Along-wind Response Research Articles

Experimental investigation on coupled vibration characteristics of wind-excited tall buildings

Contemporary tall buildings constructed with high-strength and light-weight materials become relatively flexible and lightly damped, and the fluctuating wind forces acting on the buildings may cause excessive vibrations, especially at the vicinity of vortex lock-in wind speed, where the natural frequency of the buildings is synchronized with the vortex shedding frequency. Given that tall buildings tend to be designed with unconventional shape involving innovative structural systems and complex geometry, the correlations among three force components may accentuate building motions significantly. In this study, the coupling characteristics between the alongwind and crosswind vibrations of tall buildings with symmetric shape and distinct natural frequencies in two directions are investigated through a serious of aeroelastic model tests. The response standard deviations and power spectral densities are calculated, respectively, based on the displacement data measured at multiple levels of wind speed and structural damping ratio. Then the coupled response is extracted from the alongwind response in frequency domain through Fourier transform and inverse Fourier transform, and the standard deviations of the coupled response are calculated based on time history analysis, which are compared with that of the crosswind response to investigate the relationship between the alongwind and crosswind motions. Moreover, the amplitude ratio, phase difference, and coherence of the response components are also calculated for further discussing the coupling effects and examining the coupled vibration characteristics.

A numerical simulation method in time domain to study wind-induced excitation of traffic signal structures and its mitigation

Traffic signal structures, commonly used to control traffic, have exhibited fatigue failure in their connections due to wind-induced vibration. This study focuses on developing a generalized method to predict the coupled across- and along-wind responses of a traffic signal light structure in normal or yawed wind by combining the aerodynamic properties of such a multi-component structure with a numerical simulation technique to generate wind loads and resulting responses in the time domain. The methodology and data presented here can be applied to any signal structure to explore its dynamic behavior, estimate its fatigue life and devise mitigation means such as dampers. The tip response of the mast arm and the maximum stress at its joint were calculated for a given signal light structure and validated with field measurements to demonstrate the methodology for a range of wind speeds and yaw angles. Results indicate that yawed wind below a speed of 9 m/s from the backside of the signal light and vortex shedding of the mast arm are the primary reasons of large-amplitude vibration, and the maximum stress exceeds the endurance limit that can cause fatigue failure over time. A modified signal light design to mitigate this problem is proposed.

Wind-induced response analysis of wind turbine tubular towers with consideration of rotating effect of blades

This study discusses the wind-induced response of existing pitch-controlled 1.25 MW wind turbine structures, with a particular focus on the influence of the blade-rotation effect, cross-wind loads of the tubular tower and the wind direction, and compares numerical responses with the measured dynamic responses. An integrated finite-element model consisting of blades, a nacelle, a tower and a foundation is established. The aerodynamic loads exerted on the rotating blades and the aerodynamic loads acting on the tubular tower are then obtained. A wind-induced response calculation method of the wind turbine structures corresponding to different wind speeds and wind directions is established for performing a wind-induced response analysis. Finally, comparisons between the measured responses and the corresponding numerical response results are performed to verify the accuracy of the proposed wind-induced response calculation method. The results indicate that neglecting the cross-wind aerodynamic loads of large-scale wind turbine structures can lead to unsafe design. The wind direction has different influences on the along-wind and cross-wind dynamic responses. The statistical values of the measured dynamic responses are slightly greater than those of the numerical analysis results, but the magnitudes of the responses are the same. Therefore, the proposed wind-induced response calculation method for wind turbine structures is feasible and reasonable. It can be used to conduct the fatigue life prediction of wind turbine tubular towers in future research which is an important issue in the structural design of wind turbine tubular tower structures.

The Role of Belt Wall in Minimizing The Response Due To Wind Load

Outrigger is one of the tall building structural systems that are used to reduce the building responses due to the wind. Outrigger is a stiff beam that connects the core wall to exterior columns and this enables the vertical shear to be transferred from the core to the external columns, thereby forcing the perimeter columns to participate in carrying the overturning moment due to the wind. Belt wall is often added to a building with outrigger system to further reduce the displacement and acceleration of a tall building having an outrigger system. However, it is not known how effective the belt wall is in further reducing the building responses. Thus, 64 story reinforced concrete buildings are studied in order to determine how the belt wall improves the building responses due to the wind. Buildings with an outrigger system and buildings with a combination of the outrigger and belt wall system are analysed by a structural engineering software in order to determine the natural frequencies and eigenvectors in the along-wind, across-wind and torsional direction. The along-wind responses are determined by employing the procedures from the ASCE 7-16 while the across-wind responses of the buildings are calculated based on the procedures and wind tunnel data available in a database of aerodynamic load. Results from the analysis show that the belt wall reduces the along-wind and across-wind responses slightly. However, belt wall reduces the torsional acceleration of the buildings significantly, which otherwise cannot be reduced by the outrigger system.

