Buffeting Response Research Articles

Finite element formulation of the self-excited forces for time-domain assessment of wind-induced dynamic response and flutter stability limit of cable-supported bridges

In this paper it is shown how unsteady self-excited aerodynamic forces modelled by rational functions can be introduced into a finite element beam model, using the nodal displacement degrees of freedom of the element to characterize the aeroelastic system. The time-dependent part of the self-excited forces is obtained introducing additional degrees of freedom in each node, the so-called aerodynamic degrees of freedom. The stability limit and buffeting response obtained in the time domain, using different shape functions to discretise the self-excited forces, are compared with results predicted by a traditional multimode approach. It is concluded that both the stability limit and the buffeting response can be obtained using this aeroelastic element, which implies that structural nonlinearities may be more easily introduced in time-domain analysis of the wind-induced buffeting response.

The Influence of Turbulence Integral Scale to Buffeting of Long-Span Bridge

In this paper, the influence of turbulence integral scale to buffeting responses of long-span bridge is analyzed by adopting 2-D buffeting theory. One cable-stayed bridge and one suspension bridge are selected as analysis object. Buffeting responses are calculated under two different wind speeds and different size of turbulence integral scales, which range from 10m to 80m in this paper. The numerical results show that buffeting responses do not change with turbulence integral scale linearly and when turbulence integral scale increases to one value, buffeting responses reach a peak. In addition, turbulence integral scale corresponding to peak value of buffeting responses rise with growth of wind speed.

Experimental Investigation on Wind-Resistant Behavior of Chaotianmen Yangtze River Bridge

Chaotianmen Yangtze River Bridge in China is a semi-supporting, steel-truss, and tied arch bridge with a main span of 552 m, marking the world’s longest center span of the same type. The wind-resistant behavior under yaw winds was investigated via wind-tunnel tests of 1:100 scale-downed full bridge aeroelastic models. The service stage and four key construction stages were considered in the tests. The tests were carried out in both smooth and simulated boundary layer wind fields with various wind yaw angles. The aeroelastic models were elaborately designed and manufactured, and the dynamic properties in every stage were investigated before the tests. The results show that the bridge has enough aerodynamic stability for all stages and different yaw wind angles, and the most unfavorable buffeting responses occur in yaw wind case with a yaw angle at 0°.

Estimating aeroelastic effects from full bridge responses by operational modal analysis

This paper deals with the estimation of structural modal parameters of long-span bridges from their recorded wind-excited response, by separating structural properties from aeroelastic effects using information on the incoming wind velocity. Specific attention is devoted to structural damping ratios, as their accurate estimations are of crucial importance in bridge engineering. However, uncertainties affecting damping ratios estimates often complicate any attempt towards their accurate assessment. More importantly, in the case of long-span bridges, aerodynamic damping often hides the actual structural one, even at low wind velocities. In this paper, the use of a data-driven stochastic subspace approach, specifically conceived to eliminate, as much as possible, analyst's arbitrariness and to deal with the non-whiteness of the wind excitation, is proposed for system identification. Structural properties are then separated from aeroelastic effects via nonlinear regressions of the modal parameter estimates at different mean wind velocities. Application of this technique to field measurements and numerically simulated buffeting response data referred to a real suspension bridge is finally presented, showing its effectiveness for separating structural from aerodynamic damping in practical case studies.

An experimental study of flutter and buffeting control of suspension bridge by mechanically driven flaps

The alternative solution for flutter and buffeting stability of a long suspension bridge will be a passive control using flaps. This method not only enables a lightweight economic stiffening girder without an additional stiffness for aerodynamic stability but also avoid the problems from the malfunctions of control systems and energy supply system of an active control by winglets and flaps. A mechanically control using flaps for increasing flutter speed and decreasing buffeting response of a suspension bridge is experimentally studied through a two dimensional bridge deck model. The result shows that the flutter speed is increased and the buffeting response is decreased through the mechanical drive of the flaps.

EXPERIMENTAL MODAL TEST AND TIME-DOMAIN AERODYNAMIC ANALYSIS OF A CABLE-STAYED BRIDGE

To determine its actual dynamic responses under the wind loads, modal identification from the field tests was carried out for the Kao Ping Hsi cable-stayed bridge in southern Taiwan. The dynamic characteristics of the bridge identified by a continuous wavelet transform algorithm are compared with those obtained by the finite element analysis. The finite element model was then modified and refined based on the field test results. The results obtained from the updated finite element model were shown to agree well with the field identified results for the first few modes in the vertical, transverse, and torsional directions. This has the indication that a rational finite element model has been established for the bridge. With the refined finite element model, a nonlinear analysis in time domain is employed to determine the buffeting response of the bridge. Through validation of the results against those obtained by the frequency domain approach, it is confirmed that the time domain approach adopted herein is applicable for the buffeting analysis of cable-stayed bridges.

