Abstract: For the health monitoring of civil structures, the study of finite element model updating or damage detection mainly focuses on undamped systems. Thus, their objective has been exclusively restricted to the correction of the mass and stiffness matrices. In contrast, this paper performs the model updating and damage detection for damped structures. A theoretical contribution of this paper is to extend the cross-model cross-mode (CMCM) method to simultaneously update the mass, damping and stiffness matrices of a finite element model when only few spatially incomplete, complex-valued modes are available. Numerical studies are conducted for a five-story frame structure with multiple damaged elements. The numerical results reveal that applying the CMCM method, together with an iterative Guyan reduction scheme, can yield good damage detection in general.
Abstract: The present paper investigates the dynamic characteristics and stability of moving functionally graded material rectangular thin plate. Based on Voigt model, the material properties are assumed to vary continuously through their thickness according to a power-law distribution of the volume fractions of the plate constituents. By the first order shear deformation theory, the differential equations of motion of the moving FGM rectangular plate are derived. The vibration frequencies are obtained from the solution of a generalized eigenvalue problem. Entire computational work is carried out in a normalized square domain obtained through an appropriate domain mapping technique. Results of the reduced problem revealed excellent agreement with other studies. The dimensionless complex frequencies of the moving FGM rectangular plate with four edges simply supported are calculated by the differential quadrature method. The effects of gradient index, aspect ratio, and dimensionless moving speed on the transverse vibration and stability of the moving FGM rectangular plate are analyzed. Results are furnished in dimensionless amplitude–frequency vs. dimensionless moving speed in the form of curves and pictorial representations of some vibration mode shapes are made.
Abstract: Based on the ground penetrating radar's work mechanism, this article briefly introduces the working principle and the data processing method of ground penetrating radar detecting the tunnel lining. In view of the lining quality detection's characteristics, it summarizes a series of atlas reflection characteristic of the examination target such as the lining thickness, the backfill quality, the steel bar reinforcement situation, the adjacent formation structural feature and so on, and analyses and comments on them with project examples. The research believes that under appropriate working condition, as an important means to guarantee the construction security and maintain the tunnel health, ground penetrating radar technology can examine the lining quality fast and effectively, and meet the needs of the tunnel lining quality detection with suitable equipment, working method and data processing plan.
Abstract: While rigid or pinned assumptions are adopted for steel frames in traditional modeling via finite element method, the actual behavior of the connections is usually neither. Semi-rigid joints enable connections to be modeled as partially restrained, which improves the quality of the model. To identify the connection stiffness and update the FE model, a newly-developed cross modal strain energy (CMSE) method is extended to incorporate the connection stiffness estimation. To illustrate the capability of the proposed parameter estimation and model updating algorithm, a four-story frame structure is demonstrated in the numerical studies. Several cases including Semi-rigid joint(s) on single connection and on multi-connections, are investigated. Numerical results indicate that an excellent updating is achievable and the connection stiffness can be estimated by CMSE method.
Abstract: Detection of structural damages is critical to ensure the reliability and safety of structures. So far, some progresses in structural identification have been made. The extended Kalman filter (EKF) has been one of the classic time-domain approaches for the identification of structural parameters. However, since the extended state vector contains both the state vector and the structural parameters, EKF approach can identify limited numbers of nonlinear structural parameters due to computational convergence difficulty. To overcome such problem, a two-stage Kalman estimation approach, which is not available in the previous literature, is proposed for the identification of structural parameters. In the first stage, state vector of structures is considered as an implicit function of the structural parameters, and the parametric vector is estimated directly based on the Kalman estimator. In the second stage, state vector of the structure is updated by applying the Kalman estimator with the structural parameters being estimated in the first stage. Therefore, analytical recursive solutions for the structural parameters and state vector are respectively derived and presented, by using the Kalman estimator method in a two-stage approach. The proposed approach is straightforward. Moreover, it can identify more numbers of nonlinear structural parameters with less time of iteration calculation compared with the conventional EKF. A numerical example of identifying the parameters of an 8-storey shear-frame structure is conducted. Simulation results show that the proposed approach is effective and accurate.