Along-wind response control of chimneys with distributed multiple tuned mass dampers

The effectiveness of distributed multiple tuned mass dampers (d-MTMDs) for multimode control of chimney for along-wind response is presented. A concrete chimney considered herein is an assemblage of two-dimensional (2D) beam elements, each assumed to have constant diameter over the element length. Along-wind forces are simulated using the Kaimal wind spectrum. The response of the chimney is to be controlled by installing tuned mass dampers (TMDs). Suitable locations of the TMDs are identified along height of the chimney based on its uncontrolled (NC) mode shapes. A TMD unit is placed where the mode shape amplitude of the chimney is the largest or larger in a particular mode to be controlled and is tuned with the corresponding modal frequency—the approach is called multimode vibration response control. The number of modes to be controlled is decided according to desired total modal mass participation. The coupled differential equations of motion for the system are derived and solved using Newmark's step-by-step iteration method. The displacement and acceleration responses of the chimney under the along-wind forces are computed to study the effectiveness of the d-MTMDs as compared with single tuned mass damper (STMD) and with arbitrarily installed d-MTMDs (ad-MTMDs). In addition, suitable mass and damping ratios for the STMD, ad-MTMDs, and d-MTMDs are obtained to achieve improved dynamic response control. It is observed that the d-MTMDs are effective controllers being designed as per vibration mode to be controlled.

Wind Loads on Tall Buildings: A Comparative Study of the International Wind Codes and Numerical Simulation

Wind codes and standards have been used commonly when designing regularshaped tall buildings to withstand wind loads. High-Frequency Base Balance (HFBB) data analysis and Computational Fluid Dynamics (CFD) have now emerged as alternative techniques to these wind codes and standards. This paper compares wind-induced building responses estimated from CFD analysis and those obtained using major international wind codes: AS/NZS1170.2:2011 (Australia/New Zealand), AIJ-RLB-2004 (Japan) and Eurocode-2005 (Europe), with HFBB predictions. The initial comparison was done on a rectangular 60-storey building model and subsequently, the study was extended to building models with different b/d ratios (breadth/depth) under three height categories. The results show that there are minor discrepancies between the code-predicted alongwind responses and those obtained using different approaches with different b/d ratios. Moreover, the across-wind responses predicted by the wind codes significantly deviate from the HFBB results, especially when the wind direction is normal to the shorter face of the building. The deviations intensify as the b/d ratio decreases. Nevertheless, the CFD predictions correspond well with the HFBB predictions for along-wind responses having deviations under 10%, highlighting the capability of CFD simulation for predicting global wind-induced responses of tall buildings.

Dynamic along wind response of tall buildings using Artificial Neural Network

This paper proposes a simplified approach for estimating the dynamic along-wind response of tall buildings using Artificial Neural Network (ANN). Tall buildings are usually slender and are sensitive to lateral drift due to the wind load. The wind load on such buildings can be calculated using wind load code for some specific H:b:d ratios of the building. However, the wind loads for building dimensions ratios not specified in the code, are estimated by wind tunnel testing. These tests are more expensive in terms of valuable resources, time and cost. In the present study, ANN models are developed for predicting the dynamic along-wind response in terms of base shear and base bending moment based on Indian Wind Code IS 875 (Part -3):2015 (IWC). The predictions made by the developed ANN models have shown good agreement with the desired output. Finally, the paper proposes a series of charts for predicting dynamic along wind response of the building for few configurations which are not included in IWC.

Aeroelastic Response from Indicial Functions with a Finite Element Model of a Suspension Bridge

The present paper describes a comprehensive analysis of the aeroelastic bridge response in time-domain, with a finite element model of the structure. The main focus is on the analysis of flutter instability, accounting for the wind forces generated by the bridge motion, including twisting as well as vertical and horizontal translation, i.e. all three global degrees of freedom. The solution is obtained by direct integration of the equations of motion for the bridge-wind system, with motion-dependent forces approximated from flutter derivatives in terms of rational functions. For the streamlined bridge box-girder investigated, the motion dependent wind forces related to the along-wind response are found to have a limited influence on the flutter velocity. The flutter mode shapes in the time-domain and the frequency domain are consistent, and composed of the three lowest symmetrical vertical modes coupled with the first torsional symmetric mode. The method applied in this study provides detailed response estimates and contributes to an increased understanding of the complex aeroelastic behaviour of long-span bridges.

