3,391 research outputs found
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An Experimental Study of an Electro-Optical Displacement Sensor
This paper presents the results of an experimental study on an innovative electro-optical fiber sensor developed for measuring the dynamic response of civil structures such as buildings and bridges, which can be used for non-destructive evaluation of structural systems. This electro-optical sensor employs an electric circuit, LC oscillator, in which inductance and capacitance are connected in parallel. The resonant frequency of the LC oscillator is modulated by the external displacement transmitted through the core of the induction solenoid. This frequency is detected from the optically-transmitted oscillatory signal and the LC oscillator is optically powered. Compared to the conventional optical fiber sensors developed so far, the proposed sensor has two significant advantages: 1) the sensing head is an electric circuit (rather than an optical fiber cable), which can sense a specific physical quantity without interference from miscellaneous effects and is expected to be much more durable than the sensing head made of optical fiber cable as seen in usual extrinsic optical fiber sensors; 2) the LC oscillator is a well understood and reliable circuit with its resonant frequency measurable and transmittable without attenuation or distortion through an optical fiber cable over a long distance to recording and other devices. These advantages make the sensor extremely simple to design and manufacture, durable, reliable, robust to use, and hence, more readily deployable in civil structural applications. A prototype electro-optical strain sensor has been developed and its static and dynamic characteristics were experimentally tested. This sensor was also installed on a steel frame to measure the dynamic strain response when subjected to seismic ground motions during a shaking table test. The experimental study using the prototype demonstrated excellent performance of the electro-optical sensor in terms of accuracy, wide frequency range, and other advantageous characteristics for civil structural applications
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Vibration Control of Tall Buildings Using Mega Sub-Configuration
An innovative vibration-control system is proposed to reduce the dynamic response of tall buildings to wind and seismic loads. This system takes advantage of the so-called megasubstructure configuration, which is especially popular in tall buildings. Substructures contained in the megastructure serve as energy absorbers so that no additional mass is required for the intended vibration control as seen in the conventional mass damper systems. The proposed system naturally resolves the difficulties in augmenting damping capacities of tall buildings associated with the high rigidity and deformation in the dominant bending mode. Dynamic characteristics of the proposed control system including the frequency response and the energy flow are investigated. Optimal values of structural parameters such as the damping ratio and stiffness of the substructure are determined. The feasibility and effectiveness of this unique control system in improving human comfort and protecting structures under both wind and earthquake loads are demonstrated through analytical and numerical analysis
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Instantaneous damage detection of bridge structures and experimental verification
An extended Kalman filtering (EKF) method was developed and applied to instantaneously identify elemental stiffness values of a structure during damaging seismic events based on vibration measurement. This method is capable of dealing with nonlinear as well as linear structural responses. Identification of the structural elemental stiffness enables location as well as quantification of structural damage. The instantaneous stiffness values during an event can provide highly useful information for post-event capacity estimation. In this study, a large-scale shaking table test of a three-bent concrete bridge model was performed in order to verify the proposed damage detection method. The bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. The elemental stiffness values of the structure were instantaneously identified in real time during the damaging earthquake excitations using the EKF method. The identified stiffness degradations and their locations agreed well with the structural damage observed by visual inspection and strain measurements. More importantly, the seismic response accelerations analytically simulated using the instantaneous stiffness values thus identified agreed well with the measured accelerations, demonstrating the accuracy of the identified stiffness. This study presents an experimental verification of a structural damage detection method using a realistic bridge model subjected to realistic seismic damage
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Structural Health Monitoring by Recursive Bayesian Filtering
A new vision of structural health monitoring (SHM) is presented, in which the ultimate goal of SHM is not limited to damage identification, but to describe the structure by a probabilistic model, whose parameters and uncertainty are periodically updated using measured data in a recursive Bayesian filtering (RBF) approach. Such a model of a structure is essential in evaluating its current condition and predicting its future performance in a probabilistic context. RBF is conventionally implemented by the extended Kalman filter, which suffers from its intrinsic drawbacks. Recent progress on high-fidelity propagation of a probability distribution through nonlinear functions has revived RBF as a promising tool for SHM. The central difference filter, as an example of the new versions of RBF, is implemented in this study, with the adaptation of a convergence and consistency improvement technique. Two numerical examples are presented to demonstrate the superior capacity of RBF for a SHM purpose. The proposed method is also validated by large-scale shake table tests on a reinforced concrete two-span three-bent bridge specimen
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Vibration control of super tall buildings subjected to wind loads
Excessive vibration due to wind loads is a major obstacle in design and construction of a super tall building. The authors recently introduced an innovative method for controlling the wind response of super tall buildings, which takes advantage of the so-called mega-sub structural configuration. Preliminary investigation was performed under the assumption that the wind load is a white noise and the building can be modeled as a shear structure. In this paper, a more reasonable tall building model (a cantilever beam) and a more realistic wind load model (a non-white stochastic process in time and space) are employed to design passive and hybrid mega-sub control systems and to examine the performance of such controlled buildings. Building vibration in both along-wind and across-wind directions is examined. The control parameters of the proposed systems, including the frequency ratio of the sub to the mega structures, the damping ratio of the sub structure, and the feedback gains of the actuator force, are studied and their optimal values are obtained. For comparison, a tall building without control and one with the conventional tuned-mass-damper control are also studied under the same load conditions. The significant cost-effectiveness of the proposed mega-sub systems is demonstrated in reducing the acceleration and deformation responses of tall buildings to wind loads, not only enhancing the safety of structure and its contents but also improving the comfort of occupants
A Vision-Based Sensor for Noncontact Structural Displacement Measurement
Conventional displacement sensors have limitations in practical applications. This paper develops a vision sensor system for remote measurement of structural displacements. An advanced template matching algorithm, referred to as the upsampled cross correlation, is adopted and further developed into a software package for real-time displacement extraction from video images. By simply adjusting the upsampling factor, better subpixel resolution can be easily achieved to improve the measurement accuracy. The performance of the vision sensor is first evaluated through a laboratory shaking table test of a frame structure, in which the displacements at all the floors are measured by using one camera to track either high-contrast artificial targets or low-contrast natural targets on the structural surface such as bolts and nuts. Satisfactory agreements are observed between the displacements measured by the single camera and those measured by high-performance laser displacement sensors. Then field tests are carried out on a railway bridge and a pedestrian bridge, through which the accuracy of the vision sensor in both time and frequency domains is further confirmed in realistic field environments. Significant advantages of the noncontact vision sensor include its low cost, ease of operation, and flexibility to extract structural displacement at any point from a single measurement
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Large-Scale Shake Table Test Verification of Bridge Condition Assessment Methods
Methods that identify structural component stiffness degradation by pre- and postevent low amplitude vibration measurements, based on a linear time-invariant (LTI) system model, are conceptually justified by examining the hysteresis loops the structural components experience in such vibrations. Two large-scale shake table experiments, one on a two-column reinforced concrete (RC) bridge bent specimen, and the other on a two-span three-bent RC bridge specimen were performed, in which specimens were subjected to earthquake ground motions with increasing amplitude and progressively damaged. In each of the damaged stages between two strong motions, low amplitude vibrations of the specimens were aroused, and the postevent component stiffness coefficients were identified by optimizing the parameters in a LTI model. The stiffness degradation identified is consistent with the experimental hysteresis, and could be quantitatively related to the capacity residual of the components
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