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Inelasticity in reinforced concrete (RC) frame structures due to seismic loads is generally considered to be concentrated in the form of hinges in beams, columns, and joints. In this paper, the parameters for rectangular RC beams, columns, and nonseismically detailed beam-column joints are suggested, keeping the simplicity of the original pivot hysteresis model. With the proposed parameters, the existing model can be effectively used to perform nonlinear dynamic analysis of nonseismically detailed RC structures. Two major improvements in the parameters for columns as compared to the original model are: 1) new parameters cover the complete range of axial load on the column; and 2) it gives due consideration to the transverse reinforcement on pinching behavior of the members. Additionally, several parameters are proposed for poorly detailed exterior joints. It is shown that the model with the proposed parameters nicely captures the hysteretic behavior of RC members, joints, and structures.
Keywords: hysteresis; nonlinear; nonseismic detailing; pivot model; reinforced concrete; seismic analysis.
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INTRODUCTION
Reinforced concrete (RC) construction, especially designed following old and nonseismic norms, is known to be vulnerable against seismic loading; over time, earthquakes across the world have exposed this repeatedly. With the growing need to perform nonlinear dynamic seismic analysis of RC structures, it is important to develop hysteretic models that are efficient and easy to implement while being accurate enough to sufficiently capture the hysteretic behavior of the structures. The inelasticity in RC frame structures due to seismic loads is generally considered to be concentrated in the form of plastic hinges in beams, columns, and as shear hinges in the joints. Although the shear hinge formation in the joints is undesirable and new regulations try to prevent the same, the joints of old structures with no joint shear reinforcement are particularly vulnerable to shear hinge formation. Thus, to perform a realistic seismic analysis of nonseismically detailed RC structures, it is important to have models to capture the hysteretic behavior of beams, columns, and joints.
Researchers have used various hysteretic rules to model the nonlinear behavior of RC members, starting from very simple elasto-plastic rules to more complex rules. Probably the most well-known flexural hysteretic model is the Takeda Degrading Stiffness Model,1 which has also been further modified by...