Zhi Zhou

Structural Health Monitoring System for the Shandong Binzhou Yellow River Highway Bridge

The Binzhou Yellow River Highway Bridge is a cable-stayed bridge in China. A structural health monitoring system was implemented on this bridge during its construction for monitoring its structural health status and assessing its safety for long-term service. This paper describes the design, implementation and functions of this system, and presents the measured responses of the bridge subjected to moving vehicle loads. The system includes a sensor module, a data acquisition module, a wired and wireless data transmit module, a structural analysis module, a database module, and a warning module. It is integrated by using LabVIEW software and can be remotely operated via Internet. After two years of service, the system operates well and confirms the current reliability of the bridge.

Applications of FRP-OFBG sensors on bridge cables

It is still a practical problem how to effectively install FBG sensors on bridge cabes. In this paper, a simple and effective solution is introduced to develop smart bridge cables using FRP-OFBG bars developed in HIT (Harbin Institute of Technology). Here, the FRP-OFBG bar acts as one component of the cable and shows force resistance and well-protected sensors in service. The installation techniques and the sensing properties of FBGs in three kinds of cables, FRP cables, common steel-wire cable and extruded-anchor cable, are introduced and tested under dead load. Moreover, the preliminary introduction of a practical field application based on this solution has been also given. The experimental results show that the deformability of FRP-OFBG bars in the smart cables can reach the terminal and show wonderful accuracy, which shows that such kind of smart cable is practical in field application.

Techniques of temperature compensation for FBG strain sensors used in long-term structural monitoring

FBG strain sensors are more and more accepted in the area of structural health monitoring, especially in civil infrastructures. However, due to the fact that FBG senses both strain and temperature simultaneously. And moreover the wavelength shift induced by 1°C is almost equivalent to that induced by 10με. So temperature compensation for FBG strain sensors of long-term structural monitoring is indispensable. In this paper, based on the FBGs strain and temperature sensing principles, the techniques of dual FBGs temperature compensation and the environmental temperature compensation are brought forward. The experiment of cement paste curing monitroed by dual FBGs was carried out. And the advantage of the technique of dual FBGs temperature compensation are proved, which is proper for long-term structureal monitoring system for civil infrastructures.

A new kind of smart bridge cable based on FBG sensors

The feasibility and advantages of smart bridge cable based on FBGs are discussed. And the sensing properties of FBGs installed in the cables under dead load are tested. The experimental results and practical applications show that the smart bridge cable is proper to be used in bridge cables transfer, construction control and long-term health monitoring.

Interface strain transfer mechanism and error modification for adhered FBG strain sensor

The application of adhered FBG strain sensor is affected by interface strain transfer and error modification. In his paper, firstly, based on the characterstics of forces and damage, the fundamental hupotheses are given, and the general expression of interface transferring mechanism is derived. After that, united form of the characteristic value-λ for the general equation is geven for the multi-layer coatings. Finally, according to the error-modified equation of adhered FBG sensor, the relationships the error rate η against the shear modulus and the thckness of the glue are given. With regard to the glue applied in engineering (thickness is from 4mm to 60mm, shear modulus is from 30MPa to 200MPa), the error rate η is about 5~10%, and the correction coefficient k is about 1.05~1.11. Hence, the error modification must be considered when adhered FBG strain sensors are used in civil engineering.

Interface transferring mechanism and error modification of embedded FBG strain sensor based on creep: Part I. linear viscoelasticity

As strain-sensing elements in the structural health monitoring, the research and application of the Fiber-optic Bragg Grating sensor (FBG) has been widely accepted. Although there are some significant achievements on the interface transferring mechanism and error modification of FBG, the theoretical research on the creep behavior of FBG sensors is rarely taken into account. Because the optical fiber and adhesive is macromolecular polymer, when loaded in long term or high temperature, the creep characteristic of these material is emerging which influences the accuracy of FBG sensors. This paper presents the theoretical part on creep behavior of FBG sensors. Firstly, based on the linear viscoelastic constitutive relations, the general expression of multiplayer interface strain transferring mechanism is derived, and the error modified equation of FBG sensors is obtained. Secondly, the transient and steady-state responses of FBG sensors are presented. Finally, the elasticity-viscoelasticity corresponding principle is proposed, which is used for solving a class of interface strain transferring linear viscoelastic problem.

