Page:Popular Science Monthly Volume 90.djvu/616

 It's Sheer Weight That Keeps a Pier in Place

Here is an inexpensive way to get the necessary amount

���The new type of pier instead of being cast into a solid block is made in the form of a hollow semi-circle the ends of which are extended backward in the form of two parallel walls

��TRESTLE ■■"^BRIDGE SEAT

���ONLY a few years ago, the piers which sup- ported the shore ends of a highway bridge were made of huge, massive blocks of concrete. The sheer weight of the con- crete steadied them and prevented their slipping away or overturning with the bridge into the river. Upon this principle of op- eration, however, these piers could never be made too large. Indeed, the danger lay in possibly making them too small. Evidently, they were very expensive.

No wonder then that engineers have been giving the problem of the highway bridge much attention. The result has been most satisfactory. An American engineer has lately brought out a highway pier which works on a more scientific principle. His pier, illustrated in the accompanying photo- graph, is just one half as expensive as the older types, while in some cases, it has even proved better and stronger than they could have been.

��DOWNWARD SLOPE OF ABUTMENT TO CONFORM WITH EARTH FILL

��ABUTMENT PROJECTION COVERED BY EARTH

Plan of the new type of pier. The convex face of the semi- circular wall faces the river

��Instead of casting the piers into a solid block, those of the new type are being made more in the form of a nollow semi- circle. The ends of this semi-circle are prolonged backwards in the form of two parallel walls. The convex face of the semi- circular wall faces the river. A wide rectangular-shaped notch is left at the top of this part, directly in front. The land-end of the bridge fits into the bridge-seat thus formed. The prolonged ends of the pier slope downwards away from the river.

The piers are made a foot thick all around. A number of heavy steel rods are cast in the concrete of each pier. These rods run nearly parallel with each other around the piers as shown in the diagram and they greatly reinforce the entire structure. Earth is dumped into the pier to fill up the hollow inside. The two extending walls are then deeply buried in earth also. It is the weight of this earth which prevents the pier from slipping.

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