The Russellville Democrat., 1880-02-05

1 floated into the swift stream on pontoons and lifted bodily into place by the rising of the tides and by new arrangements of haudraulic rams" In 1S4S the 400. foot spans of the Conway tubular bridge each weighing 1,1S0 tons. nearly six times as heavy as the Fay trusses, were | raised in this manner by Robert Steph- enson. The immense tubes for the Britannia bridge at the Menai straits, each 400-foot span, and weighing l,57e tons, were raised by Stephenson year or two later
 The central arch of the St. Louis bridge is 250 feet in clear span between the masonary piers, and is tine longest fixed span in the world It s sixty feet longer than the Menai straits span, and nearly two and half times as long as the longest spans of the Fay bridge. It is made of cast-steel and the immense structure was hung up in two halves by enormous chainsor guys, depending from temporary wooden towers erected on the masonry piers. The navigation be- meath these two half arches was uninter- rupted; and the arch was completed by the joiningof the two parts at the mid dle of the span. On each side of the central arch of cast-steel, having clear span of 502 feet. All three of these im- mense arches were erected in this man. ner.
 We do not mean to say that such length of spans and magnitude of piers as constitute the St. Louis bridge were needed at the river Fay, but we wish to show the absurdity of claiming that that bridge was wonderful piece of engineer ing. The facts prove it to be very de- fective one. The largest piers of the Fay bridge are formed of single tubes, thirty-one feet in diameter. They there. fore rest on an area of 800 square feet. The piers of the St. Louis bridge are solid hexagonal masses of masonry, each placed on the bedrock, and each one rests upon an area five or six times as large as those of the Tay-one of them covers an area of 5000 square feet: about the size of the largest public dining room in New York city.
 None of the piers of the Fay bridge were sunk over seventy feet deep. Some of those of the St. Louis bridge rest 136 feet below the high-water mark of the Mississippi. The weight of the largest piers of the Fay bridge will not exceed 4,500 tons. One per of the St. Louis bridge is, therefore, equal to ten such piers. The piers of both bridges were sunk down to their resting-places by the same methods. The engineer of the Fay bridge had the full benefit of the improved devices designed by MT. Eads for sinking and controlling the monster piers in the Mississippi. At St. Louis provision had to be made against acres of floating driftwood during the floods. and against fields of Ice in winter, yet so complete were the plans for meeting these difficulties that scarcely any inter- ruption occurred from them. The work men on the bedrock of the river under the piers, although working in an atmos- phere fifty pounds per square inch great CT than the normal pressure, were in constant telegraphlc communication with the office of the chief engineer and that of the superintendent of construc- tion, and the work was actually carried on during several days at one of the piers in the river where the floating ice prevented all communication with the shore except by the electric wire, stores of materials, bedding and food for the workmen and engineers having been previously provided at the pier for such d contingency.
 At the official test of the Fay bridge five locomotives and their tenders were put upon the largest spans. At the official test here, fourteen locomotives and their tenders were coupled together, and run back and forth over each track of the bridge. Then they were arranged in two separate trains of seven each, and these were run side by side back and forth over each span, and this test was made while the upper roadway tor wag- on roadD and footpaths were covered with passengers and traffic.
 The usual wind pressure assumed as possible by English engineers is forty pounds per square foot of exposed sur face. We do not know what pressure per square foot was assumed as possible for the Fay bridge. The fact that thir- teen girders were blown away is ample proof that the possible pressure was un- derestimated. On the bridge at St. Louis it was believed possible that the wind pressure of a tornado might reach 100 pounds per square foot, and the wind bracing of the structure was made to meet such contingency. Enormous bolts or iron extend from the end of the spans of the upper roadway down into the body of the massive piers, and are there anchored securely, while the size of these bolts is so great that this enor- nous wind pressure, if ever exerted would not tax them beyond one-quarter of their ultimate strength, Besides these massive bolts each arch has complete system of wind-bracing from end to end, formed of cast-steel rods carefully tested to nearly twice as great strain as the wind-pressure of 100 pounds per square foot could prod"ce.
 There is no doubt that the error in tine Tay bridge was in underestimatine the force of the wind. Experiments to measure this force are invariably made near the earth's surface, and the velocity of currents there is assumed to be the same as at greater heights. It by no means follows, however, that because an instrument on the top of tour-story house indicates velocity of sixty miles an hour that the wind 100 feet higher is moving at much greater velocity. We might as well expect to find an equal velocity of current at the bottom of d river, or that the velocity of the gulf stream is as great near the bed of the ocean as it is near its surface, as to sup pose that the winds are not retarded by the frictional resistance of the earth's surface The spans of the Fay bridge that were blown away were the highest ones, and to the top of them tho height was fully 100 feet or more.
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