Bao TengFei

Crack status analysis for concrete dams based on measured entropy

The integrity and safety of concrete dams are seriously affected by the existing cracks in dam bodies, and some serious cracks may cause dam failure or disaster. The propagation of cracks in concrete dams is accompanied by changes in energy distribution, which can be represented by changes in the structure’s system entropy. Therefore, the entropy theory can be used in analyzing the behavior of dam cracks. Due to the randomness and locality of crack propagation, it is difficult to predict the location of cracks by traditional monitoring methods. To solve this problem, the influence of spatial positions of monitoring points on inspection zones is represented by a weight index, and the weight index is determined by the distance measure method proposed in this paper. Through the weighted linear fusion method, the entropy of multiple monitoring points is obtained for analyzing the behavior of dam cracks in the selected zones. Meanwhile, the catastrophe theory is used as the variation criterion of an entropy sequence in order to predict the instability time of dam cracks. Case studies are put forward on a high arch dam, and the fusion entropy is calculated according to the monitoring data from strain gauges. Results show that the proposed method can effectively predict the occurrence time and location of dam cracks regardless of the layout of monitoring instruments, and it is a new way to analyze the occurrence and propagation of dam cracks.

Application analysis of empirical mode decomposition and phase space reconstruction in dam time-varying characteristic

In view of some courses of the time-varying characteristics processing in the analysis of dam deformation, the paper proposes a new method to analyze the dam time-varying characteristic based on the empirical mode decomposition and phase space reconstruction theory. First of all, to reduce the influences on the traditional statistical model from human factors and assure the analysis accuracy, response variables of the time-varying characteristic are obtained by the way of the empirical mode decomposition; and then, a phase plane of those variables is reconstructed to investigate their processing rules. These methods have already been applied to an actual project and the results showed that data interpretation with the assists of empirical mode decomposition and phase space reconstruction is effective in analyzing the perturbations of response variables, explicit in reflecting the entire development process, and valid for obtaining the evolution rules of the time-varying characteristic. This methodology is a powerful technical support for people to further master the rules of dam operation.

A novel cracking sensing fiber sensor with wide range

The health of concrete structures is usually reflected by cracking. For some structures, small cracks may have little influence on the safety of the structures.But maintenance measures have to be taken if the cracks continue to develop. A sensing fiber sensor with wide range was developed in this paper based on the theory of macro bending loss of fiber. The sensing concept was introduced and the feasibility of this sensor was studied by a cracking simulator. Finally, the sensor was embedded in a concrete beam and the actual application ability of it was studied. The experimental results showed that the sensor has a real-time monitoring capability in cracks monitoring.

Bend type fiber Bragg grating crack sensor with big measurement range

Fiber Bragg grating (FBG) sensing technique has been widely applied to structual crack monitoring due to its advantages over other sensors. However, the meausrement range of FBG sensors is small due to easy breakage of silica fiber. In this paper, using current research results for reference, a simple bend type FBG crack sensing setup was designed. The performance of the sensor was verified through experiments. The experimental results show that the crack sensing of the sensor is reliable, the measurement range can be extended a lot compared with traditional FBG crack sensors, and that the sensor possesses good repeatability to cope with the uncertainty of crack development.