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This case study investigates two of the wind-induced vehicle accidents that occurred on a cable-stayed bridge in Korea over the past 20 years. Both of these incidents happened at the approach deck of the bridge, where the elevation from the sea level was only about 57% of the main span height. The investigation was focused on determining whether specific structural components or geometrical characteristics around the accident locations were responsible for these incidents. To achieve this, scaled-down vehicle and bridge deck models were used in a series of wind-tunnel tests. The results show that the wind load on the vehicles increased by 3–4 times near the accident locations. The primary cause of this anomaly was attributed to the rapid change in deck width. Furthermore, a risk assessment, which considered traffic and wind environments, showed that the risk level at the accident location was 100 times higher than at any other location on the bridge due to these unique characteristics. Additionally, further risk assessment revealed that two measures, traffic control and wind barrier installation, could mitigate the risk at the accident location. [ABSTRACT FROM AUTHOR]

Summary: Cables are among the most important structural components of cable‐stayed bridges; however, their vibrations due to the wind and vehicles significantly affect the serviceability of bridges. To overcome the expensive and time‐ and effort‐intensive installation of sensors in measuring cable vibrations, computer‐vision‐based displacement methods have been introduced. Even with the improved accuracy and convenience of vision‐based displacement methods, there are two main issues in their application in measuring cable vibrations: the manual selection of the region of interest (ROI) and loss of feature points using traditional tracking algorithms. To address these, this paper proposes a new specialized method to measure the structural displacement of cables. The proposed method automatically selects the ROI using a convolutional neural network and tracks the feature points in the cable more robustly using a modified Kanade–Lucas–Tomasi (KLT) algorithm. The automatic cable ROI selection network (Cable‐ROI Net) predicted the cable with an intersection over union of 89.59%. Meanwhile, modified KLT (Uni‐KLT) successfully measured the cable displacement with a root mean square error of 1.077 pixels, the conventional KLT failed to track the feature points. The on‐site validation test at a cable‐stayed bridge in Korea demonstrated the ability of the proposed method to automatically select the ROI and successfully measure the cable vibration for the entire duration of 30 min, whereas the traditional method required manual ROI selection and lost all feature points four times throughout the test. Therefore, the proposed method is expected to improve the current methods for measuring cable vibrations. [ABSTRACT FROM AUTHOR]

This study was focused on the effects of vortex-induced vibration (VIV) in parallel twin cable-stayed bridges. A series of wind tunnel tests were performed to investigate the effect of the relative differences in the setup of the natural frequencies of parallel decks during VIV. The differences in the natural frequencies of the two decks are represented in terms of the frequency ratio (FR) as defined by the ratio of the natural frequency of the upstream deck to that of the downstream deck. Six FRs were examined to cover all the potential ranges of relative differences in the natural frequencies of the two decks. The interactive motions of the two decks were examined with normalization parameters to demonstrate the fundamental mechanics of complicated VIV of parallel twin cable-stayed bridges from the viewpoints of fluid and structural dynamics. [ABSTRACT FROM AUTHOR]

A stabilizing cable (SC), used for mitigating buffeting vibration in a cantilevered structure of a cable-stayed bridge during construction, is normally installed with pretension. When a situation arises where only SCs are allowed in side spans, heavy counterweights in the center span are required to satisfy the force balance. The mitigating effect of unpretensioned cables was investigated using a wind tunnel in an attempt to eliminate the need for counterweights. An elastic wind tunnel test at a scale of was prepared, and a series of comparative wind tunnel tests were performed. The vertical displacement at the cantilever tip of the center span and the horizontal displacement at the top of the pylon were measured, and stabilizing effects were then estimated. An unpretensioned cable produces a nonlinear motion because of a loss of tension. A quantitative evaluation of the stabilizing effect of an unpretensioned stabilizing situation indicated that the counterweight could be removed only when a moderate level of stabilization is required for a small- or medium-sized, cable-stayed bridge. [ABSTRACT FROM AUTHOR]

Abstract: A vortex-induced vibration (VIV), amplified by an interference effect caused by two parallel decks, was observed in the upstream deck of a twin cable stayed-bridge. This represents the first case of such an observation in an actual long-span cable-supported bridge. The observed VIV was successfully reproduced in a wind tunnel. Both decks were equipped with vanes and the single deck alone showed an allowable performance, in terms of VIV, based on wind tunnel tests that were carried out. It therefore appears that the observed vibration was affected by the parallel arrangement of the decks. A particle image velocimetry technique was successfully applied to investigate the complicated flow field between the upstream and downstream decks. Alternating eddies were formed in phase with the upstream deck motion and were transmitted to the downstream deck introducing “Ω” and “℧” shaped flow fields as a result. Following the alternating eddies, upward and downward wind streams were in turn fed into the gap and these flows amplified the vibration in the upstream deck of the bridge. Several modifications of aerodynamic additives were not effective in reducing this VIV. However, an increase in structural damping effectively mitigated the vibration. [Copyright &y& Elsevier]

