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CONTENTS
Volume 33, Number 5, November 2021
 


Abstract
This paper presents the results of an experimental investigation performed at an open circuit boundary layer wind tunnel carried out with the purpose to evaluate the performance of a solitary "Fish-plan shape" building model for various angles of wind incidences with a mean wind velocity of 10 m/s and turbulence intensity of 12%. Mean pressure coefficients of all the faces are calculated from pressure values for each direction of wind incidence and pressure contours are plotted and explained in detail for all faces. Detailed analysis of peak and average mean pressure coefficient for each face is carried out. From the present experiment, it is observed that at 00 wind incidence face-value of the windward face is lesser than for the standard square model at IS 875 (Part 3) 2015. The study also presents higher magnitudes of peak suction and pressure coefficients at skewed angles of wind incidences i.e., 300, 600, 1200, and 1500 due to stagnation of fluid near the adjacent edge of depressed exposed faces. The magnitude of the overturning moment in across wind direction is dominating the overall behavior of the model due to the unsymmetrical cross-sectional shape of the model in across-wind direction. The orientation of the building at 900 to wind incidence should be avoided due to the peak magnitudes of CMD, CML, and CMT as compared to other wind directions.

Key Words
face average Cp; overturning moments; tall building; vortex shedding; wind-induced pressure

Address
Supriya Pal:Delhi Technological University, Delhi, India

Rahul Kumar Meena:Delhi Technological University, Delhi, India

Ritu Raj:Faculty of Civil Engineering, Delhi Technological University, Delhi, India

Mingshui Li:Faculty of Civil Engineering, Delhi Technological University, Delhi, India

Abstract
Validation of CFD tornado wind field with experimental or field measurements is limited to comparison of tangential velocity profile at certain elevations above the ground level and few studies are based on comparison of pressure profile. However, important tornado vortex features such as touchdown swirl ratio (ST), core radius (rc), maximum tangential velocity (Vtmax), elevation of maximum tangential velocity (zc) and pressure distribution over a range of varying swirl ratios which strongly influences tornado forces on a building have not been accounted for validation of tornado wind field. In this study, important tornado vortex features are identified and validated with experimental measurements; the important tornado features obtained from the CFD model are found to be in reasonable agreement with experimental measurements. Besides, tornado chambers with different geometrical features (such as different outlet size and location and total heights) are used in different works of literature; however, the effect of variation of those key geometrical features on tornado wind field is not very well understood yet. So, in this work, the size of outlet and total height are systematically varied to study the effect on important tornado vortex parameters. Results indicate that reducing outlet diameter in a tornado chamber increases ST, Vtmax and zc and decreases rc. Similarly, increasing total height of tornado chamber decreases ST, Vtmax and rc whereas zc remains nearly constant. Overall, it is found that variation of outlet diameter has a stronger effect on tornado wind field than the variation in total height of tornado chamber.

Key Words
3D tornado simulation; CFD flow validation, Tornado chamber geometry variation

Address
Sumit Verma:Department of Civil Engineering, University of Arkansas, Fayetteville, AR 72701, U.S.A.

Rathinam P. Selvam:Department of Civil Engineering, University of Arkansas, Fayetteville, AR 72701, U.S.A.

Abstract
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.

Key Words
field measurement; structural dynamic property; super high-rise building; typhoon; wind-induced response; wind tunnel experiment

Address
Chunlei Liu:State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510641, China

Zhuangning Xie:State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510641, China

Lele Zhang:State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510641, China/ China Construction Second Engineering Bureau Co. Ltd. South China company, Shenzhen 518045, China

Biqing Shi:State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510641, China

Jiyang Fu:Guangzhou University-Tamkang University Joint Research Center for Engineering Structure Disaster Prevention and Control,Guangzhou University, Guangzhou 510006, China

Ting Deng:Guangzhou University-Tamkang University Joint Research Center for Engineering Structure Disaster Prevention and Control, Guangzhou University, Guangzhou 510006, China



Abstract
Recent hurricanes have shown that coastal elevated houses are still vulnerable to wind-induced damage, mostly to envelope systems. This paper discusses the performance of elevated houses against hurricane wind loads, particularly wind flow characteristics and the distribution of the peak pressure coefficient (Cp_min) corresponding to the underside of the floor system. Computational fluid dynamics (CFD) analysis was utilized to investigate the effect of interior piers and the wind direction (0° ,45° and 90° ) on the distribution and the magnitude of Cp_min. The CFD results show that the distribution of Cp_min and its maximum value are dependent on pier distribution (e.g., pier location and spacing) and wind direction. The distribution of Cp_min for the 90° wind direction is more similar to the 0° wind direction, but the leeward parts of the floor system are exposed to higher negative pressures. The maximum of Cp_min belongs to the 90° wind direction, which occurs at the windward edge and behind the interior pier due to recirculation zones and subsequent vortices. The results of this study indicate that current design standards and provisions need to be updated to include proper design requirements for the floor system, particularly around piers, to help reduce direct/indirect wind-induced damage to elevated houses in coastal areas.

Key Words
angle of attack; computational fluid dynamics; elevated buildings; LES; peak wind pressure coefficient; wind loads

Address
Mehrshad Amini:Department of Civil and Environmental Engineering, Pennsylvania State University, State College, PA 16802, U.S.A.

Ali M. Memari:Department of Architectural Engineering and Department of Civil and Environmental Engineering,
Pennsylvania State University, State College, PA 16802, U.S.A.


Abstract
Porous structures have a very wide spectrum of application fields. Among them, building engineering and architecture have recently shown the trend of adopting what are called permeable double screen façades as cladding. These are made up of two façades (or skins): the inner one is usually a sealed continuous glazed facade while the outer one is characterized by a porous metallic screen. When it comes to the assessment of the wind loading on such cladding, the aerodynamic behaviour of the outer skin plays a crucial role. This is one of the reasons why the wind's interaction with these porous panels is currently an open research field. The complex 3D shapes the porous skin may have and the intrinsic multi-scale nature of the wind's interaction lead to the need for a general reduced-order model that fully represents the aerodynamic behaviour of the permeable structures. This paper addresses the implementation of a tensorial numerical model that describes the aerodynamics of 3D porous screens, with no geometrical modelling of the porous layer in the computational domain. The proposed reduced-order model is able to address the substantial three-dimensionality and anisotropy of the modern porous structures by full-tensor implementation of the classical Darcy-Forchheimer porosity model. The tensorial formulation of the model together with easy numerical implementation and limited computational onerousness are the strengths of the model proposed here. It is presented together with a validation of the same in the form of a fully resolved CFD solution in which the porous screen is explicitly reproduced. The results reflect the new model's capability to catch the global effects due to the porous structures, in terms of both pressure and velocity fields.

Key Words
anisotropy; CFD; Darcy-Forchheimer; Open-FOAM; porosity model; porous double skin facade

Address
Giulia Pomaranzi:Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156, Milan, Italy

Ombretta Bistoni:Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156, Milan, Italy

Paolo Schito:Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156, Milan, Italy

Alberto Zasso:Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156, Milan, Italy


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