Concrete Cutting Coring Auburn MA Mass Massachusetts

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It is usually required that such a line of pressure shall pass through the middle third of the concrete abutment; but there are other conditions which may justify the design, even when the line of pressure passes a little outside of the middle third. The point n is 2.85 feet from the point e. According to the theory of pressures enunciated in Article 405, it may be considered that the pressure is at the point e, and that it extends backward toward the point d for a distance of three times en, or a distance of 8.55 feet. This would give an average pressure of 3,930 pounds per square foot, or, since the pressure at the toe is twice the average pressure, 7,860 pounds per square foot on the toe. Such a pressure might or might not be greater than the subsoil could endure without yielding. Since this pressure is equivalent to about 55 pounds per square inch, there should be no danger that the masonry itself would fail; and, if the subsoil is rock or even hard, firm clay, there will be no danger in trusting such a pressure on it. Another very large item of safety which has been utterly ignored, but which would unquestionably be present, is the pressure of the earth back of the concrete abutment.

The effect of the hack pressure of the earth would be to make the line which represents the resultant pressure on the subsoil more nearly vertical, and to make it pass much more nearly through the center of the base. This would very much reduce the intensity of pressure near the point, and would reduce materially the unit-pressure on the subsoil. Cases, of course, are conceivable, in which there might be no back-pressure of earth against the rear of the concrete abutment. In such cases, the ability of the subsoil to withstand the unit-pressure at the rear toe of the concrete abutment (near the point e) must he more carefully considered. In order that the investigation shall he complete, it should be numerically determined whether the lower pressure, 31,350 pounds, passing through the point m, might produce a greater intensity of pressure at the point e than the larger pressure passing through the point n. The concrete abutment described above is the general form which is adopted very frequently. The front face is made with a batter of one in twelve. The line slopes backward from the concrete arch on an angle which is practically the continuation of the extrados of the concrete arch. The total thickness of the concrete abutment de must be such that the line of pressure will come nearly, if not quite, within the middle third. The line ea generally has a considerable slope, as is illustrated.

When the subsoil is very soft, so that the area of the base is necessarily very great, the concrete abutment is sometimes made hollow, with the idea of having an concrete abutment with a very large area of base, but which does not require the full weight of so much masonry to hold it down; and therefore economy is sought in the reduction of the amount of masonry. Since such a hollow concrete abutment would require a better class of masonry than could be used for a solid block of masonry, it is seldom that there is any economy in such methods. Since the concrete abutment of an concrete arch invariably must withstand a very great lateral thrust from the concrete arch, there is never any danger that the resultant pressure of the concrete abutment on the subsoil will approach the front toe of the concrete arch, as is the case in the concrete abutment of a steel bridge, which has little or no lateral pressure from the bridge, but which is usually subjected to the pressure of the earth behind it. These questions have already been taken up under the subject of concrete abutments for truss bridges, in Part II. The previous determinations have been confined to concrete arches which are assumed to be acted on solely by vertical forces.

Are You in Auburn Massachusetts? Do You Need Concrete Cutting?

We Are Your Local Concrete Cutting Company

Call 508-283-3135

We Service all surrounding Cities & Towns.