Damage Detection Of Shear Connectors For A Concrete-steel Composite Component

Steel-concrete composite components are widely used in long-span girder of bridge, crane beam of industry construction and floor system of high building. Shear connectors in composite components play an important role in providing composite integral behavior and any deterioration or failure of connectors will cause a decrease in the shear-resistant capacity in the interface and then a decrease in structural global stiffness and load-carrying capacity. Because of the inaccessibility of shear connectors in steel-concrete composite beams, it is difficult to detect the interfacial damage by direct inspection. It is crucial to develop reliable non-destructive damage detection and monitoring methods for the connectors in composite structure.In this paper, the damage detection of connectors of a steel-concrete beam was carried out by the variation in global natural frequencies and modes, local nonparametric model and impedance of PZT patches. The main contents of this paper are as follows:1. A scaled steel-concrete composite beam with removable bolt connectors was designed and constructed in the lab. A number of bolt connectors are employed to connect the flange of the steel beam and the concrete slab and can be easily unscrewed and removed after the concrete has been cured for the purpose of mimicking the damage in shear connectors. Different damage scenarios were mimicked by removing some of the connectors.2. Impact tests were implemented on the composite beam and the corresponding impact force and acceleration responses were recorded. Using the Polymax methods, the global modal parameters such as natural frequencies and mode shapes were identified and were employed to detect the damage of interfacial connectors.3. A local shear connector damage detection approach with nonparametric model was proposed to identify the performance of the bolt connectors. Vibration tests on the composite beam in different damage severity scenarios were carried out, and the corresponding acceleration time series of a substructure including the bolts were recorded. Using acceleration time series at certain location of an intact substructure of the composite beam, a nonparametric model for the substructure was established based on a neural network, which was employed to act as a nonparametric base-line for damage detection of certain shear connectors. When the connectors are loosened or removed, the acceleration response measurements of the structure close to the connectors to be monitored do not meet the output of the corresponding neural network model. The difference between the output and the measurement provides an index for damage detection of the connector.4. A bolt connector damage detection method based on the PZT impedance measurement was proposed. In the impedance measurement tests, each PZT was used as actuator and sensor at the same time. Before and after some connecters were removed, impedance of each PZT was measured. A damage detection index based on the variation in the impedance measurement of PZTs located at different location was defined and employed to determine the existence and severity of the damage in the bolt connectors.