On Some Common Errors in Iron Bridge Design

30 In arranging rivetted joints it is recomm ended that there should be a width of solid metal at least equal to 1 j diameters of a rivet between each rivet hole and its neighbour or between a rivet hole and the edge or end of the plate, for drilled work, and for punched work, that the shearing area of the rivets be 20 per cent, in excess of the tearing area of the plate, and that the aggregate diametral bearing area or sum of the products of the diameters of all the rivets piercing a given plate into the thickness of such plates shall be not less than half the tearing area of that plate. ° If a weak rivetted joint be discovered in an existing structure, and it is not possible to increase the number of the rivets, an improvement way often be made by removing the rivets one or two at a time, carefully enlarging the holes with a suitable cut- ting tool, and inserting larger rivets. • This may be clone very advantageously in punched work, for the metal removed is that which was damaged in the process of punching, and therefore of little value. In eyebars the attempt is usually macle to secure perfect effi- ciency, in other words to make the joint as strong as the bar, and when the bar is very long there is great economical advantage, as the whole of the material is then utilized fully. In order to do this the proportions of the eye must be carefully attended to. These have been determined experimentally by Brune], Sir Chas Fox, and Berkley in England, and Shaler Smith and’ others in America, and their conclusions may be generally summed up as follows, averaging the results when the authorities differ, as they do, to a small extent. (<•?) The internal diameter of the eye or diameter of the pin must never be less than two-thirds of the width of the bar, and if the bar lias a thickness of more than one-fifth its width this should be progressively increased, till, when the thickness is half the width, tins diameter is 1-2, and when, equal, the bar having a square section, 1 -9 times the width. (Z>) Ihe sectional area of the metal on both sides of the eye should be 1-33 that of the body of the bar for bars whose thickness does not exceed one-fifth of the width, increasing to 176 when the thickness equals