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To address the challenges in predicting the aeroelastic phenomenon and the resulting wind-induced forces on slender bridges, a real-time aeroelastic hybrid simulation (RTAHS) system was developed. The RTAHS system directly measures the aerodynamic and aeroelastic forces through load cells. It controls the next step's position of the deck section model with linear motors by solving the governing equations of motion in real time. Given the complex shape of a bridge deck section geometry, load cells are chosen for force measurement instead of as pressure sensors. In the previous RTAHS system proposed by the authors, the inertial forces of a rectangular section model were eliminated from the measured forces under the assumption of the model's rigid-body motion. However, when conducting RTAHS experiments with a realistic bridge deck section model, increasing the mass ratio between the mass of the model and the target mass input to the hybrid system results in unstable vibrations. This instability is primarily attributed to forces generated by the model's flexibility. This study developed an improved RTAHS system, which took into account the inertial forces arising from the nonrigid motion of the flexible bridge deck section model. An accelerometer was additionally installed at the midpoint of the model, and the inertial forces caused by the nonrigid behavior were compensated using a calibration factor derived from impact hammer tests. This approach was validated by comparing the spring-supported experiments conducted on a realistic bridge deck section model. [ABSTRACT FROM AUTHOR]

A section model test effectively assesses the aeroelastic behavior of long-span bridges in a wind-resistant design. The conventional approach uses springs to support a mass-calibrated physical section model scaled to the similarity principle. Modal damping can also be modeled using sticks soaked in oils. Although this procedure has been successfully applied to most bridges, it involves physical limitations in selecting the model scale and vibration frequencies. Also, certain degrees of time and effort are required for the calibration and modification of dynamic properties in order to achieve precision. This study proposes a new real-time aeroelastic hybrid simulation (RTAHS) approach that eliminates the potential drawbacks of the conventional spring-supported section model test. With this new approach, the aeroelastic force on the physical section model is directly measured using supporting load cells. The equation of motion is solved numerically, and linear electric motors impose the expected movement of the model in a real-time fashion. The hardware of the RTAHS consists of linear electric motors, motor drivers, sensors, and an Ethernet for Control Automation Technology (EtherCAT) based real-time motion controller. The hardware is controlled with three control loops, i.e., numerical integration, time-delay compensation, and PID control of the position. For this study, a series of comparative wind tunnel tests was used to demonstrate the validity of the proposed RTAHS concept. [ABSTRACT FROM AUTHOR]

Considerable levels of stay cable vibration in cable-supported bridges pose significant challenges for safety, operation, and maintenance. An accurate understanding of the specific causes and types of vibration is essential for effectively addressing this problem with an optimal design for mitigation measures. This study aims to investigate the cause of an extraordinary low-frequency vibration that occurred at a stay cable by employing comprehensive methodologies. The modal properties and vibrational characteristics of cable vibrations were first obtained through finite element modeling, operational modal analysis, and vision-based displacement measurements. Subsequently, the primary cause of low-frequency vibrations was investigated using field observations and wind tunnel tests. Field-monitoring data revealed that stay cables were excited by small deck vibrations. The critical wind speeds at which deck vibrations occurred in a wind tunnel experiment were aligned with the ranges of wind speeds that produce low-frequency cable vibrations, which confirmed that these two phenomena are manifested under similar wind conditions. A calculated support excitation amplitude, determined via the use of an empirical equation, exhibited consistency with vision-based measured displacement obtained in field experiments. These findings underscore the potential risk of support excitation between minor deck vibrations and cables, which provides valuable insights that could mitigate cable vibrations. • Investigation into the cause of low-frequency cable vibration in a cable-stayed bridge using finite element analysis, operational modal analysis, wind tunnel tests, and vision-based vibration monitoring. • Findings revealed that the small amount of vortex-induced vibration in the bridge deck, along with the close frequencies between the cable's first-vertical mode and the bridge's second-vertical mode, resulted in support excitation of the cables. • To prevent cable support excitation, it is recommended to suppress even minor levels of vortex-induced vibration during the design phase. [ABSTRACT FROM AUTHOR]

