New Suspension Bridge over the Manawatu

Progress, Volume XIV, Issue 1, 1 September 1918, Page 305

New Suspension Bridge over the Manawatu

inches, each being 3 feet and 6 inch x If inches diameter. A 5-8 rod passes through the pipes attached to bottom and top chords with stay bolts of truss, the number of rods being 412, There are pipe rods to the number of 202, with 404 cast iron sockets top and bottom of pipes, or 614 rods in the truss. The total number of bolts used in the bridge is 2,030 (anchor bolts not included). The timber used in the construction of the bridge was about. 30,000 feet, joist 9 inch x 4 inch and 9 inch x 3 inches, decking 8 inch x inch. All the timber is of black birch. The strength and stability of the bridge have been well tested, many loads of flax having passed over it. Each load, drawn by two horses on light rails, consists of two trucks, each truck having about four tons of flax. One thing that impresses experts who have examined the structure is the way in which the

(Contributed)

The suspension bridge over the Manawatu River, erected for the Tane Hemp Company by Mr. Joseph Dawson, of Pahiatua, is said to be the biggest bridge of the kind that has yet been built in New Zealand. The site is on the Foxton line, about 9 miles from Palmerston North. The dimensions and character of the structure are as follows •—The anchors and towers are of concrete; height of towers from foundations to top of saddles 68 feet, from deck to top of saddles 52 feet. There are 180 cubic yards of concrete in the towers on each side. Three cement arches are spaced between each tower, requiring six tons of iron reinforcement. The weight of concrete in the towers is about 280 tons. Twenty cubic yards are used in each anchor, or 80 cubic yards for the

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four. The cables are of the best plough steel, and arc 16 in number. They have a breaking strain of 60 tons each, or a total of 960 tons, and are fastened to the anchors with steel channel iron and 2-inch diameter iron rods. The rods pass through a pike fixed in the concrete, and are screwed up at the back with strong nuts. There are a number of rods 32 x 30 feet long of 2-inch iron, to which the cables are attached, the length of the bridge over all being 473 feet. The cables, which go over saddles, rest on wheels to save friction to the ropes. The total length of each cable is 750 feet, and 12,000 feet of steel rope are used in the 16 cables. The suspending rods (404) arc double, and of £ inch iron, which are fixed to the cables with strong clips, the longest rods being 48 feet, and the shortest 8 feet. The truss is 4 feet 6 inches from joist to top of chord, the timber being of 7-inch x 5-inch, and 5inch x 5-inch. Vertical poles are spaced at 4 feet 6

suspending rods and chords are - bolted, and the extraordinary freedom from vibration. Mr. Dawson says: The cost of the bridge, including all engineering expenses, was £2,653 9s. 9d., the bridge being 473 feet over all and taking a train load of 8 tons or more, and. any ordinary traffic. This bridge was, built in war time and cost under £6 the foot run of the bridge; and I. was the contractor for a suspension bridge approved by the Government engineer, 320 feet span, the cost being £B,OOO, or £25 the foot run of the bridge. ,1 got the timber on the site for about 16/- per hundred feet. The timber for the Rangiotu bridge (described in this article) cost about 25/-, and the iron £3O a ton, instead of £lO for the Government bridge. 1 built another suspension bridge for the Government which cost about £2,500 for a 220 feet span; this bridge had wood towers, the anchors being concrete, and cost £ll per foot run, and built in the cheap times.”

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