OPENING OF THE ALEXANDRA BRIDGE.

Dunstan Times, Issue 1050, 2 June 1882, Page 3

OPENING OF THE ALEXANDRA BRIDGE.

This ceremony took place on Thursday, Ist June, and was attended by one of tho largest concourses of people we remember ever to have seen in the district for years past; there being fully 700 people, representing every class and from every centre within a radious of 50 miles Familiar and wellknown faces from the Teviot, Bannockburn, Cromwell, Ophir, and other places were to be seen, and one and all alike expressed their satisfaction at being present to participate in the day’s proceedings. Time will not allow ns, nor do we think that our pen is facile enough on the spur of the moment to enter into details as to what was said or done, we shall content ourselves by merely saying that the utmost goodwill and harmony was shown throughout, and that no eff rt was spared and nothing left undone by the townspeople of Alexandra to give pleasure and satisfaction to the visitors, and had tho weather been equally as propitious no exception could he taken. In the midst, however, of the day’s programme a very disagreable misty rain fell, nee. ssi tating an adjournment from the open air to the Town Hall, and to some extent marred the affair.

The pioceedinps were opened by a precession, hea led by the Alexandra Brass Band which numbered some 18 performers, followed by the members of the Vincent County Council, the Alexandra Borough Council, and other notables, the members of the 1.0. G.T., and A.O.F. lodges in full regalia and banners following, the public bringing up the rear. After marching through the town on reaching the Eastern approach to the bridge a halt was called, when Or McGinnis, in the name of the Vincent Council, in a neat and appropriate speech declared the “Alexandra Bridge” open for traffic. A move was then made to the centre of the bridge, when Mrs Simmonds, wife of one ot the contractors, in due form per'ormed the christening cer. mony by breaking the orthodox l.ottle of champagne. The procession then moved on, and alter passing the entire length of bridge and w« stern appioach returned to the eastern approach and halted at a platform on which those appointed to carry out the programme at ore went. Speeches followed by toas.s were now given in due course, including the ‘ Queen,” “ Vincent Council,” “Th Engineer.” “The Contractors, “ Th p Borough Council of Alexandra,” “The Pastoral, Agricultural and Mining Interests,” and the whole followed up by the wealth of Vincent Pyke, Esq., M.H.8., for the Dunstan District, after which the proceedings closed and each and all alike then followed the bent of their own inclinations As we said, neither time nor space will admit of us going into detail of the speeches ; it may be, however, safely averred that everything said was coltur de rose.

We will now, for the benefit of those of our readers who have not st-en the structure over the opening of which such rejoicings have taken place, append a description of the work itself.

It is constructed for the greater part on the suspension principle, the m an spaa altogether so, but the subsidiary or side spars are a combination of the suspension and truss, and there is one small span of trussed beams.

The number of spans or openings is four, the largest being 262 ft 6in in the clear, the side spans 72ft in the clear, and the small span 20ft. The whole length of the timber platform is, however, 454 ft., the width of piers, abutment walls etc having to be added to the before-mentioned distances; and the total length of the finished structure from end to end of the masonry abutments is 552 ft. Now having given our readers some idea of the general arrangement of the bridge we will proceed to describe the works in detail. First as to the masonry supports. These consist of two main piers carrying the wire cables, one small pier on. which rests one end of a 72ft. span and one end of the 20ft. span, and two abutments, the largest of which, on the North bank of the river, besides carrying one end of a 72ft. span, resists the pull cf the cables which are anchored in it. The other abutment carries one end of the 20ft. span and is used partially for the same purpose as the one previously mentioned.

A description of the larger of the two main piers may not be uninteresting. It is founded on a tolerably hard reef, about from 18 to 20ft. below the average level of the river. In the original design it was intended to commence with the masonry, hut it was found after the paddock was taken out that the reef was scarcely pood enough, and the engineer therefore decided to excavate some three feet iu depth and fill in with concrete.

The masonry, therefore, commences on this and is continued up for about 14 feet in what is known as coursed rubble. From this point upwards to the level of the platform of bridpe it consists of coursed rubble faced with ashlar, and is relieved by two

arches pi iced one above the other, the bottom one being 18ft. high by 12ft. wide, and the other 12ft. high by Oft. wide. These arches lighten the appearance of the pier considerably, besides saving something in masonry, while they in no way diminish the strength of the structure. At the roadway level commence the two pillars earn ing the wire cables. These are hurt of a finer class of masonry known as ashlar, with a chisel draught round the face of each stone ; and commencing at a height of 18 ft. an arch is turned, tho keystone of which is 24 ft 6 in. above the floor level. Above this there is a bold cornice plastered in cement, the whole being surmounted by two urns, one over each pier, making a nice finish. The height of this pier from the bottom of the concrete to the top of one of the urns is 97ft., but only about 80ft. of that height is visible. Its thickness at the base is 20ft. 4in. iaporing up to Oft. at the tops of the pillars. The other main pier is similar in appearance, and is founded on solid rock at about water level.

Of the other masonery there is not much to be said ; it is of an inferior class to that before mentioned, but is very heavy and massive in appearance. It might, how-ever, be of interest to some to learn that the larger of the two n hutments is founded on timber piles driven into the shingle, connected with walings at the top, and covered with planking. The driving of these piles was one of the moat difficult portions of the work and occupied no inconsiderable time.

We now come to the cub Vs, from which the mail way is suspended. These are eight in number, four on each side of the bridge, and are made of the best steel wire. Each rope is three inches in diameter, and contains in cross section about 4J square inches of met'd. They are attached at each end to larger iron rods which pass through box girders and are then confined. These girders hear against large cast iron pbites which are imbedded in concrete, and tbesr in turn, bear, on the north side, against the block of masonry before spoken of, and on the south side against the solid rock, which is here found in a very convenient position, shafts and tunnels are driven or built so that every portion of this important part of the bridge can be examine ', and paurted as occasion requires. On the top of each pitlar is placed a heavy' cast iron bed plate with planed upper surface. Otr this is placed a set of heavy rollers, and on the top of these a cast iron saddle with deep groves in the upper surface in which the cables rest. From the cables the roadway is suspended by iron rods. The roadway consists of large cross eills on which are placed longitudinal beams securely bolted to the cills. On these is laid the planking. The handrail consists of a system of upper and lower chords, (each doubl-) vertical posts, and iron diagonal braces, arranged in the form known as a “ Pratt” truss. It does duty not only as a handrail, but stiffens the platform to a great extent; preventing oscillations during the p itsage of loads, and resisting the effects of high winds, one of the greatest sources of danger to this class of bridge. Other stiff niug braces are used which are connected at one end to the tops of the suspension rods, and at the other to the cross cills, and act directly on the cables. There are also a few wire stays running each way from the tops of the main pie. s which assist in resisting the action of a passing b ad. Such is a meagre description of this line structure. There are many parts of the work which have not been touched upon, but they cannot be described within the limits which this ai tide must assume, and indeed must be inspected personally to be pi operly understood. Before closing, however, it might lie well to give to our readers some idea of the strength of this bridge.

The breaking strain or ultimate strength of each of the wire cables is about ISO tons. There being eight of these cables the total strength is 1,440 tons. The greatest load (calculated at SOlbs. per square foot of platform) together with the. weight of the bridge, may be taken at 200 tons. This load will produce a strain ou tbc cables at the pier (at which point the strain is greatest) of 340 tons, and the breaking strains of tbe ropes being 1.440 tons it follows that the co-efficient of safety in nearly 4), or in other words, it would take a load 4| times greater than could possibly come upon the bridge’to break it. down.