Section Model Wind Tunnel Test Research Articles

Investigation of vortex-induced vibration of a Π-type bridge girder and its suppression using G-shaped apron combination measure

The Π-type steel-concrete composite girder, a commonly used bridge deck composed of an upper concrete slab and two lower lateral I-side steel girders, often suffers from severe vortex-induced vibrations (VIVs). Herein, the VIV response and triggering mechanism of a Π-type girder are systematically investigated, by adopting 1:50 scale section model wind tunnel tests and flow-field numerical simulations. Afterward, several aerodynamic measures were designed to mitigate the significant VIVs present in the original section, and an effective measure composed of the G-shaped apron and lower central stabilizer plate was found. Numerical simulation results show that the Π-type girder's upper and lower surfaces both exhibit severe vortex shedding, and both contribute significantly to the occurrence of VIVs. Consequently, the aerodynamic measures introduced for the Π-type girder must be able to simultaneously improve the flowing bypassing situation around the upper and lower surfaces of the section, and the G-shaped apron and the lower central stabilizer plate could both accomplish this simultaneously. The results show that the VIV suppression effect of this G-shaped apron combination measure is greatly affected by the height of the G-shaped apron's vertical plate and the height of the lower central stabilizer plate. Only both of them to a certain height, this measure can entirely prevent the Π-type girder from VIVs. After shape optimization, a G-shaped apron combination aerodynamic measure that can eliminate completely the Π-type girder's VIVs at low damping ratios of about 0.5% is proposed, of which the vibration-suppressing effect was verified by wind tunnel testing of 1:20 section model.

Full bridge analysis of nonlinear vortex-induced vibration considering incomplete span-wise correlation of vortex-induced force

Responses of vortex-induced vibration (VIV) of long-span bridges are commonly measured at first via wind tunnel tests of sectional model and then converted to the prototype ones of the corresponding full bridges by some approximate formulae. In this paper, a time-domain full bridge analysis method was presented for predicting nonlinear VIV responses mode-by-mode based on a polynomial type of nonlinear mathematical model of vortex-induced force (VIF) on bridge deck cross section. In this method, the motion-dependant self-excited force (SEF) components of VIF were regarded as fully correlated span-wise in the case of smooth flow, while the motion-independent harmonic pure vortex-shedding force (PVSF) component of VIF was regarded as incompletely correlated along the bridge span. To take into account the incomplete span-wise correlation of PVSF, an equivalent generalized PVSF including the effect of the incomplete span-wise correlation of PVSF was defined by using a span-wise correlation coefficient of PVSF which could be obtained through a sectional model wind tunnel test of simultaneous pressure measurement. As an application example, the VIV responses of 12 vertical modes of a steel box deck cable stayed bridge with a main span of 688 m were analysed, and were compared with those converted with two approximate converting formulae, respectively, based on Scanlan’s linear and nonlinear mathematical model of VIF. It is found that the influence of the incomplete span-wise correlation of PVSF on the bridge VIV response is very small and can then be ignored.

Sectional Model Wind Tunnel Test and Research on the Wind-Induced Vibration Response of a Curved Beam Unilateral Stayed Bridge

The linear curve distribution of the beam and the asymmetrical layout of the stay cables may have beneficial or adverse influences on cable-stayed bridges. Sectional model wind tunnel tests and numerical simulations were used to analyze the influence of these two factors on the wind-induced vibration characteristics of a curved beam unilateral stayed bridges (CBUSB) and the interaction between its stay cables and curved beams. According to the basic similarity law, the sectional models of a CBUSB example were designed and manufactured. The aerodynamic force and wind-induced vibration of the models were measured in an atmospheric boundary wind tunnel laboratory to obtain the aerodynamic coefficient and displacement, respectively. Based on the wind tunnel test results, the verified finite element model was used to determine the displacement, acceleration, and cable tension of the CBUSB excited by the buffeting force under 5 curvature cases and 4 cable layout cases. Then, band-pass filter technology and fast Fourier transform technology were used to analyze the influence of these two parameters on the wind-induced vibration characteristics of the CBUSB. Results show that the CBUSB had good aerodynamic stability in the wind tunnel at low and high wind speeds. With increasing curvature, the high-order modal vibration and modal coupling vibration of the CBUSB may be generated. The frequency, the proportion of wind-induced vibration response components, and the distribution characteristics of spectrum energy of CBUSB will be affected by 4 cable layout schemes. Cables arranged on both sides of the bridge and near the center of curvature can improve pedestrian comfort and reduce wind-induced vibration, respectively. Affected by the interaction between cable and bridge, the cable and bridge transmit their own vibration to each other, both of which contain the response components of each other.

