Effect of Load Pattern in the Generation of Higher Harmonic Amplitude in Concrete Using Nonlinear Ultrasonic Test

Abstract

Non-destructive testing is used in monitoring health of structures. In this paper, nonlinear ultrasonic test was done to analyze the sensitivity of the fundamental and higher harmonics with the internal damage in concrete. Good sensitivity produces significant quantitative changes in the nonlinear spectral amplitude parameter corresponding to the deviation of load. In actual conditions, structures have different design strength with varying water cement ratio. In addition, it is experiencing loading and unloading. These are considered as major factors that induce effect in the behavior of ultrasonic test result in concrete. Past researches have only considered increasing application of load with single loading pattern. This study aims to investigate the effect of load application pattern in the generation of higher harmonics. Ordinary concrete specimens of size 150mm x 150mm x 150mm with water-cement ratio WC40 and WC60 were casted and tested using uniaxial compression machine with two load patterns: a.) single loading pattern from 0% to 100% and, b.) multiple loading/unloading pattern. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record the fundamental and higher harmonic generation in the concrete. The experimental results showed that there was a good sensitivity for 3 rd harmonic amplitude parameter D A when it was subjected to single loading pattern for both WC40 and WC60. On the other hand, good sensitivity was only observed for 2 nd harmonic amplitude parameter D A when it was subjected to multiple loading/unloading pattern for both WC40 and WC60. This showed that the 2 nd harmonic amplitude was consistent and sensitive when repeated load was applied for low and high water cement ratio.

Investigation on the Sensitivity of Ultrasonic Test Applied to Reinforced Concrete Beams Using Neural Network

“…Pilot testing for plain concrete cubes of 150 mm size [5,20,22] and reinforced concrete beams were done in the laboratory to ensure that the nonlinearities or the presence of higher harmonics resulted from the material nonlinear response due to mechanical damage and not from the instrumentation used in the test.…”

“…The influence of load history greatly affects ultrasonic parameters. As an example, A3 is sensitive to single loading path for pure concrete cubes [17], while A2 is more sensitive to a multiple loading paths [20]. Step load for the four-point bending with loading/unloading branches.…”

“…For single loading pattern, A3 is sensitive compared to A2. On the other hand, in multiple step loading pattern A2 is sensitive to all water-cement ratio introduced [20]. It is also suggested that the amplifier is at high power level during experiments to produce better sensitivity in the generation of higher harmonics [21].…”

“…The parameter A3 is not sensitive to load for WC60C where concrete without reinforcing bars are experienced. This is also experienced by WC60 with repeated load where A3 became insensitive while A2 is sensitive [18][19][20]. To further investigate the sensitivity of all parameters with increasing load, simulations are done for all five variable parameters having the other four input parameters as constant (0.5 in value).…”

“…The amplitudes A1, A2, and A3 behaved similarly with PPA, where it is decreasing with respect to increasing load. A previous study shows that in concrete cubes, different loading patterns greatly influence the higher harmonics generation [20]. Complexity in its damage level is recognized when different sizes of aggregates inside the concrete are present [22].…”