Across-wind Response Research Articles

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.

Computing dynamic across-wind response of tall buildings using artificial neural network

This paper presents the development of artificial neural network (ANN) model for predicting the dynamic across-wind response of tall building as per the provisions given in Indian Wind Code (IWC), IS 875 (Part-3):2015. IWC has given the procedure for estimating across-wind load response for limited aspect ratios of the building. For calculating the across-wind response not conforming to the ratios specified in the code, additional time-consuming and expensive studies are required. In order to minimise such tedious studies, an efficient computational technique is essential to determine wind response. ANN proves to be a promising alternative technique for analysing complex engineering problems. Thus, in this paper, using the best-fit model of ANN, predictions are made for the building configurations that are not included in IWC. The results are plotted as a series of charts in terms of base shear and the base bending moment. It is found that the predictions made using the trained and developed ANN models are in good agreement with the desired output.

Wind loading on high-rise buildings and the comfort effects on the occupants

The design of low to medium-rise buildings is based on quasi-static analysis of wind loading. Such procedures do not fully address issues such as interference from other structures, wind directionality, across-wind response and dynamic effects including acceleration, structural stiffness and damping which influence comfort criteria of the occupants. This paper studies wind loads on a prototype, rectangular cross-section building, 80 m high. Computational Wind Tunnel (CWT) tests were performed using Autodesk Flow Design with the buildings located in London and New York City. The analysis included tests with and without the surrounding structures and manual computation of wind loads provided data for comparison. Comfort criteria (human response to building motion) were assessed from wind-induced horizontal peak accelerations on the top floor. As expected, analytical methods proved conservative, with wind pressures significantly larger than those from the CWT tests. Surrounding structures reduced the mean component of the wind action. As for comfort criteria, across-wind direction governed the horizontal accelerations with wind targeted on the building’s narrow face. CWT tests provide a cheaper alternative to experimental wind tunnel tests and can be used as preliminary design tools to aid civil engineers, architects and designers with high-rise developments in urban environments.

Wind-induced responses of tall buildings under combined aerodynamic control

The new trend towards constructing taller buildings makes modern tall buildings be increasingly susceptible to wind excitations. Therefore, a combined aerodynamic control, including the shape optimization of the cross-section (passive aerodynamic control) and air suction (active aerodynamic control), is put forward to achieve a more considerable reduction of the wind-induced responses of a tall building with square cross-section, so as to improve its wind-resistance performance. Firstly, based on the wind excitations acquired by wind tunnel test of four suction controlled tall building models with different cross-sections (consists of the square, corner-recessed square, corner-chamfered square and Y-shaped cross-sections, and are denoted as Models 1–4 respectively), the wind-induced responses of the prototype tall buildings and simplified mass-spring models are calculated using the time history analysis method. Secondly, effects of the suction flux coefficient CQ, shapes of the cross-sections and wind direction angles θ on the characteristics of the wind-induced responses are analyzed. The results show that the combined aerodynamic control is very effective in reducing the along-wind and across-wind responses at most cases, however, it can sometimes be unfavorable to the torsional responses. Among the four tall buildings, Model 2 has the best performance in the along-wind direction, with a maximum reduction of the extremum tip displacement of 34% caused by the shape optimization, and 29% caused by the air suction and a total of 63% caused by the combined aerodynamic control at a relatively low CQ (CQ = 0.0159). However, the regularity is quite different for the across-wind responses; when θ is equal to 0°, the maximum reduction of the extremum tip displacement in the across-wind direction caused by the shape optimization and air suction are 49% for Model 4 and 47% for Model 1 respectively. Finally, a quantitative discussion on the reduction of the wind-induced responses of tall buildings caused by the combined aerodynamic control is conducted, which can provide a valuable reference for further studies or potential engineering applications.

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.

