Torsional Vortex-induced Vibration Research Articles

Experimental study of wind-field characteristics and torsional vortex-induced vibrations for a split three-box deck sitting above water waves

The wind-field characteristics of a split three-box deck sitting above water waves and its torsional vortex-induced vibrations (VIVs) were experimentally investigated using wind-tunnel and wave-flume tests. The wind field was measured using turbulent flow instrumentation (TFI) Cobra probe. To test the VIVs of the split three-box deck, a test system that could elastically suspend the deck sectional model by eight springs and guarantee free oscillation of the deck sectional model only in the heaving and torsional directions was constructed. The test results indicated that the regular wave height (H) and regular wave period (T) mainly promoted the overall turbulence-intensity (Iuvw) and turbulence-intensity component (Iw). These contributions were further strengthened by an increase in H and a decrease in T, respectively. In general, the variations in Iuvw and Iw, particularly the latter, should be regarded as the major cause of the change in the maximum torsional VIV amplitudes of the deck sectional model with a scale ratio of 1:60 when compared to the mean local wind speed (U) and wind-speed component (w). The differences in these amplitudes under different cases in the first lock-in regions were not evident, whereas those in the second lock-in regions were significant. In the second regions, the smaller the relative bridge clearance (a/H), the smaller the maximum torsional VIV amplitudes, and the maximum torsional VIV amplitudes increased with T, which were all smaller than those in the corresponding wind-only case. Moreover, the larger the bridge clearance (a), the larger the maximum torsional VIV amplitudes in the wind-only cases (a = 0.30, 0.42, 0.50, and 0.58 m). Evidently, the presence of water waves is conducive to the suppression of torsional VIVs of the split three-box deck when VIVs occur.

Study on VIV performance of streamlined steel box girder of a sea-crossing cable-stayed bridge

The frequent occurrence of vortex-induced vibrations (VIVs) poses significant challenges for the operations of large-span sea-crossing bridges subjected to wind loads. A wind tunnel test device for large-scale section models is developed for a sea-crossing bridge to investigate the VIV performance of a streamlined box girder. A new type of aerodynamic countermeasure combining horizontal stabilizers and deflectors is proposed to address vertical and torsional VIV mitigation. To achieve optimal control effects, adjustments are made to the layout of deflectors and the width of horizontal stabilizers. The effects of varying structural damping ratios and low turbulence on vertical VIVs are also thoroughly examined. The VIV triggering mechanism of the girder by maintenance rails is revealed through numerical simulations using the Shear Stress Transport (SST) k−ω model. Finally, the suppression mechanism of the countermeasures is elucidated. The instantaneous vorticity distribution indicates that implementing the countermeasures effectively reduces the size of alternating shedding vortices on the trailing edge of the main girder. This research provides valuable insights into the VIV mitigation of streamlined box girders.

Spatio-temporal distribution of aerodynamic forces and their associated vortex drift patterns around a closed-box girder during torsional vortex-induced vibration

Torsional vortex-induced vibrations (VIVs) pose potential risks to prototype bridges with increasing spans and lower damping levels. However, the underlying mechanism remains unclear. Wind tunnel tests revealed that torsional VIVs occurred at an initial attack angle of + 3°. To unravel the VIV mechanism throughout the lock-in range, encompassing the ascent stage, amplitude extremum, and descent stage, the spatio-temporal distribution of aerodynamic forces around the bridge girder was analyzed. The results demonstrated the presence of traveling pressure waves with approximately 2.5 wavelengths and three uniformly distributed separated vortices over the upper side throughout the lock-in range. The primary source of these travelling pressure waves stemmed from the vortex drift patterns, with the aerodynamic wave travelling velocity equating the vortex drift velocity. The formation of separated vortices, known as the “double-vortex model”, occurred at the windward barrier on the upper side and windward maintenance rail on the lower side. These vortices directly imposed travelling pressure waves on the girder, thereby inducing torsional VIVs. Among them, the former vortices contributed more to the VIVs than the latter. Therefore, the formation of separated vortices and their related aerodynamic waves in the windward edge with the 2nd SVM/AWM modes predominantly governed the occurrence of torsional VIVs. Furthermore, both the ratio of the wave travelling time to the vibration period and the mean value of the wave travelling velocity ratio exhibited an inverse relationship with the VIV responses. However, the actions exerted by the vortex drift patterns were proportional to the VIV responses on both the upper and lower sides. Therefore, there existed evolutionary characteristics of aerodynamic waves and their related vortex drift patterns throughout the lock-in range, which was responsible for the “lock-in” phenomena.

