• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.20-29
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• 2022

The operational modal analysis (OMA) technique, which extracts the modal parameters of a structural system using ambient vibrations, has been actively developed as a field of structural health monitoring of cable-supported bridges. In this paper, the short and long-term modal parameters of a cable-stayed bridge were evaluated using the acceleration data obtained from the two ambient vibration tests (AVTs) and three years of continuous measurements. A total of 27 vertical modes and 1 lateral mode in the range 0.1 ~ 2.5 Hz were extracted from the high-resolution AVTs which were conducted in the 6th and 19th years after its completion. Existing OMA methods such as Peak-Picking (PP), Eigensystem Realization Algorithm with Data Correlation (ERADC), Frequency Domain Decomposition (FDD) and Time Domain Decomposition (TDD) were applied for modal parameters extraction, and it was confirmed that there was no significant difference between the applied methods. From the correlation analysis between long-term natural frequencies and environmental factors, it was confirmed that temperature change is the dominant factor influencing natural frequency fluctuations. It was revealed that the decreased natural frequencies of the bridge were not due to changes in structural performance and integrity, but to the environmental effects caused by the temperature difference between the two AVTs. In addition, when the TDD technique is applied, the accuracy of extracted mode shapes is improved by adding a proposed algorithm that normalizes the sequence so that the autocorrelations at zero lag equal 1.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.647-657
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• 2006

Probabilistic Risk Assessment considering statistically random variables is performed for the preliminary design of a Cable Stayed Bridge, which is Prestressed Concrete Bridge consisted of cable and plate girders, based on the method of Working Stress Design and Strength Design. Component reliabilities of cables and girders have been evaluated using the response surface of the design variables at the selected critical sections based on the maximum shear, positive and negative moment locations. Response Surface Method (RSM) is successfully applied for reliability analyses for this relatively small probability of failure of the complex structure, which is hard to obtain through Monte-Carlo Simulations. or through First Order Second Moment Method that can not easily calculate the derivative terms of implicit limit state functions. For the analysis of system reliability, parallel resistance system consisting of cables and plate girder is changed into series connection system and the result of system reliability of total structure is presented. As a system reliability, the upper and lower probabilities of failure for the structural system have been evaluated and compared with the suggested prediction method for the combination of failure modes. The suggested prediction method for the combination of failure modes reveals the unexpected combinations of element failures in significantly reduced time and efforts compared with the previous permutation method or system reliability analysis method, which calculates upper and lower bound failure probabilities.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.57-64
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• 2004

Stay cables, such as are used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Several methods have been proposed and implemented to mitigate this problem, though each has its limitations. Recently some studies have shown that semiactive dampers can potentially achieve performance levels nearly the same as comparable active devices with few of the detractions. This paper presents the results of a study to evaluate the performance of semiactive dampers for mitigating the vibration of stay cables. Moreover, a number of recently proposed semiactive control algorithms are formulated for use with shear mode MR damper to compare the efficiency of each algorithm through numerical simulation. Numerical simulation considers a stay cable excited by shaker and controlled by shear mode MR dampers. In simulation, the response with a semiactive damper is found to be dramatically reduced compared to the uncontrolled case. Furthermore, it is verified that the algorithm based on Lyapunov control theory is very efficient in mitigating the cable vibration.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.264-271
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• 2006

Stay cables, such as used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. It has been reported that a semiactive control system using MR dampers could potentially achieve both the better performance compared to a passive control system and the adaptability with few of the detractions. However, a control system including a power supply, a controller and sensors is required to improve the control performance of MR dampers. This complicated control system is not effective to most of large civil structures such as long-span bridges and high-rise buildings. This paper proposes a smart damping system which consists of an MR damper and the electromagnetic induction (EMI) part that is considered as an external power source to the MR damper. The control performance of the proposed damping system has been compared with that of the passive-type control systems employing an MR damper and a linear viscous damper.

• Structural Engineering and Mechanics
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• v.39 no.5
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• pp.661-667
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• 2011

In the famous equivalent elasticity modulus method proposed by Ernst for the geometrical nonlinear analysis of stay cables, the cable shape was assumed as a parabolic curve, and only a part of the gravity load normal to the chord was taken into account with the other part of gravity load parallel to the chord being ignored. Using the actual catenary curve and considering the entire gravity load of stay cables, the present study has derived the equivalent stiffness method to analyze the sag effect of stay cables in cable-stayed bridges. The derived equivalent stiffness can be degenerated into Ernst's equivalent elasticity modulus method with some approximations. Therefore, the Ernst's method is a special and approximate formulation of the present method. The derived equivalent stiffness provides a theoretical explanation for the famous Ernst's formula.

