| ABSTRACT: | THEORY AND APPLICATION OF MEM PROCESSED IMPACT-ECHO FOR DETECTING
VOID IN PC DUCT
K. Tadashi, S. Tomoaki2, and G. Kunio3
1Japan Highway Public Corporation, Tokyo, Japan; 2Applied Research Co, Tsukuba, Japan; 3Tokai
University, Hiratsuka, Japan
The collapse of prestressed concrete bridges that is caused by the corrosion of cables because of the defect
of grout mortar occurs occasionally. However, no any reliable nondestructive detecting method has been
developed yet. In this study, a new nondestructive detecting system was developed. It was based on a new
signal processing technology of impact-echo method. First, the properties of elastic waves induced by dull
impaction of usual impacters were studied experimentally and analytically. Then, the transient responses to
the impaction were analyzed on the finite element models of many prisms with voids, Finally, the actual size
structures with the cable ducts fully or partially grouted were tested and the transient responses of it were
computed. The flexural oscillation of duct i.e. void delayed the arrival of the reflection from void. The plate
waves and flexural oscillations of surface following the arrival of reflection wave disturbed pure echoes and
the echo spectra although the results of both of finite element models with voids in ducts and the structure
showed clear reflections from ducts. Maximum entropy method is known as one of artistic signal processing
techniques that is capable to get a stable spectrum even in short time series. Impact-echo detecting system
optimized by the new signal processor succeeded in test on actual size structure with intricate cable ducts.
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