Experimental studied on suppressing vortex-induced vibration of closed-box girder bridges with various moveable guide vanes

A new moveable guide vane with the combination of the spring and guide vane was proposed to suppress the vortex-induced vibration (VIV) of closed-box girder bridges. This paper studies the influence of two important parameters (i.e., horizonal length and spring stiffness) of a moveable guide vane on controlling the VIV of a super long-span suspension bridge with closed-box girder by using VIV control tests. The VIV test of 1:50 scaled ratio of sectional model of the original closed-box girder under three wind attack angles were firstly conducted. The suppression ratios of vertical and torsional VIV displacements of the closed-box girder as well as the movement characteristics of moveable guide vane were then analyzed, respectively. The results show that the movable guide vane could significantly reduced the Root Mean Square (RMS) values of VIV displacement of the closed-box girder are after installing, especial for the torsional VIV displacement. A moveable guide vane with a relative smaller horizontal lengths or a relative larger spring stiffness could produce a better outcome of VIV control. The double VIV amplitude of the moveable guide vanes results in the energy dissipation of the closed-box girder in the lock-in VIV wind speed region, while the vertical displcement of the moveable guide vane are close to those of the closed-box girder in non-VIV wind speed region. Besides, the nonlinear exponential fitting function could effectively reflect the relationship among the wind speed, the VIV displacement of the MGV and the closed-box girder.

Research on Mechanism of Vortex-Induced Vibration Railing Effect of Double-Deck Large-Span Suspension Bridge

Large-span suspension bridges are susceptible to wind loads. Therefore, a more precise analysis of their wind-induced vibration response is necessary to ensure the structure’s absolute safety. This investigation conducted wind tunnel tests for the construction and completion stages to reveal the vortex-induced vibration (VIV) phenomenon of a double-deck suspension bridge. The results showed that no VIV occurred during the construction stage. However, the inclusion of railings significantly deteriorated the aerodynamic performance of the suspension bridge, leading to significant VIV at +3° and +5° wind angles of attack. Additionally, reducing the railing ventilation rate can significantly suppress the VIV amplitude. A new analysis method based on computational fluid dynamics (CFD) simulation is proposed to investigate the VIV mechanism of the double-deck truss girder. Twenty-nine measurement points were used to explore the vortex that causes VIV. The numerical simulations found that the area above and aft of the upper deck dominated the vertical VIV, while the aft of the lower deck dominated the torsional VIV. Furthermore, the intensity of the vortex in these areas was significantly lower during the construction stage. Moreover, reducing the railing ventilation rate significantly suppresses the torsional VIV by reducing the intensity of the vortex in the region behind the lower deck.

Investigation of Vortex-Induced Vibration of Double-Deck Truss Girder with Aerodynamic Mitigation Measures

The long-span double-deck truss girder bridge has become a recommend structural form because of its good performance on traffic capacity. However, the vortex-induced vibration (VIV) characteristics for double-deck truss girders are more complicated and there is a lack of related research. In this research, wind tunnel tests were utilized to investigate the VIV characteristics of a large-span double-deck truss girder bridge. Meanwhile, the VIV suppression effect of the aerodynamic mitigation measures was measured. Furthermore, the VIV suppression mechanism was studied from the perspective of vortex shedding characteristics. The results indicated that the double-deck truss girder had a significant VIV when the wind attack angles were +3° and +5°. The aerodynamic mitigation measures had an influence on the VIV response of the double-deck truss girder. The upper chord fairing and lower chord inverted L-shaped deflector plate played a crucial role in suppressing VIV. Numerical analysis indicated that vortex shedding above the upper deck or in the wake region may dominate vertical VIV, while vortex shedding in the wake region of the lower deck may dominate torsional VIV. The upper chord fairing and lower chord inverted L-shaped deflector plate disrupted the original vortex shedding pattern in both regions, thereby suppressing VIV. This research can provide a foundation for bridge design and vibration suppression measures for large-span double-deck truss girder bridges.

