IRON BRIDGES OF LONG SPANS.

Inangahua Times, Volume II, Issue II, 28 April 1880, Page 2

IRON BRIDGES OF LONG SPANS.

Speaking of the recent unexplained bridge disasters, a St. Louis conteßi* porary remarks that half a centnry ago such spans as the fallen ones of the St. Charles and Tay bridges, for such loads as they were calculated to support, were impossible. Now they are far from being of the first magnitude. There are ten truss bridges across the Mississippi above St. Louis which are not regarded as very wonderful structures, and yet seven of them have spans as long as those of the Tay bridge. The bridges at Winona, L* Crosse, Dubuqne, Keokuk, and Hannibal have spans of 240, that at Book Island of 250, and that of Louisiana of 256 feet. The span which gave way at St. Charles was 320 feet in leDgfh. yet the same bridge has two spans 406 feet long- Over the same river is a truss bridge, at Leavenworth, with three spans 340 feer, and another at Glasgow with five of 315 feet. Acros3 the Ohio there is a truss bridge at Steubenville with, a span of 320 feet, one at Parkersburg of 350, one at Cms cinnati with a span of 615 feef, the longest truss yet built, and one at Louisville with a span of 400 feet. The truss bridge over the Kentucky river, on the Cincinnati and Southern Railroad, has three spans- 375? feet in length, resting on iron piers 175 feet high. The bridge over the Hudson at PougLkeepsie has five spans of 500 feet with piers 135" feet above high water, In Europe there is a truss bridge over the Vistula at Graudenz with twelve spans of 300 feet. The truss bridge of Lessart,,in France, has a. span

of 311 feet, aDd was pushed across from one abu'ment to (he other after being put together. Tbe btiJge over the Rhine at Wesel has fonr spans of 313 feet. The Knlenhnrg bridge in Holland which was the mnmrdi truss before the construction of the Cincinnati bridge, has a span of 492 feet. From these examples it would seem that the St. Charles and Tay bridges, instead of being risky engineering ventures, are entirely within the domain of experience. But nevertheless the fact remains that, notwithstanding tbe bold« ness with which tbe engineers of the present day meet the exaction* of the locomotive, they are comparatively novices in the use of iron. The first iron bridges were of cast iron, an.? soon proved to be too lightly proportioned. Does it remain to be proved thai; the wrought iron work of the past twenty years betrays too great a confidence in the material P Were the St. Charles and Tay disasters unaccountable accidents, or were they fair tests of current engineering theories ? These are questions which engineers would do well to discuss.