| Based on the investigation of research and application of concrete-filled tubular column to steel beam connections in China and abroad, according to engineering practice, six full-size specimens that the joints composed by concrete-filled square tubular column and I-shape steel beam divided as A and B groups have been tested under cyclic-loading in this paper. The three specimens of group A are connected by bolt-weld and the group B connected by welded at the end of beams. Results of the experiment show that six specimens' story deflection ductility ratio μ≈2.28~3.86,elastic ratio of story deflection rotation φy≈ 0.011-0.014rad, elastic-plastic ratio of story deflection rotation φu≈0.0297 ~0.0424rad,relative plastic rotation ratio of beam-column θu≈0.0163~0.0343rad and energy dissipation ratio E≈1.946~2.216. All the specimens of group A and B have excellent seismic behavior, the ductility of the specimens A is better than specimens B but the energy dissipation capacity of the specimens B is a bit better than specimens A under the same axial compression force ratio. However, both of the A and B specimens satisfy requirements of the structural seismic design. Some suggestions for improving joint construction are presented according to the results of experiment research.Based on the achievements in theoretical research, the nonlinear FEM model involving geometric large deformation, contact-friction of high-strength bolts and materials nonlinear is presented. The Von.Mises failure criterion and multiplier kinematical hardening stress-strain relationships have been used for steel and the William-Wamke failure criterion and elastic-plastic stress-strain relationships used for concrete . The concrete cracking and contact-friction of bolts connections are used for the discriminating criteria in terms of ANSYS6.1. The 3D models of beam-to-column connections with internal diaphragms by 3D solid elements are founded. And the capacity behavior of connections under the monotonic loading and cyclic loading are analyzed. The results of nonlinear FEM analyses can show the stresses distribution in the joints better, so that it provides the possibility to patch up the defects that couldn't observe in experiments in the details. And then, various factors of the influences of joints capacity behavior can be analyzed such as changing axial compression force ratio and concrete strength etc. Finally, some suggestions for improving joint design are presented according to comparison of theoretic analyses with that of experimental results.According to the results of theory and experimental researches in this paper, the design provisions in the 'Technical Code for Concrete-Filled Square Tubular Structure"(Draft) are discussed. The load-carrying capacity formulations for end section of beam to at the column-beam connections are proposed. Based on the analysis of mechanism for joint region, the "frame-wall" and "aslope compression stub column" mechanical models and yielding patterns of core zone of the joints are set up. The shear load-carrying formulation for joint core zone is also given in terms of plastic ultimate analysis. And then, the comparisons between the formulas given in this paper and that of Chinese Design Code (draft) and nonlinear FEM as well are presented. Comparison shows that the formulas for determination of shear capacity of core zone at joints presented in this paper are much better, simple and safety. And the formulas also can express the changes for axial compression ratio of columns, so they can provide the reference to the engineering design. |
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