Aerodynamic performance evaluation of steel-UHPC composite deck cable-stayed bridges with VIV countermeasures

The steel-ultrahigh performance concrete (UHPC) composite girder makes the bridge deck thinner and more streamlined, but their effects on the aerodynamic performance of cable-stayed bridges are unclear. With the developed equivalent girder analysis method, the overall aerodynamic performance (e.g. vortex-induced vibration (VIV), flutter, aerostatic and buffeting performance) of a steel-UHPC composite girder cable-stayed bridge with various VIV countermeasures are systematically evaluated by conducting a series of wind tunnel tests and numerical calculation. The results show that the developed equivalent girder analysis method could simplify the sectional model design of the composite girder for wind tunnel tests. Only the guide vane removal cannot suppress the torsional VIV responses among various combinations of guide vanes removal, while the two VIV countermeasures (e.g. the removal of outside railing cornerstones, the removal of four guide vanes and outside railing cornerstones) could reach about 76% and 72% of the torsional VIV amplitudes, respectively. Although two VIV countermeasures could slightly reduce the critical flutter wind speed, their torsional divergence critical wind speeds are much larger than the limited design requirement. Moreover, the removal of four guide vanes and outside railing cornerstones has the capacity of improving the aeroelastic and buffeting performance of the bridge, as the best overall aerodynamic performance.

Vortex-induced vibration characteristics of two open girders: A comparison of experimental and numerical investigation

Open girder sections are vulnerable to vortex-induced vibrations (VIV) because of their bluff aerodynamic characteristics. A comparative investigation was conducted by wind tunnel tests and numerical simulation. Firstly, based on sectional model wind tunnel tests, the VIV performance of semi-open girder and separated edge-boxes open girder was studied with consideration of the influence of the equivalent mass, wind attack angle and damping ratio. The aerodynamic parameters Scruton number ( S c) and Strouhal number ( S t) of two girders were analyzed contrastively. In addition, VIV amplitudes corresponding to the real bridge girders were calculated by the linear and nonlinear theories. Then, flow fields around two semi-open girder sections were investigated on the basis of computational fluid dynamics. The results show that vertical and torsional VIVs of two open girders are observed, at +3°and +5° wind attack angles. There were two vertical VIV regions and the maximum amplitude in the second vertical VIV region is significantly larger than that in the first one. For the semi-open girder and separated edged-box open girder, the vertical VIV amplitudes at +5° wind attack angle is 115% and 75% larger than at +3° wind attack angle, respectively. The damping ratio could obviously mitigate the VIV of two girders and VIV amplitudes are decreased linearly with the S C number increases. There are vortexes above the girder deck at the opening position of the semi-open girder and the separated edge-boxes open girder. The oblique web and wind faring may break the large vortex into several smaller vortexes at the opening position, thus optimizing the vortex vibration performance of the girder. A thicker shear layer is formed at separated open-girder during the development of airflow towards backward of bridge deck, due to the effect of railings and the blunt boxes on the lower surface.

Control of Vortex-Induced Vibration of a Long-Span Bridge by Inclined Railings

The addition of railings inevitably changes the aerodynamic shape of a main girder, which in turn has a great effect on the vortex-induced vibration (VIV) of a long-span bridge. To ensure the railing has a positive effect, this study presents an inclined railing with improved columns arranged with a spanwise distance of 1–5H (H is the height of the bridge). The design of the improved column is inspired by a passive vortex generator (PVG). The streamwise vortices developed downstream of PVG columns can trigger the three-dimensional instability of a wake, making the shear layer less susceptible to rolling up into mature vortex streets, which are the source of VIV. An experimental study is conducted to compare the influence of traditional and inclined railings on the VIV performance of a closed-box section bridge. It is shown that the addition of a traditional railing deteriorates the VIV performance of the bare girder. However, both vertical and torsional VIVs can be completely suppressed by installing an inclined railing. The results of wake analysis indicate that an inclined railing can greatly decrease the streamwise fluctuation velocity and reduce the spanwise correlation of the streamwise velocity in the wake.

