THE FORTH BRIDGE.

Wairarapa Age, Volume XXV, Issue 10713, 27 December 1913, Page 7

THE FORTH BRIDGE.

STRENGTHENING OPERATIONS

Some important renewal work is about to be commenced at the Forth Bridge. When the Forth Bridge was designed more than 31 years ago the loads and the train speeds calculated were considerably in, excess of those then assumed as probable for a long period ,of time; but progress in these respects,* particularly in the weight and power of locomotives and the loads behind them, have advanced enormously. Therefore, although the limits have not yet been reached' so far as the strengch of the bridge is concerned, the directors of the Forth Bridge Company have decided further to anticipate the developments of the locomotive engine antf reconstruct part of the flooring and troughs in which the railway track is laid over the bridge. In order to ensure that the method of procedure will most effectively meet the requirements, it has been decided at to proceed with tile strain' section, to be followed by a reconstruction from end to end of the bridge. To show the great development in traffic over the bridge since it was opened over 23 years ago, it may be mentioned that the total number of trhins per annum increased from 37,610 to 52,944/ or about 40 per ce'nt, while the collective weight advanced from 9,941,612 tons to' 15,894,410 tons, or about 60 per cent. The 23 years' total is 1,191,500 trains and engines, while the collective weight is 317,894,789' tons. The "'average weight of the traiiis 23 years ago was afiout 260 tons. Last year it . was ju'st under 300 tons. When the Board of Trade tested the bridge before it was opened they kchose the heaviest locomotives belonging to the North British Railway Company, who were to work , the traffic., These were only of 73 tons, including tender, the axle load being under; 16 tons.' Now there are in regular use locomotives of the Atlantic type weights, . including tender, of over 120 tons, the maximum, axle load being ( 20 tons. In addition there is the all-important question of speed. That thq. structure has stobd the test of such , increasing severity proves not only that the original design, was satisfactory, but that the upkeep and maintenance had been thorough, everything being in satisfactory condition.

While there is no present reduc r tion in strength for the. supporting of the load, and still a thoroughly adequate margin of safety for increase in size of locomotives in the immediate future, *the directors have decided to prepare txmeonsly for probably developments, and have arranged to relay from end"to end part of the floor and'the troughs carrying the inner rails in both up and down lines. It is estimated that it will involve 2500 tons of structural stee! for the renewal of troughs and floor from end to end of the of the Of this total, the addition tq the weight of the present steelwork of the bridge is only 750 ,tons. This in a bridge wlyoli required 54,160 tons of steelwork is "•insignificant, and proves further the splendid character of the original conception and workmanship.'and Hlte care exercised in maintenance.

The woiJv will take some years to execute, as operations can only be carried on during summer months, and it is proposed, not to interfere with traffic, on week-days, while, even on Sundays ~one line only will be closed.