Gust Buffeting of Slender Structures and Structural Elements: Simplified Formulas for Design Calculations and Code Provisions

AbstractThe lack of simple methods to determine the simultaneous alongwind, crosswind, and torsional loading and response of slender structures and structural elements is a major shortcoming in des...

Comparative Study of Along-Wind Response of Major International Codes with Indian Code

Comparative Study of Along-Wind Response of Major International Codes with Indian Code

Aero-elastic wind tunnel test of a high lighting pole

This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

Wind-induced responses of a tall building with a double-skin façade system

To date the engineering community has seen double-skin façade systems as non-structural elements on buildings for the aesthetic desire, improving the indoor environment, reducing the energy use, and even improving acoustics in buildings. In this study, the effects of a double-skin façade system on the wind-induced responses of a tall building were investigated via a program of wind tunnel tests. Two types of wind tunnel tests, i.e. aeroelastic test and pressure test, were performed. It was found that a double-skin façade with/without vertical openings installed in front of the windward face of the building model results in very different effects on the wind-induced responses in alongwind and crosswind directions. In the alongwind direction, the façade with/without openings induces negligible effects on the wind-induced response. However, in the crosswind direction, the façade with opening(s) reduces the wind-induced response significantly, whereas the façade without any opening increases the response, compared to the bare tall building model. Therefore, in addition to achieve the purposes of the aesthetic desire, improving indoor environment and reducing energy use, the double-skin façade system with vertical opening(s) can also be used to effectively reduce crosswind responses without inducing larger alongwind responses.

Along-Wind Response of High-Rise Buildings Subjected to Hurricane Boundary Layer Winds

AbstractRecent studies show that characteristics of hurricane surface winds are different from those of nonhurricane surface winds. The characteristics relevant to analyzing high-rise buildings inc...

LQG Control of Along-Wind Responses of Tall Building Using Composite Tuned Mass Dampers

A composite tuned mass damper(CTMD) is a vibration control device consisting of an active-passive tuned mass dampers supported on the primary vibrating structure. The performance of CTMD in mitigating wind-induced vibration of tall building is investigated. Optimum parameters of a passive tuned mass damper(PTMD)for minimizing the variance response of the damped primary structure under random loads, with different mass ratio of an active tuned mass damper(ATMD) to a PTMD have been used for the optimum parameters of CTMD. The active control force generated by ATMD actuator was estimated by using linear quadratic Gaussian(LQG) controller, and the fluctuating along-wind load, treated as a stationary random process ,was simulated numerically using the along-wind load spectrum proposed by Solari .Comparing the along-wind rms response of tall building without a CTMD, the CTMD is effective in reducing the response to 40%~45% of the response without the CTMD. Therefore, the CTMD system was effective in reducing wind-induced vibration of tall building.

Across and along-wind responses of tall building

Most modern tall buildings using lighter construction materials are more flexible, which can lead to excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. It is necessary to predict and mitigate such wind-induced vibration at the preliminary design stage. Fluctuating across and along-wind loads acting on a tall building that could not be formulated theoretically were simulated numerically in the time domain using known across and along-wind load spectra. These simulated wind loads were used to estimate the across and along-wind responses of a tall building, which are less narrow-banded processes, based on the state space variable approach. The simulated across-wind response of root-mean-square value (0.0047) and that of KAREEM’s (0.0040) and the simulated along-wind response of root-mean-square value (0.021) and that of SOLARI’s (0.027) were compared. It is found that these are good approximations of closed form responses. Therefore, these numerically simulated across and along-wind loads can be used for across and along-wind responses estimation for the wind-resistant design of a tall building at the preliminary design stage.

Passive control of along-wind response of tall building

Most of modern tall buildings using lighter construction materials with high strength and less stiffness are more flexible, which occurs excessive wind-induced vibration, resulting in occupant discomfort and structural unsafety. It is necessary to predict wind-induced vibration response and find out a method to mitigate such an excessive wind-induced vibration at the preliminary design stage. Recently, many studies have been conducted in using actuator control force based on the linear quadratic optimum control algorithm. It was accepted as a common knowledge that the performance of passive tuned mass damper (TMD) could increase by incorporating a feedback active control force in the design of TMD, which is called active tuned mass damper (ATMD). However, the fact that ATMD is superior to TMD to reduce wind-induced vibration of a tall building is still a question. The effectiveness of TMD for mitigating the along-wind vibration of a tall building was investigated. Optimum parameters of tuning frequency and damping ratio for TMD under a random load which has a white noise spectra were used. Fluctuating along-wind load acting on a tall building treated as a stationary Gaussian random process was simulated numerically using the along-wind load spectra. And using this simulated along-wind load, along-wind responses of a tall building with and without TMD were calculated and the effectiveness of TMD in mitigating the along-wind response of a tall building was found out.