Investigation of vortex-induced vibration of a cable-stayed bridge without backstays based on wind tunnel tests

Cable-stayed bridges without backstays located in the abrupt valley are sensitive to wind-induced structural vibrations. The understanding of vortex-induced vibration for specific aerodynamic configuration with glass deck is of great importance for structure design. This paper thus aims to investigate the vortex-induced vibration of a cable-stayed bridges without backstays through the segmental model test and scaled full-aeroelastic model wind tunnel test. The results indicate that the bridge presents the vertical vortex-induced vibrations at the low wind speed whereas the maximum wind velocity causing the torsional vortex-induced vibrations increases to 41 m/s, which is much larger than that of the traditional bridge. The vertical and torsional vortex-induced vibrations in the smooth flow are observed at the positive wind angle of attack, owing to the responses for the bridge deck present a sharp single-frequency amplitude when the frequency of vortex-shedding is close to the flexural vibration frequency. The turbulence can effectively suppress the vortex-induced vibrations and only some small peaks are visible in the turbulent flow. The vortex-induced response of the bridge deck is significantly alleviated with increasing of damping ratio. Finally, the vortex-induced vibrations in the uniform flow disappear and the wind-induced responses are impaired with the ventilated railing in place of the airtight railing because the flow can go through the railing. It can provide a designing basis for engineering reference of cable-stayed bridges without backstays.

Investigation on aerodynamic force nonlinear evolution for a central-slotted box girder under torsional vortex-induced vibration

Central-slotted box girders are widely employed in long-span bridges owing to their advantageous flutter stability. However, the existence of a central slot can degrade their performance under vortex-induced vibrations (VIVs). To clarify the aerodynamic characteristics of a typical central-slotted box girder during VIVs, sectional model wind tunnel tests involving the synchronous measurement of pressure distributions and VIV responses were performed. The computational fluid dynamics (CFD) technique was also used to demonstrate the flow pattern development during VIV before qualitatively explaining the VIV mechanism of the central-slotted box girder. The surface pressure distributions at various amplitude-dependent VIV stages were measured and examined. The evolution of the aerodynamics was investigated from the perspective of the work done by the vortex-excited force (VEF). It was found that the aerodynamic effects on a central-slotted box girder during VIVs are featured with apparent nonlinear evolutionary characteristics. During the lock-in period, the wind-induced pressures at both upper and lower surfaces of the downstream box and the pressures at upper surface of the upstream box make greater contributions to the VEF, which are the main excitation sources of the torsional VIV. However, the contributions of the downstream and upstream boxes are opposite, showing positive and negative correlations with the VEF, respectively. It demonstrated that the positive contribution of the pressures at both upper and lower surfaces of the downstream box weakens the VIV performance of the central-slotted box girder as compared with a streamlined box girder. In addition, the central slot, which improves the correlating flow between the upper and lower regions around the downstream box, causes the distributed aerodynamic forces in these regions to enhance the VEF and perform positive work. This provides a reasonable explanation as to why the VIV effects of central-slotted box girders are typically stronger than those of streamlined box girders.

Torsional vibration of a circular cylinder with an attached splitter plate in laminar flow

