Across-wind Response Research Articles

Effects of turbulence intensity and integral length scale on wind-induced vibrations of a three-dimensional aeroelastic square cylinder

Despite a wealth of prior research on the effects of free-stream turbulence (FST) on the aerodynamics of square cylinders, there is limited knowledge about their aeroelasticity such as characteristics of wind-induced vibrations that vary with the FST properties. This paper focuses on the investigation of the effects of FST properties including longitudinal turbulence intensity and integral length scale on the wind-induced vibrations of a three-dimensional (3D) aeroelastic square cylinder with an aspect ratio of 10 (a super-tall building model). Through wind tunnel testing, displacements of the aeroelastic model are measured in smooth flow and four turbulent flows to experimentally investigate its characteristics of fluid-solid interaction, including along- and across-wind vibrations, especially vortex-induced vibration and galloping. The effects of the turbulence intensity with a higher-level than previous studies are also investigated. The results show that the root-mean-square (RMS) displacements of the along-wind responses increase with the increase of turbulence intensity and are not affected by integral length scale. For the across-wind responses, in the non-lock-in region, the RMS displacements generally increase with the increase of turbulence intensity. In the lock-in region, the RMS displacements remain unchanged with the increase of turbulence intensity, while increase with the increase of integral length scale. This paper aims to improve the comprehension of the effects of FST on the wind-induced vibrations of 3D square cylinders and to furnish valuable insights for the wind-resistant design of slender structures, such as supertall buildings.

Full-Scale Observations for the Combined Wind-Induced Responses of a Cylindrical Tower

This paper presents full-scale observations of wind-induced vibrations on a 140[Formula: see text]m high cylindrical reinforced concrete tower under non-stationary and strong wind conditions. The vibration responses of the tower in two planar orthogonal axes and rotation, in conjunction with wind speed and direction data, have been utilized to extract the response characteristics. The primary focus is on discussing the correlation of wind-induced responses in three components: Along-wind, across-wind, and torsion. Throughout the varying levels of oscillation, the tower’s responses clearly exhibit correlations among these components. The correlation coefficients between along-wind and across-wind responses, as well as along-wind and torsional responses, remain negligible across the entire dataset. In contrast, during intense oscillations, there is a near-perfect correlation between the across-wind and torsional responses. Furthermore, the probability density functions (PDFs) of the response components under strong wind conditions significantly deviate from the Gaussian distribution and closely resemble the Cauchy distribution. The joint PDFs also indicate that the along-wind response is statistically independent of the other response components, while the across-wind response correlates well with the torsion, as indicated by the non-Gaussian distribution. This paper also includes distinct observations regarding dominant oscillating frequencies, torsional amplitudes, and vertical vibration amplitudes. The importance of this research lies in its examination of the relationship between different response components, a crucial aspect in understanding how structures behave under wind loading. By emphasizing the need for full-scale measurements, this study aims to provide valuable validation for previous theoretical and experimental research findings.

Performance comparison of linear and nonlinear compliant liquid dampers-inerter in controlling across-wind response of benchmark tall building

The potential of compliant liquid dampers-inerter (CLDI) for response control of tall buildings, capitalizing on the mass amplification property of the inerter, has been explored. However, the influence of the compliance connection on the damper displacement, energy dissipation, and inerter force is never addressed. The present work introduces a nonlinear compliant liquid damper-inerter (NCLDI), in which the compliance connection is achieved by joining the tank with the building through nonlinear spring and linear dashpot elements. The nonlinear mechanism (restoring force) is generated by connecting two linear springs in series. The effectiveness of NCLDI in reducing the across-wind response of tall buildings is examined and compared with that of a CLDI. For numerical demonstration, the 76-storey benchmark tall building is considered and subjected to across-wind loading. With the building's available mass, damping, and stiffness matrices, the uncontrolled and controlled structural responses are obtained using the Newmark–Beta method in the MATLAB environment. Iterations are executed at each time step to address the nonlinear stiffness term incorporating the Newton-Raphson method. Optimization is performed to estimate the optimum damper parameters utilizing MATLAB's multi-objective genetic algorithm solver, ‘gamultiobj’. The four selected objective functions are the peak and root-mean-square values of the roof displacement and acceleration. The performance of both the dampers is investigated for different inerter topologies with variable inertance ratios. The CLDI is found to be efficient when the inertance ratio and topology are less. However, an enhanced mitigation effect of the NCLDI compared to the CLDI is observed for higher inertance with a large topology. In addition, the stroke length of the damper is reduced significantly in case of NCLDI, which is a notable advantage for any passive damping device.

