MANY-BRIDGED N.Z.

Evening Post, Volume CIX, Issue 124, 28 May 1930, Page 13

MANY-BRIDGED N.Z.

CHANGING DEMANDS

BUSY PERIOD ARRIVES

WOOJ) STILL USEFUL

Few countries have as many streams at frequent intervals as New Zealand) and it is therefore natural that bridges should figure prominently in all transport routes, and that they constitute a .■considerable proportion of the manifold J cares of the Main Highways Board. There is just now a bigger programme of repairs to bridges and, where repairs will no longer meet the need, of reconstruction, than has probably previously been known to engineers here. More activity was seen in the period of the Dominion's greatest expansion, when many of the bridges now needing repairs were built, no doubt, but as bridges have their" alloted span of years, and it is by no means three-1 score-and-ten, it follows that that earlier period of activity in construction is now being followed by a period of repairs, .in some cases overdue. MODERN NEEDS. It must not bo thought that until now it has not been necessary to repair the earlier-built bridges. This work has been going steadily on for the past twenty years as occasion arose, but to tho effects of decay ,has been added a new reason for reconstruction, the dcmdnds of heavy motor traffic, and now the Public . Works Department classes bridges us inadequate which are stvue-. turally unsafe, too light, for modern traffic, too narrow for modern traffic, are on poor alignment, or unsatisfactory and often dangerous because of combiiied road and rail traffic. The speeds and weights of road freights, added to the speed and frequency of motor passenger traffic, have made better approaches and wider bridges essential. A FORMIDABLE LIST. In the "Wellington district alone £75,000 is being spent on the larger bridges as follows: Aorangi, £14,000; Fitzherbert, £40,000; Kokotau, £12,000; Ruarnahunga, £11,000. Tho extent of the reconstructions and reconditioning, rendered necessary by time and the motor traffic may bo gauged from, the fact that the total New Zealand programme runs, to £440,000, including the following bridges:— North Auckland.—Kahoe, £5000; Puhoi, £0000; Skelton's, £0000; Waiwcra, £8000; Whau, £5000. Total, £30,000. ' Gisborne.—Awatere, £6000; To.Arai, £6000; Waipo.ua, £15,000. Total, £27,000. Hawkcs Bay.—Magatewainui, £8000; Porangahau, £6000; Rissington, £4000; Waipukurau, £22,000. Total, £40,000. King Country.—Manganui-O-To-Ao, £7000. Taranaki.—Urenui, £6000. ■Warigauui.—Bulls, £40,000; Hautapu, £5000; Vinegar Hill, £6000. Total, £51,000. Nelson.—Newton, £6000; Wairoa, £9000. Total, £15,000. West . Coast.—Ahaura, £15,000; M'Douald's, £4000. Total, £19,000. North Canterbury.—Hurunui, £17,000; Ashley, £22,000. Total, £39,000. Can terbury Central. —Waimakariri, £19,000. - Canterbury • South. —, Ashburton, £19,000; Pareora, £15,000. Total, £34,000. Otago Central.—Alborfrown, £6000. South Otago.—Clutha, £56,000. Southland.—-Aparhna, £-20,000. Theso figures deal'only with traffic bridges, or those for duel purposes, and do not include new railway bridges on existing lines, or repairs to existing bridges. The Public Works Department is building a big bridge at Feilding over the Oroua River,, the Aorangi bridge above mentioned. There will be twelve 48ft sparis, and a five-foot footpath, in reinforced concrete, and the bridge will be for double traffic, A good deal of attention is being paid to the approaches. The Fitzherbcrl; bridge at Palmerston North is another big one. • OLD SPANS USEFUL. Following out the principle that it is safer in these days of change to build in temporary materials, tho big bridge erected two years ago on tho Shannon-i'oxtou highway was built of 60ft plate steel girders on hardwood piles. When the Mauawatu River has been put into its :new position, the present channel of the river will be a mere backwater, and the spans, as in the case of other bridges, will be available for use elsewhere. Ironbark and steel allows of this where reinforced concrete would mean a loss. Some of the spans of the original ShannonFoxton bridge have been used near Dannevirke, carted out in the summer, and a real good job has been, made of a bridge there at half the cost of new material. It should stand for at least another thirty years. In the case of the renewal of the bridge for the railway at Otaki, and at other places, it will be quite possible that whole spans which, are getting on the light side for heavy rail traffic will be made available for local bodies to bridge streams in outlying districts, an especially valuable matter in Taranaki, where many small streams are met. EASING LOCAL BODIES. Many bridges which are in existence on main highways to-day are 'One-way bridges, built many years ago at a time when narrow bridges created no danger to the travelling public. They served the purpose of stream, crossing well enough in the ease of slow moving traffic, but bridges to-day must move forward with the. transport problem. Tho Main Highways Board has adopted the principle of two-way traffic bridges on all the more important highways, and oven where bridges are being built for to-day's, needs tho prospective traffic several years hence is taken into account when deciding whether1 a twoway bridge is necessary or not. The subsidy paid by the Main Highways Board on bridges has gradually advanced from £1 for £l.to £2 for £1 up to £10,000, and to £3 to £1 in excess of £10,000. The board, in granting this higher rate of subsidy over ordinary construction works, has recognised that tho construction of Jargo bridges falls very heavily on local authorities. It will bo satisfactory to other sections of the community to realise that tho increased subsidy conies largely from motorists.