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Suppose that, at a point 1 inch beyond, the moment in the concrete beam is so reduced that the tension in the bar is 14,900 pounds instead of 15,000 pounds. This means that the difference of pull (100 pounds) has been taken up by the concrete. The surface of the bar for that length of one inch is four square inches. This will require an adhesion of 25 pounds per square inch between the steel and the concrete, in order to take up this difference of tension. The adhesion between concrete and plain bars is usually considerably greater than this, and there is therefore but little question about the bond in the center of the concrete beam. But near the ends of the concrete beam, the change in tension in the bar is far more rapid, and it then becomes questionable whether the bond is sufficient. Although there is no intention to argue the merits of any form of patented bar, this discussion would not be complete without a statement of the arguments in favor of deformed bars, or bars with a mechanical bond, instead of plain bars. The deformed bars have a variety of shapes; and since they are not prismatic, it is evident that, apart from adhesion, they cannot be drawn through the concrete without splitting or crushing the concrete immediately around the bars. The choice of form is chiefly a matter of designing a form which will furnish the greatest resistance, and which at the same time is not unduly expensive to manufacture. Of course, the deformed bars are necessarily somewhat more expensive than the plain bars. The main line of argument of those concrete construction engineers, who defend the use of plain bars, may be summed up in the assertion that the plain bars are "good enough," and that, since they are less expensive than deformed bars, the added expense is useless. The arguments in favor of a mechanical bond, and against the use of plain bars, are based on three assertions: First: It is claimed that tests have apparently verified the assertion that the mere soaking of the concrete in water for several months is sufficient to reduce the adhesion from - to If this contention is true, the adhesion of bars in concrete which is likely to be perpetually soaked in water, is unreliable. Second: Microscopic examination of the surface of steel, and of concrete which has been molded around the steel, shows that the adhesion depends chiefly on the roughness of the steel, and that the cement actually enters into the microscopic indentations in the surface of the metal. Since a stress in the metal even within the elastic limit necessarily reduces its cross-section somewhat, the so- called adhesion will be more and more reduced as the stress in the metal becomes greater. This view of the case has been verified by recent experiments by Professor Talbot, who used bars made of tool steel in many of his tests. These bars were exceptionally smooth; and concrete beams reinforced with these bars failed generally on account of the slipping of the bars. Special tests to determine the bond resistance showed that it was far lower than the bond resistance of ordinary plain bars. Third: There is evidence to show that long-continued vibration, such as is experienced in many kinds of factory buildings, etc., will destroy the adhesion during a period of years. Some failures of buildings and structures which were erected several years ago, and which were long considered perfectly satisfactory, can hardly be explained on any other hypothesis. Owing to the fact that there are comparatively few reinforced-concrete structures which have been built for a very long period of years, positive information as to the durability and permanency of adhesion is lacking.

Are You in North Hampton New Hampshire? Do You Need Concrete Cutting?

We Are Your Local Concrete Cutter

Call 603-622-4441

We Service North Hampton NH and all surrounding Cities & Towns