Estimation of Anchorage Strength Through Bending Shear Tests on RC Beams With Second-Layer Bars Cut Off

Abstract eng:
The amount of reinforcement required in a reinforced concrete building has increased due to the increased demand for highrises and advanced seismic performance. In particular, the amount of reinforcement required at the ends of a beam has increased, and the reinforcement tends to be arranged in multiple stages, where the second-layer reinforcement is frequently cut off at the central part of the beam. However, since there have been few studies on the bond behavior of cut-off longitudinal reinforcements, the bond strength based on the effective bond length is not evaluated appropriately, and it is difficult to design the cut-off reinforcement with a rational anchorage length. Experiments were conducted on the reinforced concrete beam arranged with second-layer bars cut off in order to study the influence of the bond reinforcement on the bond-splitting strength or anchorage behaviors. The longitudinal bars were reinforced with transverse bars having different configurations (separated and closed types) and strengths (σy=295 and 1275 N/mm2). The bond strength of the second-layer bars reinforced by separated-type bars was almost equal to the strength of those reinforced by closed-type bars. Highstrength bond reinforcement increased the bond strength by 30%. The test results also showed that the bond strength of the second-layer cut-off bars was considerably higher than the calculated value based on the AIJ design guidelines. A new reduction coefficient for the second-layer cut-off bars was proposed to reasonably estimate the bond strength for anchorage failure.

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