Experimental Study On Seismic Performance Of Concrete-filled Square Steel Tubular Column And Steel Beam Connections

The concrete-filled square steel tubular composite structures possesses some special properties, such as high-strength, good ductility, better fireproofing behavior and excellent seismic performance. In addition, it is easy to design and construct due to its rectangular geometry that were widely used. Due to these advantages of square section, it is being used more and more in steel building and skyscraper construction. The study on seismic performance of concrete-filled square steel tubular column and steel beam connections helps to understand the mechanic behavior and performance of the connection under cyclic loading, to improve the fabric and to correct the calculating equation of the load carrying capacity. These works will promote the applications of this kind of composite structures in seismic vulnerable area. In this thesis, we accomplish the works as follow: Three types of connections, namely stiffened end plate (SEP) connection, side plate welded (SPW) connection and inner diaphragm connection, were tested under low cyclic loading to review seismic performance of connections. The degradations of strength and stiffness, ductility, failure mechanism and failure characteristics of these connections under different axial-compression ratios were compared. The simplified calculation model based on the deformation and moment-rotation framework curves of the joint was established. The procedure was implemented by Matlab program to calculate the hysteretic behavior of the connections.The equations of simplified calculation method were presents to estimate the load carrying capacity of these two types of connection.The main conclusions of this work are listed below:The cyclic loops of these two types of connections are nearly rectangular, and there is no pinch or just a little effect was found. These loops indicate the good dissipation of energy.The axial-compression ratios affect little the cyclic loops in this test. Degradation of Stiffness and load carrying capacity were found in all kinds of connections. The load carrying capacity of SPW and SEP connection is not less than that of the inner diaphragm connection. If the intensity and quality of weld are assured, the ductility and energy dissipation behavior of the connection are better. There are long level or decline segments after peak value in the plot of force-deformation and moment-rotation curves. It means that the SPW and SEP connection have excellent ductility.The results from the simplified calculation model based on the deformation and moment-rotation framework curves of the beam, the column and the joint area correct well with that from testing.The results from the equations of load carrying capacity simplified calculation match the testing data very well. It means that the equations can be applied in primary design.