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.

WIND TUNNEL TEST ON TRI-COMPONENT FORCE COEFFICIENTS OF THE TRAIN-BRIDGE SYSTEM FOR A LONG-SPAN RAIL-CUM-ROAD CABLE-STAYED TRUSS BRIDGE

To investigate the aerodynamic characteristics of train-bridge systems in a complex traffic condition, a section model wind tunnel test was carried out for a long-span rail-cum-road cable-stayed truss bridge. The tri-component forces on the train-bridge system were measured under different angles of attack when a single train, two trains or three trains passed. The effects of the track positions, bridge towers, road traffic flows, meeting of the trains on the tri-component coefficients of the vehicle and the truss were studied. The results show that when a train moves from the windward track to the leeward, the drag coefficients of the vehicle and the truss gradually decrease, while the lift coefficient of the vehicle and the moment coefficient of the truss reach the maximum on the leeward track. As a train passes through the tower, the average surface wind pressure of the shielded vehicle is significantly reduced, and the shielding effect is most obvious when it is on the windward track. However, the surface wind pressure near the tower edges remarkably fluctuates. When two trains meet on the bridge, the drag and lift coefficients of the vehicle increase with the meeting spacing. When three trains meet on the bridge, the drag and lift coefficients of the vehicles behind the windward train significantly decrease. The middle train has the smallest lift coefficient and a negative drag coefficient. As the number of trains on the bridge increases, the drag and lift coefficients of the truss gradually increase, while the moment coefficient remains almost the same.

Wake-induced vibrations of iced pin joint hangers of suspension bridges based on wind tunnel test and new method of transiting test

The wind-induced vibration of suspension bridge hangers may be due to hanger icing. This study presents a new test method named transiting test method, combining with the section model wind tunnel test, to investigate the wake-induced vibrations of iced pin joint hangers under limited conditions. Results reveal that according to wind tunnel test and DenHartog galloping theory, the attack angle of 3° is the angle at which the wake galloping of iced pin joint hangers is most likely to occur. The driving wind field is stable in the transiting test and exhibits relatively minimal interference from the external factors under limited conditions. The predominant frequencies of vehicular vibration in the transiting test exhibit no marked relation with the fundamental frequency of the model, thereby demonstrating transiting test can satisfy the requirements of wind-resistant research on iced pin joint hangers. The wake galloping-reduced wind speed of iced pin joint hangers with D-shaped ice and a 30 mm icing thickness is 165, and the leeward iced hanger is vulnerable to endurance failure. The wake galloping critical wind speed of pin joint hangers with icing is lower than that without icing. The findings have important implications for the wind-resistance of suspension bridges with pin joint hangers.

Comfort Evaluation of Double-Sided Catwalk for Suspension Bridge due to Wind-Induced Vibration

Buffeting response of a double-sided catwalk designed for Maputo Bridge was investigated considering wind load nonlinearity, geometric nonlinearity, and self-excited forces. Buffeting analysis was conducted in time domain using an APDL-developed program in ANSYS, and the results were compared with the buffeting response under the traditional linear method. The wind field was simulated using the spectra representation method. Aerostatic coefficients were obtained from section model wind tunnel test. Parameter study has been carried out to investigate the effects of cross bridge interval and the gantry rope diameter on buffeting response. Referring to the ISO 2631-1(1997) standard and the annoyance rate model, the comfort of catwalk due to wind-induced vibration was evaluated. The results indicate that traditional linear calculation methods will underestimate the buffeting response of the catwalk, and enlarging the gantry rope size as well as decreasing the cross bridge interval would increase the comfort level. Moreover, the effect of gantry rope diameter was obvious than that of cross bridge interval. Annoyance rate model can evaluate the comfort level quantitatively compared to the ISO standard.

