Non-linear Vibration Based Study On Compactness Identification Of CFST

In recent years, CFST is widely used with the development of structures forms, the buildings become higher and higher, the span also become longer and longer. CFST has a lot of advantages, but there are also some disadvantages, such as: debonding. Debonding has serious influence on the mechanical properties and deformation performance of the members. The typical detection methods of CFST are all aimed at void but invalid with debonding.The author of this paper use the contact nonlinearity of CFST to detect the damage of CFST. Contact nonlinearity is derived from friction. With the vibration of CFST, the friction of steel tube and concrete dissipates energy. So the frequency of CFST is changed. The friction will be serious when the members are intact, then the nonlinearity of members is obvious.The author firstly use this method to detect the damage of short CFST columns in the lab, then some CFST columns in a real project have been tested. The advantages and disadvantages of the method are both discussed. Then the feasibility of using this method to detect the project CFST structures has been proved. The main conclusions and results of this paper are as follows:â‘ The reasons of debonding and the changes of mechanical properties are both been analyzed. Most methods for detecting the damage of CFST and the repair measures for CFST are also been referred.â‘¡All kinds of signal processing methods have been discussed, the author focus on filtering and Hilbert transform.â‘¢Two experiments were conducted, then use filtering and Hilbert transform to process the signals. Base on the curves of frequency and amplitude, the level of debonding can be analyzed.â‘£The level of debonding has influence on the fundamental frequency, but some other factors can also change the fundamental frequency, so the difference of fundamental frequency could not be the index of judging the level of debonding. The level of nonlinearity will be raised if the areas of debonging are decreasing. The slope of the curves of frequency and amplitude is decreased with the increase of amplitude.The feasibility of using this method to detect the project CFST structures and short CFST columns in the lab has been proved.