Experimental Research On Seismic Behavior Of New Type Of External Hoop Joints

With the rapidly development of China’s urbanization level,the urban population is increasing,and the contradiction between land supply and demand is constantly increasing.Combining with China’s national conditions,RC frame-light steel mixed structure is a good solution currently,but due to the large change in the quality and rigidity of the light steel structure and the lower original structure,it is easy to appear weak layers during design,how to ensure the synergy of the upper and lower structures and the safety of the overall structure have become the primary issues in seismic analysis.Therefore,the design of the connection joints of new and old structures has become the key to the design of such mixed structures.Based on the existing light steel build-up connection joints,a new type of external hoop joints is proposed.The quasi-static test is used to comPare the seismic performance of traditional planted-bar joint and new type of external hoop joint.The correctness model of the new type of external hoop joint was established by ABAQUS finite element software,and its force characteristics,failure mechanism and related Parameters were studied in depth,and reasonable design suggestions were put forward.It provides a certain reference value for joints design in the RC frame-light steel mixed structure.The research work of this paper mainly has the following contents:(1)Through reading the literature,understand the structure of RC frame-light steel mixed structure and the research status interiorly and abroad in recent years,and put forward the research work based on the existing problems.(2)Designed a new type of external hoop joint test piece,and made a 1:2 scale model of the traditional planting joint and the new type of external hoop joint.The quasi-static test under low-cycle reciprocating load is used to comPare and analyze the seismic performance of hysteresis curve,plastic end of beam end,skeleton curve,strength degradation,stiffness degradation and energy dissipation.The results show that the plastic hinge failure of the beam ends occurs at both ends,but the new type of external hoop joint can make the plastic hinge away from the beam root and effectively protect the core area of the node.At the same time,the structural measures of the new joint outer hoop steel plate improve the initial stiffness,bearing caPacity and energy consumption of the test piece,and slow down the degradation rate of stiffness and strength.It shows that the seismic performance of the new type of external hoop joint is much better than the traditional planting joint.(3)The ABAQUS finite element software is used to simulate the new type of external hoop joint by nonlinear finite element method,and its failure mode and force transmission mechanism are clarified.By comParing with the experimental results,the correctness of the establishment of the finite element model is verified.The results show that the reinforced concrete beam is mainly subjected to bending moment and shearing force at the initial stage of loading,and the longitudinal reinforcement of the beam is subjected to yielding under the action of tension and compression.Due to the fastening effect of the bottom plate of steel column and the annular steel plate,the crack development is limited,and the main crack appears at the edge of the steel column bottom plate.As the loading displacement continues to exPand,the concrete beam gradually loses its bearing caPacity.The bending moment at the root of the joint is transmitted to the steel column bottom plate and the annular steel plate through the four outer hoop screws.The anchor bolt also increases rapidly under tensile force and enters yielding.Until the final bearing caPacity of the joint drops to 85%of the ultimate bearing caPacity,it is confirmed that the damage is reached.(4)The influence of relevant Parameters on the seismic performance of new joint is studied.By changing the axial compression ratio,the stiffness ratio of beam to column and the corrosion rate of steel bars,the influence of the Parameters on the seismic performance of the new type of external hoop joint is analyzed.①With the increase of axial compression ratio,the horizontal bearing caPacity and initial stiffness of the joint increases slightly,and the stiffness decreases faster in the elastic range.The ultimate degradation degree of stiffness and hysteretic curve do not change significantly.②With the increase of the stiffness ratio of beam to column,the horizontal bearing caPacity and initial stiffness of the joint increases greatly.The hysteresis curve is fuller.The energy dissipation caPacity is stronger,and the stiffness decreases faster in the elastic range.③With the increase of steel corrosion rate,the horizontal bearing caPacity of the joint decreases slightly,and the hysteresis curve and stiffness degradation does not change significantly.According to the above rules,the optimum design range of Parameters is determined,and reasonable design suggestions for new type of external hoop joint are put forward.