Experimental Study On Seismic Performance Of Rectangular Concrete-filled Steel Tubular Column To Steel Beam Connections

The rectangular concrete-filled steel tubular (CFST) composite structures have the special properties, such as high-strength, good ductility, better seismic behavior, and convenient construction, etc. Study on the seismic performance of rectangular concrete-filled steel tubular column to steel beam connections has the important theoretical significance and huge engineering values, and also helps to understand the mechanic behavior and configuration of the connection, to promote the applications of this kind of composite structures in seismic area of China.In this thesis, four types of steel beam-rectangular CFST column connections, including normal welded flange plate (WFP) connection, bolted flange plate (BFP) connection, stiffened end plate (SEP) connection and double split-tee plate (DST) connection, were designed based on the configuration of steel frame connection. Total 8 models, 2 models of each kind of connections were tested under low-reversed cyclic loading at the end of CFST columns. The relationships between force and displacement at the end of columns, the relationships between the moment and rotation of the joints, degradations of strength and stiffness, ductility, failure mechanism and failure characteristics of these four connections under different axial-compression ratios were presented. The main conclusions are listed as follows:1. All the cyclic loops of the connections are close to rectangle, and no or little pinch effects can be found. These loops indicate the good dissipation of energy.2. The axial-compression ratios affect the cyclic loops obviously, and stiffness degradation can be found in all kinds of connections.3. There are long level or decline segments after peak value in the skeleton curves. That means the connections have excellent ductility.4. The integral seismic behaviors of other three kinds of connection, namely BFP, DST, and SEP connections are better than that of normal WFP connection.By the way, finite-element (FE) analyses were conducted to predict the influence on CFST structure under different kinds of elements, mesh density, load manners and boundary conditions. After that, a special program was designed to define the constitutive relationship of concrete material in CFST structures based on APDL in ANSYS program. The preliminary FE nonlinear analyses were concucted on the cyclic-behavior of the WFP and BFP connection under low-reversed cyclic loading by combining the ANSYS and this special program. This kind of work is just the beginning of the cyclic analyses of steel beam to CFST column joints.