Interface transferring mechanism and error modification of embedded FBG strain sensor

As the strain sensing element of structural health monitoring, the study and application of the fibre-optic Bragg grating (FBG) has been widely accepted. The accuracy of the FBG sensor is highly dependent on the physical and mechanical properties among the bare optical fibre, protective coating, adhesive layer and host material, namely, the strain interface transferring characteristics among layers. This paper takes the embedded FBG sensor as an object of study. Firstly, the general expression of multiplayer interface strain transferring mechanism is derived. Secondly, based on the defined average strain, the error modified equation of FBG sensor is obtained. Finally, in the light of embedded tube-packaged FBG and FRP-OFBG strain sensors, which developed by ourself, the corresponding strain transferring error, laws were studied, and the corresponding error modification coefficients were given too, which were validated by experiments. The achievements provide theories for the development and application of the embedded FBG sensors.

Fiber bragg grating sensors for arch bridge suspender health monitoring

Firstly, Wavelength shift of Fiber Bragg Grating (FBG) sensors that monitor the arch bridge suspender tension due to strain or temperature change has been studied theoretically, and theirs sensitivity coefficient is gotten through calibrating experiment. Secondly, the FBG strain and temperature sensors have been successfully installed in some key suspenders of Sichuan Ebian Dadu river arch bridge. Techniques of installation of FBG sensors and suspender repairing have been explored in-service arch bridge. Thirdly, the change of suspender strain and temperature, and the effect of the same loading to different length suspender have been monitored with the FBG sensors. The monitoring results show that the FBG sensors can monitor correctly the change of traffic loading and temperature, possible fatigue damages, FBG sensors are more adaptive to long-term structural health monitoring than the electric strain gauges.

Health monitoring of binzhou yellow river highway bridge using fiber bragg gratings

Binzhou yellow river Highway Bridge with 300 meter span and 768 meter length is located in the Shandong province of China and is the first cable stayed bridge with three towers along the yellow river, one of the biggest rivers in China. In order to monitoring the strain and temperature of the bridge and evaluate the health condition, one fiber Bragg grating sensing network consists of about one hundred and thirty FBG sensors mounted in 31 monitoring sections respectively, had been built during three years time. Signal cables of sensors were led to central control room located near the main tower. One four-channel FBG interrogator was used to read the wavelengths from all the sensors, associated with four computer-controlled optic switches connected to each channel. One program was written to control the interrogator and optic switches simultaneously, and ensure signal input precisely. The progress of the monitoring can be controlled through the internet. The sensors embedded were mainly used to monitor the strain and temperature of the steel cable and reinforced concrete beam. PE jacket opening embedding technique of steel cable had been developed to embed FBG sensors safely, and ensure the reliability of the steel cable opened at the same time. Data obtained during the load test can show the strain and temperature status of elements were in good condition. The data obtained via internet since the bridges opening to traffic shown the bridge under various load such as traffic load, wind load were in good condition.

Optical FBG's sensing properties and practical application in civil infrastructures

Sensing properties of the bare FBG have theoretically and experimentally been studied in this study, and then a temperature compensation method for FBG strain sensors was proposed. Due to the fragility of bare FBG, a technique of encapsulating bare FBG in a capillary steel tube was developed and the strain and temperature sensing properties of the encapsulated FBG were furthermore studied. With the consideration of the practical application in civil infrastructures, the technique of FBG to adhere or embed on steel and in reinforced concrete structures was studied. With successfully affixing and embedding bare FBGs and encapsulated FBGs sensors on a steel truss and in a reinforced concrete beam, respectively, the experiment of using the above FBG sensors to monitor the structural strain and deformation process. In order to verify the quasi-distribution sensing ability of FBG, the test that 3 bare FBGs were connected one by one and adhered on a steel truss was done and the independently sensing strain ability was found. Finally, FBGs strain sensors were successfully embedded in a reinforced concrete bridge to monitor the strain history and distribution under construction and in service. The measuring signals indicated that the embedded FBGs could precisely and long-term monitor the strain history, therefore, they can be employed to evaluate the fatigue life for the bridge.