Diagnosis Of Interface Debonding In Steel-concrete Composite Structures Using Air-coupled Impact Resonance Test

Steel–concrete composite structures are widely used in high rise buildings and bridges because of its advantage of bearing capacity,seismic performance,fire resistance and convenience of construction.Debonding defects tend to appear at the interface between concrete and steel due to lack of quality in construction or the shrinkage and creep of concrete,which could led to the lack of synergy between concrete and steel and further decrease the bearing capacity and deformability of the component.Therefore,it is essential to accurately assess and diagnose the debonding defects of steel–concrete composite structure.While traditional Non Destructive Testing methods can hardly indentify this kind of defect,Air –coupled Impact Resonance Test using microphones is proposed to di agnose the debonding defects cost effectively,rapidly and effectively.In theoretical aspect,the region of steel slab or shell with any debonding defect is considered as a small slab or shell with all the boundaries constrained.Based on the natural frequency formulation of rectangular slab and circular slab with all the boundaries constained,the natural frequency of debonding defect with specific geometry characteristic could be estimated.In experimental aspect,two specimens,one steel –concrete composite slab component and one concrete filled steel tube component,are made for the Air–coupled Impact Resonance Test.Two same groups of local debonding defects are made by foams sticked to the inner side of steel plate or steel tube,while each group of defects contain conditions with different shape and different areal.Hammers are used to stimulate the vibration at local debonding defect area,and the microphones are used to collect the following sound pressure response of vibration at the hammered area.Spectural analysis of the sound pressure response is carried out to compare the frequency spectrum characteristics between the condition with stimulation at decfective area and intact area.After tentative test that determine the relative position of the exciting points and microphone sensors,Air –coupled Impact Resonance Test is carried out to figure out how the frequency response function of sound pressure is affected by the areal,shape and depth of the local debonding defects.Modal test is carried out to further ascertain that the impact resonance test based on microphones could accurately reflect the vibration information of the local defect plates and shells.Imaging test of specific defect condition is carried out using microphone arrays,which shows the potential of Air–coupled Impact Resonance Test to be applied in engineering.In simulative aspect,the sound pressure field of the air above the impacted surface with or without defect is simulated by means of explicit dynamic analysis.The sound wave signal caused by the vibration of the steel plate or shell was collected and compared to verify the feasibility of Air –coupled Impact Resonance Test.Natural frequency of each debonding defect caldulated by modal analysis is used to verify the authenticity of the experiment.Four types of commonly used Non Destructive Test method which aim at the same two components is used to compare their ability of imaging the defects.Advantages and disadvantages of each method are concluded,which shows the great potential of Air–coupled Impact Resonance Test method in the future.