Study On The Relationship Between Ultrasonic Wave Velocity And Strain Of Concrete Members In The Environment Of Increasing Basement Layer

It is very important to obtain the stress-strain state of the existing structure in the basement building.The commonly used stress-strain detection method is difficult to meet the need of detecting the existing structure in the condition of increasing basement layer.In order to study the possibility of applying ultrasonic single plane test method to the full strain detection of axial compression concrete members,a special ultrasonic transducer fixture was designed and made,and the testing parameters related to the wave velocity test were determined.By testing the wave velocity and strain of the concrete specimen,the influence of concrete strength,reinforcement ratio and environment temperature and humidity on the relationship between wave velocity and strain is studied,and the relationship between wave velocity and strain is integrated into a unified multi-factor wave velocity-strain relationship.The main work and results of the thesis are as follows:(1)The type of coupling agent and the coupling pressure are tested and analyzed by using the designed transducer fixture,and the coupling agent and the optimum coupling pressure are determined.The results show that: 1.Considering the acoustic permeability and fluidity of the coupling agent,it is determined that vaseline is the best coupling agent for the detection of the relationship between velocity and strain of concrete.2.The coupling pressure has an obvious effect on the wave velocity measurement.Combined with the test results,47.50 KPa is determined as the unit coupling pressure of the experiment.3.Under the condition of reasonable measurement and collocation,it is feasible to apply the ultrasonic testing method to the strain diagnosis of concrete axial compression members.(2)The influence of concrete strength,reinforcement ratio,environment temperature and humidity on the relationship between wave velocity and strain was studied.The results show that:1.The effect of concrete strength on the relationship between wave velocity and strain is obvious,and the higher the strength is,the higher the wave velocity will be;2.The ratio of reinforcement mainly affects the speed of wave velocity changing with strain,that is,the higher the ratio of reinforcement is,the faster the speed of wave increases with strain;3.The change of ambienttemperature and humidity has little effect on the relationship between wave velocities and strain under normal temperature and humidity.(3)According to the measured wave velocity and strain data,the relationship between wave velocity and strain is fitted by Origin,and the corresponding relationship between concrete strength,reinforcement ratio and relevant parameters in the fitting equation is analyzed.The applicability of the fitting formula is verified.The results show that: 1.Linear fitting can well describe the relationship between wave velocities and strain of plain concrete and reinforced concrete in elastic range.2.The strength of concrete mainly affects the intercept in the fitting formula,while the reinforcement ratio mainly affects the slope of the fitting formula.The influence of the two factors is independent of each other.Strain relation model;3.The results of wave velocide-strain test under random pressure show that the fitted formula of multi-factor wave velocity-strain relationship is practical for testing concrete wave-velocity-strain in elastic range.