After briefly alluding to various formulae for the calculation of the strength of beams, and particularly the experiments and formulae of Mr. Hodgkinson, as published in several of his Essays in the Philosophical Transactions, and Reports of the British Association, and in a more accessible form in the second part of his new edition of Tredgold’s Essay on the Strength of Cast Iron, and which were exemplified by numerous diagrams, Mr. Ward observed, I do not find that the strength of wood beams trussed with rods of wrought iron has been investigated by any writer on the Strength of Materials. I have given some consideration to the obtaining a formula for finding the additional strength which the rod of iron gives to the wood beam, and, for many cases, I think the following formula may be employed:— ![Formula][1] , C being the tensile strength of the rod, A its area, and D the depth from the neutral area of the beam, say at ⅔ of its depth, to the bolt under the beam over which the trussing rod passes, or to which it may be attached. I think this formula will apply when the strength gained by the rod is greater than the original strength of the beam, or when the trussing rod is attached to a pillar much deeper than the beam. In the former of these cases it will also be needful to ascertain if the beam be strong enough, as a pillar, to bear the compression of ... [1]: /embed/mml-math-1.gif
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