Aerodynamic characteristics of trains on a viaduct with non-uniform cross-section under crosswinds by wind tunnel tests

This paper focuses on the aerodynamic characteristics of trains on a non-uniform double-track railway bridge under crosswinds through a scaled 1:40 sectional model wind tunnel test. Pressure measurements of five cross-sections of two types of trains, one with round roof and one with blunt roof, at the upstream and downstream tracks of the bridge were conducted under crosswinds with wind attack angles between −12° and 12°. The mean wind speed and turbulence intensity profiles around the windward surface of the train in the downwind and upward directions were also measured using cobra probe to obtain the boundary layer above the bridge surface. The results show that the shapes of train and bridge, as well as the wind attack angle, affect the aerodynamic characteristic of the train on the non-uniform bridge girder. The mean and fluctuating pressure coefficients are similar for all five cross-sections of the trains while the train is at the upstream track. However, when the train is at the downstream track, the extreme mean and fluctuating pressure coefficients around the windward and top surfaces of each cross-section on the train are different. At the downstream track, the mean wind speed profile and the turbulence intensity profile around the top of the train vary dramatically due to the separation flow caused by the leading edge of the bridge girder.

Effects of Vertical Motion on Nonlinear Flutter of a Bridge Girder

Abstract This study addresses the effects of vertical motion on the nonlinear flutter response of a double-deck truss girder based on section model wind tunnel tests. Six dynamic systems with the s...

Flutter mitigation of a superlong-span suspension bridge with a double-deck truss girder through wind tunnel tests

As flutter is a very dangerous wind-induced vibration phenomenon, the mitigation and control of flutter are crucial for the design of long-span bridges. In the present study, via a large number of section model wind tunnel tests, the flutter performance of a superlong-span suspension bridge with a double-deck truss girder was studied, and a series of aerodynamic and structural measures were used to mitigate and control its flutter instability. The results show that soft flutter characterized by a lack of an evident divergent point occurred for the double-deck truss girder. Upper central stabilizers on the upper deck, lower stabilizers below the lower deck, and horizontal flaps installed beside the bottoms of the sidewalks are all effective in suppressing flutter for this kind of truss girder. By combining the structural design with aerodynamic optimizations, a redesigned truss girder with widened upper carriers and sidewalks, and double lower stabilizers combined with the inspection vehicle rails is identified as the optimal flutter mitigation scheme. It was also found that the critical flutter wind speed increases with the torsional damping ratio, indicating that the dampers may be efficient in controlling soft flutter characterized by single-degree-of-freedom torsional vibration. This study aims to provide a useful reference and guidance for the flutter design optimization of long-span bridges with double-deck truss girders.

Hysteresis response of nonlinear flutter of a truss girder: Experimental investigations and theoretical predictions

Nonlinear flutter response with hysteresis loop characteristics is a special aerodynamic instability phenomenon, and is of great importance and of practical interest to long span bridge designs. This paper presents a comprehensive study on nonlinear flutter of a bridge deck that has hysteresis loop characteristics over a range of wind speeds close to the flutter onset speed, using a section model wind tunnel test and theoretical analyses. The evolutions of the hysteresis loop in both the single degree of freedom (SDOF) system in torsion and the 2 degrees of freedom (2DOF) system in the vertical direction and in torsion are studied. The formation mechanism of the hysteresis loop is discussed using the equivalent total damping as a function of vibration amplitude. Two nonlinear mathematical models for the SDOF and the 2DOF systems are proposed to predict the nonlinear flutter responses, in which both the structural and aerodynamic damping are expressed as functions of time-varying displacements. An approach is proposed to identify the aerodynamic parameters based on the displacement time histories using a harmonic balancing technique. Using the identified aerodynamic parameters, a distinct dynamic system with the same section was used to validate the accuracy of the proposed models.

Vortex-Induced Vibration Optimization of a Wide Streamline Box Girder by Wind Tunnel Test

Although the streamline box girder exhibits an excellent aerodynamic performance, they are often suffer severe Vortex-Induced Vibrations (VIVs) due to complicated separation and reattachment of air flows. It is necessary to apply control measures on the streamline box girder to suppress VIV. In this study, the VIV optimizations of a super wide streamline box girder were conducted via a series of section model wind tunnel tests. The effects of wind fairings, inspection vehicle rails, guide vanes, traffic barriers and handrails on the heaving VIV performance of the wide streamline box girder were analyzed. The test results show that the inspection vehicle rail and handrail are the main members to induce the heaving VIV of the box girder. A sharper wind fairing without changing the distance of railings is favorable to the heaving VIV performance. However, the countermeasures of changing the position of inspection vehicle rail and installing guide vanes under the girder have slight influences on reducing heaving VIV responses. Inspired by the spanwise sinusoidal perturbation method, the traffic barriers sealed with plates by regular intervals along the bridge deck can suppress the heaving VIV of the box girder successfully. The porosity of handrails has a significant effect on the heaving VIV. By using a sharp wind fairing and circular simplified handrails, the VIV performance of the wide streamline box girder was greatly improved. Their mitigation abilities were verified by a large-scale section model wind tunnel test.