Uncertainty in the dynamic properties of tall buildings and propagation to the wind‐induced response

SummaryThe response of tall buildings to wind actions is commonly assessed through the quasi‐static approach considering mean, background, and resonant components of the action. The latter accounts for the amplification due to resonance and depends on the dynamic properties of the buildings, that is, modal mass, frequency, and damping ratio. Selecting appropriate values of the modal parameters of tall buildings is not immediate and is usually done using predictive models. These contain uncertainty, which eventually propagates to the dynamic response. The main aim of the paper is the assessment of uncertainty in the dynamic response of flexible buildings to wind action arising from a not perfect knowledge of their dynamic properties. The paper explicitly refers to the dynamic models given by Eurocode 1, but the approach is general, and the analyses can be repeated selecting any other model. It is found that the bias in the dynamic factor is always less than one, with values on average between 0.86 and 0.98. This indicates that the approach of Eurocode 1 is conservative. The only exception is that of the acrosswind response of steel buildings with an high aspect ratio, in which case the bias can be as large as 1.16. As to randomness, the coefficient of variation of the alongwind dynamic factor is very seldom found to exceed 10%, with average values around 5%. Such values are much lower than those of the coefficient of variation of damping, which is in the order of 50% or more. This indicates that uncertainty attenuates when it propagates to the response. On the other hand, the coefficient of variation of the acrosswind and torsional dynamic factors reaches values of 20% or more, indicating that such attenuation is much lower in that case.

Experimental study of the vortex-induced vibration of a circular cylinder considering coupling effect in along- and across-wind direction

Tower-like structures with circular section are prone to unexpected across-wind vortex-induced vibration (VIV), and the along-wind response is usually neglected due to its amplitude being much smaller than that of VIV. Recent research pertaining to tall buildings has revealed, nevertheless, that the structural responses in the along-wind and across-wind directions are coupled in a way that results in a decrease in the across-wind response at the wind speed of VIV along with an increased along-wind response. However, the impact of coupling on tower-like structures has not yet been examined. Moreover, tower-like structures with a circular cross section undergo tip-induced vibration at the wind speed higher than vortex-resonance wind speed. However, the impact of this coupling effect on the tip-induced vibration remains uncertain. In this paper, a two-degree-of-freedom rocking model wind tunnel test is carried out under low turbulence and turbulent flow to investigate the coupling effect of tower-like structures. Experiment results show that the coupling effect exists at both the vortex-resonance vibration wind speed and the tip-induced vibration wind speed. Besides, when the along-wind response is coupled with the across-wind responses, it illustrates a steady harmonic vibration with a hardened non-Gaussian characteristic, and its kurtosis decreases to 1.5. Finally, the measured tip-associated vortex shedding frequency suggests that there is a “lock-in” phenomenon of the tip-induced vibration, this new finding improves the understanding of the wind-induced response at high wind speeds.

Across-wind response characteristics of tall-square towers in urban flow: An experimental study focused on the aeroelastic effects

To fully use the land resource in the urban regions of metropolises, high-rise buildings of large aspect ratio maybe preferred for the new constructions. To systematically investigate the across-wind responses of these quite slender structures, the urban boundary layer flow of high turbulence intensity was simulated in the wind tunnel, and aeroelastic tests realized by the pivot model setup were carried out for the square cross section towers of various heights resulting in large aspect ratios (λ = 12, 16, 20). No appreciable aeroelastic behaviors have been observed for the λ = 12 tower even for a very low damping ratio (0.57%). This is in line with the many previous studies for the tall-square tower with an aspect ratio not higher than 10, likely due to the very high turbulence intensity in the urban terrain, mitigating the occurrence of possible aeroelastic behaviors. In contrast, the λ = 16 and (especially) the λ = 20 towers exhibit strong oscillations known as the across-wind galloping, evidenced by the monotonic increase in the amplitude–velocity curve and the clear characteristics of simple-harmonic oscillations. Moreover, it is observed that for a certain range of low damping ratios, these large oscillations were initiated at the same wind speed very close to the vortex-resonance wind speed. The interaction mechanism between vortex induced vibration and galloping is thus supposed responsible for this observation (even in urban flow). Finally, peak across-wind responses at various damping ratios were provided as well, serving as a useful reference for the future design of similar tall-square towers.

