Optimization of Nonlinear Ultrasound Results to Determine Dynamic Properties of Concrete

Abstract

This paper presents the development of a new algorithm to identify dynamic properties of concrete by comparing simulated and experimental results of nonlinear ultrasound testing. Prismatic concrete specimens with different water-cement (w/c) ratios, 0.45, 0.60, and 0.75, were prepared. The specimens were damaged progressively by loading them in compression up to 20, 40, 60, and 80% of the ultimate strength. After each load step, the load was released, and the specimens were tested for the fundamental, second-, and third-harmonic frequencies. An algorithm was developed to determine the dynamic properties of the specimen through the progression of damage. The proposed algorithm used ABAQUS to simulate the dynamic response of the specimens. A MATLAB program was used to update the material properties by minimizing the sum of squared differences between the measured and simulated harmonic frequencies. Excellent agreement was obtained between the reconstructed elastic modulus values and values obtained by testing the prisms according to ASTM C 215. Damping ratios provided by the reconstruction were observed to increase with increasing damage and with increasing w/c ratio.