Investigation of Turbulence Effects on the Aeroelastic Properties of a Truss Bridge Deck Section

Abstract This paper presents the flutter derivatives (FDs) extracted from a stochastic system identification (SSI) method under different turbulent flows. The objective of the study is to investigate the effects of oncoming turbulence on the flutter of suspended long-span bridges using a section model wind-tunnel test. Several wind-tunnel tests were performed on a truss bridge deck section with different oncoming turbulent properties involving reduced turbulence intensities and turbulent scales. This study includes an investigation of the effect of oncoming flows on modal dynamic responses. The transient and buffeting response data from the wind-tunnel test are analyzed using the system identification technique in extracting FDs, and the difficulties involved in this method are discussed. The time-domain SSI is applied to extract all FDs simultaneously from one and two degree-of-freedom (1DOF and 2DOF) systems. Finally, the results under different conditions are discussed and conclusions are formed.

Effect of stabilizer on flutter stability of truss girder suspension bridges

An aerodynamic optimization measure of the flutter stability of long-span suspension bridges with truss girder is presented in this paper. At first, the improvement of several kinds of central stabilizers and horizontal stabilizers on flutter stability is examined through series of section model and full aeroelastic model wind tunnel tests. Subsequently, the flutter derivatives of the truss girder with and without stabilizer are identified based on two degrees of freedom coupling free vibration method. Furthermore, based on the identified flutter derivatives, the critical flutter velocities of the truss girder section with and without stabilizer are analyzed through two dimensional flutter analysis method and the critical flutter velocities of the full bridge with and without stabilizer are analyzed through three dimensional method. Afterwards, the influence of each flutter derivative on the flutter stability of the truss girder is investigated. The results indicate that central upper stabilizer can effectively increase the critical flutter velocity of the truss girder. In contrast, the central lower stabilizer and horizontal stabilizer have less influence. Setting up central upper stabilizer leads to an obvious decrease in the value of the flutter derivatives A2* and H2*, while the flutter derivatives H1*, H4*, A1* and A3* are little influenced. The two dimensional and three dimensional flutter analysis results agree well with the sectional model and full model wind tunnel test results respectively.

Experimental investigation of correction factor for VIV amplitude of flexible bridges from an aeroelastic model and its 1:1 section model

Evaluation of the maximum amplitudes of vortex-induced vibrations (VIV) in suspension bridges is mainly relied upon section model wind tunnel tests of bridge decks. Extrapolation to prototype responses requires addition correction to take into account the differences both in structural mode shape and in spanwise correlation of excitation forces between the section model and the prototype. The paper presents the results of VIV amplitudes measured on an aeroelastic model and on its section model with the same size of cross-section. The aeroelastic model is a new, elastically multi-supported one which is capable of reproducing the closely-spaced vertical modes of a suspension bridge. The vortex-induced vibrations for a number of vertical modes were successfully measured from the aeroelastic model test in smooth flow. The spring-mounted section model having the same size of cross-section as the aeroelastic model was also tested in smooth flow at the same mass, damping ratio and vibration frequency. It is shown that both the VIV onset wind velocity and lock-in range for each mode of vibration are in good agreement between the aeroelastic model and the section model. The aeroelastic model consistently produces a roughly 30% higher maximum amplitude than the section model for the observed modes of vibration. It is confirmed that the combined three-dimensional (3D) effects due to mode shape and imperfect correlation of excitation forces amplify the VIV amplitudes and disregarding these effects may underestimate the VIV amplitudes for section model tests. A correction factor of 1.3 for the VIV amplitude of vertical modes in suspension bridges may be adopted for practical use when extrapolating the section-model results to their corresponding full-scale values.

VIV-galloping interaction of the deck of a footbridge with solid parapets

A series of experimental investigations have been carried out to assess the aerodynamic performance of a pedestrian bridge with solid parapets in the UK. Section model wind tunnel tests were conducted in laminar flow conditions: these tests identified the presence of a strong VIV-galloping interaction which led to a rather severe broad-band non-divergent dynamic response of the structure occurring within the design wind speed range of the project site. This technical paper describes the wind engineering work that was conducted on the bridge deck, from the preliminary wind tunnel tests – which included the exploration of a number of mitigating aerodynamic measures, to the final tests conducted on a stiffer structure – where the sensitivity of the wind-induced response of the deck to variation of the mass-damping parameter was also investigated.

