1845;] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



381 



EXPERIMENTS ON THE STRENGTH OF CAST IRON GIRDERS. 



In a paper read by Mr. Redman, at the Institution of Civil Engineers, an 

 account was given of some experimeuts on the strength of the girders which 

 'support the platform of tlic Terrace Pier, Gravesend. We cannot avail our- 

 selves of the whole of Mr. Redman's paper, as the auhjcct has been already 

 noticed in this Journal. The following particulars will however be accept, 

 able. 



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The columns of the pier are held together at their tops by means of east- 

 iron cross-bracing frames, fitted between the caps and bolted to them (fig. 

 I) ; they were provided with a projecting clip at each angle, to support them 

 while fitting, before the bolts were placed in. 



A B represents one of these braces at right angles to the length of the 

 platform. The columns supporting the platform are arranged three by three, 

 consequently the brace is attached in three places — its centre and two ends. 

 The figure aKo shows truncated portions of the lougitudinal girders (A, B C,) 

 and some of the cross joists of the platform. 



The three girders which support the platform over the esplanade, from the 

 ahutments to the first tier of columns, and those of the T head of the pier 

 are east to one section (fig. 2) ; the nine girders forming the three main 

 openings are also of one section (fig. 3) ; six of them are 54 ft. 9 in. long, 

 and the three next the T head are 55 ft. 9 in. long; they are all of a parallel 



Fig. 3. 



depth and breadth top and bottom, and the long girders are cambered 1| 

 inch in their length ; they are all provided with projections on the top fianch 

 to receive the joists. The weight of these girders is very materially reduced, 

 by making the sectional area of the ends about one-half of that at the centre 

 (figs. 2 and 3). The smaller girders were proved to 20 tons on the centre, 

 with which they dLllcctcd, on an average, ^ inch, and the large girders 

 were proved to 45 tons on the middle. Their deflection averaged 1^ inch, 

 and the results, as shown by the table of experiments were very regular. 

 The section at the end of the abutment girders is marked a, the section at 

 the centre b; c h the section at the end of one of the top girders, and d 

 the section at its centre. 



The girders are secured from lateral twist and vibration by wrought-iron 

 ties, 2 inches diameter, with clip ends, embracing the top flanches of the 

 outer girders, and keyed to them ; they are screwed up to a casting fitted 

 and keyed upon the centre girder. These ties are fixed over the centres of 

 the main spans ; the abutment girders and those of the T head on the N.E., 

 S.E., N.W., and S.W. sides (which are most exposed) are secured in a similar 

 manner, the ties being, however, shorter, and secured to the joists which 

 form the tie. 



To test the quality of the iron, bars I inch square and 3 feet 3 inches long, 

 were cast horizontally from the ladles from which the castings were run, 

 and were broken across with a hearing of 3 feet. The average breaking 

 weight, of sixteen experiments, was 7H2 lb. ; the highest result was 896 lb., 

 and the lowest G72 lb. ; in this latter case the bar was barely of the prescribed 

 size, and two small air-holes appeared in the fracture. The other cases that 

 yielded the least amouut of resistance were also, generally, barely of the pro- 

 per dimensions, or there were air vacuities. In most cases, where air-bubbles 

 occurred, the bars did not break at the centre, but they discovered the faulty 

 place nearest to the centre, in some cases as much as 2 inches from it. 



Table of Experimental Tests of the Strength of the Cast Iron Girders, 

 showing the deflections at their centres in iuches, 



ABUTMENT and T-HEAD GIRDEnS. 



LONG GIRDERS. 



Section of the abutment girderi 



Section of long girders. 



After reading the paper referred to, Mr. Redman added that with respect 

 to the form and the dimensions of the cast iron girders, he would not in 

 future, for several reasons, reduce the thickness to such an extent towards 

 the extremities. The parallel form had been adopted, on account of the 

 greater facility afforded for attaching the entablature and the platform, but 

 the beams (which were of great length) twisted much in cooling, in conse- 

 quence of the inequality of thickness of the metal, and this gave some trouble 

 in fixing them. The girders had returned to their original camber after the 

 removal of the strain, applied in testing them. He had not observed that 

 there was any perceptible deflection from their own weight, before the strain 

 was applied. 



Mr. J. R. McClean said, in allusion to the length of the cast iron girders, 

 the longest beams that had been executed in Staffordshire were those for the 

 bridge on the Tame Valley Canal ; they were designed by Messrs. Walker 

 and Burges, and were cast at the Ilorseley Iron Works. 



The dimensions of the girilers of the bridge at Perry Bar, and of the Tow. 

 jng Path Bridge at the junction of the Birmingham and fazeley Canal, were — 



