Detecting Deterioration behind Gfrp Wrap Strengthning of Bridge Columns

A radar NDE (nondestructive evaluation) technique using an airborne antenna operating in the far-field condition is developed for detecting damages such as delamination and concrete cracking in GFRP (glass fiber reinforced polymer)-wrapped concrete columns. The far-field airborne radar (FAR) NDE technique is advantageous for distant measurement of bridge columns in practical applications. Far-field radar measurements were made on artificially damaged specimens in the compact RCS (radar cross section)/antenna range facility. Normal incidence and oblique incidence measurement schemes were applied to study the specular effect in reflected signals. Preliminary measurement results indicate the presence of artificial defects behind the GFRP wraps as shown in the frequency-angle imagery. A finite difference-time domain (FD-TD) numerical simulation capability for the electromagnetic (EM) wave propagation and scattering is developed and applied to GFRP-wrapped concrete cylinders. It is shown that this far-field radar NDE technique has potential in identifying structural damages in the surface regions of concrete columns wrapped with GFRP. The importance of data de-noising and filtering along with further image processing is emphasized and planned for further work.