Papers by Author: Mao Sen Cao

Abstract: In this study, an experiment program is presented to study the bonding mechanism between corroded bolts and grout and in particular the influence on bonding behavior in terms of different corrosion sections along anchor. With respect to four groups of manufactured bolt specimens, the noncorroded and the corroded, respectively, on the front, middle and rear section along anchor, a pullout test is conducted to reveal the relationship between load and loading-end slip and to investigate the bond-stress distribution characterization along full anchor. Experimental results show that corrosion product, acting as lubricating effect at the interface between bolts and grout, can result in the degradation of bonding mechanical behavior. Meanwhile, corrosion on different sections along anchor has a different effect on the anchorage capacity of bolts. Especially, corrosion on the front section induces the greatest decrease of anchorage capacity of bolts. Thus, it is concluded that the front section along anchor is the key region affecting the bonding mechanical behavior between bolts and grout.

Abstract: Most of existing studies on rock damage are focused on investigating the macroscopic stress-strain relationship, and only limited research is available on analyzing the microscopic crack propagation due to measurement difficulty, cumbersome data reduction procedures, and complexity of damage in micro-level. In this study, a powerful image-processing program is developed to extract the microscopic crack distribution from the digital image of microscopic crack status of red sandstone, and the microscopic crack propagation of red sandstone under single-axial pressure is then evaluated by the technique of multifractal. It demonstrates that the microscopic crack distribution possesses the multifractal character, and the capacity dimension of multifractal singular spectrum can be used to quantitatively characterize the microscopic crack propagation of red sandstone. By comparing the stress-strain relationship with the one of stress-capacity dimension, the capacity dimension is capable of acting as a physical quantity to effectively reflect the damage of red sandstone by the means of characterizing its microscopic crack propagation.

Abstract: A new definition of vibration transmissibility, “the ratio of FRFs (Frequency Response Functions)”, is proposed to provide novel structural damage indices, i.e., vibration transmissibility and its real and complex curvatures. Using the FRF and its real and complex curvatures as references, the fundamental studies on performance of damage indices to reflect structural low-level damages are conducted using vibration-based nondestructive evaluation of a frame structure. The experimental results demonstrate that the sensitivity of the damage indices increases in the order of vibration transmissibility or FRF, and its real and complex curvatures. While the vibration transmissibility and its real and complex curvatures possess higher damage sensitivity than the FRF counterparts. The proposed novel damage indices are promising to develop viable and advanced structural nondestructive evaluation techniques.

Abstract: In this study, the fractal behavior of crack development in damaged concrete materials and its application to structural damage assessment are experimentally investigated. The experimental results demonstrate that the crack evolving is closely related to the characteristics of fractal behavior, and the surface-crack distribution of the damaged concrete structures possesses fractal characteristics. It thus indicates that the fractal may be capable of performing quantitative characterization of crack development, which cannot be comprehended by Euclidian geometry. The application of fractal characteristics of surface-crack distribution in structural damage assessment is then investigated. By correlating the fractal dimension of surface-crack distribution with the model parameters (e.g., natural frequency) of different magnitudes of damage, a linear relationship exists between the fractal dimension and natural frequency. Since the natural frequency is one of the most fundamental damage characteristic factors, the above linear relationship shows that the fractal dimension of surface-crack distribution is able to effectively act as an effective damage characteristic factor. Different from the conventional damage characteristic factors generated from vibration tests, this factor reflects structural damage from a new perspective of fractal analysis, and provides a viable and novel approach for health monitoring and safety evaluation for concrete structures.