유효 깊이가 상이한 헤드철근간의 비접촉 겹침이음에 대한 실험적 연구

Abstract

Headed bars have been used to the anchoring of the tension or compression longitudinal bars and of the shear reinforcing bars. Recently, lap splices of headed steel reinforcements have been attempted to the joints of precast concrete members and to the connections between old and new concrete members. New moment-resisting precast concrete beam-column joint was proposed for moderate seismic regions. It has the connection headed reinforcing bars, penetrated the joint. The connection headed reinforcing bars and the bottom headed bars of precast beam are in noncontact lap splices with different effective depths. In this research, a test program was conducted to evaluate the lap splice performance of the noncontact headed reinforcements with different effective depths. Five lap splice specimens were tested. Their variable was the lap length(6~14 times the diameter of D25 bar). Test results showed that the specimen, which had the lap length as fourteen times the diameter of reinforcement,had the nominal tensile strength of reinforcement. Specimens which had the lap length less than twelve times the diameter of reinforcement failed with the slip of reinforcements and the vertical crack in the lap zone. The ratios of the test maximum strength and the maximum strength by CCD method were 7.10∼13.37. It was caused by the reduction of lap length, where headed reinforcements were located less than 1.5 times lap length from three or more edges, and by consideration of only the bearing stress of heads except the bond stress of reinforcements. The ratios of the test maximum strength and the maximum strength assumed by ACI 318-08 for headed deformed bars were 1.70∼2.17. To develop a reliable design guideline of the lap strength of headed reinforcements, it needs to consider the effect of transerse reinforcement, material strengths, edge distance,and spacing of head bars.