Knocking-Induced Vibration and Sound Signal Characteristics and Fractal Analysis for Distinguishing Concrete and...

Accurately distinguishing between concrete walls and masonry walls in nondestructive testing of building structures is of crucial importance for structural maintenance and renovation. This study proposes a wall recognition method based on impact response and fractal theory: by collecting sound and vibration signals excited by impact, it is found that there are significant differences between the two types of walls in terms of time-domain characteristics (peak duration of sound signals, vibration amplitude) and fractal characteristics (fractal dimension distribution, intercept of fitting line). Independent sample test results confirm that these differences are statistically highly significant (p < 0.05), effectively ruling out the influence of random factors. Concrete walls exhibit longer peak duration of sound signals, significant vibration amplitudes, and high-dimensional fractal characteristics; masonry walls exhibit instantaneous sound signal response, zero vibration amplitude, and low dimensional fractal aggregation. Furthermore, the fractal-fitted curves exhibit exceptionally high linear correlation, ensuring the reliability of feature parameter extraction. The study delves into the underlying physical mechanisms: the high fractal dimension of concrete walls stems from heterogeneous scattering effects induced by their dense internal structure, while the low-complexity response of masonry walls is attributed to rapid energy dissipation at mortar interfaces. This method provides a new technical means and theoretical basis for nondestructive testing of walls, which helps to improve the accuracy and efficiency of testing and lays the foundation for future automatic identification product design.