Experimental Study On Seismic Behaviours Of Flush End-Plate Composite Joints

From the Northridge earthquake in 1994 and the Kobe earthquake in 1995, it is found that the rigid connections of beam-column have poor ductility and result brittle fractures easily. It is well know that the end plate composite joints have better ductility, larger strength resistance and stiffness, which can increase damp, prolong period and decrease swing of structure. So it can reduce the damage and is one of the best choices for resisting earthquake. However, because study on external end-plate composite joints was very limited, cognition on the damage mechanism of this type of joints was rather inadequate. The external joints are often considered as pinned, which underestimate the property of such joints and reduce to much conservation in design, so analysis and response the damage mechanism of external flush end-plate composite joints under seismic load is significant for theory and practice.One flush end-plate external joint under monotonical loading and the other four joints under cyclic loading were tested. Failure modes and the effects of reinforcement ratio and concrete in column flange were synthetically considered during cyclic loading. Results of the experiments show that external flush end-plate composite joint also have quite hysteretic behaviors, better strength resistance and stiffness that are worth to promotion in seismic area.Based on experimental results and plastic analysis simplified formulas on moment resistance of semi-rigid composite joints were introduced. Rotational stiffness and effective width of concrete slab was also discussed. The calculated results were shown to be good agreement with the test results.Part of reasons for lack of practical usage of such joints is that the classification of joints from rigid or pinned connections is not clear, so the classification systems of composite joints in common reinforcements ratio are presented in the paper.According to experimental and mechanical study, the restoring force model of composite joints was presented in this paper. The proposed models can be applied to seismic analyses of flush end-plate composite joint of composite moment frame.The seismic behaviors of connections are great importance for structure field and the foreground of study and application is very wide. Experiments and theoretical analyses presented in this paper may well fit the realistic behaviors of flush end-plate composite joints under seismic load. The conclusion can be useful for design of engineering and make a favorable base for analyzing the seismic behaviors of whole composite structure.This study is funded by research grant of Jiangsu Committee of Science and Technology(Project No BJ95089) and Jiangsu Construction Bureau(Project No JS200001).