The Simulation Research Of The Two Dimensional Rayleigh Wave Field Of Concrete Crack

With China’s economic take-off, the domestic infrastructure construction in the short term has been developed vigorously, all kinds of geotechnical structures were built, especially represented by reinforced concrete material of large engineering construction.Although the modern architecture has provided the safe and comfortable environment for people’s life, after use for a long time, with the influence of the internal and external effects, all kinds of concrete structures would appear some defects, which would influence the normal work of the structures, the crack is the most common type of the effects. The existence and development of those cracks, will strong influence the safety of the building structure. Therefore, it is necessary to detect internal cracks in engineering structures,to confirm the parameter characteristics of the fracture, therefor estimate the harm for the building structure, then take corresponding measures to repair it, reduce property loss and guarantee the safety of the people.In the field of nondestructive testing of concrete cracks, ultrasonic method and the impact of elastic wave method applied earlier, also obtained the certain effect, but at the same time it still has shortcomings, especially for deep fracture detection. Because the Rayleigh surface wave has in inhomogeneous medium dispersion characteristics, at the same time through the change of the wavelength of Rayleigh surface wave can change its penetration depth, based on the characteristics of Rayleigh surface wave, in recent years, Rayleigh surface wave method gradually developed as a new method to apply in the field of cracks in nondestructive testing. It has high resolution, wide detection range, simple equipment and a series of advantages, especially for deep fracture detection, more obvious advantage.The various methods and basic theories of concrete crack nondestructive testing were introduced in this paper, especially made a detailed analysis of the Rayleigh wave method and its theory. In view of the shortage of the frequency domain analysis in Rayleigh wave method, this paper analyzes the results of numerical simulation and physical simulation,,and proposed combination the spectrum ratios of Rayleigh wave to juedge the depth of the crack, at the same time for different crack depth model the Rayleig wave dispersion characteristics are analyzed, the concrete research content is as follows:1. Through the finite element software to simulate the two dimensional crack medium model of seismic wave field, we show the wave propagation characteristics with crack existed intuitively.2. DO analysis of the Rayleigh surface wave dispersion property in the results of numerical simulation and physical simulation respectively, extract the dispersion curve, the study found that the Rayleigh wave dispersion curves can well reflect the features of the depth of the crack, relative to the deep cracks, the characteristics of Rayleigh wave dispersion curve in the shallow crack is more clear.3. Rayleigh wave after cracks will appear obvious attenuation, the numerical simulation results show that with the increase of crack depth, Rayleigh wave energy attenuation also increase subsequently, based on the transmission characteristics of Rayleigh wave, put forward through calculate the amplitude ratios before and after the crack in frequency domain to determine the depth of the crack.4. through the analysis of experimental model with different crack depth, we found that with the increase of crack depth, the energy of the Rayleigh wave in low frequency attenuation increases, from the seismic wave spectrum diagram after crack,wo can see that it’s center frequency had a trend to move to a low frequency.The research of this paper illustrates the feasibility to determine the crack depth through the dispersion characteristic of Rayleigh wave, at the same time provides the theoretical basis of using frequency domain analysis for Rayleigh wave detection method. It is important for the further development of Rayleigh wave detection method applied in the field of concrete crack detection.