Mechanical And Experimental Behavior Of Concrete-filled Rectangular Steel Tubular Column-beam Connections

Concrete-filled rectangular tubular column composite frame systems with steel beams have been widely used in moment-resisting frames for engineering practice. In this study a variety of connection details to concrete-filled rectangular tubular(CFRT) columns that have been developed by different researchers were reviewed. The research on CFRT connections was divided into three phrases. The first phase dates back to the late sixties of twentieth century, when the steel moment-resisting frames were regarded as one of the most ductile systems. The second phase is defined as the period from mid 90 s to early 2000 s, during the early stage of which the Northridge earthquake and Kobe earthquake occurred and the conventional knowledge of traditional connections were subverted, leading to the requirement of paying more attention to the investigation of connection behavior under seismic loading. The third phase lasts until the present. During this phase, various connection alternatives were proposed and studied.Experiments have been conducted on four through-diaphragm connections, two new internal-diaphragm connections and one extended thick-walled through-diaphragm connection. The variables in the experiments include the geometry of the diaphragm, the configuration of the weld access hole, horizontal stiffeners, and the methods of connecting beam webs to columns. The strength, stiffness, ductility and energy dissipation capacity were evaluated at different load cycles. It is shown that the connection configuration provided stable hysteresis behavior with appropriate level of strength and stiffness. The results indicate that this connection can offer ductility and energy dissipation capacity appropriate for its potential application in composite ordinary moment frames or composite intermediate moment frames in seismic region.Theoretical studies were conducted into the behavior of the through-diaphragm to concrete-filled rectangular hollow section(RHS) columns subjected to tensile force or shear force. Component-based models have been developed and used for predicting the strength of the column component of concrete-filled RHS columns under tensile load imparted through a through-diaphragm connection. The strength models are based upon defining a rigid plate deformation pattern for the column face and then applying the virtual work principle, taking into account the membrane action and strain hardening. The hand calculation procedures for yield and ultimate deflection were also developed. The load-deformation curve consists of three segments: the first representing the elastic behavior from the classic plate theory, the second obtained by plotting the deformation at the ultimate strength against the maximum load, the third horizontal line stretching to the failure point. The mechanical models were compared with a large range of experimental results and good agreement was shown between them. The proposed method can be used in the component-based method for connections involving a through-diaphragm component in tension. The mechanical model for shear strength was presented according to the simplified trilinear shear-deformation relationship for connections. A theoretical method was proposed to evaluate the shear strength of the concrete compression strut at the yielding point of the steel tube. In addition, the contribution of steel frame mechanism in the panel zone was taken into account in the proposed model. Excellent agreement was found between theoretical and experimental results for both yield and ultimate shear strengths for connections.The through-diaphragm connection detail has been identified as a good choice for attaching HSS beams to concrete-filled rectangular tube columns in engineering applications. In this research program an analytical study was conducted to comprehend the behavior of this detail and develop the accompanying design guidelines. Two analytical models were established to predict the shear stiffness and yield shear strength of the HSS beam and panel zone, respectively. Theoretical results based on the proposed model well agreed with the experimental data. Finally, design provisions were introduced to check the strength in the connections.