Effects of turbulence intensity and exterior geometry on across-wind aerodynamic damping of rectangular super-tall buildings

Y. Quan,H.L. Cao,M. Gu 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.22 No.2

Across-wind aerodynamic damping ratios are identified from the wind-induced acceleration responses of 15 aeroelastic models of rectangular super-high-rise buildings in various simulated wind conditions by using the random decrement technique. The influences of amplitude-dependent structural damping ratio and natural frequency on the estimation of the aerodynamic damping ratio are discussed and the identifying method for aerodynamic damping is improved at first. Based on these works, effects of turbulence intensity Iu, aspect ratio H/B, and side ratio B/D on the across-wind aerodynamic damping ratio are investigated. The results indicate that turbulence intensity and side ratio are the most important factors that affect across-wind aerodynamic damping ratio, whereas aspect ratio indirectly affects the aerodynamic damping ratio by changing the response amplitude. Furthermore, empirical aerodynamic damping functions are proposed to estimate aerodynamic damping ratios at low and high reduced speeds for rectangular super-high-rise buildings with an aspect ratio in the range of 5 to 10, a side ratio of 1/3 to 3, and turbulence intensity varying from 1.7% to 25%.

Effects of turbulence intensity and exterior geometry on across-wind aerodynamic damping of rectangular super-tall buildings

Quan, Y.,Cao, H.L.,Gu, M. Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.22 No.2

Across-wind aerodynamic damping ratios are identified from the wind-induced acceleration responses of 15 aeroelastic models of rectangular super-high-rise buildings in various simulated wind conditions by using the random decrement technique. The influences of amplitude-dependent structural damping ratio and natural frequency on the estimation of the aerodynamic damping ratio are discussed and the identifying method for aerodynamic damping is improved at first. Based on these works, effects of turbulence intensity $I_u$, aspect ratio H/B, and side ratio B/D on the across-wind aerodynamic damping ratio are investigated. The results indicate that turbulence intensity and side ratio are the most important factors that affect across-wind aerodynamic damping ratio, whereas aspect ratio indirectly affects the aerodynamic damping ratio by changing the response amplitude. Furthermore, empirical aerodynamic damping functions are proposed to estimate aerodynamic damping ratios at low and high reduced speeds for rectangular super-high-rise buildings with an aspect ratio in the range of 5 to 10, a side ratio of 1/3 to 3, and turbulence intensity varying from 1.7% to 25%.

나선형 형상의 초고층건물의 공력감쇠의 특성

김원술,이진학,타무라유키오 대한토목학회 2017 대한토목학회논문집 Vol.37 No.1

Characteristics of aerodynamic damping ratios of a helical 180° 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 180° 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 180° 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 180° 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 amping ratios, it may be possible to adopt the triggering levels of “standard deviation” or “ 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. 본 연구에서는 변위 및 가속도 응답의 저감 효과에 있어서, 유리한 형상인 180° 나선형(Helical 180°) 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 180° 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 180° 나선형모형의 공력감쇠율의 특성과는 다른 양상을 보이는 것을 알 수 있었다. 특히 풍향 변화에 따른 180° 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 “ ×응답의 표준편차”를 적용하여 평가한 공력감쇠율은 매우 유사한 결과 값과 분포를 보이는 것으로 나타났다.

초고층건물의 공력감쇠율

김용철(Kim, Yong-Chul) 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.8

Aerodynamic damping ratios play an important role in the estimations of wind-induced responses of modern super-tall and slender buildings and structures. In the present study, along- and across-wind aerodynamic damping ratios of a square cross-sectional conventional and tapered super-tall buildings with height of 448m were investigated using the Random Decrement Technique (RDT) for the responses obtained from the aeroelastic wind tunnel tests. Wind tunnel tests were conducted under the urban flow condition. Effects of building shape, normalized velocity and wind direction on aerodynamic damping ratios were comprehensively discussed. It was found that the along-wind aeroelastic aerodynamic damping ratios show similar linear increasing trends on the normalized velocities at small wind directions regardless of building shapes. But the across-wind aerodynamic damping ratios show clear differences depending on building shapes, showing different peaks and different normalized velocities at which peaks of aerodynamic damping ratios occur and positive aerodynamic damping ratios become negative. Lastly the effect of trigging value in RDT on aerodynamic damping ratios was examined by changing it from one standard deviation to three times of standard deviation. By enlarging the trigging value, the differences in aerodynamic damping ratios increase, implying the optimal trigging values may exist between one standard deviation and √2 times of standard deviations in the current experimental conditions.

