The Daily News. THURSDAY, OCTOBER 17. A NEW WORK.

Taranaki Daily News, Volume L, Issue 61, 17 October 1907, Page 2

The Daily News. THURSDAY, OCTOBER 17. A NEW WORK.

The opening of the new bridge over the Waiwakaiho river at l'itzroy lhi > after-' noon is an event of more than ordinary interest to the district, and even to all | other parts of tlie Djminion. It marks a new era in bridge-building, consequent : on the material lucil in its construction being ferro-concrcte—a method that bids j fair to replace all substances that have up to the present been utilised for bridge j work, (structures for ail'ording a pus- j sage over streams, valleys, and gullies are always more or less costly, and in a country like New Zealand these facilities have been and still remain a -serious item of expense. More particularly is this tlie case in a district like Taranaki, which is remarkable for the number of streams intersecting the land in all directions. The problem of roading has consequently been a matter of dilliculty to solve, and, while every effort within tl:c power of the local authorities lias been made to secure the best results in the past, the upkeep of bridge work, owing to such a perishable substance as v.'L'ud being used, has entailed a heavy burden on the ratepayers.

The new departure effected by the use reinforced concrete )nav well be hailed I vi:h every sign of satisfaction. Not I only arc the structures composed of this | material permanent, but they offer ro i point of attack for any deteriorating or I I decaying influence, lieyond the ordinary upkeep of the surface metal there is no expense, and the longer the concrete stands the greater is its solidity and strength. In short, the first expense of construction is practically the only outlay, the renewal of surface metal being hardly worth taking into account. It will be seen, therefore, that wo have entered upon another line of progress in Taranaki, and one, moreover, that will in the future result in a great saving to the settlers. The evolution of bridge-making has probably been of a slower and move spasmodic nature than has characterised other branches of engineering. There is no doubt that the earliest bridges were composed of trunks of trees. Our own pioneers in the backblocks, even to the present day, have by necessity had to adopt this primitive method—the only means available. The arched bridge, as we know it, appears to have been quite unknown to the ancients. Even the enlightened Creeks had not sufficient acquaintance with it tct apply that form of structure; but the more practical Romans, who were the tirst to employ that principle, saw its advantages, and with thom it was a case seeing and adopting. If the same spirit with regard to road-making which was such a marked feature of the Romans were only more evident in the legislators of New Zealand, the piteous outcry from the roadless backblocks wottlu not have been heard.

Tlie significance of tlie reading policy of the Romans is emphasised°by the fact that the art of bridge-making was at a standstill from the time of the fail of the Roman Empire until the eighteenth century when French architects commenced improvements resulting in the ei cation of masterpieces of art. it is, however, only within the last halfcentury that tlie stimulus supplied by railway works has brought to light the numerous inventions in this department of public works that have resulted in i .-using bridge-building to a fine art as well as a precise science. After emerging from tlie stage of rough wooden structures, stone was einplovcd, and subsequently iron. By the use of iron or stee much more liberty was given to the architect in framing his plans, while t Le greater cohesion and adaptibility of the metal permitted an extensive width of span _ It is nearly 150 years since the first iron bridge was constructedthe material then employed being east iron ami it was much later when wrought iron or steel came into general use. From that time onwards this material has, m one shape and another, been mostly used for bridge construetion.

The late bridge over the Waiwakaiho nn, a familiar landmark to the settlers, and though lor many years past it has >ccu exhibiting signs of growing decay, it presented that striking and attractive appearance which is common to all structures erected on the bowstriih? girder principle. Tlie contrast .between the old and new bridges could not well be greater Hie former, a narrow but massive erection, having lows rising high into the air, tlie latter of service able width, arched from the pier ill graceful curves, slim and neat, v-t of immense strength and durability-. J\o one who sees the new bi'id"c can fail to be pleased with its elegan-e Willie Its suitability for the work it lias to perlorm is apparent to tlie meanest comprehension. Its construction has been watched with the keenest interest not only by the settlers in this district but by those interested in bridgebuilding throughout the; Dominion. The laranaki County Council have the honor rf being the first public body in New Zealand to adopt ferro-concrete for bridge-building, and the now Waiwakaiho bridge is regarded by experts i;s the best and cheapest in tlie Dominion.

J Hioe who look below tiio surface of tilings in general will naturally inquire into the merit* and advantages of the new process. .Briefly, they consist of I economy in construction, strength, duraj bility, and absence of maintenance expenses. With regard to cost of construction, it may be said that although in the minds of some of our conservative engineers there exists au impression that i'crro-coiicrete bridges are more costly than steel, experience has emphatically proved that there is a saving which may fairly be estimated at a third. Another important feature is that the work can be cabled out by . unskilled labor under the supervision of a conipcteut overseer. The significance of tills in relation to building bridges in eouutry districts should not be lost sight of, inasmuch as not only is the work freed from liability of temporary suspension owing to want of skilled men, but it opens up a new avenue for utilising unskilled labor. Then, again, the material, with the exception of the disused iron rails, is obtained in New Zealand.

Apart from tlie question of cost, the chief points in bridges are strength and durability. It is here that ferro-con-crete asserts its superiority. The cooperatiuu of these two materials results iu tlie attainment of extraordinary strength while presenting to the eye a structure ol light and elegant appearanee. Concrete is brittle, technically speaking, weak in tension, but very strong iu compression. Tlie process of reinforcing that material with steel adjusts tlie balance and prevents fractures, and the metal takes the tension while Die concrete bears the compression, the expansion of both being equal. Thus the two. by joining forces, ensure the necessary strength at a far less cost than it (inly slcel were employed. As to durability, these bridges may be said to be good for all time, for the longer concrete stands, the stronger it becomes, while tlie steel buried therein is preserved from corrosion and decay, the chemical action of' the silicate in the concrete automatically absorbing or eating out any oxidisation that may arise, and keeping the metal as bright as il it were polished. This result practically eiiiniuates all need for repairs and reduces maintenance expenses to the trilling cost of renewing the surface metal on the roadway. As a striking contrast, wc wojild point, to the overbead steel footbridges ill the vicinity of the railway station. A more convincing lesson in demonstrating tlie effects of I oxidisation could not well tic found.

11 is abundantly evident that (lie preparation of the plans and specifications for the AVaiwakailio bridge must have entailed a vast amount of thought and care. The process adopted being new to Xew Zealand engineers naturally added to the anxiety inherent to such important works, but the result lias been lit.le ■short of a triumph, and will doubtless

lead fo a general adoption of the ferroconcrete system. Taranaki has every reason til be proud of the new Waiwakaiho bridge. It has been constructed after the most up-to-date design, and will doubtless be a lasting memorial of ihe administrative wisdom of tlie County Council, as well as to the constructive ability of the engineer who bas set up such an excellent example of what a bridge should lie when constructed in | accordance with tlie most recent methods and on the soundest and most economical lines. The opening ceremony Ibis afternoon should lie in tlie nature of a vc.l-leiler day for Taiaiiaki. and another evidence of the existence u f the pro- I gre«ivo spirit of our settlers.