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The flow-induced vibrations (FIVs) of staggered two-degree-of-freedom cylinders with a constant streamwise offset (L/D = 2, L is the streamwise spacing between the cylinders of diameter D) and varying cross-stream offset (0 ≤ S/D ≤ 5, S is the cross-stream spacing) were numerically simulated. The effects of S/D on the in-line and cross-flow vibrations, flow fields, distributions of the surface pressures, and the energy properties were comprehensively investigated to study the characteristics of the FIVs. The upstream cylinder primarily experiences vortex-induced vibrations (VIVs), while distinct FIVs of the downstream cylinder occur when S/D ranges from 0 to 3, and the flow characteristics vary with the reduced velocity (Vr) and S/D. When Vr = 3, vortex pairs along with reverse-flow reattachment are observed within the gap zone at small S/D. The pressures on the downstream cylinder become asymmetric due to the vortex strong interactions. When Vr = 7 and 11, a merging vortex emerges and moves closer to the rear surface of the downstream cylinder with increasing S/D, which increases negative pressure on the lower part of the downstream cylinder, further influencing the promoting effect of the merging vortex on structural vibrations. Moreover, when S/D ≥ 3, the effects of the upstream cylinder on the downstream cylinder diminish. Both cylinders exhibit identical vibrations and wake patterns, and the mean power distribution on the downstream cylinder becomes symmetrical with a magnitude similar to that of the upstream cylinder, which can be considered as two independent cylinders undergoing VIVs. [ABSTRACT FROM AUTHOR]

The three-dimensional large-eddy-simulation coupled with a mode superposition method was applied to numerically simulate the flow-induced vibrations (FIVs) of tandem dual flexible cylinders at Re = 1000 with three different spacing ratios (Sx/D = 2.5, 3.5, and 5, Sx is center-to-center spacing for tandem cylinders, and D is the diameter of the cylinder), corresponding to the reattachment flow, transition flow, and co-shedding flow regimes in stationary tandem cylinders, respectively. The effects of Sx/D on structural vibrations, flow fields, distributions of the surface pressures, and energy properties were investigated to reveal the mechanism for the FIV. Increasing Sx/D weakens the influence of the upstream cylinder on maximum response amplitudes and lock-in region for downstream cylinder. The wake patterns for tandem flexible cylinders are more complex compared to stationary or vibrated rigid tandem cylinders. The shielding effect reduces surface pressure on the downstream cylinder significantly when its vibrations are smaller, leading to a decrease in mean power as well. Furthermore, different mechanisms contribute to amplified FIV in downstream cylinders depending on Sx/D: when Sx/D = 2.5, the upstream vortices collide with the downstream cylinder's front surface and merge with the vortices generated by the downstream cylinder, increasing negative pressure on both front and rear surfaces of the downstream cylinders and promoting FIV; however when Sx/D =3.5 and 5, a binary vortex street forms behind the downstream cylinder without obvious negative pressures on its front surface, the dominant causes of FIV are primarily attributed to interactions among upstream and downstream vortices. [ABSTRACT FROM AUTHOR]

This paper introduces a new accelerating algorithm, efficient match slimmer (EMS), specifically designed to lighten computational loads of sophisticated template matching algorithms, enabling these algorithms to be effectively run on single‐board computers. Utilizing EMS in conjunction with a robust template matching algorithm, we have developed Raspberry Vision—a compact, cost‐effective, and real‐time vision‐based system. Its compactness and portability facilitate a practical measurement strategy that not only minimizes the camera‐to‐target distance but also simplifies the camera calibration process in bridge displacement monitoring, thereby enhancing measurement accuracy. The performance of the system is estimated on two operational suspension bridges. The results demonstrate that Raspberry Vision, equipped with the measurement strategy, can significantly improve the measurement accuracy in the long‐span bridge test and is also suitable for cross‐sea bridge measurements. [ABSTRACT FROM AUTHOR]