Experimental study of aerodynamic damping of a twisted supertall building

The aerodynamic damping ratios and aeroelastic instability of a 180° helical supertall building with good aerodynamic behavior in both the along-wind and across-wind responses were investigated using an aeroelastic model test (rocking vibration model test). The aerodynamic damping ratios for the 180° helical and square models were evaluated using the random decrement technique. Furthermore, the effect of the triggering level and number of time segments on the evaluation of the aerodynamic damping ratio was also investigated. It was found that both the mean and fluctuating displacement responses of the 180° helical model in the along- and across-wind directions showed better aerodynamic behaviors than those of the square model. Aeroelastic instability of the 180° helical model was not observed at any of the reduced velocities considered in the study. In the along-wind direction, the aerodynamic damping ratios of the 180° helical model exhibit similar trends to those of the square model. However, in the across-wind direction, the aerodynamic damping ratios of the 180° helical model show significantly different trends than those of the square model. Furthermore, there was no effect of the variation in the wind direction on the aerodynamic damping ratio of the 180° helical model. We found that in the evaluation of the aerodynamic damping ratio, it is possible to adopt the triggering level at the value of the standard deviation or √2 times of the standard deviation of the displacement responses if the random decrement signature has a high number of triggering points.

Use of modal interference approach (MIA) to reduce wind-induced building motions

A new method of structural optimization to reduce across-wind responses of tall buildings, named MIA (modal interference approach), is proposed in this paper. This method is based on an observation that if there are multiple modes participating in vortex-induced oscillations, these modes tend to interrupt each other, resulting in considerably smaller amplitude of vibration in comparison with a single mode response. A theoretical analysis was performed to describe this phenomenon, based on which MIA was developed. The new method is to stimulate multi-mode responses to vortex excitations by rotating the modal directions away from the wind-susceptible building directions and separating the frequencies between the participated modes. Wind tunnel studies of a high-frequency force balance model and a stick aeroelastic model verified the effectiveness of the proposed method.

Across-wind load on rectangular tall buildings

This article looks at the calculation of across-wind response of structures. The focus is on the calculation of cross-wind response of rectangular buildings, which is not covered by Eurocode 1, Part 1-4 (BS EN 1991-1-4) or BS 6399-2.

나선형 형상의 초고층건물의 공력감쇠의 특성

본 연구에서는 변위 및 가속도 응답의 저감 효과에 있어서, 유리한 형상인 <TEX>$180^{\circ}$</TEX> 나선형(Helical <TEX>$180^{\circ}$</TEX>) 초고층건물을 대상으로 공력진동실험 수행하여 나선형 초고층건물의 공력감쇠율의 특성을 조사하였다. 공력감쇠율은 RD법(Random decrement technique)을 이용하여 평가하였다. 또한 RD법에서 부분 샘플의 개수와 초기 조건 값의 변화가 공력감쇠율에 어떤 영향을 미치는지 조사하였다. 실험 결과, 최소 2000개 이상의 부분 샘플을 이용하여 앙상블 평균을 적용하면 공력감쇠율의 불규칙한 변동의 폭을 줄일 수 있음을 검증했고, 기존 연구들과도 잘 부합되는 것을 알 수 있었다. 정방형 모형과 <TEX>$180^{\circ}$</TEX> 나선형 모형의 공력감쇠율의 결과를 살펴보면, 풍방향 공력감쇠율은 건물의 형상이 다름에도 불구하고 무차원 풍속에 따른 공력감쇠율은 매우 유사한 경향을 보였다. 한편, 정방형 모형에 대한 풍직각방향의 공력감쇠율은 <TEX>$180^{\circ}$</TEX> 나선형모형의 공력감쇠율의 특성과는 다른 양상을 보이는 것을 알 수 있었다. 특히 풍향 변화에 따른 <TEX>$180^{\circ}$</TEX> 나선형 모형의 Y방향에 대한 공력감쇠율은 풍향의 변화와 상관없이, 전반적으로 0에 가까운 값을 갖는 경향이 나타났고, 무차원 풍속의 증가와 함께 변동의 폭은 작지만 점진적으로 증가하는 경향을 보였다. 초기 조건 값의 변화에 따른 공력감쇠율을 평가한 결과, 초기 조건 값을 "응답의 표준편차" 또는 RD 함수에 대한 최적화 "<TEX>${\sqrt{2}}{\times}$</TEX>응답의 표준 편차"를 적용하여 평가한 공력감쇠율은 매우 유사한 결과 값과 분포를 보이는 것으로 나타났다. Characteristics of aerodynamic damping ratios of a helical <TEX>$180^{\circ}$</TEX> model which shows better aerodynamic behavior in both along-wind and across-wind responses on a super tall building was investigated by an aeroelastic model test. The aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement (RD) technique. Further, various triggering levels in evaluation of aerodynamic damping ratios using RD technique were also examined. As a result, it was found that when at least 2000 segments were used for evaluating aerodynamic damping ratio for ensemble averaging, the aerodynamic damping ratio can be obtained more consistently with lower irregular fluctuations. This is good agreement with those of previous studies. Another notable observation was that for square and helical <TEX>$180^{\circ}$</TEX> models, the aerodynamic damping ratios in along-wind direction showed similar linear trends with reduced wind speeds regarding of building shapes. On the other hand, for the helical <TEX>$180^{\circ}$</TEX> model, the aerodynamic damping ratio in across-wind direction showed quite different trends with those of the square model. In addition, the aerodynamic damping ratios of the helical <TEX>$180^{\circ}$</TEX> model showed very similar trends with respect to the change of wind direction, and showed gradually increasing trends having small fluctuations with reduced wind speeds. Another observation was that in definition of triggering levels in RD technique on aerodynamic damping ratios, it may be possible to adopt the triggering levels of "standard deviation" or "<TEX>${\sqrt{2}}$</TEX> times of the standard deviation" of the response time history if RD functions have a large number of triggering points. Further, these triggering levels may result in similar values and distributions with reduced wind speeds and either may be acceptable.

