Shear Failure Mechanism of Reinforced Concrete Columns and Beam-Column Joints under Tri-lateral Excitations and Prevention Design Method

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Objective of the study is to investigate the influence of shear failure in columns or beam-column joints on earthquake resistant performance of a R/C frame building subjected to varying axial and bi-lateral loads by testing three-dimensional beam-column subassemblage specimens. Two specimens were approximately half a scale model removed from first story in middle-rise R/C frame, and had two columns with orthogonal beams in longitudinal and transverse direction at comer position of a plan view. One specimen was designed to fail by column shear and the other by beam-column joint shear. Force transducer made from steel was placed at the center of full-span beam to measure both axial force and shear force induced to the beam. In supplementary test to calibrate the force transducer incorporated in the center of R/C beam specimen, it was verified that the force transducer did not hamper hysteretic behavior of a beam under reversed cyclic loading. Bi-lateral shear forces and varying axial loa … More d from compression to tension were applied simultaneously at each column top in R/C subassemblage test. Both specimens failed in supposed manner, i.e., one by shear at the middle portion of columns and the other by shear in beam-column joint panels. In column failure specimen, shear cracks occurred in the exterior column at first. However, shear failure in the interior column became remarkable due to bi-lateral shear loading.Two isolated columns with the same dimension and steel arrangement as the three-dimensional subassemblage specimen were tested under uni-lateral and axial loading to investigate the difference of shear performance caused by uni-lateral or bi-lateral loading. Tests were carried out by providing anti-symmetric bending moments at the top and bottom of a column. Compressive axial load to interior column was kept constant through testing whereas varying axial load was applied to exterior column from tension to compression. Two isolated columns subjected to uni-lateral load reversals failed in shear. Many diagonal shear cracks occurred uniformly in entire surface of a column. On the contrary, shear cracks concentrated in the middle region of columns in the three-dimensional subassemblage specimen. Shear strength of interior and exterior columns subjected to bi-lateral loading was 0.78 times and 0.86 times smaller respectively than that of corresponding isolated columns subjected to uni-lateral loading. Less