206 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



IJultj 



lead me tu tlieconclusion,tliatllie girder broke in the middle from its weak- 

 ness to resist the strain, increased hy tlie laying on of the ballast. 



"The opinions of Mr. Stephenson and iMr. Locke, founded uu the alleged 

 facts as til the paint on the tender, the broken carriage-wheel, and the snips 

 in the chairs, appear to fall to the s'louml, as they must have been misiu- 

 formed on those particulars, which can all be disproved. 



"HtNRY Robertson, Engineer." 

 " Chester. June 15,1817. 



Captain Symonds, K.E., and Mr. Walker, who were retained by Go- 

 vernment to examine into the cause of the accident, presented to the in- 

 i|uest a very lengthened report, the following are extracts from it : — 



"That the bridge was of suflii-ient strength if the cast and wrought iron 

 be supposed to act together, each taking its equal proportion of the strain. 



•'That there is groat difficulty in insuring the joint action, and that if 

 this is a part of the principle of the bridge, we do not approve of it. 



"That neither the wrought nor the cast iron, taken separate'y, was suf- 

 ficient for perfect slahility ; and that, to have insured this, the cast iron 

 girders alone should have been of sullicieni strength to carry the whole 

 weight, wiih an ample allowance for the various circumstancei (some of 

 them peculiar to this bridge) which we have explained. 



"That, with the exception of the bends, or warps in the lop flanges, the 

 castings are of good quality. That the wrought iron is also of good quality. 

 " That Ihe stonework of the piers and abutments is good ; and in no way 

 conlributed to the failure. 



" We now come to the question, what was the immediate cause of the 

 accident > As the bridge had carried as great or greaier loads before, the 

 suggestion that there was something peculiar in this case, as the end of a 

 raifhaving projected from the straight line and been struck by the engine, 

 or the tender having got off Ihe line and struck the girder laterally, is not 

 improb.ible. The engineers who were called by the Railway Company 

 considered thai the breaking of one leaf of the wrought iron that was next 

 the tender, the piece that was struck out of the girder, and the damage to 

 the abutment wall, are all proof of Ihe fact that the accident was caused by 

 the lender having got otf the line, and broken Ihe girder by a heavy lateral 

 blow. We refer to the evidence of Mr. Robert Stephenson, Mr. Locke, 

 Mr. Vignoles, and Mr. Gooch, who were also of opinion that the strength 

 of the girder was sufficient. As to this latter point, we have already slated 

 Ihe principles upon which alone this conclusion could have been arrived 

 at, and our own opinion. As to the tender or Ihe carriage immediately 

 behind it having got olV the railway and damaged Ihe abutment walls, there 

 is no doubt ; and if Ihe lender struck the side of the girder, when the latter 

 was under great strain, a fracture was the probable consejuence. This is 

 on the presumption of the lender having got off ihe line from some oiher 

 cause than the breaking of the girder. 



" Our own decided opinion, formed from the statement we have made as 

 to Ihe strength of the girder, and from the position in which the broken 

 pieces were found, Ihe two halves being each in a straight line, or nearly 

 so, but at an angle with one anoiher, is that Ihe tirst fracture took place in 

 the centre of the girder, and not at the end which rested on the abutment. 



" In corroboration of this last view, the addition that was made to the 

 permanent weight of the bridge, immediately before the accident, by Ihe 

 ballast spread over it, and the fact that when a weight, partly permanent 

 and partly passing, but which together formed a considerable portion of 

 the breaking weighi of the girder, are in continual operation, flat girders 

 iif cast-iron suffer injury, as Iheir streu;;th becomes reduced ; and if, when 

 this has taken place, the momcnliim of Ihe passing weight is increased by 

 an irregularity of the rails, or in ihe motion of ihe engine, to which Ihe best 

 made and managed railways are subject, a fracture is likely to follow. 

 The proliabilily of ihis having been so in Ihe present case, and the fact of 

 the tender having been off the line, and having been drivvn up with great 

 violence, so as to break the end piece of the girder by the blow, are to be 

 weighed against each other in assigning Ihe cause of the accident. 



" Having reference to other cises, it is proper to state that Mr. Robert 

 Stephenson slated in his evidence that he had erected a number of bridges 

 on the same principle as this, and that this was the first failure. We have 

 not examined these bridges ; they are staled to be all of a less span than 

 the Chester bridge, but that Ihe dimensions of Ihe parts are proportionally 

 less ; and it may perhaps be argued from the above numerous examples, 

 and the opinions of Ihe eminent engineers opposed by ihis one failure, that 

 we are mistaken in considering the weakness of Ihe girder to be the cause 

 of the failure in the present case, and unnecessarily cautious in the objec- 

 tion we eiilerlained, and have expressed, as to the principle of this bridge 

 and its security; hut, as we entertain these opinions very decidedly, it is 

 our duly (by no means an agreeable one) to express them." 



Tlie Verdict of the Jury. 



After an hour's deliberation, the foreman, Sir E. Walker, returned the 

 following as the unanimous verdict of the jury : — 



"We find that (Jeorge Roberts, John Matlhews, and Charles Nevitt, 

 were accidentally k illed on the evening of Ihe 24lh of May last, in the parish 

 of St. Mary on the Hill, in the city of Chester, by being precipilated along 

 with a train of carriages on the bank or bed of the river Uee, from the 

 breakage of one of the 12 cast iron gilders constituting the railways-bridge 

 over that river. 