Investigation of the effects of free-stream turbulence on wind-induced responses of tall building by Large Eddy Simulation

In this study, a square rectangular tall building is considered to investigate the effects of turbulence integral length scale and turbulence intensity on the along-wind responses, across-wind responses and torsional responses of the tall building by Large Eddy Simulation (LES). A recently proposed inflow turbulence generator called the discretizing and synthesizing random flow generation (DSRFG) approach is applied to simulate turbulent flow fields. It has been proved that the approach is able to generate a fluctuating turbulent flow field satisfying any given spectrum, desired turbulence intensity and wind speed profiles. Five profiles of turbulence integral length scale and turbulence intensity are respectively generated for the inflow fields by the DSRFG approach for investigating the effects of turbulence integral length scale and turbulence intensity on the wind-induced responses of the tall building. The computational results indicate that turbulence integral length scale does not have significant effect on the along-wind (displacement, velocity and acceleration) responses, across-wind displacement and velocity responses, while the across-wind acceleration and torsional responses vary without a clear rule with the parameter. On the other hand, the along-wind, across-wind and torsional responses increase with the growth of turbulence intensity.

Steenbergen, R.D.J.M., Vrouwenvelder, A.C.W.M., Geurts, C.P.W., 2012. The use of Eurocode EN 1991-1-4 procedures 1 and 2 for building dynamics: A comparative study. Journal of Wind Engineering and Industrial Aerodynamics 107–108, 299–306

The Journal of Wind Engineering and Industrial Aerodynamics published a paper (Steenbergen et al., 2012) providing a wide parametric analysis aimed at comparing the results by procedures 1 and 2 of Eurocode 1, in order to evaluate the dynamic alongwind response of buildings. Based on such analysis, that paper pointed out that the differences between the two procedures and the theoretically correct values are small with reference to the structural factor. For the comfort level, instead, larger differences occur and procedure 2 is preferable. This discussion shows that procedures 1 and 2 involve variations typical of different approximations and calculation methods and that such differences are almost negligible with respect to the variations obtained when taking duly into account crosswind and torsional accelerations. A wider prospect on the code evolution is also drawn.

Active Control of Along-Wind Response of a Tall Building with AMD Using LQR Controller

Most of modern tall buildings using lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. The optimal control technique for reducing along-wind vibration of a tall building based on the linear quadratic regulator (LQR) is presented in this work. Actively controlled reduced along-wind vibration response is obtained from the tall building installed in an active mass damper (AMD) with a LQR controller. Fluctuating along-wind load is generated using numerical simulation method, which can formulate a stationary Gaussian white noise process. Simulating wind load in the time domain using known spectra data of fluctuating along-wind load is particularly useful for estimation of windinduced vibration which is more or less narrow banded process such as a along-wind response of a tall building. In this work, fluctuating along-wind load acting on a tall building treated as a stationary Gaussian white noise process is simulated numerically using the along-wind load spectra proposed by G. Solari in1992. And using this simulated along-wind load estimated the reduced along-wind vibration response of a tall building installed in an AMD with a LQR controller.

LQG Control of Along-Wind Response of a Tall Building with an ATMD

Modern tall buildings use lighter construction materials that have high strength and less stiffness and are more flexible. Although this results in the improvement of structural safety, excessive wind-induced excitations could lead to occupant discomfort. The optimal control law of a linear quadratic Gaussian (LQG) controller with an active tuned mass damper (ATMD) is used for reducing the along-wind response of a tall building. ATMD consists of a second mass with optimum parameters for tuning frequency and damping ratio of the tuned mass damper (TMD), under the stationary random load, was used. A fluctuating along-wind load, acting on a tall building, was treated as a stationary Gaussian white noise and was simulated numerically, in the time domain, using the along-wind load spectra proposed by G. Solari in 1993. Using this simulated wind load, it was possible to calculate the along-wind responses of a tall building (with and without the ATMD), using an LQG controller. Comparing the RMS (root mean square) response revealed that the numerically simulated along-wind responses, without ATMD, are a good approximation to the closed form response, and that the reduced responses with ATMD and LQG controller were estimated by varying the values of control design parameters.