This paper proposes a novel emergency aerodynamic measure, i.e. suspended flexible sheets (SFSs) with high strength, to suppress the vortex-induced vibrations (VIV) of bridge decks. The cost of the SFSs is very low, and the SFSs can be readily installed for an operational bridge in a short time. The control effectiveness of the SFSs is tested for a bluff box girder using wind tunnel experiments (the model scaling ratio is 1:36 and the range of Reynolds number is 1. 7 1 × 1 0 3 to 1. 1 2 × 1 0 5). The relevant parameters of the SFSs (installation location, height, counterweight form, and arrangement form) are systematically optimized. The experimental results show that the in-wind postures of the SFSs are critical for the control performance. The random waving of SFSs can disturb the airflow around the bridge deck at the lower surface, weaken the interaction between the vortex shedding from the upper and lower surfaces, and hence reduce the VIV response. The control performance of the aerodynamic measure can be significantly increased by using appropriate arrangements of the SFSs and counterweights. For the tested cases, the maximum reduction ratio of the VIV amplitude approximately reached 2/3. [ABSTRACT FROM AUTHOR]

Existing studies optimized the tuned mass damper (TMD) for vortex-induced vibration (VIV) control of bridges based on an empirical linear model or Scanlan's nonlinear model, which cannot accurately simulate the effect of the vortex-induced force and hence results in a TMD design that lacks effectiveness or robustness. Four vortex-induced force models are considered to systematically analyze the influence of force models on TMD design for VIV control. The design results based on various vortex-induced force models, as well as three design formulas, are compared in terms of effectiveness and robustness. Numerical results suggest that the empirical linear model and Scanlan's nonlinear model significantly underestimate the TMD mass ratio required to suppress the VIV amplitude to be lower than a threshold. The empirical linear model may overestimate the robustness of the TMD to changing the frequency ratio, while Scanlan's nonlinear model may overestimate or underestimate the robustness depending on the threshold VIV amplitude. The TMD design based on the polynomial model is considered more accurate since it can accurately predict VIV responses at various effective damping levels. The aerodynamic envelope model can be used as a convenient model for TMD optimization. The results generated using the free vibration formula are the closest to that of the polynomial model. An appropriate safety factor should be considered to convert the TMD design based on sectional model experiments to real bridges. [ABSTRACT FROM AUTHOR]

The empirical envelope (EE) method based on the amplitude-modulation and frequency-modulation (AMFM) decomposition is effective for identifying the modal parameters of time-varying and weakly nonlinear systems. However, the identification accuracy of the EE method is sensitive to noises which often exist in vibration measurements of real structures. In this study, an improved empirical envelope (IEE) method is proposed to achieve robust modal parameter identification from noisy measurements. Specifically, the idea of sliding window threshold denoising is introduced to reduce the error in the instantaneous envelope induced by abnormal extreme points, and a moving average filter is utilized to reduce the error in the instantaneous frequency induced by high-frequency noises. Two numerical examples and an experimental example of a full-bridge aeroelastic model are analyzed to validate the accuracy of the IEE method and highlight the superiority of the IEE method relative to the original EE method. It is concluded that the IEE method is robust to measurement noises (the considered signal-to-noise ratios include 5–90 dB) and that the IEE method is more accurate than the EE method. Hence, the IEE method serves as a promising alternative for modal parameter identification of time-varying and weakly nonlinear systems. [ABSTRACT FROM AUTHOR]

Applying a subpixel refinement technique in vision‐based displacement sensing can significantly improve the measurement accuracy. However, digital image signals from the camera are highly sensitive to drastically varying lighting conditions in the field measurements of structural displacement, causing pixels expressing a tracking target to have nonuniform grayscale intensity changes in different recording video frames. Traditional feature points‐based subpixel refinement techniques are neither robust nor accurate enough in this case, presenting challenges for accurate measurement. This paper proposes a robust subpixel refinement technique—self‐adaptive edge points matching (SEPM)—to obtain accurate subpixel‐level displacements under drastic illumination change conditions. Different from traditional feature points‐based methods, the gradient and shape information of the target edge contour are used in the SEPM calculation. Three tests under different illumination conditions were conducted to evaluate the performance of the SEPM. The results show that the SEPM is capable of producing accurate subpixel‐level displacement data with less 1/16‐pixel root mean‐square error. [ABSTRACT FROM AUTHOR]

