Ultrasonic Guided Wave-Based Evaluation Method For RC Structures With Interface Damage

Reinforced concrete(RC)structures are of vital importance in fundamental civil engineering constructions,and the effective cooperation of the steel and concrete is the guarantee of design,construction and service.Ultrasonic wave(UW)detection is a hot research and practical application in civil engineering which derived from metal detection due to its convenient operation,damage sensitivity and human safety.In this thesis,UW was applied to detect the cross section loss of the steel and the interface defect of RC structures.After analyzing the wave propagation in steel and RC structures,energy ratio and Time Reversal Method(TRM)damage index(DI)were computed to evaluate the severity of the defects.Then numerical simulation and experimental testing were carried out to analyze the interface defects,and the simulations and experiments showed the same trend in defect evaluation which verified that the two parameter analysis were both applicable in RC structure defect detecting.This thesis provided theoretical and practical guidance for civil structure UW detecting.The research contents are as follows:Firstly,the conventional defects of RC structures and the UW detecting condition were introduced to summarize the main problems in UW detecting RC structures.Then the UW wave propagation and attenuation model was recommended which set a foundation for the actuated signals choosing and the sensors setting.Secondly,COMSOL Multiphysics software was used to build the numerical simulation of NDT for steel and RC structures.At the beginning,2-D axisymmetric models were analyzed and gave the equal precise but better efficiency than 3-D models.Then 2-D axisymmetric model was chosen to analyze the 20 cases consisting of concrete cover effect on wave propagation in steel,cross section losses of steel and the debonding defects along the interface of RC structures.The results showed that the concrete cover absorbs most of the wave energy in steel so that the input signal in experiment should be exaggerated,the energy ratio and the DI value was almost linear to the defect severity.To compare the difference of concrete-steel interface and concrete-hole interface,TRM was also performed both on the intact and damaged RC cross sections on the four sides,and the reversed wave field only focused on the boundary of damaged one.Thirdly,experimental platforms were designed to perform the defects detection of RC structures.Six steel samples and six RC samples with different defect severity were prepared to perform the UW testing.Ultrasonic sensors were set to actuate and receive signals,then the energy ratio of the direct wave and the DI value of the reconstructed direct wave were calculated to evaluate the defects.The experiments showed the same trend as the simulation results which concluded that this kind of defect evaluation is robustness for RC structures detecting.