Papers by Author: Hui Li

Abstract: Compressive sampling also called compressive sensing (CS) is a emerging information theory proposed recently. CS provides a new sampling theory to reduce data acquisition, which says that sparse or compressible signals can be exactly reconstructed from highly incomplete random sets of measurements. CS broke through the restrictions of the Shannon theorem on the sampling frequency, which can use fewer sampling resources, higher sampling rate and lower hardware and software complexity to obtain the measurements. Not only for data acquisition, CS also can be used to find the sparse solutions for linear algebraic equation problem. In this paper, the applications of CS for SHM are presented including acceleration data acquisition, lost data recovery for wireless sensor and moving loads distribution identification. The investigation results show that CS has good application potential in SHM.

Abstract: In this paper, a data-driven approach to localizing structural damage subjected to ground motion is proposed by using the fractal dimension of the time-frequency features of structural dynamic responses. The time-frequency feature is defined as the real part of wavelet coefficient and the fractal dimension adopts the box-counting method. It is shown that the proposed fractal dimensions at each story of linear system are identical, while the fractal dimension at the stories with nonlinearity is different from those at the stories with linearity. Therefore, the nonlinear behavior of structural damage caused by strong ground motions can be detected and localized through comparing the fractal dimensions of structural responses at different stories. Shaking table test on a uniform 16-story 3-bay steel frame with added friction dampers modelling interstory nonlinear behavior was conducted. The experiment results validate the effectiveness of the proposed method to localize single and multi seismic damage of structures.

Abstract: A new method is proposed to identify multi-axial seismic loadings from structural dynamic responses on limited degrees of freedom. The seismic loadings acting on structures are modeled by Hartley series approximation, and the sensitivities of structural dynamic response with respect to the unknown approximation coefficients are derived. The identification equation is set up based on best fitting structural measured and calculated responses, and is solved with the damped least-squares method. A five-story three-dimensional steel frame structure excited by El-Centro seismic accelerations is studied for validating the proposed method. Numerical simulations with measurement noise and model errors show that the proposed method can accurately identify all seismic loadings from only several responses of the structure.

Abstract: In this paper, some smart sensors or material used to make the smart sensors, such as piezoresistance composite, piezoelectric polymer, piezoelectric cement and corrosion monitoring sensor, developed by Harbin Institute of Technology were introduced. Piezoresistance composite is made with carbon nanotube and resin, one character of the work is the carbon nanotube is orientation arranged by magnetic field. Piezoelectric polymer is made with PZT particles and PVDF, in order to improve its performance a few carbon nanotube are also mixed in the composite. Piezoelectric cement is one kind of sensing material whose primary raw materials are cement and piezoelectric ceramic particles (or fiber). The sensing performance of piezoelectric cement is coming from its functional phase, the piezoelectric ceramic. The corrosion monitoring sensor is made with solid-state reference electrode, whose surface is one kind of binary alloy membrane produced with physical vapor deposition technology. The main producing technology, performance and applications of above sensors were introduced in this paper.

Abstract: This paper includes five parts. The first is the sensing technology, in which ultrasonic-based sensing technology for scour monitoring of bridge piers, electro-chemistry-based distributed concrete cracks and automobile wireless sensors are introduced. The second is the application of compressive sensing technology in structural health monitoring, in which the recovery of lose data for wireless senor networks, spatial distribution of vehicles on the bridge and localization of acoustic emission source by using compressive technique are included. The third is damage monitoring and identification of seismically excited structures, in which data-driven seismic localization approach and nonlinear hysteretic model identification approach are proposed. The fourth is the monitoring for wind and wind effects of long-span bridges, the vortex-induced vibration of deck, suspended cables and stay cables is observed and the buffeting of bridge under Typhoon is also measured. The last one is the data analysis, modeling and safety evaluation of bridges based on structural health monitoring techniques.