Inerter-assisted pendulum-tuned mass damper for across-wind response control of tall buildings

The present study proposes an inerter-assisted pendulum-tuned mass damper (IA-PTMD) to control across-wind response in tall buildings. An inerter is introduced between the pendulum’s mass and structure, thereby enhancing the structural control effectiveness of a classical one-story pendulum-tuned mass damper (PTMD). Across-wind response of a benchmark tall building with IA-PTMD is investigated in this study. The combined equations of motion were solved numerically using the state-space variable method. The design of the IA-PTMD was carried out using this numerical analysis, and optimum parameters were obtained. It is found that with a lower mass and inerter ratio, the structure does not require the addition of viscous dampers. With an identical structure mass ratio, IA-PTMD outperforms the PTMD and was found fairly robust against off-tuning due to uncertainties in building stiffness. From the results observed in this study, it can be concluded that an optimally designed IA-PTMD effectively controls across-wind response in tall buildings.

Experimental study on the aeroelastic response of a square supertall building considering twisted wind effect

For high-slenderness supertall buildings, the aeroelastic effect has been carefully addressed, as the ignorance of aeroelastic response may significantly affect the serviceability of the building. Several state-of-the-art researches have analyzed the influence of twisted wind field (TWF) on aerodynamic wind loads on tall buildings. In this study, the influence of TWF on the aeroelastic response of buildings is studied experimentally. The displacement time histories, trajectories and correlation coefficients of wind-induced responses, statistical characteristics, probability density functions and power spectra of across-wind displacement under various levels of reduced wind speeds are examined. The experimental results show that TWF greatly affects the aeroelastic behaviors of buildings. When reduced wind speed is lower than the critical vortex-resonance wind speed, TWF strengthens the coupling effect between the along-wind and across-wind responses, while for reduced wind speed beyond the critical vortex-resonance wind speed, TWF weakens the coupling effect, and weakens more for the case of larger structural damping level. Also, it is found in this study that TWF strengthens stochastic buffeting and suppresses the vortex-resonance vibration. Furthermore, TWF may modify the lock-in region of vortex-resonance. Overall, it is crucial to reproduce TWF when reduced wind speed is lower than the critical vortex-resonance wind speed, as the TWF-induced across-wind responses can be increased by 89 % in this wind speed region, while for larger wind speeds (i.e., Ur > 10), the across-wind responses are generally weakened in the presence of twisted wind and the wind-resistance design can be accomplished based on the experimental results obtained under CWF. This study contributes to a better understanding for the aeroelastic characteristics of buildings under twisted wind.

Effects of side and corner modification on the aerodynamic behavior of high-rise buildings considering serviceability and survivability

This study explores the complementary effects of side and corner modification on the aerodynamic behavior for high-rise buildings across representative design wind speeds. Twelve doubly-symmetric prismatic models were examined using high-frequency force balance (HFFB) wind tunnel testing at the University of Florida. The effectiveness of the aerodynamic strategies was quantified using roof drift and roof acceleration under different design wind speeds covering serviceability and survivability. The results show that both corner and side modifications can achieve promising aerodynamic performance under high design wind speeds. However, the effectiveness of the aerodynamic strategies is significantly reduced under low design wind speeds. With a corner modification strategy, the vortex shedding frequency is increased, leading to worse across-wind response at lower design wind speeds when compared to the square benchmark model. To address this issue, side modifications (i.e., side protrusions) can be used to preserve the vortex shedding frequency and achieve competitive aerodynamic performance while simultaneously maintaining the floor area and geometry. This research explores new aerodynamic modification options for owners, architects, and structural engineers with the aim of better aerodynamic performance for high-rise buildings without compromising other design objectives.

