Bond and anchorage of reinforcement and deformed bars
The cement in concrete cast around steel reinforcement adheres to the steel just as it does to the particles of the aggregate and this adhesion plays its part in the transfer of tensile stress from the concrete to the steel it is of importance ,therefore, that the steel reinforcement be clean and free the scale, rust and oily oy greasy coatings.
Under load, tensile stress tends to cause the reinforcement to slip out of bond with the surrounding concrete due to the elongation of the member. This slip is partly resisted by the adhesion of the cement to the steel and partly by the frictional resistance between steel and concrete. To secure a firm anchorage of reinforcement to concrete and to prevent slip it is usual practice to hook or bend the ends of bars as illustrated.
Deformed bars, offer a greater surface of frictional resistance than do plain bars and this can obviate the necessity to use hooked or bent ends for anchorage to prevent slip.