A damage assessment and warning method for stay cables based on the acoustic emission (AE) technique and fractal theory was developed. First, the AE signal features of Higuchi's fractal dimension (FD) were analyzed at various scales. The analytical results indicated that the FD was associated with the frequency response. Meanwhile, it was found that the curve length of the original signal reflected the fluctuation of the AE signal in the time domain. Both the FD and the curve length of the original signal were related to damage evolution. Based on the above analysis, a damage index, namely, the FDbased damage assessment index, was defined by the fractal features of AE signals generated by damaged structures, including the curve length of the original signal and its FD. Fatigue tests of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) cables with AE sensors were performed to validate the . proposed approach. The time-history responses and frequency responses of the AE signals and the corresponding damage modes were analyzed during the entire cyclic loading process. The FD-based damage indices for all the FRP cables were obtained through analysis of the AE signals. The relationships of both the time-history responses and the frequency responses with the FD-based damage index were investigated. The results indicated that the FD-based damage index increased little with the number of loading cycles at the early loading stage but increased dramatically at the final stage of the fatigue test. The results of this article demonstrate that an FD-based damage index can quantify the evolutionary process of fatigue damage in FRP stay cables.

No abstract

A two-dimensional mesoscale modeling framework, which considers concrete as a four-phase material including voids, is developed for studying the effects of voids on concrete tensile fracturing under the plane stress condition. Aggregate is assumed to behave elastically, while a continuum damaged plasticity model is employed to describe the mechanical behaviors of mortar and ITZ. The effects of voids on the fracture mechanism of concrete under uniaxial tension are first detailed, followed by an extensive investigation of the effects of void volume fraction on concrete tensile fracturing. It is found that both the prepeak and postpeak mesoscale cracking in concrete are highly affected by voids, and there is not a straightforward relation between void volume fraction and the postpeak behavior due to the randomness of void distribution. The fracture pattern of concrete specimen with voids is controlled by both the aggregate arrangement and the distribution of voids, and two types of failure modes are identified for concrete specimens under uniaxial tension. It is suggested that voids should be explicitly modeled for the accurate fracturing simulation of concrete on the mesoscale.

No abstract