Field measurements of wind effects on a super high-rise building during typhoons

Chunlei Liu,Zhuangning Xie,Lele Zhang,Biqing Shi,Jiyang Fu,Ting Deng 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.33 No.5

Field measurement is the most reliable method to evaluate wind effects on super high-rise building; it is also the only approach to obtain actual structural dynamic properties. A self-developed wireless acceleration sensor was used to continuously monitor a 201 m high building in Shenzhen, and acceleration response signals atop the building during Typhoon Pakhar and Typhoon Mangkhut were obtained. The field data of approximately 58 hours were analyzed using random decrement technique and modified Bayesian spectral density approach, and the variation characteristics of the first two-order modal frequencies and damping ratios of the measured building under strong vibrations were obtained. Finally, field measurements of the maximum peak accelerations were compared with wind tunnel test results. Results show that (1) the frequencies decrease with increasing amplitude. In addition, they decreased initially and then increased with time, showing a “V” shape change. The maximum change rate of the frequencies was 11.5%. (2) During Typhoon Pakhar, the damping ratios were discrete. During Typhoon Mangkhut, the damping ratios increased with increasing amplitude in general, but the damping ratios were relatively discrete at small amplitudes. During Typhoon Mangkhut, the damping ratios increased initially, and then decreased with time. In addition, the first two-order damping ratios during the maximum wind speed were approximately 1.7% and 1.5%. (3) The wind tunnel test results are in good agreement with the field measurement results, thereby verifying the reliability of the wind tunnel test.

Coupling Vibration between Wind-Induced Internal Pressure and a Flexible Roof for Buildings with a Dominant Opening and Background Leakage

Xianfeng Yu,Zhuangning Xie,Ming Gu 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.9

After considering the combination of internal pressure and external pressure acting on the roof, the coupling dynamic equations to describe the relationship between wind-induced internal pressure and flexible roof are reviewed and further refined. The internal pressure responses and the first order modal response of a flexible roof can be evaluated by the coupling equations. Wind tunnel test was carried out on an aeroelastic roof model which was treated as a single-degree-of-freedom system. Three factors, approaching wind velocities at the center of the dominant opening, acceleration responses at dominant opening areas and background leakages, which have effects on roof acceleration responses were studied. On this basis, the effectiveness and calculation precision of the coupling equations were verified. Results show that the root-mean-square (RMS) value of roof acceleration increases with the increase of the approaching wind velocity and dominant opening area, and in background leakage decreases. Meanwhile, theoretical calculation values of RMS internal pressure and RMS acceleration response corresponding to the first order modal of flexible roof agree well with the wind tunnel experimental data.

Verification of a tree canopy model and an example of its application in wind environment optimization

Yi Yang,Zhuangning Xie,Tim K.T. Tse,Xinyang Jin,Ming Gu 한국풍공학회 2012 Wind and Structures, An International Journal (WAS Vol.15 No.5

In this paper, the method of introducing additional source/sink terms in the turbulence and momentum transport equations was applied to appropriately model the effect of the tree canopy. At first, the new additional source term for the turbulence frequency ω equation in the SST k-ω model was proposed through theoretical analogy. Then the new source/sink term model for the SST k-ω model was numerically verified. At last, the proposed source term model was adopted in the wind environment optimal design of the twin high-rise buildings of CABR (China Academy of Building Research). Based on the numerical simulations, the technical measure to ameliorate the wind environment was proposed. Using the new inflow boundary conditions developed in the previous studies, it was concluded that the theoretically reasonable source term model of the SST k-ω model was applicable for modeling the tree canopy flow and accurate numerical results are obtained.

