WHEN BRIDGES BREAK

Greymouth Evening Star, 18 April 1929, Page 9

WHEN BRIDGES BREAK

REMARKABLE CRASHES Broken bridges are' such a rare occurrence in England, says a writer ip a London newspaper, that it is dimcult to. realise that- throughout the world there are dozens of failures every year. A well-made steel bridge looks as though nothing less than an earthquake could shift it. But actually it is* quite a delicate, structure, and only one of the vital steel girders need be damaged for the whole bridge to crash. , , . In November, 1922, a carelessly driven car smashed one of the end girders of a bridge at Tyrone, Pennsylvania. The result was that one side of the bridge .was ripped off its bear!ings at one end,, badly twisted, and damaged beyond 1 repair. But, strangely enough, the floor held gQOp. The ■bridge was closed for rebuilding, but ■a Jew nights later a second car crashed through the barricade, swept the red light out of its path, got out of ' control on the tilted roadway, and plunged through the handrailing into the river on the other side. But it hardly damaged the bridge at all. The first car hit a vital spot-;- the second did not. In December of the same year a' swingbridge in England that carried the South-Eastern and Chatham Railway over the RivOr Swale met its. fate. The river is only 58ift. wide where' the bridge spans it, arid the 7000 tori' steamer Gyp* was endeavouring to make the passage. The' boat was 48ft. wide, and the owners were warned not to: take the risk, as there, was so little clearance for it to get past the bridge. But they decided to! try. In the middle of th© narrow stream the steamer swerved, hit one' of the bridge piers, and took it on with it up ■ the river. Many a bridge has suffered from river traffic in this way. Four years ago ( the lumber schooner Martha missed ■ its course, on a river in Oregon. There was a big steel bridge carrying the Southern Pacific Railroad over the stream, with a 180 ft. opening span ip the middle. The steamer missed/ the channel and hit orie of the fixedspans of th© bridge at the side of the /opening. The spari weighed 300 tons, , but the Mriftha knocked it' off- its piers, and it sank in 28ft-. of water.

Bridges are very rarely bl'oiyn dbwff nowadays, since engineers profited by the lessons of- the Ta’y Bridge disaster, but plenty of them are swept away by flood's. One' case occurred where a ' whole railway bridge was washed' out/ ’and offly the rajils spanning the fidb’d; with the Sleepers clinging , off here and there.

, ' AN UNLUCKY BRIDGE. Iff Jdhuary* 1923-, fifteen.people were drowned when one of the five-strand cables of a suspension bridge snapped at Kelso, in Washington. The disaster would, not have been so, serious,- but the floor of the bridge sagged and was caught by the swift six-mile-an-hQur i current of the' CowMtz River. The remaining cables parted like, pistol shots; the timber towers at the ends® Of- the bridge were' overturned, and- in less than a minute the- wreckage. Was complet.e. The: bridge was particularly unlucky, fl's it was only built in 1905, was washed out next year, replaced in 1907, and theh crashed ag'ain/iO years later. . As ‘it cost spine to build, and off tpp. ofr this the, epufity . Was found ■ffablff 4 t&c the aecidffnt; the/ of

Washington must have thought themselves very badly used. Among the old timber bridges of Canada and the United States hundreds have been burned down by sparks from locomotives crossing them. But probably the most serious case of destruction by fire was that of a suspension bridge at Franklin, in Pennsylvania. The fire broke out in ff building at one end of the bridge. Slowly, as the heat became greater snd greater, the lead securing the cables into their anchorage sockets melted. At last the cables pulled out, and the whole bridge tipped into the river.

Many, failures are hot so easily accounted for as these. Only a few years ago a concrete arch was being built over the River Bigge, in Germany. It was noticed that the concrete did not, seem to haye set very well at the centre of the span, but the bridge was finished and the . temporary timber staging was removed from under it. At first nothing happened, then suddenly at noon the arch collapsed. Only by a great piece of luck were there no casualties,-as the crash came just after the workmen had knocked off for lunch. Probably the most unaccountable of all crashes was that of a timber bridge at Log Angeles in 1924. ’ The day be-, fore the smash an eight-ton roller and a five-ton asphalt truck had been at Work on the bridge, with many’other vehicles crossing at the same time. The bridge, which was inspected annually, stood the loads perfectly. Next day, when the roller and truCk had left, it broke under the weight of one pedestrian and a motor-car and fell 40,ft to the riVPr-bffd.