Research On Smart Film Monitoring Method For Cracks Development Of Concrete Bridge Structure And Its Application

The appearance and development of cracks are the most common source of structure degradation and failure in concrete bridges. Crack monitoring in the pivotal area of concrete bridge structure is an important subject of concrete bridge health monitoring. Sponsored by the National Natural Science Foundation of China funded project:"Research on Smart Film Monitoring Method for Cracks of Concrete Bridge Structure"(No.50808188) and the West Transportation Construction Technology Project:"Development of Bionic Monitoring System for Cracks of Concrete Bridge Structure"(No.2009318814065), a comprehensive theoretical research on the method of bionic monitoring for width-limited cracks in concrete bridge structure is conducted, and the project application was constructed subsequently. The main research contents and results are as follows:1. Crak width is the most important parameter in evaluating the safe-state of concrete structure. In the present paper, the charateristic crack width were specified as cracking and a series of sequential crack width(0.10mm,0.15mm,0.20mm,0.25mm,0.3mm) based on analysis of various criterion in limit of crack width and envirment of concrete bridges in freeway system. By simulating the functions of biological sensory neurons to perceive wounds, and meeting the demands of monitoring charateristic crack width, a method both monitoring the appearance and width of crack was proposed by means of pasting smart sensing wire on the surface of concrete bridge structure.2. In this paper, theoretical model of a laminated-composite material is developed upon that the composite material consists of three subsequent layers:concrete, cohesive and smart sensing wire. The McCartney method is employed to analyze the stress and strain of laminated structure at the moment of fracture of smart sensing wire after cracking of concrete. Unified parameter differential equation in terms of displacement, stress and strain of three layers is fomulated, which can indirectly reflect the relationship between diameter of smart sensing wire and crack width when the wire is fastened to fracture.3. Over1600sets of data were obtained from239concrete specimen trial tests, those specimens were pasted with different specifications smart sensing wire in diameter of0.05mm,0.06mm,0.07mm,0.08mm,0.13mm and0.20mm respectively. Over200sets of data aquired from three concrete beams trial tests, those beams pasted with smart sensing wire in diameter of0.05mm,0.08mm,0.13mm and0.20mm. The X2-Checking Mothed and Maximum Entropy Theory are employed to process those data from trial tests. The results show that he crack width is snapped to the Normal Distribution Law when the smat sensing wires were tightened to failure.4. The comparison between the result of small specimens and the result of beams shows that cracks have similar average width and standard deviations when smart sensing wires with the same diameter were tightened to failure. The result also illustrated that the diameter of smart sensing wire is related to crack width, apart from the size of specimen, when them were tightened to failure. Furthermore, the statistic experimental data of crack width from specimens and beams validated the theoretical model of the laminated-composite material. According to the statistic data from two series of experimental and the theoretical calculation results, smart sensing wire with a diameter of0.05mm,0.06mm,0.07mm,0.08mm,0.13mm and0.20mm is corresponding to crack width0.07mm,0.08mm,0.09mm,0.10mm,0.18mm and0.25mm, respectively, and the relationship between failure width and diameter can be fomulated as w=1.2456d+0.0058.5. The width-limited crack bionic monitoring system for concrete bridge structure was built, which comprises five modules:the sensor module, data acquisition module, data processing module, control module and data communication module. In hardware aspects, this paper focused on design and manufacture of alert network sensor and the intermediate processor. In system software aspect, various applications designed for achieving the function of each module were built.6. In order to monitor the crack development and width (its limitation is0.20mm or0.25mm) on the surface of cable tower of long-span cable-stayed bridge, a monitoring network system was developed upon smart film method with smart sensing wires in diameters of0.05mm,0.13mm and0.20mm. The corresponding hardware and software are constructed to complete the monitoring network system. The developed monitoring system is validated by engineering application, which verified the capability and reliability of this system in monitoring appearance and development of craks on the surface of cable tower.