Wind-resistant performance is a major concern in the design and operation of pipeline suspension bridges. The mean aerodynamic force coefficients (MAFCs) are essential parameters for quantifying the wind loads on a bridge. However, a systematic investigation of the MAFCs of typical pipeline suspension bridge girders is unavailable. Specifically, the effects of design parameters (perforation rate of grate plates, horizontal spacing between pipelines, vertical spacing between pipelines, pipeline number, pipeline diameter, and pipeline surface roughness) and Reynolds number on MAFCs remain to be investigated. This study systematically investigated the MAFCs of three typical pipeline suspension bridge girders in wind tunnel experiments. The galloping stabilities of these girders were examined based on the quasi-steady galloping theory. The experimental results show that the effect of pipeline surface roughness on the Reynolds number effect of drag force coefficient is similar to that on the Reynolds number effect of a circular cylinder. Closing the grate plates may deteriorate the galloping performance of a bridge girder, whereas increasing the pipeline surface roughness may strengthen the galloping performance of a bridge girder. Unlike parallel circular cylinders, the horizontal spacing between pipelines slightly affects the MAFCs. Optimizing the vertical spacing between the pipelines can significantly reduce the MAFCs. In addition, optimizing the shape and roughness of the pipeline can reduce the lift force and pitching moment, and optimizing the shape of guardrails and truss stiffening girder can reduce the drag force. These research results can provide a basis for quantifying the aerodynamic loads and a reference for the wind-resistant design of pipeline suspension bridges with similar bridge girders. [ABSTRACT FROM AUTHOR]

Under strong wind actions, some long-span flexible deck bridges have been observed to exhibit significant lateral vibrations. Accurate quantification of the self-excited forces induced by lateral vibration is of great significance for the evaluation of the wind-resistant performance of bridges. Three typical deck sections, including a 5:1 rectangular section, a streamlined section, and a central-slotted section, are used to comprehensively address this issue using the unsteady Reynolds-averaged Navier–Stokes simulations. The applicability of the linear analysis method for quantifying the self-excited forces is reexamined for different lateral vibration amplitudes and reduced wind speeds. The results show that the self-excited drag force induced by lateral vibration agrees well with the linear theory for the three sections. However, the self-excited lift force and torsional moment induced by lateral vibration cannot be quantified by the linear formulations. For the rectangular section, the self-excited lift force and torsional moments are much smaller than the vortex-induced counterparts. For the streamlined and central-slotted sections, the ratios of the self-excited components to the vortex-induced components are closely related to the reduced wind speed and vibration amplitude. The ratios increase with an increase in vibration amplitude and a decrease in reduced wind speed. Thus, particular attention should be paid to the self-excited lift force and torsional moment induced by lateral motions for bridge decks. [ABSTRACT FROM AUTHOR]

Pressure measurements for rigid models fail to take aeroelastic effects into account, as well as forced vibration tests only consider the effect of an oscillating model on wind flow and cannot include the feedback from wind flow to the oscillating model. To investigate the characteristics of unsteady aerodynamic forces and predict the aeroelastic response of a tapered prism during VIV–galloping, hybrid aeroelastic-pressure balance (HAPB) wind tunnel tests at different reduced wind velocities were carried out. Unsteady pressures and tip responses of a tapered test model were synchronously observed. Both the aerodynamic and aeroelastic characteristics of the tapered prism during VIV–galloping instability were discussed in terms of aeroelastic response, force spectrum, coherence coefficient and pressure distribution. Subsequently, the VIV–galloping response was predicted by unsteady aerodynamic forces and compared to quasi-static calculations and experimental results. It was found that large-amplitude periodic vibrations took place at approximately twice the onset wind speed of VIV, which was recognized as VIV–galloping. Moreover, structural oscillation would have a significant effect on aerodynamic characteristics in the crosswind direction. In addition, the HAPB test was efficacious in measuring unsteady aerodynamic forces on the test model, which were effective to predict VIV–galloping instability of bluff bodies. [ABSTRACT FROM AUTHOR]

