal to themoment of the couple tending to bend the beam at thissection, or to what is called the bending moment ; nowthe bending moment in this simple case is due to the up-ward vertical reaction Pj at N and the equal downwardforce with which the frame Aj bears on the tongue Tj;for it is clear that, neglecting the weight of the frame,if a weight W on frame Aj is borne by two forces P and Pjat t
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectencyclo, bookyear1902