구조물의 이력거동 특성에 따른 비탄성 내풍설계

In this study, inelastic wind design was performed by using single-degree-of-freedom models, and their inelastic alongwind and across-wind responses depending on hysteretic models were compared. For along-wind responses, damage accumulation occurred due to the mean component of along-wind load. From the nonlinear time history analysis results, an increase of yield strength and self-centering hysteretic model appeared to restrict the damage accumulation with ratcheting effectively. Across-wind responses were highly affected by the energy dissipation depending on hysteretic models. Hysteretic models for steel structure and concrete structure with good hysteretic behavior showed less maximum displacement than the elastic response.

Application scope of equivalent linear technique for across-wind response analysis of tall flexible structures considering nonlinear aero-elastic effect

Large across-wind response of tall flexible structures becomes an increasing concern due to the significant nonlinear aero-elastic effect. The nonlinear aerodynamic damping, which is in phase of time-variant structural velocity, is usually employed to describe nonlinear aero-elastic effect. For the sake of evaluating the across-wind response of tall flexible structures within the framework of linear random vibration theory, equivalent linear aerodynamic damping model is required, which can be deduced from either harmonic balance (HB)- or statistical linearization (SL) technique. This study addressed clarifying application scope of various equivalent linear techniques for evaluating across-wind response of tall flexible structures. By conducting the Monte Carlo simulation and free-vibration wind tunnel test, it is clarified that the root-mean-squared (RMS) response calculated by the HB equivalent linear aerodynamic damping is acceptable, while is not satisfactory with respect to the SL technique especially when the structure is with lower damping level, and in the vicinity of vortex lock-in wind speed. Moreover, it is found that neither HB- nor SL technique can accurately predict the peak response. It is revealed in this study that accuracy of various equivalent linear techniques is essentially affected by probability density function of across-wind response.

Next generation PBWE: Extension of the SAC-FEMA method to high-rise buildings under wind hazards

This paper proposes a method for the Performance-Based Wind Engineering (PBWE) of buildings by extending the well-established SAC-FEMA method originally implemented in seismic engineering for the evaluation of the mean annual frequency (MAF) of pertinent structural Limit States (LSs) in frame buildings. The development of such a method, that we will call the “SAC-FEMA WIND” method, implies the consideration of specific wind engineering peculiarities, like the classification of the across-wind response in two distinct regimes due to buffeting and vortex shedding phenomena, with the consequent adaption of the analysis procedures already defined for earthquakes to these two regimes. The method is then applied for the MAF evaluation of the occupants’ comfort LS for a high-rise steel building: the SAC-FEMA WIND is calibrated by comparing the obtained results with those coming from a Monte Carlo numerical analysis. This allows the definition of appropriate analysis procedures and shows the reliability of the SAC-FEMA WIND in evaluating MAFs. The SAC-FEMA WIND can be viewed as a “next generation” method for PBWE, in the sense that, after years of developments of the PBWE in research, now simplified methods like the SAC-FEMA WIND are needed for the implementation in Standards and in the design practice of explicit probabilistic PBWE approaches.

Experimental study on the coupling effects of wind-induced vibration of square-sectioned high-rise buildings with different stiffness ratios

