Research On The Impact-echo Method To Detect Prestressed Bridge Duct Grouting

Because of the small cross-section, stiffness, crack resistance and durability, high comprehensive economic benefits and so on, prestressed concrete structure has been widely applied in architecture around the world, more than95%new bridges have adopted the prestressed concrete beam in our country. Duct Grouting quality is directly related to the stability and durability of the structures, but the ducts became obscura after grouting, quality was hard to check, once appeared accident, the economic loss were huge. Detection of grouting quality has been the focus of the research field, while the existing detection methods can not identify the duct defects well. For example, the coring method damage the structure, radar method susceptible to interference metal, ray method poor operability and safety, ultrasonic testing must be two-sided test, but the impact echo may overcome these difficulties actually. It is a great innovation if this approach can be applied to identification and pre-grouting quality control. This article depends on the finite element numerical simulation and model test, using impact-echo method on post-tensioned prestressed duct grouting quality examination research.Firstly, according to the characteristics of prestressed ducts and current detection method, described the background and significance of the paper after referring to a large number of relevant literature, described the development of domestic related fields.Secondly, introduced the basic theory of stress wave, elaborated on the propagation of stress waves in media and the reflection and transmission at the interface of different impedance, and described the basic principle and operation method of impact-echo.Thirdly, carried on numerical simulation using ANSYS/LS-DYNA. Analysed the propagation characteristics of surface and internal in different grouting conditions, verified the reliability of impact-echo method. Carried on the Fourier transformation to the velocity time curve of surface nodes, obtained the spectrograph.Analysised frequency characteristics of typical defects, provided theoretical support for following model tests.Finally, produced models according to the typical defects, obtained examination result in different defects, analysed critical frequency characteristics, put forward a set of test programme to practical engineering. Test results coincided with preset defects, fit with finite element simulation, enhanced the status in the actual project, and provided reference for future research.