| The steel structures have a rapid development trend in the structural field of architectures and bridges due to the advantages, such as high strength, light weight, superb plasticity and so on. The one of main lightweight steel structures is the I-shaped cold-formed thin-walled steel, and its stability problem is considerably significant. In order to improve the global stability of the I-shaped steel beam, some investigators changed the top or bottom flanges into steel tube to form up the hollow flange I-shaped steel beam, such as HFB whose top and bottom flanges are both triangular steel tubes, LHFB whose top flange are rectangular steel tubes, and RHFB whose top and bottom flanges are both rectangular steel tubes, etc. Compared with the conventional I-shaped members, the hollow flange I-shaped steel beam has superior behavior of global stability and structural properties.In this paper,the rectangular steel tube of LHFB is poured into concrete that called CFSFB in this article, and the new type of I-shaped steel-concrete composite beams CFSFBs are researched meticulously. There is no unified theory to calculate the bearing capacity of the CFSFB for global stability because of the complex cross section. In addition, there are few experiments about the bearing capacity of the CFSFB for global stability both in china and abroad because the experiment requirements of global stability are difficult to meet, such as the boundary condition and load condition. Therefore, the global stability of CFSFB is researched meticulously by the experiments and finite elements analysis in this paper. The main works of are as follows:(1)The global stability behavior experiments of three CFSFBs with concentrated load at middle span are finished. A set of support clamp and vertical loading device used in the global stability behavior experiments are designed. In addition, in order to study the global mechanical behavior of the rectangular concrete-filled steel tube top flange, the axial compression experiments of six short rectangular concrete-filled steel tube columns whose rectangular steel tubes are taken from CFSFB were finished as well. The global instability phenomena is appeared for the three experimental CFSFBs and complete test data was acquired that can provide powerful test reference for related scientific research.(2)The experimental results of three CFSFBs are analyzed systematically. The variation rules of section strain, lateral displacement and angle inside and outside plane along with the change of loading during the process of experiment are researched. Through the experiments it can be find that CFSFB-1 is the elastic-plastic buckling failure, CFSFB-2 is the elastic buckling failure, and the flange of CFSFB-3 appears local buckling at mid-span.(3)The finite element model of CFSFB is established by ANSYS finite element software and its validity is verified by experiments. Based on the verified finite element model, the impacts of flange width, flange height, web height, material strength, and the location of load on the stability bearing capacity of CFSFB are investigated. |
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