The Mccook Tribune

FASCINATING DANGER
The Perils That Beset the Builders of Big Bridges.

The design of a long bridge span is one of the most elaborate mathematical problems that arise in constructive work. The stresses produced by its own weight, by the weight of traffic, by locomotive drivers, by the hammering of flattened wheels, by the action of brakes on an express train, by the high speed on a curved track, by the wind and by the expansion and contraction of the steel in summer and winter are all accurately calculated. The deflection of the loaded and unloaded bridge is determined, and complete drawings are made of every member of it. The bars of steel are tested in machines which will pull in two a horsehair or a steel bar strong enough to lift half a score of the heaviest locomotives at once, and which will crush an eggshell or a steel column, and accurately measure the stress in each case. The different kinds of members are forged, riveted, bored, or planed in perhaps half a dozen remote shops, and, although usually not fitted together there, are examined and measured by specialists to see that they are correct, and are then shipped by scores of carloads to the site of the proposed structure, where steam derricks unload them and pile them many feet high in stacks covering acres of ground.

The bridge piers may rise above the water hundreds of feet apart. It remains to place them on a thousand ton structure, high above a savage chasm, over an impassable current or roaring tide, where the water is deep, the bottom of jagged rocks or treacherous quicksand, or where an old bridge must be removed and the new one built in its place without interrupting traffic on the bridge. To accomplish this the engineer has timber, bolts and ropes, hoisting engines, derricks and a band of intrepid builders who have perhaps followed him for years through more hardship and danger than fall to the lot of almost any other calling.

The complicated framework of a great span is a skeleton with many accurate joints and thousands of steel sinews and bones, each of which must go in exactly the right place in exactly the right order. The builder must weave into the trusses pieces larger, heavier and far more inflexible than whole tree trunks, swiftly hoist and swing them to place hundreds of feet high, fit together the massive girders and huge forged bars with watchmaker's accuracy, support the unwieldy masses until they are keyed together and self sustaining, and under millions of pounds of stress must adjust them at dizzy heights to mathematical lines. This he may need to do not deliberately, but in dangerous emergencies, at utmost speed, putting forth his whole strength on narrow, springing planks in a furious tempest, in bitter cold or in blazing heat. He may be in the heart of an African desert, menaced by bloodthirsty fanatics, or in a gorge of the Andes, hundreds of miles from tools or supplies, where there is absolutely no supplement to his own resources.

Under such conditions bridge building is one of the most fascinating and difficult of engineering problems and requires a different solution for almost every case.—Frank W. Skinner in Century.