RANGITATA BRIDGE.

Ashburton Guardian, Volume IV, Issue 1065, 4 October 1883, Page 2

RANGITATA BRIDGE.

We are indebted to the Timaru Strald for the following report of what took place at yesterday’s meeting of the Geraldine County Council The Ashburton County Council having made a peremptory demand for half the cost of the Kangitata traffic bridge extension, carried out by them, at their last meeting this Council resolved to employ Messrs Marchant and Meason, engineers, to make a professional examination and report upon the work. Their report was now tea ' :n follows :

The Chairman, Geraldine County Council. As directed by a resolution of your Council, we have the honor to enclose our report on the strength and condition of the Rangitata bridge extension. We may say that evidence concerning the manner in which the iron piles were driven has been collected from several and trustworthy sources, and having inspected and contract plans at Ashburton, we have every confidence that the details set forth in our report represent as nearly as possible the tru; facts. We carefully examined the bridge extension, and tested each span and pier by means of a travelling load of about 24 tons, and results of which will be found in our report. We have, etc., F. W. Marchant, G. Laing-Meason. REPORT ON THE RANG tT AT A BRIDGE EXTENSION.

Wrought Iron Pile Foundations. These consist of 18 piers of 4 piles each, or 72 piles in all. The piles are 38ft long and 6in in diameter; each being in three lengths, scarf welded together. We found that 13 piles out ofjyz were broken in driving, at first weld from head of pile. None of these broken piles were drawn or replaced by new ones, so that there are 59 piles in the bridge of full length, and 13 about 26ft long. The fracture of these 13 piles took place in nine cases above the capsill level and in four cases below it. We believe that the piles which broke above capsill level were driven down to that level, while those that broke below were drawn up a few feet above the level, and then re-driven to it. The condition of these four piles must be considered very unsatisfactory. Fortunately not more than one of them exists in any one pier, and we feel convinced that the other three piles composing a pier must be sound and fully driven, or they would not have stood our test as satisfactorily as they have done. We may add that no apparent necessity existed for such a proceeding, as there are at the present time four or five full length extra piles still unused. Inspection of the broken pile ends shows that breakage was due principally to unsound welding, besides which the iron exhibits a highly crystalline and “ cold-short” fracture. We cannot offer any decided opinion on the condition of the lower welds of piles beyond the fact that should the welding be defective, the l tendency to fracture whilst being driven would be considerably less in their case than in the case of the upper welds. Load Test on Bridge.—To enable us to form a sound opinion of the strength of the bridge, and the manner in which it has been built, we tested each pier and span by means of a travelling load of- 24 tons weight. In no case did we find any vertical movement in the iron piles composing the piers, while the lateral vibration was only that which the soundest and strongest material would have exhib ted under the circumstances. Though we think that the arrangement and jointing of the girder members might have bee 1 iniproved upon, still they are of ample strength, [the deflection of the girders under the test jload being within reasonable limits, and without permanent set. Abutment at North end of Bridge.—This is supportel by the walls of a concrete culvert previously existing at this • point. The wing walls and face of the abutment have been protected by a boulder apron, consisting of stones to an average size of about half a cubic foot. There is no doubt this boulder apron will be swept away by a very moderate stream, and we think some inexpensive means might be adopted to enable the abutment to resist more scour than it will be able to do with the present protection. However, should the river really set in at that point the only safe course to adopt will be to extend the bridge still further. Conclusion.—After having very carefully considered all the forces in connection with this work, and having made the necessary calculations, we have formed the following conclusions 1 That the bridge is of sufficient strength to withstand the heaviest travelling load ; 2 that in no case would the point of the shortest piles be less than 14ft below the lowest scour of the river, which we consider a sufficient depth ; 3 that the piers are of sufficient strength to withstand the lateral pressure of the swiftest and deepest flood occurring in the river, even if only two piles in each pier were sound and of full strength. (In this conclusion allowance has been made for the collection of flood rfibbish round the piles.) (Signed) F. W. Marchant, A.M. Inst. O.E, G. Laing-Meason, O.E. The report was considered very satis? factory by the members present. The Chairman expressed himself well satisfied with the test. It was made with two wagons loaded with shingle. They started from the north end, and he advised them not to take the loads over the old bridge —he did not believe it safe, but he did not know whether they took his advice or not.

la reply to a question whether any writ had yet been received from the Ashburton Council, the Chairman said he had written to the Chairman of that Council asking, as a favor, that the writ should be withheldluntil after this meeting at any rate, seeing that steps were being taken to obtain an engineer’s opinion about the work.

Mr Talbot thought it would have been quite unjustifiable for the Ashburton Council to go the length of issuing a writ. However, the engineers’ report being satisfactory they must now see about paying. The accounts ought to be examined first'to see that they were correct and fair. A rate must bo struck, but it would take some time to collect, and as the Council had some money on fixed deposit, he would suggest that that sum be handed over in the meantime. He would move first—“ That notice be given in accordance with the Rating Act 1882, that a rate of one farthing in the pound on the rateable value of the County will bo struck at a special meeting of the Council to be held on Saturday, 20th October, the same to be a general rate for the period ending March 31st, 1884, and payable in one sum on November 10th next.” Mr Talbot spoke in favor,of making th« rate as low as possible in view of the dulness of the times, and a rate of one farthing he showed would be quite sufficient. They had about L 1,700 in hand, and such a a rate would produce about L 4,100, so that after paying the Ashburton Council’s claim of about L 4,000 and deducting expenses, they ought to have a balance of L 1,500. The following motion was also carried:— Moved by Mr Talbot, and seconded by Mr Ululee—“ That the Ashburton County Council be asked to accept the sum of L 1,500 now available for immediate handing over to them, and that the balance be allowed to stand over pending the collection of the rate now to be struck, this Council guaranteeing full liquidation on or before December 31st, 1883.