A model updating procedure for developing a finite element model for the Seohae Bridge is proposed. The bridge is a slab-on-stringer cable-stayed bridge with a main span of 470 m and has been in operation since 2000. Natural frequencies and mode shapes identified from ambient vibration measurements with the dense application of 80 accelerometers were used as target values in developing the model. The procedure consists of two consecutive steps. The first step is to establish a baseline model using a manual tuning method, which utilizes construction and maintenance history as well as the initial design information. Variations in natural frequencies due to temperature changes are also considered in the manual tuning with the help of long-term monitoring data regarding natural frequencies and temperature. Although the manual tuning was done efficiently, errors between the analysis and measurement of the dominant natural frequencies are estimated to be 5-12%. In the second step, the baseline model is calibrated by an automated model updating procedure. Sensitivity-based optimization is used to construct the final model, in which the updating parameters are selected on the basis of a preliminary sensitivity check. In order to obtain physically meaningful solutions, the changes in the updating parameters are also minimized by including them in the objective function in the form of penalty function. The optimization procedure results in a finely tuned model that shows the maximum differences in natural frequencies to be less than 3% for the lowest two modes and 6% for the other modes. The changes in the updating parameters still remain within the allowable ranges of 5-15% specified for each parameter, based on an engineering judgement. [ABSTRACT FROM AUTHOR]

Recent tragedies around the world have shown how accidents in the cable-stayed bridges can wreak havoc on the society. To ensure the safety of the cable-stayed bridges, several studies have estimated the cable tension force using the vibration of cables. Most of these methods for estimating the tension of a cable start with measuring the displacement of the cable. Recent development of commercial cameras provide opportunity for more convenient and efficient method for measuring the displacement of cable. However, traditional vision-based displacement measurement methods require the assumption that the movement of the cable should be measured in parallel to the camera plane. This assumption limits the installation location of the camera when measuring the displacement of a cable. Therefore, this study introduces a new vision-based cable displacement measurement system that can measure the displacement of a cable in various locations even when the camera is installed in the side of the cable. The proposed method consists of three phases: (1) camera projection matrix estimation, (2) cable tracking in the image coordinate, and (3) cable displacement estimation in the world coordinate. To validate the performance of the proposed method, a simulation-based validation test, a lab-scale validation test, and an on-site validation test were conducted. The simulation-based validation test verified the performance of the proposed method in an ideal condition, and the lab-scale validation test showed the performance of the method in physical environment. Finally, the on-site validation test showed that the proposed method can measure the cable displacement with a side view camera. [ABSTRACT FROM AUTHOR]

The Mokpo cable-stayed bridge has become a new landmark in Mokpo city, Korea. This bridge has a unique feature from an aesthetic and structural point of view and will be the second longest cable-stayed bridge in Korea with a main span length of 500 m. This paper presents a summary of design and construction of the Mokpo Bridge, mainly focused on the superstructure of the cable-stayed bridge and wind-related consideration. [ABSTRACT FROM AUTHOR]

This study was focused on the vortex-induced vibration (VIV) in parallel-disposed twin cable-stayed bridges. A series of wind tunnel tests were carried out to investigate the gap distance between two bridge decks and its effect on VIV. The gap distances examined covered a wide range of from one to twenty times the depth of the upstream deck. The amplitudes of VIVs in both decks were estimated using the variations in wind velocity. Particle image velocimetry (PIV) tests were performed to identify streamline changes between two decks for different gap distances. Also, the distribution of the swirling strength of the generated vortices was evaluated based on the velocity data obtained from PIV testing. According to the research results, gap distances of five to seven times the depth of the upstream deck critically affected the interactive VIV in two parallel cable-stayed bridges. The vulnerable gap distance was closely related to the moving distance of one vortex during a period of oscillation of the deck. [ABSTRACT FROM AUTHOR]

• A displacement-based damping identification method is proposed for low-frequency dominant structures. • The method uses the dynamic displacement reconstructed from acceleration by FFIR filter. • Displacement reconstruction effectively suppressed high-mode components in response. • The method identifies the damping of fundamental modes even with a small model order. • The effectiveness is validated by the application to a cable-stayed bridge in operation. This paper proposes a new concept for the estimation of modal damping ratios. This new concept is based on an operational modal analysis (OMA) technique that uses dynamic displacement reconstructed from measured acceleration. The reconstructed displacement physically suppresses the high-mode components in measured acceleration data and leads to modal participant factors that are sequentially arranged from low- to high-frequency modes. Thus, compared with the conventional approach that utilizes acceleration data, the proposed procedure provides a more reliable and robust damping estimate regardless of the model order selection. Furthermore, the use of reconstructed displacement guarantees the equilibrium of the system all the time. The OMA adopts a natural excitation technique (NExT) combined with an eigensystem realization algorithm (ERA). A finite element method (FEM)-based finite impulse response filter is adopted to reconstruct the dynamic displacement. The effectiveness and accuracy of the proposed approach is demonstrated for low-frequency dominant structures by using the numerical simulation study of a 9-story shear building and an actual field test of a cable-stayed bridge under operation in Korea. These examples allow a comparison of modal damping ratio estimates using reconstructed displacement and accelerations. [ABSTRACT FROM AUTHOR]