Splitter plates are widely used for drag reduction and vibration control or enhancement of circular cylinders. The effects of a splitter plate on the vertical flow-induced vibrations of a circular cylinder have been well studied. However, its effects on the vertical-torsional coupled vibrations require further investigation. In this paper, the three-degree-of-freedom (TDoF) flow-induced vibrations of a circular cylinder with an attached splitter plate are numerically investigated at a Reynolds number of 100. The ratio between the torsional and vertical natural frequencies is varied within f θ , 0 / f h , 0 = 6, 4, 3, 2, and 1. Numerical results show that the flow-induced vibrations of a TDoF cylinder-plate assembly, depending on the frequency ratio, may differ significantly from those of a single-degree-of-freedom (SDoF) vertical or torsional assembly. For cylinder-plate assemblies with f θ , 0 / f h , 0 = 6–2, the vibrations can be divided into a vertical vibration-dominated branch (V branch), a torsional vibration-dominated branch (T branch), and a coupled vibration-dominated branch (C branch). The V branch vibration of a TDoF assembly is similar to that of an SDoF vertical assembly at the same reduced flow velocity, while the difference increases with decreasing the frequency ratio. The T branch vibration of a TDoF assembly is almost identical to the vibration of an SDoF torsional assembly at the same reduced flow velocity. The ratio between the torsional and vertical vibration amplitudes increases with decreasing the frequency ratio in the C branch. For the assembly with f θ , 0 / f h , 0 = 1, vertical-torsional coupled vortex-induced vibrations are observed with the largest torsional amplitude as high as 46.3°. The vibrations of TDoF assemblies with all considered frequency ratios may be more severe than those of SDoF vertical and torsional assemblies within specific ranges of reduced flow velocities. The mean drag coefficients for the f θ , 0 / f h , 0 = 6–2 assemblies are lower than a stationary circular cylinder but often higher than a stationary cylinder-plate assembly. The mean drag coefficients for the f θ , 0 / f h , 0 = 1 assembly in the lock-in range are considerably larger than that of a stationary circular cylinder. For TDoF assemblies with f θ , 0 / f h , 0 = 6–2, the V branch and C branch vibrations are mainly driven by the interaction between the assembly and the shear layers, while the T branch vibrations are excited by the typical 2S mode of vortex shedding. The 2S vortex shedding mode is also observed in the lock-in range of the f θ , 0 / f h , 0 = 1 assembly. [ABSTRACT FROM AUTHOR]

The large-amplitude postflutter vibrations of long-span bridges have attracted extensive attention, which is of significant importance to accurately assess the potential wind-resistant capability of bridges. However, the conventional free vibration testing apparatus cannot effectively fulfill the task of evaluating the postflutter performance of a bridge deck. This study introduces a new experimental device that can effectively avoid various nonlinear factors involved in the traditional device and thereby ensure the accuracy of large-amplitude vertical-–torsional coupled free vibration tests. The excellent working performance of the experimental setup is validated by carrying out free vibration tests of a bridge deck sectional model in still air. Large-amplitude wind tunnel tests of two bridge decks are conducted by using the new setup, and it is found that the novel testing device is a preferable choice for wind tunnel tests to comprehensively evaluate the postflutter performance of bridge decks. [ABSTRACT FROM AUTHOR]

The wind–rain-resistant performances of aeroelastic models of simplified suspension bridges and cable-stayed bridges at the erection stage are experimentally investigated. Several typical deck sections, i.e., two bluff decks, two thin flat plates, and a quasi-streamlined deck, are included to cover a wide range of possible alternatives. Under different conditions of wind speed, rainfall intensity, and initial attack angle, the vertical and torsional displacements at the deck end tips and middle sections are measured. The comprehensive measurement results reveal that in the possible and even extreme range of rainfall intensity, the aerostatic and aerodynamic responses are almost independent of the rainfall intensity for all testing cases, which may contradict with the intrinsic conception of most researchers in the wind engineering community. The results suggest that the rainfall loads effect on bridges are trivial, and it might be unnecessary to comprehensively investigate the rainfall loads on bridges similar with the considered cases. [ABSTRACT FROM AUTHOR]

