Study On Application And Method Of Diagnosing Flaw In Concrete Structure After Fire Using Ultrasonic Wave

Every year there is a tremendous number of fire hazards in our country for the huge population and crowed buildings, which cause significant loss to our country. Besides the extensive damage of life and property brought by the fire, the effect on the buildings is also extraordinary severe. Therefore, knowing the variation of the build bearing capacity, detecting the flaw in concrete structure after fire is a key to renew the using ability of the buildings after fire and reduce the loss caused by fire. Detecting flaw of the concrete structure after fire are especially important because majority of the structures are made in concrete. Damage diagnosis technique using ultrasonic is an active research domain in current structure engineering and has strong engineering background, the correlative theory and technology are developing continuously. Wavelet analysis is a new time-frequency analysis method which has raised a research upsurge internationally in recent years. It is regarded as a breakthrough after Fourier analysis. It is applied widely to eliminate noise interference efficiently and detection singularity on signal. It is proved that the wavelet analysis detects all kinds of singularity discontinuous point effectively. The method of elimination noise interference efficiently and localize flaws accurately by wavelet transform was introduced in the article. The most research work deal with:(1) According to damage mechanics and the theory of elastic waves propagation; combining the characteristic of damaged concrete, the damaged media model of concrete is presented. The perfect concrete is regard as isotropic medium. The wave equation of ultrasonic propagation in concrete is established. The rule of ultrasonic transmits in concrete after fire is obtained. (2) Using the method of reconstructing signal after wavelet transform and elimination noise, the noise in ultrasonic signal is reduced perfectly. It is more easily to distinguish the damage of concrete.(3) Analyzing the received ultrasonic signal using the theory of singularity, the singular point is found by wavelet transform. The time parameter of singular point is equivalent with the position parameter of damage in concrete. Calculating the Lipschitz exponent is ascertained.(4) The ultrasonic diagnose instrument is developed. The technology of coupling without using liquid can detect concrete rapidly. The efficiency and accuracy is improved.(5) Disassembling the received ultrasonic signal using wavelet packet, BP artificial neural network is used in the rapid diagnosis the damage of structural after fire. The results show that this method can reduce the complexity of diagnosis and improve efficiency and precision.The achievement in this disquisition will make the ultrasonic diagnosis techniques be applied in concrete structure after fire. Author deeply believes that the technique detecting concrete after fire using ultrasonic will have vast prospect in application. It will be more accurately and quickly that assess the quality of concrete after fire.