Experimental Study Of Axial Compressive And Seismic Behavior Of Concrete-filled Circular Steel Tubular Y-joints

This paper is based on the Cloud Tower in Chengdu.The total height of structureof this building is one hundred and eighty five point one meters and its superstructure isframe-reinforced concrete core wall structure system which the frame is composed ofconcrete filled steel tubular columns, steel beams and composite slabs.The structure andstress of the building are complex, especially the big dimension concrete filled steeltubular Y-Joints in the frame.It is difficult to use software to simulate the stressperformance, failure mode and structural measures,so the designer Southwest DesignInstitute commissioned use to test the Y-Joints.Six tests of four joints are made to research ultimate bearing capacity, failuremode, stress and strain distribution of steel and the intersecting area of the Y-Joints andverifying the effectiveness of the structural measures under monotonic static andseismic loading, and the effectiveness of the structural measures. The finite elementanalyses are compared with experimental results for verifying the rationality andreliability of the test results when the tests completed. The main works are as follows:①The first group of tests includes three tests of two joints, respectively, thehollow steel tube joints, joints which the concrete only filled in inclined column, andconcrete filled steel tubular joints, which are beared monotonous static loading (amongthese, the concrete only filled in inclined column is the supplementary test).We mainlystudy the ultimate capacity of the joints, failure mode, and verifying the effectiveness ofthe structural measures in hollow and filled concrete.②The second group of tests have the same joints in the first one, the both two arebring to bear repetitive loading. We mainly study the seismic performance, failure mode,and verifying the effectiveness of the structural measures in hollow and filled concrete.Based on experimental researches and analyses, the main conclusions are asfollows:①The ultimate axial bearing capacity of hollow joints under the monotonic staticand repetitive loading reach1.02times and0.76times of design value; the ultimateaxial bearing capacity of the joints filled concrete reached1.7times and1.6times ofdesign value,which outdistance the design value and the joints maintain axial capacity.The stress of steel and the intersecting area of joints filled with concrete are less thanthe yield strength when the loads reach design value, indicating that the design is safe and reliable.②The failure locations of the two hollow joints under the monotonic static andrepetitive loading are in steel of inclined column but not in the intersecting area of joints;Strain of the intersecting area of joints is less than the steel when the joint filled withconcrete,indicating that the intersecting area of joints don’t be damaged before othercomponents of the building, it insures that the structure has good deformability andperformance of energy dissipation under seismic load, realizing the seismic designphilosophy of "strong joint weak component".③Compared the finite element analyses with experimental results,we can findthat the force and displacement curves of both results of hollow steel tube joints andconcrete filled steel tubular joints under the monotonic static loading fit better,so we canuse the finite element analyses results to verify the reliability of the experimentalresults.