Prestressed concrete bridge crack detection
(Sichuan Shengtuo Detection Technology Co., Ltd. X, Chengdu, Sichuan 610045)
Abstract: This article includes examples of crack detection of prestressed concrete for overpass bridges. We tested and verified the depth of cracks. The main method used is surface wave detection, which can be applied to tunnels, retaining walls, and foundations. Other types of cracks in reinforced concrete structures and dams are nondestructively tested.
Key words: bridge crack detection, prestressed concrete crack detection, bridge prestress testing, prestressed concrete beam inspection, prestressed concrete beam crack detection, Sichuan Shengtuo detection technology
According to a large number of observations, most of the cracks in concrete structures have been produced within 1-2 years after completion. Choosing the right patching scheme and timing, it's very important to know its depth, length, and width. With the use of the concrete multi-functional non-destructive tester manufactured by Sichuan Shengtuo Detection Technology Co., Ltd., the equipment can perform non-destructive testing on reinforced concrete structures such as bridges, tunnels, retaining walls, and foundations as well as various types of cracks in dams. Borehole sampling verification. The key technology is mainly the surface wave method. The "surface wave method" was first proposed in the 1960s, but it has not been practical. The reason is that the test error for energy attenuation is large. For this reason, we have developed a high-precision energy attenuation test technology based on the “bi-directional excitation technology†(which has obtained the national invention patent, patent number: ZL200510021851.5), which greatly improves the The "surface wave method" test accuracy and practicality.
Original test method (surface wave method)
In response to the deficiencies of the existing technology, we have developed a new crack depth detection technology (abbreviated as "surface wave method"). This method uses the attenuation characteristics of Rayleigh waves (a type of surface wave) in an impact elastic wave to test the depth of cracks in a concrete structure. The method has a wide range of tests and is less affected by fillers, steel bars, and moisture, and is particularly suitable for testing deeper cracks.
1) Basic principle of surface wave method
Rayleigh waves are formed due to the interaction of P-waves and S-waves on the boundary surface of media. Their propagation speed is slightly slower than that of S-waves, and they are mainly concentrated on the surface and shallow parts of the media. Their characteristics are very suitable for detecting the depth of cracks.
(1) The Rayleigh wave has the highest energy in the elastic wave generated by the impact on the media surface, and the signal acquisition is easy;
(2) Dependent on the shear mechanics properties of the material, which is more sensitive to cracks;
(3) Most Rayleigh wave energy is concentrated in the range of 1 wavelength from the surface.
Rayleigh waves occur in the propagation of the geometric attenuation and material attenuation. It can be corrected by the system while keeping its amplitude unchanged. However, when Rayleigh wave encounters a crack, its propagation is blocked to some extent, and the energy and amplitude of the wave will decrease after passing through the crack. Therefore, according to the change (amplitude ratio) of the amplitude of the wave before and after the crack, the depth can be estimated.
1) Key Test Technology
The "surface wave method" was first proposed in the 1960s, but it has not been practical. The reason is that the test error for energy attenuation is large. For this reason, we have developed a high-precision energy attenuation test technology based on the “bi-directional excitation technology†(which has obtained the national invention patent, patent number: ZL200510021851.5), which greatly improves the The "surface wave method" test accuracy and practicality.
2) Characteristics of surface wave method
(1) The surface wave method has a wide range of test cracks, up to several meters, and is less affected by filling materials and moisture. High test accuracy. However, this method belongs to semi-theory and semi-empirical method, and the theory is not particularly strict.
(2) For a dam surface and the like approximate to a semi-infinite plane body, it is very suitable for the surface wave method test. However, it is not suitable for narrow structures because surface waves are greatly affected by boundary conditions (sidewalls, corners, etc.).
(3) The use of dual-direction oscillatory regression techniques reduces test errors and improves test accuracy.
(4) In case of peeling, plate waves and vibrations may be caused, resulting in large test errors.
Prestressed Concrete Beam Crack Detection (Daxi University of Foreign Studies, 2013.07)
Datong-Xi'an Railway Passenger Dedicated Line starts from Datong, Shanxi Province in the north, and reaches 95.9 kilometers from the 9 cities of Chuzhou and Taiyuan to Xi’an in Shaanxi. The line design speed is 250 km/h. Entrusted by the construction unit, we tested and verified the crack depth of the continuous steel structure of a flyover bridge of the Taiyuan high-speed rail section.
Test results show that the crack depth is generally between 2 and 5cm, indicating that the crack does not exceed the protective layer.
Figure Field Test Scene
Features
1) High integration and good test accuracy
In this set of test equipment SCE-MATS, a variety of crack testing techniques are integrated, and various test technologies can complement each other and confirm, thus improving test accuracy as much as possible.
2) Wide range of testing
This technique can test cracks up to 2 meters deep.
3) Test the direction of crack extension
Scope of application
1) Various reinforced concrete and plain concrete structures, asphalt concrete;
2) Earth-rock dams and rock masses: