Health Monitoring Of Hollow Concrete Filled Steel Tube Brace Based On Piezoelectric Smart Sensors

The hollow concrete filled steel tube brace is a new type of brace member that makes full use of the synergistic effect of steel and concrete,depending on its high bearing capacity,large bending rigidity,convenient construction,and low steel consumption,it has been used in building structures,bridge engineering and pit engineering in recent years.The research on mechanical properties of this component is still at the stage of theoretical derivation and experimental verification.Monitoring the compression performance of the hollow concrete filled steel tube brace which in service,detecting damage in time and evaluating the damage degree accurately are important to ensure the component can be used for a long time.An embedded piezoelectric smart sensor is made based on piezoelectric ceramic materials in this paper,which realizes the health monitoring of a whole process of concrete from hardening to compressive damage.The contents include the following aspects:(1)Designed an embedded piezoelectric smart sensor depend on material performance of piezoelectric ceramics and the method of structural health monitoring,introduced the manufacturing process in detail,and used two methods for sensitivity calibration which included applying forced vibration and the impact load of hammer.The experiment results showed that the piezoelectric smart sensors had good dynamic response characteristics,and its more significant to impact loads.(2)The piezoelectric smart sensors were embedded in a hollow concrete filled steel tube specimen,and used the piezoelectric wave method to monitor the early strength of the concrete during the concrete curing period,analyzed the monitoring results in time domain and frequency domain,and introduced the energy analysis method to establish the relationship between concrete strength and the energy value,obtained the relationship between the energy value and the strength-energy ratio fitting function expression,at last,realized the early strength monitoring of the core concrete in the hollow concrete filled steel tube brace.(3)Designed four hollow concrete filled steel tube brace scale models with slenderness ratio and hollowness as independent variables,piezoelectric smart sensors were embedded in the models as the driving ends and the sensing ends to carry out the axial compression static load experiment,the load-bearing capacity of the specimen,the damage characteristics and influence factors were summarized;The output voltages of the sensors were collected by passive monitoring,according to calculate the signal energy value per unit time during entire process of loading to realize damage monitoring,and concluded the destruction process and characteristics of the specimens in the view of energy.(4)By means of transmitting excitation signals,the hollow concrete filled steel tube brace scale models were monitored actively for four times during the loading process,and analyzed the voltage signal with the wavelet packet energy analysis method,introduced the damage judgment index to establish the relationship between the damage index and the sensor output voltage,then proved that the active monitoring method based on piezoelectric smart sensors could reflect the damage degree of the structure relative to the health state at a certain moment effectively.