Abstract: Damage identification and health monitoring is an important aspect in the evaluation of structural safety recently. This paper presents a modal experiment and analysis of a 2×2 bay (6.128m×6.128m) 1 storey (1.4m) RC flat plate frame structure on rigid foundation. The displacement mode experiments were carried out by hammer-hitting excitation method in the age of frame concrete. The varieties of the modal parameters of the flat plate were obtained by dynamic testing along with the growth of elastic modulus of concrete and change of the environment temperature. it can be used to identify the location and form of the damage. Base on the missing of some specific structure modal shapes and reduction of the frame horizontal stiffness, it can be revealed that the interior slab-column connection cannot transfer the unbalance moment well. Further more, modal parameters of the RC flat plate with the interior column removed had been exhibited and discussed. A 3-D solid finite element models with the interior column fixed/hinged were constructed, they were validated to match the frame natural frequencies and mode shapes. The results demonstrate the effectiveness of modal parameters identification method in estimate the damage of column in RC flat plate frame. Additionally, the dynamic modulus of elastic is obtained by the comparison of experimental test and FEM simulation analysis.
Abstract: In this paper, a technique is proposed for non-parametric identification of structural nonlinearity with limited input and output measurements. The identification algorithm is based on the classical Kalman estimator for the displacement and the velocity responses and the recursive least square estimation for the unmeasured excitation and the restoring force. Two different models are used to simulate nonlinear structures: One is a 4-storey shear-frame structure with excitation on the top floor and the nonlinearity occurs at the bottom floor. The other is also a 4-storey shear-frame structure with both excitation and the nonlinearity at the top floor. Two numerical examples are carried out for the two kinds of models. Bouc-Wen hysteretic models are used to simulate the nonlinear impact. The simulation results demonstrate the efficiency of the proposed technique with limited output measurements.
Abstract: In China, many highways were built near high mountains where landslide often happened and threatened the traffic safety. Slope monitoring is key issue that could reduce long-term losses and ensure traffic safety on the highways. In this paper, based on the research project sponsored by government, the slope stability monitoring plan was discussed. On the basis of investigation of the art of state methods, synthetic monitoring system was chosen for the landslide early-warning system of national highway 104. It comprised of Time Difference on Arrival monitoring method on the roadside surface as well as inside the underground methods such as borehole inclinometers, piezometers and the earth pressure cells. Then Time Difference on Arrival methodology was focused on, and the location error was analyzed in detail. According to, the theoretic analysis and practical consideration, the optimized arrangement plan of Time Difference on Arrival transducers was proposed. The sketch of all kinds of sensors for the whole system was provided as well, which will ensure the installation of the early-warning system.
Abstract: This paper presents the random decrement (RD) technique based on the sampling method for parameter identification of linear dynamic system. The development of RD technique was elaborated briefly in the aspects of identifying the dynamic properties, and then this paper summarized the corresponding parameters recognition problems due to the quantity and quality of measured sampling segments. Detailed analysis of two kinds of sampling method (the probability-proportional-to-size and two-stage sampling) is conducted to investigate its adaptation range in extracting RD signatures. The results of two simulated examples indicates that in view of the different vibration parameter recognition situation, the above provided RD technique based on different sampling methods could improve the quality of RD signature obviously, and lead to a quite accurate frequency and the damping ratio of structural system under the effective use of all measured sampling segments.
Abstract: In order to effectively evaluate the security status of shaft and to make timely and accurate forecasts before the shaft break disaster, lead into fiber brag grating technology in the mine shaft deformation monitoring. Designing laboratory experiments verified FBG sensing the reliability of deformation and strain transfer law in reinforced concrete beams, while provide practical experience to the FBG sensors installed on the actual shaft structure. According to the structural condition of the main shaft of JINCHUAN Mine No.3, designed 8 monitoring sections in different level ingate upper and lower and installed fiber optic grating sensors, forming a fully automatic real-time and long-term deformation monitoring system. Initial monitoring results indicate that only the No.4 (down) sensors was failure, but the other seven monitoring sections can effectively detect the corresponding strain, and the monitoring system was stable. The fiber optical sensing technology has broad application prospects in the state's long-term monitoring deformation of the mine project, for the mine shaft deformation monitoring provides a more reliable monitoring method.