Design Method Research On Concrete-Filled Steel Tube Beam-Column Joints Of Tall Buildings

With the development of the economy and the city construction, many tall buildings with concrete-filled steel tubular structure have been built up in China. Steel tubes filled with concrete to form a composite member are refereed as concrete-filled steel tubes (CFT). It is well known that CFT members exhibit many advantages to achieve high seismic performance in terms of strength and ductility. However, many problems in the high-rise structural system of CFT have not been solved. For example, the analysis method of whole structures, the design method of beam-column joints, and so on. So, the design method of beam-column joints is focused on in the thesis and a new calculation method of beam-column joint shear strength is proposed. (1)CFT beam-column joints of tall buildings that often been used in engineering are surmised and a new taxonomy, accounting for shear transfer route, is proposed. The joints that shear can directly transfer to the infill concrete are called perforated joints. The joints that shear transfer to the infill concrete through the tube walls are called non-perforated joints. The new taxonomy distinguishes the shear transfer route clearly and makes it convenient to research on beam-column joint shear strength. (2)Multifarious factors influencing joint shear strength are discussed, based on the analysis of the state of joints in real buildings, the mechanism that joints sustain shear forces and the failure modes that joints may suffer when they are subjected to horizontal shear forces. The general method that predicts the joint shear capacity is presented. This method respectively calculates the shear capacity of the infill concrete, the tube wall, the reinforced concrete circle beam and the steel circle diaphragm.(3)The calculation formulas of perforated joint and non-perforated joint shear strength are proposed respectively. And the graphs showing the relations between shear strength and column moment, between shear strength and axial load and between shear strength and vertical shear at the end of the beam, is presented. Some principles about joint shear strength are obtained. (4)To validate the proposed theory, calculation result is compared to the experimental result that obtains in the experiment done in Southeast University. The comparison shows the proposed prediction for panel shear is higher than experimental results reasonably. The proposed theory is used in the two real engineering project: Jiangsu Province Telegraph Ltd. Data & Information Transfer Building and Nanjing City Olympic Physical Science & Technology Center, to test the joint shear strength of the two buildings, and the results are satisfied. (5)ANSYS program is used to analyze the performance of the perforated joints and non-perforated joints subjected to horizontal shear forces. The proposed calculation formula is further proved.(6)The research results of Southeast University in recent years about CFT beam-column joints and short column subjected to axial load are summarized in this thesis. According to these results, the key points of the CFT beam-column design are discussed and the checking computation formula of joint shear strength is proposed, considering the current design codes. Furthermore, the checking method and calculation formula of joint compression strength and flexural strength are presented.