Consistent inflow boundary conditions for modelling the neutral equilibrium atmospheric boundary layer for the SST k-ω model

Yi Yang,Zhuangning Xie,Ming Gu 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.5

Modelling an equilibrium atmospheric boundary layer (ABL) in computational wind engineering (CWE) and relevant areas requires the boundary conditions, the turbulence model and associated constants to be consistent with each other. Among them, the inflow boundary conditions play an important role and determine whether the equations of the turbulence model are satisfied in the whole domain. In this paper, the idea of modeling an equilibrium ABL through specifying proper inflow boundary conditions is extended to the SST k-ω model, which is regarded as a better RANS model for simulating the blunt body flow than the standard k- model. Two new sets of inflow boundary conditions corresponding to different descriptions of the inflow velocity profiles, the logarithmic law and the power law respectively, are then theoretically proposed and numerically verified. A method of determining the undetermined constants and a set of parameter system are then given, which are suitable for the standard wind terrains defined in the wind load code. Finally, the full inflow boundary condition equations considering the scale effect are presented for the purpose of general use.

Amplitude dependency of damping of tall structures by the random decrement technique

An Xu,Zhuangning Xie,Ming Gu,Jiurong Wu 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.2

This study focuses on the amplitude dependency of damping of tall structures by the random decrement technique (RDT). Many researchers have adopted RDT to establish the amplitude dependency of damping ratios in super-tall buildings under strong wind loads. In this study, a series of simulated examples were analyzed to examine the reliability of this method. Results show that damping ratios increase as vibration amplitudes increase in several cases; however, the damping ratios in the simulated signals were preset as constants. This finding reveals that this method and the derived amplitude-dependent damping ratio characteristics are unreliable. Moreover, this method would obviously yield misleading results if the simulated signals contain Gaussian white noise. Full-scale measurements on a super-tall building were conducted during four typhoons, and the recorded data were analyzed to observe the amplitude dependency of damping ratio. Relatively wide scatter is observed in the resulting damping ratios, and the damping ratios do not appear to have an obvious nonlinear relationship with vibration amplitude. Numerical simulation and field measurement results indicate that the widely-used method for establishing the amplitude-dependent damping characteristics of super-tall buildings and the conclusions derived from it might be questionable at the least. More field-measured data must be collected under strong wind loads, and the damping characteristics of super-tall buildings should be investigated further.

Linearized analysis of the internal pressures for a two-compartment building with leakage

Xianfeng Yu,Ming Gu,Zhuangning Xie 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.2

The non-linear equations governing wind-induced internal pressures for a two-compartment building with background leakage are linearized based on some reasonable assumptions. The explicit admittance functions for both building compartments are derived, and the equivalent damping coefficients of the coupling internal pressure system are iteratively obtained. The RMS values of the internal pressure coefficients calculated from the non-linear equations and linearized equations are compared. Results indicate that the linearized equations generally have good calculation precision when the porosity ratio is less than 20%. Parameters are analyzed on the explicit admittance functions. Results show that the peaks of the internal pressure in the compartment without an external opening (Compartment 2) are higher than that in the compartment with an external opening (Compartment 1) at lower Helmholtz frequency. By contrast, the resonance peak of the internal pressure in compartment 2 is lower than that in compartment 1 at higher Helmholtz frequencies.

Aerodynamic force of four-bundled conductors with distorted modeling

Muguang Liu,Cheng Liu,Zhuangning Xie 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.33 No.4

The current study investigates the aerodynamic characteristics of four-bundled conductors designed by distorted approach with a series of wind tunnel tests. The distorted aeroelastic model is designed at a geometry scale of 1:25 with two different span correction coefficients of 0.8 and 0.5. Two sag ratios of 5% and 10% are considered in the test, and the sag ratio of 5% is the major focus. A continuous PVC hose is adopted to simulate the aerodynamic shape of the conductor. The aeroelastic tests are performed on three kinds of uniform turbulent flow and for four different wind directions. The test results show that the mean drag of the distorted model with four-bundled conductors is smaller than that of the normal model, although the consistency of the drag force for each conductor has been satisfied according to the distortion theory. The mean tension for the distorted models is also lower than that of the normal model. However, there is an increasing trend in the fluctuating component of drag force and tension for the distorted model, except for a decrease in the fluctuating tension when the span correction coefficient is 0.5. The increase of turbulence intensity can enlarge the mean and fluctuating values of the aerodynamic forces for the four-bundled conductors, but no significant effects are found in the relative error between the mean values of the distorted and normal models. A substantial imbalance in mean drag and tension on the upstream and downstream conductors is observed under oblique wind. And the differences between the distorted and normal model gradually decrease with the increase of wind yaw angles. The increase of sag ratio can further enhance the unbalanced effect in tension under oblique wind, and has obvious influence on the variance of the drag force and tension. For the four-bundled conductors using distorted modeling, a ratio of around 0.8 rather than a smaller ratio around 0.5 is recommended.