Abstract: A new method based on dynamic response sensitivity is proposed for the identification of local linear time-varying (LTV) system. The unknown local LTV structural stiffness is modeled by orthogonal polynomial approximations, and the sensitivities of structural dynamic response with respect to orthogonal coefficients are derived. The identification equation is set up based on Taylor’s first order approximation, and is solved with the damped least-squares method. A fifteen-story shear building is studied to validate the proposed method. Three ideal cases of LTV systems, with periodically, abruptly and randomly varying stiffness at the 8th story of the structure, are investigated to illustrate the capability of the algorithm to track the variations of the systems. Numerical simulation with noisy measured accelerations shows that the proposed method can accurately identify various kinds of local time-varying system from only several responses of the structure. This method provides a new approach for detecting local time-varying stiffness of structures with incomplete measured output information.

Abstract: As one kind of the advanced composite materials (ACM), FRP is now getting widely used in civil engineering for its advantages as light weight, electromagnetic isolation, high strength, fatigue resistance and corrosion resistance. This article wants to provide a quality control method for the FRP cables by eliminating its unwinding effect error. Firstly, two FRP-OFBG (Optical Fiber Bragg Grating) cables were fabricated in factory, and then the two specimens were tested by the MTS (material test system). Secondly, theoretical understandings with boundary conditioned formulas were provided for analysis on the unwinding process of the cable. After that the unwinding displacement of the FRP-OFBG cable was obtained by using the b-value method. Finally, a service ability assessment of the cable was given before the conclusions.

Abstract: Finite element model updating aims at reconciling the analytical model with the test one, to acquire a refined model with high-fidelity in structural dynamic properties. However, testing data are inevitable polluted by noises. In this study, the mode parameters and design variables are modeled as fuzzy variables, and a fuzzy model updating method is developed. Instead of a single optimal model, a set of satisfactory models is obtained. The most physically compatible solution is sorted by insights to the structures. The proposed method is applied to a real concrete bridge, for which a physically meaningful model is identified.

Abstract: This paper presents the analysis of strain time histories measured by structural health monitoring system. The main objective of this study is to prepare data for reliability estimation of main components as well as the entire structural system. The strain and corresponding temperature data is collected at the following stages: closure segment reconstruction stage and operating stage. The strain monitoring of the closure segment during the reconstruction stage provided valuable information on early-life strain development and reference characteristics for events such as post tensioning and temperature change. These lessons learnt from the reconstruction monitoring can be used for understanding subsequent bridge behavior, including damage detection and reference points of subsequent monitoring. Specially, the loading test results reveal the effectiveness and correctness of the strain acquiring system and provide evidence for reliable long-tem monitoring. Strain and temperature data have been recorded at sampling frequency of 62.5Hz since loading test, which would provide information linear stress-strain relationships. The long-term creep and shrinkage model were provided by Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culverts (JTG D62-2004). Through the statistical analysis of the online strain response, the probability model of long-term performance under environmental and random traffic loading are obtained which gives the potential of its application of reliability based assessment on cable stayed bridges where they evaluated the reliability of elements such as cables and stiffening girder.

Abstract: Based on fatigue test results of corroded wires obtained from dissection of actual parallel wire cables which were used on a certain domestic cable-stayed bridge, the fatigue properties of corroded parallel wire cable are investigated by the method of Monte Carlo simulation in this paper. The results of fatigue life and corrosion degree of corroded wire are presented. Comparisons between the original design information and fatigue test results, it can be seen that corrosions make the fatigue lives of wires decreasing sharply. The fatigue life of individual wire is described by Weibull distribution considered some useful parameters such as, stress range, mean stress, mean static strength and length effects. The effects of percentage of broken wire, cable S-N curve parameter on cable fatigue life are discussed. It can be seen that the cable fatigue lives are controlled by a small fraction of the cable wires with the shortest fatigue lives. Finally, the S-N curves of cable are calculated by Monte Carlo simulations based on the results of individual wire fatigue test, and compared with the results of cable fatigue test.