The workmen of the enterprise, who lived about 325 feet above this mill and about 650 feet from the south abutment, heard nothing of it, the wind having carried the noise in an opposite direction. It was not until morning that they learned of the destruction of their work and the extent of the disaster.
One hundred and sixty-nine feet of the superstructure, weighing 450 tons, had been precipitated from a height of nearly 200 feet and been broken up on the rock at 45 feet from the axis of the pier. The breakage had occurred upon the abutment, and the part 195 feet in length that remained in position in the cutting was strongly wedged between walls of rock, which had kept this portion in place and prevented its following the other into the ravine.
Upon the pier there remained a few broken pieces and a portion of the apparatus used in swinging the superstructure into place.
Below, in the debris of the superstructure, the up-stream girder lay upon the down-stream one. The annexed engraving shows the state of things after the disaster.
Several opinions have been expressed in regard to the cause of the fall. According to one of these, the superstructure was suddenly wrenched from its bearings upon the pier, and was horizontally displaced by an impulse such that, when it touched the masonry, its up-stream girder struck the center of the pier, upon which it divided, while the down-stream one was already in space. The fall would have afterward continued without the superstructure meeting the face of the pier.
DESTRUCTION OF THE TARDES VIADUCT.
Upon taking as a basis the horizontal displacement of the superstructure, which was 45 meters to the right of the pier, and upon combining the horizontal stress that produced it with that of the loads, the stress exerted upon the body may he deduced. But this hypothesis seems to us scarcely tenable, especially by reason of the great stress that it would have taken to lift the superstructure. On another hand, it was possible for the latter to slide over one edge of the pier, and this explains the horizontal distance of 45 feet by which its center of gravity was displaced. It is probable, moreover, that the superstructure, before going over, moved laterally upon its temporary supports.
The girders were, in fact, resting upon rollers, and the roller apparatus themselves were renting upon wedges, and there was no anchorage to prevent a transverse sliding.
Under the prolonged thrust of a very high wind, the superstructure, by reason of its considerable projection, must have begun to swing like a pendulum. These oscillations acquired sufficient amplitude to cause the superstructure to gradually move upon its rollers until the latter no longer bore beneath the webs. The flanges therefore finally bent upward where they rested upon the rollers, through the action of the weight which they had to support, and the entire superstructure slid off into space.