Modeling hysteretic nonlinear behavior of bridge aerodynamics via cellular automata nested neural network

A new approach to model aerodynamic nonlinearities in the time domain utilizing an artificial neural network (ANN) framework with embedded cellular automata (CA) scheme has been developed. This nonparametric modeling approach has shown good promise in capturing the hysteretic nonlinear behavior of aerodynamic systems in terms of hidden neurons involving higher-order terms. Concurrent training of a set of higher-order neural networks facilitates a unified approach for modeling the combined analysis of flutter and buffeting of cable-supported bridges. Accordingly the influence of buffeting response on the self-excited forces can be captured, including the contribution of damping and coupling effects on the buffeting response. White noise is intentionally introduced to the input data to enhance the robustness of the trained neural network embedded with optimal typology of CA. The effectiveness of this approach and its applications are discussed by way of modeling the aerodynamic behavior of a single-box girder cross-section bridge deck (2-D) under turbulent wind conditions. This approach can be extended to a full-bridge (3-D) model that also takes into account the correlation of aerodynamic forces along the bridge axis. This novel application of data-driven modeling has shown a remarkable potential for applications to bridge aerodynamics and other related areas.

AMD Application for Suppressing the Lateral and Torsion Buffeting Response of Suspension Pipeline Bridge

Active Mass Damper has been proven to be efficient in suppressing structure vibration. Previous studies of AMD have been concentrated on the vibration control of buildings under earthquake excitation, whereas few investigation of wind-induced bridge vibration control has been conducted. In consideration of the characteristics of one suspension pipeline bridge which behaves dramatic lateral and torsional response under fluctuating wind action, a two-DOFs TMD/AMD system for suppressing both lateral and torsional responses was proposed. The bridge is modeled using Ansys and the buffeting responses of the bridge under TMD, AMD control are respectively simulated and analyzed by MATLAB/Simulink. The efficiency of different control system has been studied. The results show that two-DOFs AMD system has a better performance in suppressing the buffeting response of lateral bending and torsion. In addition, AMD system can be applicable to a wider range of frequency and therefore manifests the more stable performance than TMD under fluctuating wind loads which contain various frequency components.

Bridge Buffeting Analysis Based on POD and Aeroelastic Coupling Method

The bridge buffeting response is a type of response varying with the time, space and frequency, in this paper, the bridge buffeting response analysis method based on Proper Orthogonal Decomposition (POD) and aeroelastic coupling is proposed, which can consider the contribution of effective turbulence on the bridge buffeting response. To test the proposed technique, a cable-stayed bridge is used to compare current analysis with the results using the traditional buffeting simulation method.

AN APPROXIMATION METHOD FOR COMPUTING THE DYNAMIC RESPONSES AND EQUIVALENT STATIC WIND LOADS OF LARGE-SPAN ROOF STRUCTURES

Due to their sensitivity to wind, the design of large-span roofs is generally governed by wind loads. For some flexible large-span roofs with low damping and concentrated modes, the effect of multi-mode coupling should be taken into account in computing the resonant buffeting response and equivalent static wind loads. Such an effect is considered by the modified SRSS method in this paper via the modal coupling factor. Based on the same SRSS method, the equivalent static wind loads combining the mean, background, and resonant components, are computed. Particularly, the background and resonant components are computed by the LRC method and the equivalent inertia force method considering the modal coupling effects by the modified SRSS method, respectively. The method is then applied to the computation of wind-induced vibration responses and equivalent static wind load distributions of a real large-span roof. The results show that the modal coupling effect on the resonant component can be identified by the present method with high accuracy.

Comparison of Ambient Vibration Response of the Runyang Suspension Bridge under Skew Winds with Time-Domain Numerical Predictions

Existing buffeting theories and methods for dealing with skew winds are summarized. A modified version of the mean wind decomposition method is described that directly uses wind monitoring data from structural health monitoring systems. A method for time-domain buffeting analysis is presented and implemented in ANSYS, in which self-excited forces are modeled as elemental aeroelastic stiffness and damping matrices by element Matrix27. The entire numerical procedure is implemented in MATLAB and ANSYS, and the buffeting responses can be conveniently computed with very concise input data. This method is applied to the buffeting analysis of the Runyang Suspension Bridge during Typhoon Matsa. The measured data of wind characteristics are used to predict the buffeting responses of the bridge with a finite-element model. The predicted buffeting responses are compared with those from field measurements. A reasonably good agreement between the calculation and the measurement validates the effectiveness of the metho...

