Research On Seismic Performance Of Reinforced Concrete Frames Considering Joint Models

In the past forty years, beam-column joints of reinforced concrete frames have been studied in experimental and theoretical aspects by scholars both in China and abroad. Since the forces in the core zone of the joint are very complex, most researches focused on testing and analysis based on empirical formulas. Altough the behavior of beam-column joints and the influence they may have on the overall structure are actively under investigation, there are still gaps in explaining different aspects of joint behavior based on comprehensive experimental data. In particular, there is a need for developing a general joint model to describe the monotonic and cyclic nonlinear response of joints and to predict its damage states. To achieve the full vision of the Performance Based Earthquake Engineering, all of the significant details that may contribute to the structural response should be represented by the analysis model. Considering beam-column joint models is a key element of refined modeling of the overall frames. To achieve this end, an accurate and efficient joint element model is needed.In this thesis, modeling and numerical simulation of beam-column joints of reinforced concrete frames and the seismic performance of RC frames with consideration of joint models are thoroughly and carefully carried out, the main contents are as follows:(1) Firstly, the behavior of RC beam-column joints based on the joint2D element in OpenSees is carefully studied, with consideration of the joint equilibrium and force transfer paths, the joint kinematics idealization and simplification, element characteristics and formulation, as well as the generalized one-dimensional hysteretic load-deformation response model.(2) Secondly, the shear theory and methodology of RC beam-column joints are studied: The core zone of RC joints is simplified as a two-dimensional inelastic reinforced concrete membrane element with two-way reinforcement. Three representative shear theories of reinforced concrete, i.e., modified compression filed theory (MCFT), rotating-angle softened-truss model (RA-STM), fixed-angle softened-truss model (FA-STM), are applied to RC beam-column joints. Theory verification to shear panel tests based on the three models is performed. A comprehensive comparison of the three types of shear theoretical models is carried out based on a large number of experiments, and then the appropriate shear calculation model is selected.(3) Thirdly, numerical simulation of a series of RC joint subassemblies tests is carried out. Eleven hysteresis loading tests of RC beam-column joint subassemblies are collected, their results are verified by numerical simulation based on Joint2D element in OpenSees platform. The effects of various joint models assumptions on hysteretic behavior of RC beam-column joints are compared.(4) Lastly, the seismic performance of three overall RC frames with different joint models is studied. Three-story, six-story and ten-storey RC frames are selected as case-study structures. Three joint models, i.e., the traditional center-line model, rigid joint model, and Joint2D model, are considered. Three typical earthquake records under rare earthquakes are selected to perform nonlinear time history analysis for the three frames. The statistics of the time-history analysis results under twenty-three ground motions are calculated. The incremental dynamic analysis is then further applied to investigate and compare the overall seismic performance of RC frames with different joint models.