Micro-mechanism Based Anasys Of T-stub Connections Failure Process Under Cyclic Loading

T-stub beam-to-column semi-rigid connections provide the advantages of being simple in joint structure,and the construction is convenient.It is the strongest one of all the semi-rigid connections,have broadly application prospect.Earthquake damage survey revealed that the fracture destroy of high-rise steel framing structure beam-to-column connection will lead to failure of the whole structure and collapse.There are still some problems need to explore to predicting the failure of structure in cyclic loading.The failure process of T-stub connections in cyclic loading are studied by the macroscopic-microscopic research methods.The main research work and conclusions are summarized as follows:1.Tests of Six T-stub steel beam-to-column connections under cyclic loading were carried out.Results reflect that fracture of T-stub steel component is the main reason of the failure of the connection,T-stub connection has good deformation performance,load displacement hysteresis curve of the joint arranged in Z shape and indicates pinch phenomenon,size of T-stub has most effect on joint stiffness and carrying capacity,with the increase of the cyclic loading,damage of joint is accelerated.Using the damage model given in our research can predicted the damage process of the joint under low cyclic loading reasonably.2.Taking into account the failure characteristics of materials under high strain amplitude cyclic loading and low cycle times when subjected to intense earthquake,failure test of Q235 round bar with different notch radius under large strain amplitude cyclic loading was carried out and the initial cracking position,cycle life,crack growth process,fracture morphologies and the fracture morphology were given.Progressive failure of round bar with different notch radius under cyclic loading was simulated.Results shows that using the analytical model established in our research can well simulate the crack initiation location,crack development process and stress-strain curves,and the rationality of using macroscopic-microscopic methods to simulate failure is verified.3.Considering the dimple fracture of the round bar with different notch radius under large strain amplitude cyclic loading,the combinatory work density model was used as failure criterion of material components.An constitutive model which describing the deformation and ductile fracture behavior under cyclic loading was established based on the failure criterion combine with Chaboche cyclic plastic theory.Cyclic loading material test of smooth round bar and notched round bar was carried out to calibrate the parameter of for the cyclic plastic constitutive model and the ductility fracture criterion.4.Experiment study on T-stub steel component under fixed or varying amplitude cyclic loading was carried out and the failure mode,cyclic life of crack initiation and fracture were given.Simulate the fracture process in cyclic loading by finite element method with the analytical model which describing the deformation and ductile fracture behavior under cyclic loading was established in our research.The result shows that our method can simulate the fracture process of T-stub steel component under cyclic loading accurately.5.The finite element model of the T-stub steel beam-to-column semi-rigid connection was established and the meshing,material,boundary conditions and the interaction of the model were elaborated.The finite element calculation results with different material models and different types of contact sliding were compared and analyzed.Analysis results show that Chaboche model can simulate the response of the joint under cyclic loading more accurately than isotropic hardening constitutive model..Considering the characteristic of the semi-rigid connection has large deformation,using finite sliding is more reasonable.6.Simulation and analysis of the test process of T shaped steel joints under cyclic loading was carried out by T-stub steel beam-to-column connection finite element model which considered the material cyclic plastic,face-to-face interaction of each joint component.The calculation results were compared with the test result,which confirmed that the finite element model established in this paper can describe the real loading process,hysteresis curve and the deformation characteristics.7.The hysteretic and energy dissipation performance of T-stub connections with different T-stub structures,different size of T-stubs and different beam sectional dimension under cyclic loading were compared and analyzed.Result shows that the widened connections improve the deformation capacity and the energy dissipation performance of the joint,increasing the web thickness of T-stub and the height of the beam section at a certain extent can improve the energy dissipation performance of the jointwhile too large web or flange thickness will restricted the ductility and the energy dissipation performance of the joint.