HAMILTON RAILWAY BRIDGE.

New Zealand Herald, Volume XIX, Issue 6571, 8 December 1882, Page 3

HAMILTON RAILWAY BRIDGE.

TO THE EDITOR. Sir, —The first thought suggested to the mind on viewing this structure is the possibility of a second Tay Bridge disaster occurring. The river appears to be about 400 feet wide, and the bridge is supported by a concrete pier on each bank, and two sets of piers in the river. These piers consist of two cylinders in each set, said to be 9 feet in diameter. They are sunk about 100 feet below the bed of the river ; the water is 30 feet deep, and they rise 70 feet above it, being 200 feet in all. Now, supposing these piers are not resting on a perfectly flat rock, and that the continual vibration produced by loaded trucks passing over, the action of the stream and wind, causes them to settle

say half-an-inch on one side, they will be thrown off the perpendicular about S feet 4 inches, or nearly sufficient to make them fall with their own weight. But add to this the fact, that trucks carrying from 200 to 300 tons may be passing over during a. gale, when the whole weight will be thrown on one side, and it can easily be seen that: the weight being 100 feet from the fulcrum, the leverage must be enormous. To remedy this I would suggest sinking, say, 30 feet below the bed of the river t& avoid the current undermining the base of the pier; then building an oblong base, 40 feet long, 9 feet diameter and 30 feet deep. This would bring it to the level of the river bed. Then building a pier 40 feet at the base, 9 feet thick, aud terminating at, say, 12 feet across the top. This plan would give 654 feet of base on the two piers, as against 252 feet on the present plan, and would take 2360 cubic yards of concrete, as against IS6G for the present piers. But by my plan 15,540 feet of iron sheathing would he required, as against 21,600, as now built. Thus showing 494 cubic yards of concrete; against it 60G0 feet of sheathing in favour. The excavating would be about 400 yards in favour of my plan, and much easier owing to the depth, and men could go down and bottom to see whether it was safe or not, which, I believe, could not be done in the present case, as the men could not stand the pressure ; and with such a base the resistance to lateral strain would be very great, and the viabratioa would not make it settle on one side.—l am, &c., John Wilson, 81, Queen-street.