" We find also that Isaac Powis died on the 26lh of May from injuries 



he received at ihe same time and place, and from the like cause; and we 

 find that Tluniias Anderson came by his death on the 24th of May last, in 

 the parish aforesaid, by being accidentally thrown from the lender on to the 

 rails. 



" We are further unanimously of opinion, that the aforesaid girder did 

 not break from any lateral blow of the engine, lender, carriage, or van, or 

 from any fault or defect in the masonry of Ihe piers or ahulineuts ; but from 

 its being made of a strenglh insuHicient to bear the pressure of quick trams 

 passing over it. 



" We feel that the 11 remaining girders, having been cast from Ihe same 

 pattern and of the same strengih, are equally weak, and consequently 

 equally dangerous for quick or passenger trains as was Ihe broken one. 



" We consider we should not be doing our duly lowarils ihe public if we 

 separated witlmul expressing our unanimous opinion, that no girder bridge 

 of so brittle and treacherous a metal as cast iron alone, even thuiigh trussed 

 wiih wrought iron rods, is safe for quick or passenger trains ; and we have 

 it in evidence before us, that there are upwards of lUi) bridges similar in 

 principle and form to the late one over the riier Dee, either in use or in the 

 course of being conslrucled, on v.irious lines of railway. We consider ail 

 these unsafe, more or less, in proportion to the span ; still, all unsafe. 



" We therefore call upon her Majesty's Government to in^lilule such an 

 inquiry into the merits or demerits of these bridges, as shall either con- 

 demn the principle, or establish their safely to such a degree, that passen- 

 gers may rest fully satisfied there is no danger, although such bridges may 

 deflect from 1 J to 5 inches." 



The Coroner slated that that portion which related to the death of the 

 deceased could only be taken as their verdict. Their recomnieudations, 

 however, he would forward to Ihe Railway Department oi her Majesty's 

 Government; and no doubt the press would give them due puljlicity. 



Toe bridge crosses the Dee river at an angle of about 4s°, and is con- 

 structed with three spans — skewed to the same angle — of 98 feet each in 

 Ihe clear; each span being sustained by four trussed girders, 109 feet long, 

 one on each side, and two in the middle, making Ihe two roadways inde- 

 pendent of each other ; on the inside of the botioni flange of each pair of 

 girders, shoes are cast, having a dove-taiied socket, into which wrought 

 iron cross ties are fitted, to secure the girders from springing outwards at 

 Ihe bottom. Between these, and resting upon the same flange, are strong 

 timber bearers or joists, upon which a flooring of foar-iuch planks is laid ; 

 on this Ihe longitudinal sleepers are fitted, carrying the rails and check- 

 rails, the latter being continued 20 feel beyond the span of the bridge each 

 way. 



The train passing over the bridge at the time of the accident consisted 

 of the engine and tender, following which the carriages were arranged — 

 1st. One first-class : 2nd. One second class (with break and guard-box) : 

 3rd. One second : 4th. Luggage-van : 5lh. Second-class. 



Each girder is in three lengths of cast iron, bolted together at the joints, 

 making 1U9 feel in length and 3 ft. 9 in. in depth, and surmounted over 

 each joint by a connecting scarfing, 13 feet long and 3 feet high. The 

 clear span of the bridge is 98 feet, and the bearing 5 fl. in. at each 

 end. 



The width of the top flange is 74 inches, and thickness 1^ inch on the 

 edge; thickness of the web 2i inches; width of lower flange 2 feet by 

 2J inches thick. The top section, including Ihe molding on the under- 

 side, contains 14 square inches ; Ihe lower flange and molding Cfi square 

 inches, and the web SO inches : making in all 100 square luciies. On each 

 side of the girder there are four wrought iron tension bars, in. by 1^ in. 

 the collected section of Ihe eight bars (lour on each side) contains 00 

 inches. The bars are put together in lengths, as usual for suspeusion 

 bridges; and at tlie joints of the cast-irou beam, a wrought iron bolt passes 

 through Ihe eight thicknesses of wrought iron bars and the cast iron gir- 

 der. To this cross-bt»lt are suspended two other bolls, which pass through 

 the cast iron dovetailed plale, untler the joints, and secured on the under- 

 side with screws and nuts, to bring Ihe plale up taut to Ihe flange ; and 

 the ends of the suspension bars at the abuliueul are secured to a cast iron 

 raising piece by cross keys. 



It will thus be seen that the girder consists, in section, of a cast iron 

 girder (similar in form lo fig. 2) and eight thicknesses of wrought iron 

 suspension bars : these wrought irou bars, from the very flat angle at which 

 they are set and secured lo the cast iron girder itself, seem to be a very 

 poor safeguard against the breakage of the cast iron. In fact, on account 

 of the tension bars being inclined at such a small angle, that a displace- 

 ment of the panicles of the cast iron girder, quite sufficient for iraciure, 

 would have produced scarcely any extension of the wrought irou bars, 

 and, therefore, hardly called into play any resisting force from their ten- 

 sion ; ihe tension-rods, in short, were of about as much service to the 

 girder as a piece of pack-thread passed from end to end. The scarfing 