Flutter suppression of long-span suspension bridge with truss girder

Section model wind tunnel test is currently the main technique to investigate the flutter performance of long-span bridges. Further study about applying the wind tunnel test results to the aerodynamic optimization is still needed. Systematical parameters and test principle of the bridge section model are determined by using three long-span steel truss suspension bridges. The flutter critical wind at different attack angles is obtained through section model flutter test. Under the most unfavorable working condition, tests to investigate the effects that upper central stabilized plate, lower central stabilized plate and horizontal stabilized plate have on the flutter performance of the main beam were conducted. According to the test results, the optimal aerodynamic measure was chosen to meet the requirements of the bridge wind resistance in consideration of safety, economy and aesthetics. At last the credibility of the results is confirmed by full bridge aerodynamic elastic model test. That the flutter reduced wind speed of long-span steel truss suspension bridges stays approximately between 4 to 5 is concluded as a reference for the investigation of the flutter performance of future similar steel truss girder suspension bridges.

Vulnerability assessment for the hazards of crosswinds when vehicles cross a bridge deck

A new procedure to assess the crosswind hazard of operating a vehicle over a bridge deck has been developed using a probabilistic approach that utilizes long-term wind data at bridge sites as well as the aerodynamic properties of bridge decks and vehicles. The proposed procedure for safety assessment considers the probabilities of two accident types: sideslip and overturning. The vulnerability of vehicles to crosswinds is represented by the number of days for traffic control that would be required to secure vehicle safety over a period of one year. The distribution of wind speed over a bridge deck was estimated from a section model wind tunnel test. A sea-crossing bridge was selected as an example, and a series of case studies were performed to identify the influential factors affecting vehicle vulnerability to crosswinds: vehicle type and loaded weight, the position of a running vehicle over a bridge deck, the bridge alignment relative to the dominant wind direction, and vehicle speed.

Experimental and numerical study on generation and mitigation of vortex-induced vibration of open-cross-section composite beam

Open-cross-section composite beam (OCB) tends to suffer vortex-induced vibration (VIV) due to its bluff aerodynamic shape. A cable-stayed bridge equipped with typical OCB is taken as an example in this paper to conduct sectional model wind tunnel test. Vortex-induced vibration is observed and maximum vibration amplitudes are obtained. CFD approach is employed to calculate the flow field around original cross sections in service stage and construction stage, as well as sections added with three different countermeasures: splitters, slabs and wind fairings. Results show that flow separate on the upstream edge and cause vortex shedding on original section. Splitters can only smooth the flow field on the upper surface, while slabs cannot smooth flow field on the upper or lower surface too much. Thus, splitters or slabs cannot serve as valid aerodynamic means. Wind tunnel test results show that VIV can only be mitigated when wind fairings are mounted, by which the flow field above and below the bridge deck are accelerated simultaneously.

Effects of fundamental factors on coupled vibration of wind-rail vehicle-bridge system for long-span cable-stayed bridge

In a wind-vehicle-bridge (WVB) system, there are various interactions among wind, vehicle and bridge. The mechanism for coupling vibration of wind-vehicle-bridge systems is explored to demonstrate the effects of fundamental factors, such as mean wind, fluctuating wind, buffeting, rail irregularities, light rail vehicle vibration and bridge stiffness. A long cable-stayed bridge which carries light rail traffic is regarded as a numerical example. Firstly, a finite element model is built for the long cable-stayed bridge. The deck can generally be idealized as three-dimensional spine beam while cables are modeled as truss elements. Vehicles are modeled as mass-spring-damper systems. Rail irregularities and wind fluctuation are simulated in time domain by spectrum representation method. Then, aerodynamic loads on vehicle and bridge deck are measured by section model wind tunnel tests. Eight vertical and torsional flutter derivatives of bridge deck are identified by weighting ensemble least-square method. Finally, dynamic responses of the WVB system are analyzed in a series of cases. The results show that the accelerations of the vehicle are excited by the fluctuating wind and the track irregularity to a great extent. The transverse forces of wheel axles mainly depend on the track irregularity. The displacements of the bridge are predominantly determined by the mean wind and restricted by its stiffness. And the accelerations of the bridge are enlarged after adding the fluctuating wind.