On Some Common Errors in Iron Bridge Design

31 the width and the bar becomes square. The outline of the bar must consist of easy curves, and sharp re-entering angles must be most carefully avoided, (see Fig. 37). (r) The pins must be designed as beams to endure the bend- ing moment clue to the pull of the eyebars, and if this necessitates a larger diameter than the previous rule («) gives, the eyes must be correspondingly enlarged. In America the eyebar construction in its most perfect form is almost universal in the tension, parts of the larger bridges, and a very magnificent example of recent American practice is to be seen in the great Hawkesbury Bridge, N.S.W. In Europe, India, and Australia it is less usual, and where it exists is often of very defective design, as the following examples will show. Fig 34 represents the wind bracing of the piers of the ill-fated Tay Bridge, which was destroyed by a gale in 1879, involving the destruction of a whole railway train and every person upon it. Here no attempt has been made to form a proper eye, and only about half of the strength of the bar is really utilized. Fig. 35 represents a tension eyebar from the Taptee Viaduct, Bombay, Baroda, and Central India Railway, of which the Gun- dagai Bridge, N.S.W., appears to be a copy. It is also very inefficient, utilizing less than half of the metal in the bar. Fig. 36 represents the eyebar diagonals of the great Moora- bool Viaduct on the Geelong and Ballarat Railway. The most cursory inspection will reveal how far this departs from orthodox propoi’tions with its diminutive pin, its sharp internal angle at A leading to great local intensification of stress and its two sides in the aggregate barely equal to the body of the bar instead of being 33 per cent, greater. Experiments were macle at the University on models, first in lead, then in brass, and finally in iron on a quarter full size scale, to determine the efficiency of this joint, and the results varied from 64 to 70 per cent. Further experi- ments by the Victorian Railway Department led to a practically identical conclusion. Considering that there are several hundreds of these bars in the structure it does seem strange that this defective form was decided upon without experiment, and also that the example of Brunel and others who had used fairly good 3