Splitter plates have been recognized as useful passive devices to reduce drag, mitigate flow-induced vibration, and enhance heat transfer efficiency of a circular cylinder. However, undesired torsional flow-induced vibrations due to splitter plate attachment require further investigation. This paper numerically studies the flow-induced torsional vibrations of an elastically mounted circular cylinder with an attached splitter plate in laminar flow with a Reynolds number of 100. A finite volume formulation is utilized to solve the incompressible two-dimensional fluid governing equations. Torsional vortex-induced vibrations (VIVs) are observed at lower reduced flow velocities, while a symmetry-breaking bifurcation occurs as the reduced flow velocity increases, after which the cylinder-plate assembly vibrates around a nonzero equilibrium angle. The numerical results show that the synchronization range of VIV extends, the peak VIV amplitude increases, and the critical reduced flow velocity for the bifurcation decreases with decreasing the moment of inertia. The symmetry-breaking bifurcation is due to a combined effect of the structural restoring moment and the flow-induced moment. The critical reduced velocity of the bifurcation and the nonzero equilibrium angle at any reduced velocity can be calculated based on the mean moment coefficients of the cylinder-plate assembly. The flow-induced moment is mainly induced by the pressure difference between the splitter plate's upper and lower surfaces. The phase difference between the torsional moment and displacement is 0° at lower reduced velocities, while the phase difference jumps to 180° at a reduced velocity of approximately 6.5. The mean drag coefficient of the vibrating cylinder-plate assembly is lower than the mean drag coefficient of a stationary circular cylinder but often higher than that of a stationary cylinder-plate assembly. The dominant frequency of the drag force is twice the vibration frequency before the symmetry-breaking bifurcation, while the dominant frequency becomes consistent with the vibration frequency after the bifurcation. The typical 2S mode of vortex shedding is identified for all considered moments of inertia and reduced flow velocities. However, the timing of a non-shedding vortex changes at the critical flow velocities for the phase jump and symmetry-breaking bifurcation. The observed torsional vibrations suggest that circular cylinders with splitter plate attachments may be competitive candidates for VIV-based energy harvesting, while they may not be good choices for heat exchangers.

Suppression of vortex-induced vibration of a box girder using active suction-jet slit

An active suction-jet flow control method was employed to suppress vortex-induced vibrations (VIVs) of a single-box girder based on a wind tunnel test. The flow structure around a fixed model was measured by time-resolved particle image velocimetry (PIV), and the stability of the flow field was evaluated in the controlled and uncontrolled cases according to the solution of the Orr–Sommerfeld equation. The PIV results show that the maximum value and distribution region of the turbulence kinetic energy were alleviated. The linear stability analysis indicates that the unsteady flow of the controlled cases was pushed downstream. The vibration response and flow structures of vertical and torsional vortex-induced vibrations (V- and T-VIVs) were then investigated. The results show that the amplitudes of V-VIVs and T-VIVs were greatly suppressed by the active suction-jet slit, and the momentum coefficient at 0.0301 had the most-effective control. Moreover, time-resolved PIV was utilized to investigate the flow structures of the baseline and optimal control cases. The results indicate that the vortex dissipation behind the optimal control case was accelerated, and the topological structure in the wake changed. The vortex contours show that the jet flow strongly interacted with the separated layer and alleviated the interaction of shear flow from the upper and lower surfaces, thereby weakening the unsteady aerodynamic force acting on the test model and mitigating the VIVs. Furthermore, a test of the flutter performance indicated that the critical velocity of flutter in the optimal case improved slightly.

Vortex-induced Vibration and Control of Split Three-Box Girder Bridges

The vortex-induced vibration (VIV) performance and aerodynamic mechanism of VIV control of a split three-box girder bridge were investigated numerically by Computational Fluid Dynamics (CFD). Large-scale section model wind tunnel tests show that the integrated countermeasure combined by 30% ventilation ratio grids and new scheme for maintenance tracks can effectively restrain vertical and torsional VIVs. The reliability of numerical method is verified by comparing static three-component coefficients and Strouhal numbers obtained from CFD and wind tunnel tests. The flow structure and changes of aerodynamic forces were analyzed via delayed detached-eddy simulation (DDES). For the original section, large-scale vortices form with shedding behind the safety barrier of the upstream box and behind the maintenance tracks, as well above the downstream highway box, introducing periodic pulsating lifts and moments that result in severe VIVs. The grids can effectively reduce the size of vortices in the gaps, prevent the flow from fluctuating and reduce the pressure difference between upper and lower surfaces. The torsional VIVs at non-negative attack angles are not controlled because the grids cannot interfere with the vortices behind the maintenance tracks. The new scheme for maintenance tracks, which has grid-like effects, can eliminate the torsional VIVs at non-negative attack angles by preventing the vortices behind maintenance tracks from impacting downstream boxes. The aerodynamic force components are analyzed to find that box 1 mainly contributes the mean values and box 3 mainly contributes the fluctuating values. The integrated countermeasure can reduce the mean and RMS values of aerodynamic forces to varying degrees. The streamlines and RMS pressure contours indicate that the integrated countermeasure effectively reduced the wake height and vortices motion range, which is conducive to VIV control. This work lays a solid foundation for an in-depth understanding of the aerodynamic characteristics and optimization mechanism of split three-box girder bridges.

