1.School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China;
2.Faculty of Architecture, Civil and Transportation Engineering, Beijing University of Technology, Beijing 100124, China
Abstract：Focusing on special-shaped bifurcated concrete-filled steel tube (CFT) column with multiple cavities of mega-frame structures in super high rise buildings, in order to investigate the influence of cross-sectional enhanced structures on the seismic behavior of the bifurcated short column, four specimens subjected to vertical axial load and horizontal twice loaded cyclic loading were tested. The upper part of the specimen includes two pentagonal CFT column branch with four cavities, while the lower part includes one octagonal CFT column branch with 13 cavities. As a result, a bifurcated column forms. The investigated cross-sectional structures are divided into four types: basic type, the type that the thickness of the whole tube steel plate is increased, the type that the thickness of local steel plate being far from the neutral axis is increased by welding steel angle, and the type that circular steel tube is encased in the cavities being far from the neutral axis. Based on the test results and the characteristics of section structures, numerical calculation was conducted. The test and simulation results show that for special-shaped bifurcated CFT short column, the failure mostly appears at the root part of the upper column branches on the bifurcated cross section. The main failure exhibits the tear of the steel plate far from the neutral axis and the tear of whole steel plate caused by the crack of local welding seam. The bearing capacity of the enhanced structure of encasing circular steel tube increases by 7.6%, while the deformability increases by 14.4%, and best energy dissipation ability shows. The bearing capacity of the enhanced structure of increasing thickness of local steel tube increases by 9.2%, but the deformability decreases by 18.7%. The bearing capacity of the enhanced structure of increasing thickness of all steel tube little increases, while the deformability significantly decreases. The proposed simplified finite element model for special-shaped bifurcated CFT short column with multiple cavities exhibits well efficiency. And the accuracy can full the demand of engineering design.
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