Enhancing wind performance of tall buildings using corner aerodynamic optimization

Wind-induced loads and motions of tall buildings usually govern the design of the lateral load resisting systems. The outer shape of the building is one of the many parameters that affect these design wind loads and responses. This study presents building corner aerodynamic optimization procedure (AOP) to reduce the wind load, by coupling an optimization algorithm, large eddy simulation (LES) and an artificial neural network (ANN) based surrogate model. As an illustration, corner mitigation that has limited effect on both the structural and the architectural design is presented. Two aerodynamic optimization examples focusing on drag and lift minimization that consider wind directionality and turbulence are presented. For example, reductions in the order of more than 30% both in along- and across-wind responses are obtained through a two-surface chamfering that was constrained to 20% of the building width.

Assessment of across-wind responses for aerodynamic optimization of tall buildings

A general approach of aerodynamic optimization of tall buildings is presented in this paper, focusing on how to best compromise wind issues with other design aspects in the most efficient manner. The given approach is reinforced by establishing an empirical method that can quickly assess the across-wind loads and accelerations as a function of building frequencies, building dimensions, aspect ratios, depth-to-width ratios, and site exposures. Effects of corner modifications, including chamfered corner and recessed corner, can also be assessed in early design stages. Further, to assess the effectiveness of optimization by tapering, stepping or twisting building elevations, the authors introduce a method that takes use of sectional aerodynamic data derived from a simple wind tunnel pressure testing to estimate reductions on overall wind loads and accelerations for various optimization options, including tapering, stepping, twisting and/or their combinations. The advantage of the method is to considerably reduce the amount of wind tunnel testing efforts and speed up the process in finding the optimized building configurations.

Across-wind response of tall circular chimneys to vortex shedding

A semi-empirical method for predicting across-wind response of a circular chimney due to vortex shedding during lock-in region was earlier presented by the author. This involved use of only structural damping, with suitable modification of spectrum of modal lift force through a parameter ‘fact’, having a value of 0.45. When applied to three typical chimneys, the predicted across-wind base bending moment values showed good comparison with ACI code ACI-307-2008. In this paper, by considering additional experimental data from Wootton, a non-linear relation between the parameter ‘fact’ and the normalized rms tip deflection, (σyDe) is presented. The relationship is also verified using full-scale chimney data by Galemann and Ruscheweyh, Waldeck, and Melbourne. The suggested method is simple and useful for design offices and appears equally applicable both for steel and concrete chimneys.

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.

LQG Control of Across-Wind Response of a Tall Building with AMD

Modern tall buildings are more flexible so occur excessive wind-induced vibration resulting in occupant discomfort and structural safety. Many studies to reduce such a wind-induced vibration using a feedback controller and auxiliary devices have been conducted .The optimal control law of linear quadratic Gaussian (LQG) controller is used for reducing the across-wind vibration response of a tall building with an active mass damper (AMD). Fluctuating across-wind load treated as a Gaussian white noise process is simulated numerically in time domain. And using this simulated across-wind load estimated across-wind vibration responses of tall building with AMD using LQG controller.

