Seismic Performance Analysis Of RC Beam-column Joints And Frames Based On Bouc-Wen Model

A large quantity of earthquake damage reconnaissance has shown thatbeam-column connections have been potentially one of the weak components whenreinforced concrete (RC) frames are subjected to seismic loadings. With more andmore experimental tests and analytical studies that have bee n conducted toinvestigate the performance of RC beam-column joints, the researchers haverealized that severe damage in joint panels may trigger deterioration of performanceof beam and column elements, and even the overall frames. On the other hand, thecurrent seismic design code is advancing towards performance-based design.However, structural overstrength hasn’t been considered in elastic seismic designforce theory under minor earthquake in the current code. However, since joints arean important part of RC frames, the hysteretic energy-disspation of joints will havea certain effects on seismic performance of structures as well as the overstrength.Therefore, how to consider the performance degradation of joints, how to establishan appropriate hysteretic model, and how to build refined finite element models ofRC plane and space frames with considerations of joint panel zones for static anddynamic analysis, which can provide basis for caclculation and analys is in futureseismic design of beam-column joints, is the main problems to be solved urgently.Regarding the RC beam-column joints, a series of simulation and analys is iscarried in this thesis. The seismic performance of joints and frames will be studiedthrough the following main works:(1) A smooth hysteresis model, named as Bouc-Wen model, is introduced todefine hysteretic properties of shear panel of the Joint2D elment in OpenSeessoftware. The uniaxial Bouc-Wen material in the current OpenSees version can notmodel the pinching and spreading of RC beam-column joints slips. Since the sourcecode of scientific software OpenSees is highly open which allow users to add orchange the source code, therefore, in this thesis, the Bouc-Wen material model isfurther developed on the platform OpenSees using the C++language, to simulateprogressive strength/stiffness deterioration and pinching effect by adding pinchcontrol parameters.(2) In order to accurately simulate the tests of a series of beam-column jointsubassemblies, appropriate model parameters are needed. The genetic algorithm(GA), which is capable of multi-variable optimization and global search, is chosenfor parameter identification. It is realized based on GA toolbox in MATLAB. Sincepinch control parameters have strong nonlinearities, the model can better simulateexperimental results when it is amended the identified parameters. (3) Five groups of eleven joint subassemblies tests are selected to simulate.Three types of modeling, including rigid joint, Joint2D element based on Pinching4material, Joint2D element based on the modified Bouc-Wen material, are consideredto carry out the numerical simulation. The numerical results have shown that, themodified Bouc-Wen material can well simulate the hysteresis characteristic of eachjoint, for both strength/stiffness degradation and pinch and slips effects. It can befound that energy-dissipation using the piece-wise Pinching4material is muchgreater than the experimental results; and the stiffness during the stage of loadingdeviates from the test results more and more with increasing numbers of loadingcycles. In contrary, the smooth Bouc-Wen material can well fit the shape ofexperimental results.(4) The static pushover analysis is carried out on a six-floor RC plane frame.The analytical studies show that the overstrength and the ductility of the frame sbecome greater when considering deformation and energy-dissipation of joints. It isshown by the seis mic response analysis of the overall frame that, the FE modelingconsidering joints has reduced the top displacement and story drift angls of theglobal structures, so the refined FE modeling considering joints can improve theseismic performance of RC frames. Moreover, the damage law of the middle jointsat each storey is given in this thesis. It has been found that the damage of joints hasthe same distribution patterns of story drift angles, that is, large values in higherstoreys, while small values in lower storeys. Furthermore, the strength/stiffnessdegradation and pinching of beam-column joints are both discovered. Therefore, itis necessary to consider the influences of joints in seismic design.