Experimental and numerical studies of wind-resistance performance of twin-box girder bridges with various grid plates

The thin-walled grid plate is one of the passive aerodynamic measures for suppressing vortex-induced vibration (VIV) of twin-box girder bridges. However, the effectiveness of the grid plate in aerodynamic stabilization is not fully known. In this study, we compared the flutter performance and aerostatic performance, as well as VIV performance, of a twin-box girder suspension bridge with four different grid porosities, through a series of wind-tunnel tests and three-dimensional nonlinear finite-element analyses. Results show that a thin-walled grid plate with larger grid porosity could effectively improve both the flutter performance and aerostatic performance of the bridge. This was particularly true with a plate of 100% grid porosity. Based on the 3D nonlinear bridge finite-element model, the flutter divergence mode of a 3D bridge is caused mainly by symmetrical vertical bending as grid porosity increases. Furthermore, the torsional VIV performance of a twin-box girder with smaller grid porosity is superior to those with larger grid porosity, and the application of grid plates of 30% and 50% porosity can result in VIV performance that complies fully with both the wind-resistance specification of China and the Sperling indicator.

External suction-blowing method for controlling vortex-induced vibration of a bridge

To suppress the vortex-induced vibration (VIV) of long-span bridges, an active flow control method, i.e. the external suction-blowing method (ESBM), is proposed in this study based on the efficiency of the three-dimensional spanwise-varying flow control method and the suction/blowing flow control method. The method can be achieved by cyclically arranging suction and blowing on the undersurface of the bridge. The effectiveness of the method for the vertical and torsional VIV of the bridge sectional model is verified through wind tunnel tests. The test results imply that the best perturbation position of the ESBM is the leading edge of the undersurface of the bridge. For dimensionless spanwise distances of 2–4 with single-hole flow coefficients of 2.27 × 10−3–3.03 × 10−3 and 1.45 × 10−3–1.94 × 10−3 during vertical and torsional VIV, respectively, the VIV can be completely suppressed. The results of the wake analysis show that this method can effectively suppress the scale of the spanwise vortex of the bridge, causing the VIV to disappear.

Effects of leading-edge separation on the vortex-induced vibration of an elongated bluff body

Wind-tunnel experiments were conducted to investigate the effects of leading-edge separation on the vortex-induced vibration (VIV) of an elastically-supported elongated bluff body. Solid wind barriers of various heights were fixed in the leading edge to adjust the flow separation. The vibration signals and the flow field information are acquired simultaneously by a laser-displacement system and particle image velocimetry (PIV) instrument respectively. The result shows that the VIV is excited by consecutive vortices shedding from the leading-edge shear layer. There is a critical height-to-thickness ratio (h/t)critical=0.4, the VIVs are observed when h/t≥0.4, while they are suppressed owing to the insignificant leading-edge separation when h/t<0.4. Three types of VIV are found, two of them are torsional VIV while another one is vertical VIV, which are named T1, T2, and V1 respectively. By placing a wake splitter plate at the trailing edge, V1 is suppressed entirely, T1 is weakened despite the slightly lower amplitude, while T2 transits to limit-cycle oscillations. The flow field information shows that the evolution and shedding pattern of leading-edge vortices vary from mode to mode. The status of the upper-layer leading-edge separated layer significantly affects the formation and the shedding of the trailing-edge vortices. The results reveal that leading-edge separation can play a dominant role in the vortex-induced vibrations of elongated bluff bodies.