Wind-induced traffic signal structure response: Experiments and reduction via helical arm strakes

Traffic signal structures are prone to fatigue failures due to a combination of along- and across-wind dynamic response. Stress reversal magnitudes with respect to wind speed and direction are experimentally investigated in a natural wind environment for a typical cantilevered mast arm traffic signal structure. Results show a prevalence of in-plane response induced stresses due to vortex shedding for wind speeds in the range of 4–6m/s. To better study the role of the tapered arm in the wind-induced response, the mast arm is retrofitted with helical strakes. Although the diameter of the mast arm is not directly related to the adverse stress reversals observed, arm strake installation significantly reduces the across-wind response attributed to vortex shedding. Results indicate that the slender mast arm section is critical in flow separation and vortex formation on the back side of the signal cluster backplates. As a result of the findings herein, properly designed helical arm strakes can be considered for reducing vibrations that can be attributed to vortex shedding, thus have the potential to reduce fatigue-induced damage in critical wind environments.

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.

Evaluation on Aerodynamic Across-Wind Response for a Tall Building Using Tuned Liquid Column Damper

Tuned liquid column damper (TLCD) is more advantageous in terms of space than TLD so that it is far more advantageous when it comes to installation on the actual building. To investigate the effectiveness of a tuned liquid column damper (TLCD) in mitigation wind-induced excitation motion of a tall building, aeroelastic experiments were conducted. A 1: 200 scaled model of an aeroelastic tall building was built, and TLCD models of mass ratio of 1.5% and 3%, respectively, were designed and tested with the aeroelastic model. As such, this study has installed TLCD with different lengths of horizontal pipes at the top most floor of realistic model. This is similar to the actual structure, centred on the interval where the vortex-induced vibration of low wind speed occurs, by conducting aeroelastic model tests in suburban areas and the vibration response in across-wind direction shall be found in order to figure out the wind vibration control effect according to various types (horizontal length, mass ratio) changes.

Serviceability wind risk assessment of tall buildings including aeroelastic effects

One issue that dominates the serviceability design of many modern tall buildings is wind-induced discomfort. The assessment of discomfort risk for the buildings occupants due to the wind action is, therefore, of primary importance. It can be properly carried out only through a reliable estimation of the acceleration responses which, particularly in the across-wind direction, may be influenced by aeroelastic effects. Within this context, a wide experimental campaign was carried out in this study in order to evaluate the wind-induced loads and responses of a continuous equivalent aeroelastic model of a regular square-section tall building. Measurements of surface pressures on 126 taps, overall forces, across-wind displacements and across-wind and along-wind accelerations were simultaneously carried out. Aeroelastic effects involving the across-wind response, which largely exceeds the along-wind one, are evaluated in terms of aerodynamic damping using an experimental-numerical procedure. Across-wind aerodynamic damping is found to take positive values for the model tested having high Scruton number. A general procedure for wind risk assessment of tall buildings related to comfort, in line with the Performance-Based Design (PBD) approach and the PEER (Pacific Earthquake Engineering Research [Center]) equation, is proposed and applied to a case-study building whose aeroelastic response is known from the wind tunnel tests performed.

LQG Control of Across-Wind Response of a Tall Building

Modern tall buildings using high strength and lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety . Recently, many studies have been advanced in using actuator force as an active control force based on the linear quadratic optimum control theory. It needs to predict the wind-induced response and the optimum control force to reduce the excessive wind-induced vibration. It takes a lot of time and cost to do wind tunnel test needed it, so numerical simulation approach instead of that is recommended sometimes. Simulating wind load in the time domain using known spectra data of fluctuating wind load is particularly useful for some prediction of windinduced vibration which is more or less narrow banded process such as across-wind response of a tall building. The simulation procedure is taken from Deodatis. In this study, fluctuating across-wind load acting on a tall building was simulated numerically in the time domain using the across-wind load spectra proposed by A.Kareem in1982. And using this simulated across-wind load estimated the reduced across-wind vibration response of a tall building using the linear quadratic Gaussian (LQG) control method.

Evaluation on Across-Wind Response of Tall Building According to Aerodynamic Shapes

High-rise buildings constructed in large cities are thin and long in their shape and are both unconventional and light-weight. The purpose of this study is to reduce the across-wind response of high-rise buildings (unconventional) under the influence of wind load. As a means to change the external shape of high-rise buildings, we selected the flat Y-type form. It is generally applied in domestic high-rise buildings for examination. Wind tunnel tests take place on 12 high-rise buildings, composed of three different Y-type shapes such as basic square forms with square cross sections and unconventional forms, in a suburban area (α=0.15) with a turbulence intensity of 10%.