Active sensing-based real-time nondestructive evaluations for steel bridge members

Abstract

This paper presents an experimental study on the applicability of piezoelectric lead-zirconate-titanate(PZT)-based active sensing techniques for nondestructive evaluation (NDE) of steel bridge members. PZT patches offer special features suitable for real-time in-situ health monitoring systems for civil structures, because they are small, light, cheap, and useful as built-in sensor systems. In this study, the impedance-based damage detection method and the Lamb wave-based damage detection method were applied to steel bridge members. Several damage sensitive features were selected: i.e., root mean square (RMS) changes in the impedance and wavelet coefficients, and the time of flights. Firstly, PZT patches were used in conjunction with the impedance and Lamb waves to detect the presence and growth of artificial cracks on a 1/8 scale model for a vertical truss member of Seongsu Bridge, Seoul, Korea, which caused the collapse in 1994. RMS changes in the impedances and wavelet coefficients are found to increase proportionally to the crack length. Secondly, two PZT patches were used to detect damages on a bolted joint steel plate, which were simulated by loose bolts. The time of flight and wavelet coefficient obtained from the Lamb wave signals were used. The correlation of the Lamb wave transmission data with the loose bolts was investigated. And, the support vector machine was used for damage classification. Results from the experiments showed the validity of the proposed methods.