A significant vortex-induced vibration (VIV) was observed in a suspension bridge under a wind velocity of approximately 6 and 7 m/s, and with a maximum amplitude that exceeded the serviceability limitations. Since the observation of VIV in an operating bridge was an infrequent event, this study investigated the cause of unexpected VIV. A series of wind tunnel tests revealed the main cause of the VIV was temporary screens applied over the guardrails to shield the curing surface during replacement of epoxy-coated pavement. The characteristics of the measured VIV were consistent with those from experimental results in terms of amplitude and lock-in wind speed range. The effect of Scruton numbers on VIV amplitude was examined for several dominant modes with different modal mass and damping ratios. Since the VIV amplitude is sensitive to the inherent damping ratio, the modal damping ratios of the bridge were identified from output-only modal analysis by using the frequency domain decomposition. This approach was efficient in identifying the damping ratios of high modes that were challenging due to weakly excited signals. The damping ratio of the triggered mode for VIV was the lowest among the investigated modes and estimated to be the level of the design-damping ratio. [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]

• A differential load cell is developed with a novel Wheatstone bridge circuit. • The inertia of the specimen is automatically negated during measurements. • A finite element model of the load cell is constructed and analyzed. • A prototype of the differential load cell is fabricated. • Shake table and wind tunnel tests are conducted. Load cells, also referred to as force transducers, are widely used in various engineering fields for measuring forces and torques. When load cells measure the forces of moving specimens, the measured force includes the inertia of the specimen. However, in applications where the objective is to quantify the resultant force without the contribution of the specimen's inertia, additional sensors are required, which can result in reduced accuracy or inadequate measurement. To address the inertia coupling effect, this study proposes a new sensor, called a "differential load cell," by combining two load cells using a novel Wheatstone bridge design. The primary load cell measures both the force of interest and the specimen's inertia, while the dummy load cell only measures the latter. The proposed Wheatstone bridge automatically negates the inertia, thereby addressing the coupling effect. Validation tests including wind tunnel experiments are conducted to examine the practicality and applicability of the differential load cell. [ABSTRACT FROM AUTHOR]

Despite the wind-resistant design performed during the design stage, an existing bridge may still experience severe vortex-induced vibrations (VIVs) because of the installation of new affiliated facilities during its operation period. Therefore, it is necessary to apply control measures to suppress the VIV induced by such changes in configuration. In this study, the VIV performance of a streamlined box girder bridge during the installation of new auxiliary piping system was investigated through a series of sectional model tests and flow visualization tests. Severe vertical VIVs of the bridge used in this study were observed at lower wind speed ranges during wind tunnel tests. Based on the flow pattern around the sectional model, it was inferred that the flow across the deck bottom surface was entirely separated by the new pipelines, which resulted in the periodic generation of shedding vortices in the wake zone and induced deck vibration. Twin downward vertical stabilizer plates (TDVS) were found to be an effective aerodynamic countermeasure for improving the VIV performance of the bridge and could significantly decrease the amplitude of the vertical VIV motion. Additional flow visualization investigations showed that after the TDVS were installed, the vortex shedding in the wake was mitigated, and the location of the vortex shedding was further away from the deck, and hence, considerably suppressed the vertical VIVs. It was found that the effectiveness of the TDVS in improving the aerodynamic performance was significantly dependent on the TDVS parameters, i.e., the plate height and spacing between plate elements. The optimal values of these parameters were correspondingly identified for the bridge deck used in this study after a comprehensive evaluation. • VIV performance of a streamlined box girder bridge installing new pipelines are investigated. • Using twin downwards vertical stabilizer plates (TDVS) as an effective countermeasure to suppress the VIV is proposed. • Optimal parameters of TDVS dimension to suppress the VIV are identified for the bridge deck. • Flow pattern around the deck and the underlying aerodynamic mechanism are investigated by the flow visualization. [ABSTRACT FROM AUTHOR]