Research On Axial Compression Behavior Of Joint Between Rectangular Concrete Filled Steel Tubular Column And Beam With Disconnection Column Tube At Joint Zone

Concrete filled Steel Tubular(CFST) structure has been used in construction engineering because it is able to take the full advantage of concrete and steel and also has good bearing capacity and ductility. CFST structure has unique advantages compared to concrete structure and steel structure, and the mechanical behavior is good. As an important part of CFST structure, the CFST column joint has been the hot topic of construction engineering design. Because of the limitation of economics, CFST column-RC beam joint is widely adopted in China which leads to the intersection of steel bars and steel tubular that causes a series of questions and severely restricts the development of CFST structure. A new kind of CFST column-RC beam joint was proposed by our team. The main feature of the new joint is that the steel tube is disconnected at the joint area so that the bars of RC beam can through the CFST column directly. And in order to guarantee the compression capacity of the new kind joint under axial load, the ring beam is set. And also steel mesh and vertical stirrups are set to ensure the bearing capacity and improve the performance of cracking of the new joint respectively.Our team has conducted the first experiment research in which the strength of concrete is too low and rudimentary theoretical study was also casted. In order to study the mechanical behavior of the joint under axial load further, the following works are submitted in this paper.(1)The second experimental study is carried out to investigate the impact of the height and the reinforcement ratio to the axial mechanical behavior and failure pattern which contains 9 square and 5 rectangular specimens. C30 concrete is adopted in the experiment which makes the conclusion more practical. The test results show that the new type joint has high bearing capacity and all specimens crack before failure which shows good ductility but the plain concrete specimen. The axial bearing capacity of joint is influenced by height and reinforcement ratio significantly. The axial bearing capacity decreases as the height increased. And the degree of decrease decreases as the increase of height. The axial bearing capacity increases linearly as the reinforcement ratio increased.(2)Elastic-plastic finite element analysis and parameter analysis are conducted based on previous elastic finite element analysis. The analysis can simulate the bearing capacity well but cannot simulate the stiffness perfectly due to the subsidence of loading plate during experiment. The conclusion of parameter analysis which contains two variables of height and reinforcement ratio of specimens is the same with the experiment that the bearing capacity increases as the decrease of height or increase of the reinforcement ratio and decreases as the increase of height or decrease of the reinforcement ratio.(3)Failure mechanism is discussed and a formula to calculate the ultimate axial bearing capacity of the new kind joint is proposed. The formula is compared with other studies and the applicability is validated.