Jae-Yo Kim

Early Crushing Failure of High-Rise Shear Walls with no Boundary Confinement

Currently, the ultimate compressive strain of shear walls with no boundary confinement, which is a crucial factor in determining the ductility of shear walls, is empirically assumed to be 0.003 to 0.005. In this study, a fundamental study involving experimental and numerical works was undertaken, to investigate how the actual size and load conditions of plastic hinge region affect the ductility of high-rise shear wall. According to the cyclic loading test, in the case of high-rise shear wall with no boundary confinement, early crushing failure occurred and the ultimate compressive strain was smaller than 0.004 which was generally expected value, because of the size and load condition of high-rise shear wall. According to the additional experimental study and nonlinear analysis conducted for compression zone of high-rise shear wall, it is recommended that for unconfined high-rise shear walls, the maximum compressive strain allowable for ductility design should conservatively be the strain corresponding to the maximum concrete strength and boundary confinement should be provided in the compressive zone where the strain exceeds this ultimate strain.

Secant Stiffness for Direct Inelastic Earthquake Design of Reinforced Concrete Structures

For safe and economical design to provide strong earthquake resistance, the moment redistribution and plastic rotation of structures and their members needs to be evaluated. To achieve this, an earthquake design method was developed using secant stiffness analysis. To address the variation of member stiffness due to plastic rotation and moment redistribution, a structure was modeled with a beam-column element with non-rigid end connections (NREC element). Secant stiffness for the NREC element was determined based on the ductility demands of the structure and members. By performing a conventional linear analysis for the secant stiffness model, redistributed moments and plastic rotations of the members were computed. The proposed method was applied to a moment frame and two dual systems. The design results were verified using detailed nonlinear analyses.

Shear Strength of Simply- or Rigidly-Supported RC Beams with Various Design Variables

An experimental study was performed to systematically investigate the variation of shear strength of simply- or rigidly-supported RC beams with various design variables. In this study, the tensile reinforcement ratio, load applying condition, end supporting condition, shear span to depth ratio, and prestressing force were selected as the main variables. Twenty RC beams without shear reinforcement were tested under monotonic loading, and the influences of the main variables on shear strength were analyzed with shear force-displacement relationships and failure modes. The test results indicated that the shear strength of RC beams increased as the tensile reinforcement ratio, the number of loading points, the compressive force, or the initial prestressing force increased. However, it decreased as the shear span to depth ratio increased. The influence of the end supporting condition on the shear strength of specimens was not significant. The test results were compared with the predicted values provided by design codes and existing model equations.