NEW RAILWAY BRIDGE.

New Zealand Herald, Volume LXVI, Issue 20264, 25 May 1929, Page 13

NEW RAILWAY BRIDGE.

SPAN OVER THE WAIKATO.

REPLACING OLD STRUCTURE.

ESTIMATED COST OF £30,000.

Having served for 55 years, tho railway bridge over tho Waikato River at Ngaruawaliia, is shortly to bo replaced by a steel structure of improved type. Preliminary work is being undertaken by tho Railway Department in preparation for the actual construction, which will bo done by a private firm. Tenders are to close in July, when the work will pass out of tho hands of tho department. Although the old bridge, which has stood since the railway lino was first taken through tho district, is still perfectly sound in many respects, its replacement was deemed advisablo owing to the increased loading passing over it. There is at present a speed-limit imposed on all trains passing over the bridge, and this, too, was not considered convenient. A serious factor in the decision to replace the present structure was tho larger size of locomotive now being used, increased vibration resulting in lowered resistance. In spite of their age the limbers of the old bridge aro still remarkably sound. About 250 Tons ol Steel. Constructed at an approximate cost of £30,000, the new bridge will be 451 ft. long and will carry a singlo track over six spans. There will bo three 117 ft. spans, two of 38ft. each and ono of 24ft. Tho bridge will be 35ft. lower downstream than tho present structure, and as a result it will bo possible considerably to straighten tho lino leading into Ngaruawaliia.

A total of about 250 tons of steel will be used in the- construction. Two hollow cylinders with a diameter of Bft. at the top and 10ft. at the base will carry tho central span, and on either sido of these will bo two solid cylinders on piles. Substantial abutments will bo built on either shore. A fairly heavy task will be provided in tho driving of 166 piles, whose lengths will vary from 30ft. to 50ft. Tho centre spans will consist of steel plates and the others of steel trusses. Widening ol Embankment. Preparations for the actual construction of the bridgo involve much work, as the new alignment necessitates tho extension and widening of the present embankment. A small strip of land on the west of tho present line has been acquired by the department in order to allow of the erection of tho bridge lower down stream and to permit of the partial straightening of the curve after the lino leaves tho Ngaruawaliia end of the bridge. Extensive pile-driving tests have also been made for some timo past.

When completed tho new bridge will bo one of tho most up-to-date structures of its kind on the railway system. Ample provision will be mado during construction for the passage of vessels on the river, a space of 50ft. being left between limber supports on one of tho central spans.