Non-linear buffeting response analysis of long-span suspension bridges with central buckle

The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data, a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented, in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.

New estimation methodology of six complex aerodynamic admittance functions

This paper describes a new method for the estimation of six complex aerodynamic admittance functions. The aerodynamic admittance functions relate buffeting forces to the incoming wind turbulent components, of which the estimation accuracy affects the prediction accuracy of the buffeting response of long-span bridges. There should be two aerodynamic admittance functions corresponding to the longitudinal and vertical turbulent components, respectively, for each gust buffeting force. Therefore, there are six aerodynamic admittance functions in all for the three buffeting forces. Sears function is a complex theoretical expression for the aerodynamic admittance function for a thin airfoil. Similarly, the aerodynamic admittance functions for a bridge deck should also be complex functions. This paper presents a separated frequency-by-frequency method for estimating the six complex aerodynamic admittance functions. A new experimental methodology using an active turbulence generator is developed to measure simultaneously all the six complex aerodynamic admittance functions. Wind tunnel tests of a thin plate model and a streamlined bridge section model are conducted in turbulent flow. The six complex aerodynamic admittance functions, determined by the developed methodology are compared with the Sears functions and Davenport`s formula.

The Aerodynamic Behaviour of the Deck of Stonecutters Bridge, Hong Kong

Stonecutters Bridge currently under construction in Hong Kong, with a main span of 1018 m, will become one of the longest span cable-stayed bridges in the world on its completion at the end of 2009. The design of the bridge deck contains a number of interesting aerodynamic features including the streamlined steel twin box-girder deck structure and the associated guide vanes installed at the underside of the deck. A bridge of this span will be subject to a variety of wind-induced vibration problems, including vortex-induced response, buffeting response and flutter instability. This, coupled with the extreme typhoon wind climate in Hong Kong, necessitated extensive aerodynamic investigations to address the above-mentioned aeroelastic problems. This paper gives a summary of the investigations concerning the deck of the bridge.

An approximation method for resonant response with coupling modes of structures under wind action

Effects of multi-mode coupling should be taken into account in computing the resonant buffeting response of some kinds of flexible structures with low damping and concentrated modes. In this paper, a new concept of “mode coupling factor” for computation of coupling effects between multi-mode resonant responses of the structures is proposed. On the base of the mode coupling factor, a modified SRSS method for computation of the resonant response contributed by multi-modes and their coupling effects of the structures is further raised. The roof structure of Shanghai Southern Railway Station is then taken as the case study to indicate the application and to verify the precision of the mode coupling factor and the modified SRSS method. The computaion results indicate that the mode coupling factor can quantitatively describe the contribution of mode coupling to the resonant response; and the modified SRSS method can make the computation of structural resonant response with consideration of mode coupling effects simpler.

Active Control of Vertical Tail Buffeting by Piezoelectric Actuators

A simplified method for analyzing and designing a vertical tail buffeting alleviation system is developed. The vertical tail model in this study is equipped with surface-bonded piezoelectric actuators to suppress the buffeting responses induced by aerodynamic forces. The structural dynamics of the vertical tail and the electrodynamics of piezoelectric actuators are modeled using a finite element method and realized by commercial software packages ANSYS®. Afterward, the finite element model for both the host structure and the piezoelectric patches are imported into MATLAB®, in which the dynamic equations of the system in modal coordinates are obtained through modal truncation. The motion-induced aerodynamic forces are computed by using the doublet-lattice method. The buffet input excitations are simulated by the proper orthogonal decomposition-based method. The suboptimal controller is designed to compute suitable control voltages needed to drive piezoelectric actuators. Finally, the effectiveness of the piezoelectric actuators in reducing vibratory responses due to buffet loads on the vertical tail is investigated numerically. The results demonstrate that the proposed method is feasible and effective.

Safety and serviceability assessment for high-rise tower crane to turbulent winds

Tower cranes are commonly used facilities for the construction of high-rise structures. To ensure their workability, it is very important to analyze their response and evaluate their condition under extreme conditions. This paper proposes a general scheme for safety and serviceability assessment of high-rise tower crane to turbulent winds based on time domain buffeting response analysis. Spatially correlated wind velocity field at the location of the tower crane was first simulated using an algorithm for generating the time domain samples of a stationary, multivariate stochastic process according to some prescribed spectral density matrix. The buffeting forces applied to the structure were computed according to the above-simulated wind velocity fluctuations and the lift, drag, and moment coefficients obtained from a CFD computation. Those spatially correlated loads were then fed into a well calibrated finite element model and the nonlinear time history analysis was conducted to compute structural buffeting response. Compared with structural onsite response measurement, the computed response using the proposed method has good precision. The proposed method is then adopted for analyzing the buffeting response of an in-use tower crane under the design wind speed and the maximum operational wind speed for safety and serviceability assessment.

