18 August 2003 Ultrasonic characterization of steel rods for health monitoring of civil structures
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Steel rods in the form of rebar or strands are widely used in civil engineering. The first part of this paper discusses the application of an ultrasonic technique for the measurement of applied loads in steel rods. Ultrasonic wave velocity depends on stress and temperature. The stress dependence of the velocity, known as the acoustoelastic effect, can be used to monitor the applied or residual stress. An acoustoelastic constant is defined in terms of relative variation of ultrasonic group velocity. Theoretical considerations suggest that the acoustoelastic effect is more pronounced for certain wave frequencies. The effect of the excitation frequency on the acoustoelastic response of circular steel rods and strands was investigated experimentally. A frequency-dependence of the acoustoelastic constant was found and the role of cross sectional mode shapes was considered in this context. In the second portion of the work, laser ultrasonic techniques were used for a basic investigation of dispersive wave propagation in strands. The tests used a joint time-frequency analysis based on the Gabor wavelet transform. Dispersion and frequency-dependent attenuation were studied. Those ultrasonic frequencies propagating with minimum attenuation were identified as the most suitable for field use to probe long length of the member at once.
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Piervincenzo Rizzo, Piervincenzo Rizzo, Michael D. Palmer, Michael D. Palmer, Francesco Lanza di Scalea, Francesco Lanza di Scalea, } "Ultrasonic characterization of steel rods for health monitoring of civil structures", Proc. SPIE 5057, Smart Structures and Materials 2003: Smart Systems and Nondestructive Evaluation for Civil Infrastructures, (18 August 2003); doi: 10.1117/12.482384; https://doi.org/10.1117/12.482384

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