| Concrete-filled steel tube(CFST)column is one of the most important structural members,which has attracted wide attention in the engineering world because of its outstanding mechanical characteristic in recent years.The concrete-filled steel tube component combines the core concrete and the external steel tube to form a whole and bear the force together.The "hoop effect" of steel tube on core concrete increases its bearing capacity.The internal filling of concrete makes up for the disadvantage of steel structure and effectively prevents the local buckling of steel pipe.However,the common problem of concrete filled with steel tubular(CFST)has a considerable influence on the mechanical performance of the structure,and at the same time has some concealment,which is the key and difficult problem of structure detection.In this paper,based on the practical engineering problems,based on the existing testing technology of concrete-filled steel tube(CFST)at home and abroad,the nonlinear dynamic characteristics of the structure are taken as the starting point to test the damage of the concrete filled steel tube column,and the conclusion is analyzed systematically.Due to the influence of material,boundary and geometric conditions,nonlinear factors always appear in engineering inevitably.In the process of vibration of concrete-filled steel tube column,the effect of the debonding joint on the nonlinear vibration of the component can be called "breathing effect",that is,the opening and closing of debonding joint in the process of vibration strengthen the nonlinear dynamic characteristics of components.Therefore,debonding damage can be detected by studying the variation of component frequency with amplitude.Based on the Debonding Problem and vibration characteristics of CFST,the main work of this paper is as follows:(1)Starting from the research object of this paper,the definition and phenomenon of concrete-filled steel tube debonding are clarified,the causes of debonding are analyzed in depth,and the adverse effects of debonding on the mechanical properties of concrete-filled steel tube structures are discussed.(2)In theory,the concrete-filled steel tubular component tested in this paper is simulated as a cantilever column with distributed parameter system,and the dynamic behavior of this kind of structure is analyzed in depth through the idealized physical model;the basic content of signal processing is described,the filtering and analytical methods used in the digital signal processing are discussed,and the effectiveness of using AMD and Hilbert transformation for debonding identification is verified.(3)Five concrete-filled steel tubular columns were designed and tested in laboratory.The acceleration signals of free vibration are obtained and processed by data acquisition of different hammering force,hammering position and measuring point position of the test components,and the nonlinear vibration characteristics of CFST under different debonding conditions are analyzed.(4)The results show that with the increase of vibration time,the amplitude of CFST decreases gradually,and its instantaneous frequency increases slowly;the percentage of debonding is related to the nonlinearity,the nonlinearity of CFST is large,but debonding damage weakens its nonlinearity;different debonding positions of the same component It can be determined according to the non-linear index of different measuring points.The research in this paper can provide a reference for the detection of the debonding damage of CFST. |