Aerodynamic performance of Π-shaped composite deck cable-stayed bridges including VIV mitigation measures

This study systematically investigates the influence of the cross-sectional aspect ratio (B/H) and four different aerodynamic mitigation measures, i.e., the fairing, lower central stability plate, inverted L-shaped edge plate, and lower horizontal edge plate, on the performance of cable-stayed bridges, with π-typed composite deck, i.e., π section, due to vortex-induced vibrations (VIV). The study utilized wind tunnel tests and limited CFD simulations by varying bridge dimensions. First, based on a survey of existing cable-stayed bridges with the π-typed composite deck, three-section models with different aspect ratios were studied and their corresponding vibration characteristics for the vertical and torsional VIVs were analyzed. Then, the vibration suppression effects of mitigation measures with several variants in shape were investigated to determine an effective mitigation measure, i.e., with favorable aerodynamic stability, for the π section deck. The vibration suppression mechanism for three selected cases was further assessed using numerical simulation. The results show that: (a) for the π section model with the aspect ratio in the range of 9.05–11.96, increasing the ratio value will delay the onset wind speed of the vertical and torsional VIVs; (b) In the case of a low ratio of the torsional frequency to vertical bending frequency, there are often special phenomena where the vertical and torsional vibrations coexist. However, a larger aspect ratio would result in more independent vertical and torsional vibrations; (c) Regarding the vibration suppression effect, based on the limited studied cases, a small fairing can be superior to large fairings; (d) Different forms of the lower central stability plate have a good suppression effect on the vertical VIV; (e) The use of inverted L-shaped edge plate with a ​= ​23H and b ​= ​12H is identified to result in the best vibration suppression for both the vertical and torsional vibrations among the considered mitigation measures, where a and b are the size parameters of the inverted L-shaped edge plate; and (f) The lower horizontal edge plate cannot effectively improve the torsional VIV performance. This study offers guidance on the performance of composite cable-stayed bridge with the π section in isolation and equipped with mitigation measures to aid in the engineering design practice.

Experimental and numerical study on vortex-induced vibration of a truss girder with two decks

Vortex-induced vibration (VIV) depends on aerodynamic shapes of bridge girders, which should be treated carefully in the design of long-span bridges. This paper studies the VIV performance of a suspension bridge with the truss girder which contains two separated decks. Although truss girders generally show better VIV performance than box girders, significant vibrations of this type of girders occurred in the wind tunnel tests based on a large-scale sectional model. Several lock-in regions with the same vibration frequency were observed, corresponding to different shedding vortices. Computational fluid dynamics (CFD) simulations were carried out, and monitoring points were set behind different components to study the characteristics of the shed vortices. As the truss girder consists of many members, the results show that various vortices with different dominant frequencies are formed in the wake flow. The vertical VIV of the bridge is probably driven by the vortices behind or above the upper deck, which is related to the guardrails. The torsional VIV of the bridge is probably driven by the vortices behind or below the lower deck, which is related to the service road at lower wind speeds while may be related the vertical stabilizers at higher wind speeds.

An alternative aerodynamic mitigation measure for improving bridge flutter and vortex induced vibration (VIV) stability: Sealed traffic barrier

This study proposes an alternative aerodynamic mitigation measure, i.e., sealed traffic barrier, for bridges and verifies its efficacy in improving the flutter and vortex induced vibration (VIV) stability of bridges through wind tunnel tests for three distinctive real-world bridge projects. The results show that: (1) The measure of the sealed traffic barrier with regular intervals along the bridge deck has a significant influence on the flutter and VIV performance of the bridge. Thus, a reasonable design of the traffic barrier can simultaneously improve the bridge’s flutter and VIV stability; (2) The sealed traffic barrier with vertical intervals along the bridge can effectively suppress the vertical VIVs of the bridge, while the sealed traffic barrier without vertical intervals, i.e., configured continuously along the bridge, has a better vibration suppression effect on the torsional VIV than that on the vertical VIV; (3) This proposed measure installed on both sides of the bridge deck imposes favorable suppression effect for the flutter vibration, similar to the upward central stabilizer. In case with the sealing form fixed, but a reduced height, for the barrier, the flutter stability at different wind attack angles is slightly decreased; and (4) In certain scenarios, increasing the ventilation rate of the traffic barrier results in an increase for the flutter critical wind speed at positive wind attack angles, but a decrease for the flutter critical wind speed at negative wind attack angles. This aerodynamic mitigation measure has been successfully applied to more than ten other bridge projects based on the wind tunnel tests by the leading authors, offering a reliable approach in improving both flutter and VIV for bridges.