Pipeline suspension bridges may experience ice accretion under special atmospheric conditions, and the aerodynamic characteristics of the bridges may be modified by the ice accretion. Under some specific climatic conditions of freezing rain, the dependencies of the ice size and shape on the icing duration and some structural properties (including pipeline diameter, inclination angle of wind hanger, inclination angle and size of section steel, and girder geometry) were experimentally investigated in a refrigerated precipitation icing laboratory. Typical ice accretions on pipelines, wind hangers, section steels, and girders of pipeline suspension bridges are summarized. Then the effects of some selected ice accretions on aerodynamic force coefficients of a bridge girder were further investigated through wind tunnel tests. The ice size and shape on the pipeline were closely related to the pipeline diameter and icing duration. The engineering geometric models of ice accretion on pipelines were extracted. The ice shape and size on wind hangers and section steels changed with their inclination angles. The aerodynamic force coefficients of a girder with ice accretion were much higher than those of an ice-free one. The results can provide references for simulating the ice accretion and further evaluating the effect of ice accretion on the aerodynamics of pipeline suspension bridges. [ABSTRACT FROM AUTHOR]

Ice accretion is a major concern that may endanger the operation safety of structures and even cause serious casualties in cold regions. Under freezing rain conditions, the size and shape of the accreted ice on different diameter circular cylinders are investigated in a refrigerated precipitation icing laboratory. The ice size and shape are closely related to cylinder diameter and accretion duration. The engineering geometrical models of the ice accretion on circular cylinders are extracted. The aerodynamic displacement responses of a 1:25 aeroelastic model of a pipeline suspension bridge with and without ice accretions are experimentally recorded using Micro-Epsilon sensors. Analytical expressions to calculate the vertical and lateral displacements are derived, and the differences between the conventional method and the newly derived one are further analyzed to manifest the theoretical significance. For three-degrees-of-freedom motions, the vertical and lateral displacements cannot be separately determined by the signals of vertical and lateral sensors, respectively. Some strategies are recommended to reduce the errors induced by using the conventional formulations. The influences of initial angle of attack, ice shape, pipeline diameter, and turbulence intensity on girder displacement and wind cable tensile force are comprehensively investigated. The aerostatic responses are greatly influenced by the aforementioned parameters. The aerodynamic analyses reveal that the ice accretion can obviously increase wind-induced responses, that is, deteriorate the wind-resistant performance, which should be taken into careful consideration. The present work can provide beneficial references for the wind-resistant design of similar type of bridges, especially under pipeline ice accretion conditions. [ABSTRACT FROM AUTHOR]

An aerodynamic describing function (ADF)-based model for simulating the nonlinear self-excited forces on bridge decks is developed, where the ADFs can be conveniently identified using the experimentally or numerically obtained free or forced vibration data. An efficient calculation procedure based on the ADFs is accordingly established to predict the nonlinear flutter state and/or postflutter limit cycle oscillations (LCOs). Two numerical examples are utilized to demonstrate the simulation accuracy and efficiency of nonlinear bridge flutter with the proposed ADF-based model. The capabilities of the ADF-based model in capturing typical features of nonlinear postflutter vibration such as LCO and a hysteresis phenomenon are demonstrated. A nondimensional postflutter index is designed to quantitatively assess the postflutter performance of bridge decks. Finally, the effects of structural dynamics and aerodynamic properties (e.g., structural damping ratios, natural frequencies, and aerodynamic derivatives) on the postflutter behavior of a bridge deck are examined in terms of the wind speed extension after the critical state with acceptable postcritical vibrations and the proposed postflutter index. [ABSTRACT FROM AUTHOR]

An out-put only modal parameter identification method based on variational mode decomposition (VMD) is developed for civil structure identifications. The recently developed VMD technique is utilized to decompose the free decay response (FDR) of a structure into to modal responses. A novel procedure is developed to calculate the instantaneous modal frequencies and instantaneous modal damping ratios. The proposed identification method can straightforwardly extract the mode shape vectors using the modal responses extracted from the FDRs at all available sensors on the structure. A series of numerical and experimental case studies are conducted to demonstrate the efficiency and highlight the superiority of the proposed method in modal parameter identification using both free vibration and ambient vibration data. The results of the present method are compared with those of the empirical mode decomposition-based method, and the superiorities of the present method are verified. The proposed method is proved to be efficient and accurate in modal parameter identification for both linear and nonlinear civil structures, including structures with closely spaced modes, sudden modal parameter variation, and amplitude-dependent modal parameters, etc. [ABSTRACT FROM AUTHOR]