Verification of a tree canopy model and an example of its application in wind environment optimization

Yang, Yi,Xie, Zhuangning,Tse, Tim K.T.,Jin, Xinyang,Gu, Ming Techno-Press 2012 Wind and Structures, An International Journal (WAS Vol.15 No.5

In this paper, the method of introducing additional source/sink terms in the turbulence and momentum transport equations was applied to appropriately model the effect of the tree canopy. At first, the new additional source term for the turbulence frequency ${\omega}$ equation in the SST k-${\omega}$ model was proposed through theoretical analogy. Then the new source/sink term model for the SST k-${\omega}$ model was numerically verified. At last, the proposed source term model was adopted in the wind environment optimal design of the twin high-rise buildings of CABR (China Academy of Building Research). Based on the numerical simulations, the technical measure to ameliorate the wind environment was proposed. Using the new inflow boundary conditions developed in the previous studies, it was concluded that the theoretically reasonable source term model of the SST k-${\omega}$ model was applicable for modeling the tree canopy flow and accurate numerical results are obtained.

Aerodynamic measurements of across-wind loads and responses of tapered super high-rise buildings

Ting Deng,Xianfeng Yu,Zhuangning Xie 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.3

A series of wind tunnel tests were conducted on tapered super high-rise buildings with a square cross section by applying synchronous pressure measurement technology. The effects of global strategy of chamfered modification on aerodynamic loads and wind-induced responses were investigated. Moreover, local aerodynamic strategies of opening a ventilation slot in the corner of equipment and refuge floors were carried out. Results show that the global strategy of tapered elevation increased the vortex shedding frequency, but reduced vortex shedding energy, leading to reduction of across-wind aerodynamic loads and responses. Chamfered modification suppressed the across-wind vortex shedding effect on tapered buildings. Opening the ventilation slot further suppressed the strength of vortex shedding and reduced the residual energy related to vortex shedding in aerodynamic loads of chamfered buildings. Finally, the optimized locations of local aerodynamic strategies were suggested.

Amplitude dependency of damping of tall structures by the random decrement technique

Xu, An,Xie, Zhuangning,Gu, Ming,Wu, Jiurong Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.2

This study focuses on the amplitude dependency of damping of tall structures by the random decrement technique (RDT). Many researchers have adopted RDT to establish the amplitude dependency of damping ratios in super-tall buildings under strong wind loads. In this study, a series of simulated examples were analyzed to examine the reliability of this method. Results show that damping ratios increase as vibration amplitudes increase in several cases; however, the damping ratios in the simulated signals were preset as constants. This finding reveals that this method and the derived amplitude-dependent damping ratio characteristics are unreliable. Moreover, this method would obviously yield misleading results if the simulated signals contain Gaussian white noise. Full-scale measurements on a super-tall building were conducted during four typhoons, and the recorded data were analyzed to observe the amplitude dependency of damping ratio. Relatively wide scatter is observed in the resulting damping ratios, and the damping ratios do not appear to have an obvious nonlinear relationship with vibration amplitude. Numerical simulation and field measurement results indicate that the widely-used method for establishing the amplitude-dependent damping characteristics of super-tall buildings and the conclusions derived from it might be questionable at the least. More field-measured data must be collected under strong wind loads, and the damping characteristics of super-tall buildings should be investigated further.