On Some Common Errors in Iron Bridge Design

is an immediate consequence. Strange to say, however, owing to some peculiar warp of the human mind, many persons persist on fanciful grounds in increasing the cost and diminishing the strength of structures by the introduction of curved members. A curious example of this is to be seen in. the evolution, of the frame of the modern bicycle. For years this vital part was made of ridiculous shapes presenting complex curves utterly contrary to scientific principles, and the result was, despite the most liberal employment of material, straining, weakness, and frequent fracture. The modern diamond frame, every part of which is perfectly straight, is thoroughly scientific, and, with half the material of the earlier frames, is far more rigid and absolutely free from fracture under ordinary and reasonable use. Perhaps the most extraordinary and inexcusable instance of this fault in modern times is to be seen in the huge and costly Jubilee Bridge over the Hoogly in India, described and discussed in the “Proceedings of the Institution of Civil Engineers,'’ Vol. XCII., 1888, an outline of the terminal panels of which is given in Fig. 16. Here one of two things ought to have been, done, either AB should have been macle perfectly straight, or the space C should be plated over, the latter being the only practic- able remedy now. This grave fault was animadverted upon by myself in the “ Engineer” of 5th June, 1885, and afterward by Pro- fessor Max am Ende before the Institution of Civil Engineers, London. A second and still more recent example is seen in the Warburton Bridge over the Manchester Ship canal, illustrated in “Engineering” of 26th January, 1894. But while condemning as strongly as possible such designs as the Jubilee and Warburton Bridges, I would make an exception in favour of many bowstring and hogback girders such as the new Cremorne Bridge on the Gippsland Railway near Melbourne. Here the top chord forms a bold and graceful curve, very pleasing to the eye, but the panel points where the web members come in are so numerous that the curvature in each panel or length of the chord is imperceptible. If the chord was made polygonal, each panel being straight, its outline would not differ visibly from what it is at present. A chord curved at a large radius and divided into panels so short as to be practically straight, cannot