In the wind-resistant design of high-rise buildings, the wind-induced response, excited by incident turbulence and vortex shedding of the wake flow, is an important design component. Larger self-excited across-wind responses occur when the wind speed closes to the vortex lock-in wind speed during which the vortex shedding frequency is basically equal to the natural frequency of the structure in the across-wind direction. Because of the similar natural frequency and damping in two sway directions in actual construction applications, the along-wind response will be significantly affected by the across-wind response. This phenomenon is called the coupling effect. In this paper, the coupling effect of wind-induced responses of high-rise buildings with square section is investigated using a stick aeroelastic model in wind tunnel tests. The effects of the sectional stiffnesses ratio on the along-wind and across-wind directions are clarified. Experimental results show that responses are significantly coupled when the wind speed approximates to the ‘lock-in’ region with a stiffness ratio close to 1:1. Compared with the wind-induced response measured in a single-degree-of-freedom system, the across-wind response of a two-degrees-of-freedom model decreases significantly and the along-wind response increases within the lock-in wind speed region. Furthermore, the characteristics of the along-wind response are observed to be shifted from buffeting to vortex-induced vibration with increasing responses and hardening Gaussian probability density function of the response within the lock-in region. The coupling effect can be identified from changes in the magnitude of dynamic response and probability density function of the along-wind response beyond the lock-in region. At a Scruton number of about 10.5, the coupling effect is strong with the stiffness ratios approximate 0.85:1, 1:1, and 1.15:1. However, at a Scruton number of about 20, the coupling effect only emerges when the stiffness ratio approaches 1:1.

Multiple tuned liquid sloshing dampers for across-wind response control of benchmark tall building

Multiple tuned liquid sloshing dampers for across-wind response control of benchmark tall building

Design of tuned liquid sloshing dampers using nonlinear constraint optimization for across-wind response control of benchmark tall building

The present study proposes an optimal design methodology of tuned liquid sloshing dampers (TLSDs) installed in wind-excited benchmark tall building. The TLSDs design parameters were determined using proposed optimal design methodology based on nonlinear constraint optimization technique. Top floor peak acceleration was considered as the objective function and maximum value of sloshing depth of liquid as a nonlinear constraint for the design purpose. The classical nonlinear shallow water wave theory was used for the simulation of liquid sloshing, and the basic equations of nonlinear liquid sloshing were solved using the Lax Finite Difference Scheme. The governing equations of motion of combined structure-TLSDs system were expressed as state-space variables and structural response was numerically simulated. The findings were presented and assessed on the basis of a comparison between power spectral density functions, time history analysis, root mean square, peak response, and performance criteria for benchmark building with and without TLSDs. The off-tuning effect of TLSDs due to ±15% uncertainty in the building stiffness was also investigated. Further, an attempt has been made to present the control effectiveness of TLSDs in time–frequency domain (wavelet scalogram) using continuous wavelet transformation technique. The optimal TLSDs design based on the proposed methodology was found to be quite effective in serviceability-based design of benchmark tall building under wind loads and can be very useful for the practical design of TLSDs.

Influence of vented floors on the across-wind response of tall buildings

Architectural form can be a significant factor influencing the performance of a tall building under across-wind excitation. When wind tunnel testing of a defined architectural form reveals undesirable behavior, it must be mitigated through engineering modifications such as the addition of structural material or supplementary damping devices. Alternatively, informed design of architectural forms enables a tall building’s shape to be modified in a way that has the potential to significantly reduce its across-wind response. Introducing openings in the form of vented floors was explored to reduce across-wind excitation of a prismatic square building. Single and double-vented aerodynamic treatments were applied at various locations along the height of prismatic square benchmark buildings of 7:1, 8.5:1, and 10:1 slenderness. In total, 36 distinct architectural forms were tested at Skidmore, Owings & Merrill’s experimental boundary layer wind tunnel facility to determine the effectiveness of the vents. A ‘zone of maximum influence’ was identified at approximately 60%–80% of the height of prismatic square buildings. ‘Optimal’ locations for single- and double-vents were determined within this influence zone. Full-scale peak moment and acceleration responses were estimated and compared to evaluate the dependence of venting treatment effectiveness on incident wind speed and flow turbulence.

Interference effects between two tall chimneys on wind loads and dynamic responses

The wind loads of two chimneys with different distances and incident angles were obtained by pressure measurement tests, and the results were presented as interfering factor (IF) contours. The interference effects on the across-wind loads were significantly greater than those on the along-wind loads. The dynamic responses of the chimney were calculated using the frequency domain method, and the extreme response interfering factors (RIFs) at different reduced wind velocities were obtained. For the extreme along-wind responses, the most unfavorable incident angle (MUIA) was 105°, and the maximal RIF was 1.3. For the extreme across-wind responses, the MUIA was 15° or 30°, and the maximal RIF was 1.9. Moreover, the combined envelope interfering factors (EIFsc), which were the combined maximal RIFs of all reduced wind velocities, were determined by combining the along- and across-wind responses. Because the equivalent static wind loads are determined based on the structure responses, EIFsc can be used as the IFs of the equivalent static wind loads as guide for wind-resistant designs of actual chimneys.