Identification of Flutter Derivatives of Bridge Decks in Wind Tunnel Test by Stochastic Subspace Identification

Problem statement: Flutter derivatives are the essential parameters in the estimations of the flutter critical wind velocity and the responses of long-span cable supported bridges. These derivatives can be experimentally estimated from wind tunnel test results. Generally, wind tunnel test methods can be divided into free decay test and buffeting test. Compared with the free decay method, the buffeting test is simpler but its outputs appear random-like. This makes the flutter derivatives extraction from its outputs more difficult and then a more advanced system identification is required. Most of previous studies have used deterministic system identification techniques, in which buffeting forces and responses are considered as noises. These previous techniques were applicable only to the free decay method. They also confronted some difficulties in extracting flutter derivatives at high wind speeds and under turbulence flow cases where the buffeting responses dominate. Approach: In this study, the covariance-driven stochastic subspace identification technique (SSI-COV) was presented to extract the flutter derivatives of bridge decks from the buffeting test results. An advantage of this method is that it considers the buffeting forces and responses as inputs rather than as noises. Numerical simulations and wind tunnel tests of a streamlined thin plate model conducted under smooth flow by the free decay and the buffeting tests were used to validate the applicability of the SSI-COV method. Then, wind tunnel tests of a two-edge girder blunt type of Industrial-Ring-Road Bridge deck (IRR) were conducted under smooth and turbulence flow. Results: The identified flutter derivatives of the thin plate model by the SSI-COV technique agree well with those obtained theoretically. The results from the thin plate and the IRR Bridge deck validated the reliability and applicability of the SSI-COV technique to various experimental methods and conditions of wind flow. Conclusion/Recommendations: The SSI-COV was successfully employed to identify flutter derivatives of bridge decks with reliable results. It is a proven technique that can be readily applied to identify flutter derivatives of other bridge decks either by the free decay or the buffeting tests.

Field measurement on wind characteristic and buffeting response of the Runyang Suspension Bridge during typhoon Matsa

Field measurement on wind characteristic and buffeting response of existing bridge is of great value to the development of bridge wind engineering, and the structural health monitoring system (SHMS) employed in many long-span bridges provide a research basis for the field measurement. In order to provide reliable basis for wind resistant evaluation of Runyang Suspension Bridge (RSB), two anemometers and 85 accelerometers were installed in the SHMS of RSB. In August 2005, Typhoon Matsa crossed over Jiangsu, the SHMS timely recorded the typhoon and structural vibration responses. In this paper by using the time-frequency technique and statistical theory, the recorded data were analyzed to obtain the strong wind characteristics, the buffeting response characteristics of the cable and deck, and the variation of buffeting response RMS versus wind speed. Results obtained in this study can be employed to validate the credibility of current buffeting response analysis theory techniques, and provide reference values for wind resistant evaluation of other long-span bridges.

Investigation on influence factors of buffeting response of bridges and its aeroelastic model verification for Xiaoguan Bridge

A time-domain procedure for analyzing buffeting responses of bridges is presented and implemented in ANSYS, formulated taking into account the self-excited forces, aerodynamic admittance functions (AAFs) and the coherence of buffeting forces. The buffeting forces simulated based on the span-wise coherence of buffeting forces and also considering the aerodynamic admittance functions, together with the steady aerodynamic forces are applied as external loads to the structural model to analyze the buffeting responses in time domain. In order to account for self-excited forces, elemental aeroelastic stiffness and aeroelastic damping matrices for spatial beam elements are derived following the quasi-steady theory and are incorporated in buffeting analysis through the user-defined Matrix27 element in ANSYS. The procedure is applied to the Xiaoguan Bridge, China, during the longest double cantilever stage of construction. The wind tunnel tests of four typical bridge section models are performed to measure the aerodynamic parameters of the bridge including the steady aerodynamic coefficients and aerodynamic admittance functions. The bridge aeroelastic model testing is also carried out, and coherence functions of buffeting forces are derived from the measured buffeting forces. The measurement results of the displacements and internal forces are compared with those obtained from the analytical predictions. The influence factors, including aeroelastic effect, aerodynamic admittance functions and coherence of buffeting forces, are studied in some detail. It is shown the present method inclusive of above factors gives much closer predictions of buffeting responses to the experimental results.