OPIHI NEW BRIDGE.

Timaru Herald, Volume XIIC, Issue 13678, 21 August 1908, Page 6

OPIHI NEW BRIDGE.

TEXDEItiS OPENED. At yesterday's meeting of tlic Geraldine County Council tenders wire opened for Lli-tj construction of a, new traffic bridge over, the Opilii at the Main road. The tenders were alternative, for a bridge wholly of iron-bark and for one of reinforced concrete, and w-ere as follows Iron-bark bridge, 52 spans of 30ft., 20ft. roadwayW. H. Tubb £6965, I). Hopkinson £7055, W. J. Black £'355, A. l'earee £7595, H. Green £7980, 11. Foib.es £8429.

Bridge in reinforced concrete, 24 spans of 40ft., 20ft roadway:-—E. Hall and Sons £9325, W. H. Tubb £9822, O. Praser £15,468. The Council, having considered the tenders, resolved to recommend the Levels County Council to agree to -the joint acceptance of the tender of E.. Hall and Sons, for a bridge in the permanent- material.

The principal . points about the plans for the ferro-concrcte structure are that tins piles will consist of a rolled steel core of H. section (similar to the pillars supporting the upper floor of tlie C.P.U.A. new store on Heaton street), 38ft. long, encased in concrete down to aiid below scour level. Six piles in three pairs will form each pier. The roadway will bo an arched ehoet* of concrete 7 inches thick, reinforced with longitudial steels rods, and strengthened, and tied transversely, by webs of concrete, with embedded rods at- the base, at every sft. The ■'side-rail" iis a concrete gilder 711. from base to top, the upper nienibcr or parapet being a. reinforced beam of concrete 15 inches square. The piles, it will bo r.eeu, are- entirely different from those baing used in the Auckland whai"ves, which arc mainly of concrete with light rods embedded in it. The iron beams proposed to be used in this bridge are themselves strong piles, and would stand the driving .and carry the -weight. The concrete casing will both stiffen them, and prevent rusting and wear from the scour oE shingle. Aud' anyrfwear of the? - concrete (hat may become manifest in course of years, can 'be made good by plastering on more concrete. This system of a single strong case is, in English practice, preferred to the American system of numerous small rods. In i:ecommending tlie acceptance of the reinforced concrete structure, Mr Marchant dwelt upon the value of permanence, as interruption of traffic on a main road of such importance was a serious inconvenience. And on the question of com<parative cost, he pointed out that a timber bridge would not last more than 40 years, but it would require re-decking at least twice in forty years, which would add to the difference ■ between the two lowest tenders, even allowing for the difference of interest aud sinking fund from iirst to last during that time. Moreover the concrete bridge* would have a road metal surface, safe iu all weathers, whereas: a bridge with a -wooden decking is very slippery in frosty weather. Mr Kelinan put one or two questions as to Hie satisfactory nature of the work done a.s to which he had his doubts. The chairman and other members, however, concurred that til© concrete wouldbe by far the. more durable, and there was alio a consideration not to be lost sight of and that Avas! tho safely from 4iv«. Altar their experience of th-u llaugitata bridge this wars Worth. corsid-ering. It was ,decided after some, further . discussion on the matter tlint the -chairman wait on the Levels County Council on Saturday, and submit for their approval the tender selected.