WHOLE NO. 2,575.]

ACCIDENTS FROM BROKEN BRIDGES.

BY WM. S. HUNTINGTON.

[Written for the AMERICAN RAILROAD JOURNAL.]

THE accidents from broken bridges in the United States in the last ten years are reported at 300, which, to say the least, is not flattering to American railway management. While it is certain that a considerable portion of these mishaps were purely accidental, it is a fact that the larger share of them might have been prevented by the exercise of ordinary precaution; and more correct views of true economy. Bridges have failed from being partially burned and not discovered in time, or from sudden freshets undermining their foundations, or from contraction of rods and bolts in severe weather, or some hidden defect in some member which had escaped the closest inspection. Such have been the causes of many accidents for which no one was responsible, and may be regarded as accidents or misfortunes that come in the common course of events, and cannot be prevented. But when a bridge fails from age or neglect, malconstruction, overloading, or any cause directly under control of the proper officials, who have the means of prevention at hand, it may not be regarded as accidental, but the result of incapacity, false economy, criminal neglect, or, "cussedness," which is the proper word in most cases of bridge failures.

Probably one reason for so great a number of broken bridges is that they have been subjected to rougher treatment than they were originally designed for, and their factors of safety exceeded by a greatly increased weight of locomotives and car-loads. While within a few years the weight of locomotives has been more than doubled, and a standard car-load of ten tons increased to thirty tons or more, bridges have not been brought to a condition to carry these excessive loads; hence the numerous failures of these neglected structures. A great many roads were built for light traffic, and have since been leased by trunk lines that put on heavier rolling-stock and heavier trains than the cheap structures could bear, and it is not considered a sound policy to go into expensive repairs and renewals on leased roads.

It is the practice on some roads to renew bridges after a certain amount of service, though there are no apparent signs of weakness. This has more special reference to wooden structures, although engineers of the more carefully managed roads consider it the correct thing to renew iron bridges before any outward signs of weakness appear. To some of the slipshod economists this may appear like a reckless waste of earnings, but it is noticeable that this so-called kind of extravagance in expenditures leaves cash in the till, while the "guess-it-will-last-another-year-witha-little-patching-up" management goes borrowing.

Scientists tell us of the "fatigue of metals," and practical men are well aware of the weakening effects of long

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continued strains and vibrations, and expansions and contractions from heat and cold; and when iron bridges have reached a respectable age, there is much uneasiness felt in regard to their safety. The length of time an iron bridge can safely do duty varies from fifteen to twenty-five years, according to the quality of material, style or plan of construction, length, and amount of traffic, and location; extremes of heat and cold being destructive agents. At high temperature, when every member is expanded to its maximum length, a general screwing up is necessary for safety, and this tension, together with the powerful strain of contraction in severe weather, is the cause of many failures, not only of iron but of wooden bridges which are supported by iron rods. On the slacking and tightening of these rods at the proper time depends the safety of bridges in a great measure, and closer attention to this subject would have shortened the list of bridge accidents wonderfully.

Experiment has shown that a certain number of strains and vibrations crystallizes iron and steel, and when this takes place there is no longer any safety in the material. Cannons are condemned after a certain number of discharges, although they may appear sound; and on English roads locomotive parallel rods are thrown aside after six years of service, and cast car-wheels are considered unsafe after a certain mileage, and their use after that contributes largely to the causes that place roads into the hands of receivers. This applies to bridges, and it was a knowledge of this property of iron and steel that led a daily newspaper, a year or more since, in revenge for some fancied wrong on the part of the Manhattan Elevated Road, to injure the business of that road by warning the public that the entire structure was liable to fall to the pavements at any moment, by reason of crystallization and chronic weakness, engendered by a constant vibration for a period sufficient to render the entire fabric a mass of rottenness. According to this newspaper, there was not a train on the road that was safe for a moment, and it was only a question of a very short time when there would be a general smash, after the manner of the "wonderful one hoss shay.". But Mr. R. J. Sloan, the chief engineer of maintenance of that great work, had anticipated the attack, and had been actively engaged for some time in adding strength to the structure, so that in reality the road was safer at the time the great calamity was predicted than at any time since its completion; and, under the present system of thorough inspection, and timely repairs. and renewals, there is no safer place for a person than on any train on the "L" roads. The same practice would render bridges safe, and engineers will do well to "stick a pin there."

One suspected cause of bridge failures, especially of large structures, is a jealous rivalry among engineers. An engineer is placed in charge of a road on which his prede