Behaviors Study On Semi-Rigid Composite Joints Under Low Cyclic Loading

Steel moment-resisting frames with welded beam-to-column connections were traditionally regarded as having excellent performance, and widely adopted in steel constructions, but this opinion changed after the 1994 Northrige earthquake and the 1995 Hyogoken-Nanbu earthquake. These earthquakes arouse engineers to resurvey the behavior of connections. It is well known that end-plate connections have definite flexibility, which can increase damp, prolong period, and decease swing of structure. So it can reduce the damage, and is one of the best choices for resisting earthquake. Some experiments also indicate that concret slab above steel beam has great importance on moment resistance,initial stiffness and rotation capacity of composite joints. Since experiments on end-plate composite joints were very limited, cognition on the damage mechanism of this type of joints was rather inadequate. To avoid casualties and decrease the loss in the future, analysis and response the damage mechanism of end-plate joints under seismic load is significant for theory and practice.In order to study the hysteretic behavior of end-plate joints and verify the reliability of theoretical method, One bare steel joint and three composite partially extended end-plate species were tested under cyclic loading. Failure modes and effects of reinforcement ratio on hysteretic behavior of joints were synthetically c onsidered during cyclic-loading. Results of the experiment shows that partially extended end-plate composite joints have excellent hysteretic behaviors, and the longitudinal reinforcement ratio has some crucial influence on joints behaviours.Simplified formulas on moment resistance of semi-rigid composite joints were introduced base on plastic analysis. Also rotational stiffness and panel zone response were present.The calculated results were shown to be in good agreement with the test results.The main popular theoretical method adopted to study end-plate joints is finite element technique under monotonic loading at present. This paper applies nonlinear finite element method to analyze the behavior of end-plate composite joints under dissymmetry loading. Contact elements are set between end plate and column flange.Also analysis results were compared with the experimental data.The problem of connection seismic behaviors is of great importance for structure field, and the foreground of study and application is very wide. Experiments and theoretical analyses presented inthis paper may well fit the realistic behavior of end-plate connections under seismic load. The conclusion can be useful for revising code, guiding design of engineering, and making a favorable base for analyzing the seismic behavior of whole composite structure.