BEM analysis of dynamic behavior of concrete in impact-echo test

The impact-echo method is well known as a non-destructive testing for concrete structures. Taking out resonant frequencies responsible for locations of reflectors in frequency spectra, locations of reflectors are determined. In order to improve the impact-echo method and to visually identify locations of reflectors, a new procedure has been developed by applying an imaging procedure to the data, as stack imaging of spectral amplitudes based on impact-echo (SIBIE). Concrete slabs containing ungrouted tendon ducts were tested by applying SIBIE procedure. Reflectors near the duct can be visualized clearly by SIBIE. Here, the procedure is theoretically investigated by the boundary element method (BEM). Two-dimensional BEM analysis is conducted to investigate stress distributions and dynamic deformations at frequencies corresponding to the resonances. Results show that by changing frequencies, stress distributions and deformation modes change. The cross-section deforms like a plate, generating other resonant frequencies of in-plane modes.