Optimum study on wind-induced vibration control of high-rise buildings with viscous dampers

Zhou, Yun,Wang, DaYang,Deng, XueSong Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.6

In this paper, optimum methods of wind-induced vibration control of high-rise buildings are mainly studied. Two optimum methods, genetic algorithms (GA) method and Rayleigh damping method, are firstly employed and proposed to perform optimum study on wind-induced vibration control, six target functions are presented in GA method based on spectrum analysis. Structural optimum analysis programs are developed based on Matlab software to calculate wind-induced structural responses. A high-rise steel building with 20-storey is adopted and 22 kinds of control plans are employed to perform comparison analysis to validate the feasibility and validity of the optimum methods considered. The results show that the distributions of damping coefficients along structural height for mass proportional damping (MPD) systems and stiffness proportional damping (SPD) systems are entirely opposite. Damping systems of MPD and GAMPD (genetic algorithms and mass proportional damping) have the best performance of reducing structural wind-induced vibration response and are superior to other damping systems. Standard deviations of structural responses are influenced greatly by different target functions and the influence is increasing slightly when higher modes are considered, as shown fully in section 5. Therefore, the influence of higher modes should be considered when strict requirement of wind-induced vibration comfort is needed for some special structures.

Analytical and experimental research on wind-induced vibration in high-rise buildings with tuned liquid column dampers

Liu, Ming-Yi,Chiang, Wei-Ling,Chu, Chia-Ren,Lin, Shih-Sheng Techno-Press 2003 Wind and Structures, An International Journal (WAS Vol.6 No.1

In recent years, high-strength, light-weight materials have been widely used in the construction of high-rise buildings. Such structures generally have flexible, low-damping characteristics. Consequently, wind-induced oscillation greatly affects the structural safety and the comfort of the building's occupants. In this research, wind tunnel experiments were carried out to study the wind-induced vibration of a building with a tuned liquid column damper (TLCD). Then, a model for predicting the aerodynamic response in the across-wind direction was generated. Finally, a computing procedure was developed for the analytical modeling of the structural oscillation in a building with a TLCD under the wind load. The model agrees substantially with the experimental results. Therefore, it may be used to accurately calculate the structural response. Results from this investigation show that the TLCD is more advantageous for reducing the across-wind vibration than the along-wind oscillation. When the across-wind aerodynamic effects are considered, the TLCD more effectively controls the aerodynamic response. Moreover, it is also more useful in suppressing the acceleration than the displacement in biaxial directions. As s result, TLCDs are effective devices for reducing the wind-induced vibration in buildings. Parametric studies have also been conducted to evaluate the effectiveness of the TLCD in suppressing the structural oscillation. This study may help engineers to more correctly predict the aerodynamic response of high-rise buildings as well as select the most appropriate TLCDs for reducing the structural vibration under the wind load. It may also improve the understanding of wind-structure interactions and wind resistant designs for high-rise buildings.

Aero-elastic wind tunnel test of a high lighting pole

Luo, Yaozhi,Wang, Yucheng,Xie, Jiming,Yang, Chao,Zheng, Yanfeng Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.25 No.1

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.