Non-linear modelling of vortex induced lock-in effects on circular chimneys

The paper presents results of an extended study of the model developed earlier by the authors for across-wind response of tall circular chimneys to vortex shedding. A non-dimensional parameter,“fact” is used to suitably decrease the spectral bandwidth of the generalized across-wind load spectrum, implicitly accounting for an increase in load correlation. This paper discusses similarity between the parameter “fact” of authors’ model and the ratio of the aerodynamic damping coefficients, (ka/ka,0) in Vickery’s model, with respect to enhancement of correlation of force/response due to vortex shedding under lock-in condition. However, in Vickery’s model, as recommended in CICIND code, while the variation of (ka/ka,0) with increasing normalized amplitude follows a negative curvature, the corresponding variation of “fact” exhibits a positive curvature. Recent wind tunnel experimental results by Lupi et al., showed a positive curvature for the variation of (ka/ka,0) with increasing normalized amplitude. This lends support for authors’ observation. With a suitable scaling factor, an excellent agreement is found between the authors’ results and Lupi’s experimental results. The suggested method was applied to 27 full scale steel chimney data, referred in Lupi’s paper and the response predictions show a good comparison within ±20% limits with full scale values. The usefulness of the mass damping parameter, (2me(ρD2)η) for predicting the across-wind response is also discussed.

Aerodynamic interference of straight and tapered cylinder pairs near the first critical wind speed

The present investigation is concerned with the phenomenon of aerodynamic interference across three cases: between two circular cylinders; a pair of 1:50 tapered cylinders; and a pair of 1:40 tapered cylinders—all in staggered arrangement. Experiments were conducted in the 1.6 ​m × 1.6 ​m wind tunnel at IIT Delhi. Our focus is on the enhanced across-wind response of the downstream cylinder near the first critical wind speed (at which the vortex shedding frequency matches the natural frequency of the structure). It is shown that the magnification in the response (with respect to that of the isolated cylinder) is a strong function of both the pitch and the orientation. It is evident from the current investigation that the magnification factors recommended in IS 4998 (Part 1: 1992, see Fig. 1 therein/2015) and Eurocode 1 (Actions on structures- General actions- Part 1–4: Wind actions, see Equation E. 11 therein) need to be revised upwards. Further, the rule of thumb, used in the design of tall structures, that beyond 15/20 diameters interference is negligible is not tenable, especially for structures of identical geometry.

Downstream interference effect of low-Scruton-number high-rise buildings under turbulent boundary layer flow

This paper investigates the variation of root-mean-square values of acceleration responses and corresponding aerodynamic dampings of two square cross-sectional high-rise buildings with low Scruton numbers due to interference effects caused by neighboring identical buildings. Aero-elastic vibration test is adopted for displacement and acceleration measurements of a rigid, base-pivoted aero-elastic principal building model by a two-directional sway gimbal system. The principal building is manufactured in the shape of a square prism model with an aspect ratio of eight. Twenty close interference locations are of interest, with a special focus on the across-wind responses. Results show that the variations of interfered acceleration responses and estimated damping ratios exhibit different tendencies for different interference locations at different reduced velocities. For the typical upstream interfered effect, the interfering building located at the oblique-upwind locations in this study, the acceleration response with lower Scruton number is suppressed at lower reduced velocities and is amplified at higher reduced velocities. On the other hand, for the secondary downstream interference effect, i.e., the interfering building located at downwind locations, the amplification or reduction in acceleration response is less sensitive to Scruton number but is related to the gap between two buildings. The corresponding response spectra and resultant damping ratios are then calculated to enhance the understanding of different interference mechanisms. Finally, an idealized two-dimensional CFD simulation technique is adopted to further explain the differences between the upstream and downstream interference mechanisms from the viewpoint of the vortex movement between two buildings.