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.
[Illustration: 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.
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