Optimum study on wind-induced vibration control of high-rise buildings with viscous dampers

Yun Zhou,DaYang Wang,XueSong Deng 한국풍공학회 2008 Wind and Structures, An International Journal (WAS Vol.11 No.6

In this paper, optimum methods of wind-induced vibration control of high-rise buildings are mainly studied. Two optimum methods, genetic algorithms (GA) method and Rayleigh damping method, are firstly employed and proposed to perform optimum study on wind-induced vibration control, six target functions are presented in GA method based on spectrum analysis. Structural optimum analysis programs are developed based on Matlab software to calculate wind-induced structural responses. A high-rise steel building with 20-storey is adopted and 22 kinds of control plans are employed to perform comparison analysis to validate the feasibility and validity of the optimum methods considered. The results show that the distributions of damping coefficients along structural height for mass proportional damping (MPD) systems and stiffness proportional damping (SPD) systems are entirely opposite. Damping systems of MPD and GAMPD (genetic algorithms and mass proportional damping) have the best performance of reducing structural wind-induced vibration response and are superior to other damping systems. Standard deviations of structural responses are influenced greatly by different target functions and the influence is increasing slightly when higher modes are considered, as shown fully in section 5. Therefore, the influence of higher modes should be considered when strict requirement of wind-induced vibration comfort is needed for some special structures.

Aero-elastic wind tunnel test of a high lighting pole

Yaozhi Luo,Yucheng Wang,Jiming Xie,Chao Yang,Yanfeng Zheng 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.25 No.1

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.

역추정된 풍직각방향 모달하중에 기초한 원형 실린더 구조물의 공력감쇠비 산정

황재승 한국풍공학회 2019 한국풍공학회지 Vol.23 No.1

Aerodynamic damping has been recognized as one of the most useful factors to evaluate the vortex induced vibration of a slender structure. However, conventional estimation methods of the aerodynamic damping have been mainly based on the system identification technology in associated with the structural responses, so that these have some limitations in directly understanding the role and characteristics of aerodynamic damping inherent in the vortex induced load. In this study, by directly identifying vortex induced load with force identification method, the components and the causative factors of vortex induced load are evaluated. For this purpose, the aeroelastic model test for circular section was performed in the boundary layered wind tunnel, and then the vortex induced load and the aerodynamic damping ratio are subsequently identified. From the analysis study, it is found that the vortex induced load is composed of the modal velocity induced load, where the modal velocity of the structure is converted to wind load by aerodynamic damping, and the pure vortex induced load formed by the instantaneous across wind velocity. The aerodynamic damping is changed into negative damping when vortex induced frequency is approaching to the natural frequency of the aeroelastic model, and resulting in the vortex induced resonance due to the decrease in total damping. Based on the results, the mathematical model for vortex induced load can be constructed in the turbulent wind, and it can be used to more effectively understand the across-wind response of high-rise building. 공력감쇠는 와류에 의한 풍직각방향의 응답을 평가하는데 매우 유용한 인자로 인식되어 왔다. 그러나 기존의 공력감쇠 산정방식은 구조물 응답에 기반한 시스템 식별기술을 적용하는 것으로 와류하중속에 포함되어 있는 공력감쇠의 역할과 특성을 파악하는데 한계를 가지고 있었다. 본 연구에서는 하중식별기술을 적용하여 와류하중을 직접적으로 구함으로써 와류하중을 구성하는 요소와유발요인을 평가하고자 하였다. 이를 위하여 대기 경계층에서 원형 실린더 모델에 대한 공탄성 실험을 수행하여 풍직각방향 와류하중을 추정하였으며 그로부터 공력감쇠의 특성을 분석하였다. 분석결과, 와류하중은 구조물 모달속도가 공력감쇠에 의해 풍하중으로 전환되는 모달속도하중과 변동풍속에 의해 형성되는 순수 와류하중으로 구성되는 것으로 나타났다. 공력감쇠는 최상층 평균풍속에 의한와류방출진동수가 구조물의 고유진동수에 근접하면서 부감쇠를 가지며 그 결과 총 감쇠가 작아져 응답증폭현상을 유발하는 것으로 파악되었다. 본 연구결과에 기초하면, 난류상태에서 와류하중 특성이 반영된 와류하중모델 구축이 가능할 것으로 사료되며, 구조물 풍직각방향 진동을 보다 효과적으로 파악하는데 활용될 수 있을 것으로 사료된다.