• Wind and Structures
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• v.3 no.4
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• pp.267-277
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• 2000

This paper aims to describe the aerodynamic vibrations of various structural elements of bridges, which are particular issues at present. The aerodynamic countermeasures for those vibrations are also discussed considering the generation mechanisms of the aerodynamic instabilities. In this paper, an example of vortex-induced oscillation of bridge deck and its lesson are discussed. Next, the wind-induced cable vibration and its aerodynamic countermeasures are reviewed. Then, the aerodynamic characteristics on two edge girders and their feasibility for application to long span cable-stayed bridges are considered. Furthermore, the bridge decks for future long span bridges are proposed and their aerodynamic characteristics are also discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.93-101
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• 1989

A geometrically nonlinear cable finite element is presented to use in the static or dynamic modeling of offshore and onshore structures such as guyed tower, tension leg platform or mooring buoy, submarine cable, cable-stayed bridge, suspension bridge, cable roof and so on. The cable finite element is derived directly from the compatibility equations and flexibility matrix of elastic catenary cable theory for the arbitary plane loading and geome try. A general and virsatile computer program has been developed to perform the analyses of cable member itself or cable guyed or suspened structures, in which Newmark-$\beta$ method is used to obtain a time domain solution and Newton-Raphson iteration method is used to solve the nonlinear system of compatibility equations of cable and algebraic static or dynamic equations at each time step. The results from the static and dynamic analysis of a cable member by the computer program are summarized and presented.

• Smart Structures and Systems
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• v.18 no.3
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• pp.485-500
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• 2016

Stay cables in some cable-stayed bridges suffer large amplitude vibrations under the simultaneous occurrence of rain and wind. This phenomenon is called rain-wind-induced vibration (RWIV). The upper rivulet oscillating circumferentially on the inclined cable surface plays an important role in this phenomenon. However, its small size and high sensitivity to wind flow make measuring rivulet size and its movement challenging. Moreover, the distribution of the rivulet along the entire cable has not been measured. This paper applies the videogrammetric technique to measure the movement and geometry dimension of the upper rivulet along the entire cable during RWIV. A cable model is tested in an open-jet wind tunnel with artificial rain. RWIV is successfully reproduced. Only one digital video camera is employed and installed on the cable during the experiment. The camera records video clips of the upper rivulet and cable movements. The video clips are then transferred into a series of images, from which the positions of the cable and the upper rivulet at each time instant are identified by image processing. The thickness of the upper rivulet is also estimated. The oscillation amplitude, equilibrium position, and dominant frequency of the rivulet are presented. The relationship between cable and rivulet variations is also investigated. Results demonstrate that this non-contact, non-intrusive measurement method has good resolution and is cost effective.

• Smart Structures and Systems
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• v.7 no.5
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• pp.379-392
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• 2011

This paper presents a multi-functional system, consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device, and its applications in stay cables. The proposed system is capable of offering multiple functions: (1) mitigating excessive vibrations of cables, (2) estimating cable tension, and (3) harvesting energy for wireless sensors used health monitoring of cable-stayed bridges. In the proposed system, the EMI device, consisting of permanent magnets and a solenoid coil, can converts vibration energy into electrical energy (i.e., induced emf); hence, it acts as an energy harvesting system. Moreover, the cable tension can be estimated by using the emf signals obtained from the EMI device. In addition, the MR damper, whose damping property is controlled by the harvested energy from the EMI device, can effectively reduce excessive cable vibrations. In this study, the multi-functionality of the proposed system is experimentally evaluated by conducting a shaking table test as well as a full-scale stay cable in a laboratory setting. In the shaking table experiment, the energy harvesting capability of the EMI device for wireless sensor nodes is investigated. The performance on the cable tension estimation and the vibration mitigation are evaluated using the full-scale cable test setup. The test results show that the proposed system can sufficiently generate and store the electricity for operating a wireless sensor node twice per day, significantly alleviate vibration of a stay cable (by providing about 20% larger damping compared to the passive optimal case), and estimate the cable tension accurately within a 2.5% error.

• Smart Structures and Systems
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• v.4 no.5
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• pp.697-710
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• 2008

Long steel stay cables, which are mainly used in cable-stayed bridges, are easy to vibrate because of their low inherent damping characteristics. A lot of methods for vibration reduction of stay cables have been developed, and several techniques of them have been implemented to real structures, though each has its limitations. Recently, it was reported that smart (i.e. semi-active) dampers can potentially achieve performance levels nearly the same as comparable active devices with few of the detractions. Some numerical and experimental studies on the application of smart damping systems employing an MR fluid damper, which is one of the most promising smart dampers, to a stay cable were carried out; however, most of the previous studies considered only one specific control algorithm in which they are interested. In this study, the performance verification of MR fluid damper-based smart damping systems for mitigating vibration of stay cables by considering the four commonly used semi-active control algorithms, such as the control algorithm based on Lyapunov stability theory, the maximum energy dissipation algorithm, the modulated homogeneous friction algorithm and the clipped-optimal control algorithm, is systematically carried out to find the most appropriate control strategy for the cable-damper system.