This paper proposes a new symplectic method for obtaining the natural frequencies and modes of beams resting on elastic foundations. A generalized Hamiltonian functional is first derived via the Lagrange multiplier method, and the first-order dual equation of motion in the time domain and its corresponding boundary conditions are obtained. The time coordinate is separated from the dual equation to yield the natural-frequency-related eigenvalue equation and the first-order dual equation in the frequency domain. Then, the spatial coordinate is separated from the newly derived dual equation to yield the natural-mode-related eigenvalue equation. According to the eigenvalue analyses, this paper obtains a series of eigenvalue spectra: the continuous and discrete eigenvalue spectra that represent the relationships of the two types of dimensionless eigenvalues for infinite and finite beams, respectively; these eigenvalue spectra help to understand the connection between structural vibration and wave propagation. For a finite beam with a specific boundary condition, its mode vectors are composed of transverse deflection, bending rotation, shear force, and bending moment, and they are called the full mode shape vectors (FMSVs) in this paper. These FMSVs were verified to be orthogonal according to the property of the Hamilton matrix. A simply supported and a cantilever beam were used as examples to validate the accuracy and applicability of the symplectic method. Their vibration properties, mainly the discrete eigenvalue spectra and FMSVs, are comprehensively analyzed, and some significant conclusions are drawn. [ABSTRACT FROM AUTHOR]

A vast quantity of measurements of wind-induced non-Gaussian effects on buildings call for the burgeoning development of more advanced extrema estimation approaches for non-Gaussian processes. In this study, a well-directed method for estimating the peak factor and modeling the extrema distribution for non-Gaussian processes is proposed. This method is characterized by using two fitted probability distributions of the parent non-Gaussian process to separately fulfill the estimations of the extrema on long-tail and short-tail sides. In this method, the Johnson transformation is adopted to be the probabilistic model for fitting the parent distribution of the non-Gaussian process due to its superior fitting goodness and universality. For each dataset, two Johnson transformations will be established by two parameter estimation methods to individually estimate the extrema on two sides. Then a Gumbel assumption is applied for conveniently determining the non-Gaussian peak factor. This method is validated through long-duration wind pressure records measured on the model surfaces of a high-rise building in wind tunnel test. The results show that the proposed method is more accurate and robust than many existing ones in estimating peak factors for non-Gaussian wind pressures. [ABSTRACT FROM AUTHOR]

This paper develops a new symplectic eigenvalue analysis (SEA) method for deriving the symplectic analytical solutions for the bending of Timoshenko beams resting on two-parameter elastic foundations. The SEA method accommodates various beam–foundation models with arbitrary external loads and arbitrary boundary conditions. A generalized Hamiltonian functional is first derived by introducing the Lagrange multipliers into the total potential energy functional, and then the first-order dual equation and its corresponding boundary conditions are obtained. Once the variables are separated, the beam bending is transformed into an eigenvalue problem, and the corresponding eigenvalues and eigenvectors are used to derive the symplectic solutions. In addition, a new hybrid method, which incorporates the singular functions and the variable separation method, is proposed to obtain the particular solutions with respect to arbitrary external loads. The systematic SEA method provides a new general analytical framework for studying beam–foundation interaction problems, and the comprehensive analyses on the symplectic eigenvalues help to deeply understand the characteristics of the symplectic solutions. Three examples are presented to assess the applicability of the SEA method and to validate the accuracy of the symplectic solutions. The differences and similarities between the Pasternak elastic foundation and the generalized elastic foundation are quantitatively and qualitatively investigated by the SEA method. [ABSTRACT FROM AUTHOR]

The causes of the nonlinearity of self-excited aerodynamic force of bridge are interpreted from such two aspects as amplitude and wind velocity. The concept of “generalized flutter derivative” is proposed, and its physical meaning is illustrated. The graphs of the generalized flutter derivatives of plate and Sutong Bridge section model are plotted. The characteristics of all generalized flutter derivatives are compared and analyzed, and their superiorities are verified. The results indicate that the physical meaning of generalized flutter derivatives are more explicit compared to the traditional ones. It is more convenient to understand the nonlinearity properties of self-excited aerodynamic force of bridge according to the generalized flutter derivatives graphs with the wind velocity as the horizontal coordinate. [ABSTRACT FROM AUTHOR]