The behavior of reinforced concrete beams at failure by shear is distinctly different from their behavior by bending, which is considered to be unsafe mode of failure. The shear failure of beams is usually sudden without sufficient advanced warning and the diagonal cracks that develop due to excess shear forces are considerably wider than the flexural cracks. The cost and safety of shear reinforcement in reinforced concrete beams led to the study of other alternatives. Swimmer bar system is a new type of shear reinforcement. It is a small inclined bars, with its both ends bent horizontally for a short distance and welded to both top and bottom flexural steel reinforcement. Regardless of the number of swimmer bars used in each inclined plane, the swimmer bars form plane-crack interceptor system instead of bar-crack interceptor system when stirrups are used. Test results of several reinforced concrete beams will be presented. The effectiveness of the new swimmer bar system as related to the old stirrup system will be discussed. Beam deflection is also targeted experimentally in the lab. Several deflection measurements were taken to study the effect of using new swimmer bar system on deflection. Also the crack width of the tested reinforced concrete beams was monitored.

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Abstract:Concrete strength improved substantially when lateral confinement stresses are provided. This effect has been exploited in this study in composite beams at the concrete compression zone. New type of confinement is used in this research. The confinement of concrete in the compression zone is accomplished by providing U-links and stud-plate systems. The U-links are steel bars in the shape of the letter U welded internally in a steel tube at the compression concrete zone. These tubes provide confinement effect similar to the stirrups used in reinforced concrete beams. The stud-plate element used in this study is made of steel bar welded to a horizontal plate at one of its end, while the other end is welded to the top of the steel tube at the compression zone from the inside of the tube. The main function of these two elements is to provide the concrete in the compression zone with confinement stresses. The composite beam is tested in bending under single load at the mid-span. The effect of the new confinement system is studied and compared with concrete filled tube without any confinement element. The failure mechanism is also a focus of this research along with the deflection at the mid-span of the beam. The effect of the new confinement system on the structural behavior of the composite beam is presented.