Experimental Research on Hysteretic Behaviors of Square Tubular T joint
In order to study the failure modes and hysteretic behaviors of square tubular T joints, three specimens were made to conduct the cyclic loading test. The test stimulated the constrain condition with hinge connection of both ends of chord member, and the brace was subjected to axial cyclic loading. Based on the experiment, the specimen consisting of small geometry brace showed a good ductility compared with the big one, and the obvious plastic deformation occurred at the intersection between chord and brace member, finally the welding was failure. However, the specimen consisting large size brace appeared a large deformation on the side wall of chord member. In addition, due to the poor ductility of welding on the plates contained in chord member, the welding fracture on the intersection between upper flange and web plates leaded to test end for all the specimens. Introduction Steel tube structure can be used in variety architectural appearance with large span [1] So, various references can be found related to steel tube structure. References [2][4] indicated that the commonly failure modes were local large plasticity deformation on the chord surface, while the specimens were subjected to axial loading, or axial loading accompanied with bending moment. Reference [5] researched on multilinear kinematic hardening model, isotropic hardening model by finite element analysis, and the following conclusion was that it was effective to use multilinear kinematic hardening model studying on steel tube. References [6][7] studied on full width and stepped K type gapped RHS joints by finite element analysis, the effects of geometry parameters on joints deformation, stiffness and ultimate capacity were investigated. Reference [8] conducted a cyclic loading test on full scale welded T type and N type joints, the conclusion was that the fracture occurred in welding of brace and chord intersection. References [9][10] researched on failure mode and ultimate strength of CR T joints and K joints with inner diaphragm, the failure mode of reinforced specimens were changed, so was the stress distribution. References [11][13] conducted a series of tests on square tubular T joints reinforced with collar plate, the tests revealed that the reinforced joints failed differently and strength improved greatly. Currently, the square tubular structure is widespread in domestic construction with a large section dimension and wall thickness, such as Bird's Nest and Shanghai International Circuit. However, most investigation is concentrated on static strength of square tubular T joint. So, it's necessary to conduct cyclic loading test to study the hysteretic behaviors of square tubular T joint. Experimental Program The experimental program consists three specimens and is summarized in Table 1. The test is concentrated on the effect of width ratio (b) between chord and brace member on hysteretic behaviors of square tubular T joint. So diameter of braces is different while chords is same, the configuration and geometric variables of the specimens are illustrated in Fig.1. The specimens are International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) (c) 2015. The authors Published by Atlantis Press 180 made of Q235B steel which is commonly used in Chinese construction industry, and yielding strength is fy=251.4N/mm, elasticity modulus is E=2.07x10N/mm. Table 1 Specimen detail Specimen Chord Brace b(d1/d0) l0 (mm) d0 (mm) t0 (mm) l1 (mm) d1 (mm) t1 (mm) T250 100 2,500 250 8 400 100 4 0.4 T250 150 2,500 250 8 400 150 6 0.6 T250 200 2,500 250 8 400 200 6 0.8 Testing Setup, Loading System and Testing Content Both ends of chord member are set hinge connection while brace member are subjected to axial cyclic loading. The program adopts 50t reaction frame in disaster prevention and militation laboratory of Shandong University of Science and Technology, the test arrangement is shown in Fig.2. Before the actual test, two complete cyclic loads of 10kN are applied to check the working conditions of the strain gauges and other equipment. For each specimen, the brace load is applied at 25% 50% and 75% of yield strength until specimen reaches yield. The yielding displacement 1Dy is written down, and then cyclic axial displacement is applied to the brace end. The axial displacement at the brace end will be applied at 1Dy, 2Dy, 3Dy, and each displacement is looped three times. To measure the stress distribution nearby joints, some strain gauges are set near joints. A displacement meter is set at central bottom surface of chord member to measure the overall displacement of specimen, and another displacement meter is set at the top of brace to measure brace vertical displacement, then the difference between two displacement meters is the displacement of chord upper surface. l0 d0 t0 t1 d1 l1 d0 t1 d1 l1 b 1 0 Fig.1 Schematic of T joint Fig.2 Testing setup of specimen Fig.3 Specimen: T250 100 Experiment Results and Analysis For the specimen of T250 100, upper surface of chord member reflected slightly buckling deformation while axial tension and compression increased to 93kN, and yielding displacement 1Dy was written down. The welding of brace and chord intersection occurred slightly crack in the process of 1Dy, after the second circle of 2Dy, the chord surface reflected obviously buckling, which was shown in Fig.3. The welding fracture occurred at the intersection between upper flange and web plates of chord, then the test stopped. For the specimen of T250 150, when actuator force increased to 110kN, the center of the chord upper surface appeared slightly buckling which was shown in Fig.4. In the loading process of 1Dy, the upper flange and side wall of chord appeared obvious deformation, which was shown in Fig.5. At the beginning of 2Dy process, the welding at the junction of upper flange and side wall appeared and developed quickly as shown in Fig.5, and test stopped. For the specimen of T250 200, when the tensile strength increased to 315kN, the chord bended obviously, but the side wall changed slightly. When brace was subjected to compression, the side wall of chord buckled suddenly, the welding cracked and the upper flange of chord deformed apparently, which could be seen in Fig. 6. The hysteretic loops of specimen T250 100 are the plumpest of all, however, for specimen T250 200,which is obviously brittle failure. For all the specimens, only the specimens with small size brace showed good ductility, and the upper flange of chord around the brace deformed