Torsional and across-wind response of high-rise buildings (original) (raw)
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Journal of Wind Engineering and Industrial Aerodynamics, 2001
With regard to studies conducted using aeroelastic models with the torsional degree of freedom, self-excited vortex-induced vibration and torsional flutter occur during torsional vibrations in the case of a structure with a side ratio D=B (D: depth, B: breadth) of 2 or more. These results suggested the necessity of investigating aerodynamic instability during torsional vibrations.
Dynamic torsional behavior of tall building under wind loads using CFD approach
The dynamic torsional behavior of rectangular tall buildings under wind loads has been investigated using wind tunnel tests. It has been found that one of the main factors influencing the dynamic torsional behavior of tall buildings is the dynamic characteristics of the wind such as turbulence and wake excitation. In addition to that, the dynamic characteristics of the building itself influence the torsional behavior. The Ansys CFX10 has been used to analyze the flow over building model with the wind speed profile and turbulence profile generated from AS 1170.2 for the suburban terrain category. Different aspect ratios of rectangular tall buildings have been studies from square to slab type structure. The dynamic torsional moment has been analyzed from pressure distribution on surrounding surfaces of the rigid models of tall buildings. The torsional moments are normalized in coefficient form with the maximum projected width and the maximum projected area of the building. The numerical results are being comparable with the experimental results from Cheung and Melbourne .
Wind-induced torsional aerodynamic loads on low- and medium-height buildings
Since there is limited information about wind-induced torsional loads on buildings, wind tunnel tests were carried out on a series of buildings with low and medium heights. Four buildings (scale 1:400), having the same horizontal dimensions but different heights (6, 12, 25 and 50 m), were tested in a simulated open terrain exposure for different wind directions (i.e. from 0o to 180o every 15o). The synchronized wind pressure measurements on the rigid building model allowed estimating the instantaneous shear forces and torsional moments. All results were normalized and presented in terms of mean and peak values of shear and torsional coefficients representing two load cases (torsion and shear load). Furthermore, the experimental results were compared with the existing torsion- and shear-related provisions in the National Building Code of Canada (NBCC 2010), the American Society of Civil Engineers Standard (ASCE/SEI 7-10) and the European Code (EN 1991-1-4). The results demonstrated s...
Interaction of Across-Wind and Along-Wind with Tall Buildings Authors
In our modern society, tall structures are an essential component of new civilization. These kinds of structures are sensitive to wind excitations due to their low damping and stiffness, and therefore large amplitude vibrations often happen under strong wind excitation. Focus of this study is a critical review of the research development on interaction between wind excitations and tall buildings. Wind motions occur simultaneously in along-wind mode, across-wind mode and torsional mode. The dynamic behavior and characteristics of the tall buildings are determined based on the field measurements and comparisons between across-winds and along-winds. Across-wind dynamic responses are greater than along-wind ones caused by vortex shedding. Aerodynamic modifications of the form of the tall buildings are considered to reduce the wind loads.
A Simplified Approach on Dynamic Response of Tall Buildings due to Wind loads - Thida Htun
Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure areas. In the field of structural engineering, it includes strong winds, which may cause discomfort and extreme winds such as tornado, hurricane. It plays an important role in design of tall structures because it exerts static and dynamic loads with effects on slender structures. Most international codes and standards make use of the Gust Loading Factor (GLF) by to determine the equivalent static along-wind loading on a structure. Although the traditional GLF method ensures an accurate estimation of the displacement response, it may fall short in providing a reliable estimate of dynamic response components. A single 'factor' can be assessed to account for dynamic effects resulting from gust fluctuations in buffeting wind load condition. Several analytical models have been developed in the past to calculate this dynamic factor which is multiplied by the static response to give the maximum dynamic response of the structure. This dynamic factor is usually referred to as the "Gust Response Factor". Typical high-rise buildings oscillate in the Along-wind, Across-wind, and Torsional directions The Along-wind motion primarily results from pressure fluctuations on the windward and leeward faces, which generally follows the fluctuations in the approach flow, especially in the low frequency range. Therefore, Along-wind aerodynamic loads may be quantified analytically utilizing quasi-steady and strip theories, with dynamic effects customarily represented by a random vibration based "Gust Factor Approach" [1].
Interaction of Across-Wind and Along-Wind with Tall Buildings
Australian Journal of Basic and Applied Sciences, 2014
In our modern society, tall structures are an essential component of new civilization. These kinds of structures are sensitive to wind excitations due to their low damping and stiffness, and therefore large amplitude vibrations often happen under strong wind excitation. Focus of this study is a review of the research development on interaction between wind excitations and tall buildings. Wind motions occur simultaneously in along-wind mode, across-wind mode and torsional mode. The dynamic behavior and characteristics of the tall buildings are determined based on the field measurements and comparisons between across-winds and along-winds. Across-wind dynamic responses are greater than along-wind ones caused by vortex shedding. Aerodynamic modifications of the form of tall buildings are considered to reduce wind loads.
A Stochastic Approach to Determine Along-Wind Response of Tall Buildings
IRJET, 2023
Wind velocity is turbulent in nature and hence its variation with time is random. The interaction of the turbulent wind with the building generates random vibrations in the building. When the frequency of the turbulent wind force comes in line with the natural frequency of the building, it produces resonant amplification of the building response that is undesirable for structural safety and dwellers comfort. This paper probes the application of theory of random vibration in determining the peak along wind response of a conventional tall building, rectangular in configuration. Velocity power spectral density function is a focal point in mathematical modeling of turbulent wind velocity. Different expressions for velocity power spectral density function were proposed by Simiu, Harris and Kaimal. They are used to derive corresponding displacement power spectral density functions. A peak in the displacement power spectral density function plot is observed at a frequency equal to the natural frequency of the building. The expected value of peak along wind response is calculated using principles of random vibration theory. Numeric computing software MATLAB is used for solving the mathematical equations involved in the analysis. All the three velocity power spectral density functions produced nearly equal peak displacement at the tip of the building wherein, Harris velocity power spectral density function has an edge over the others. A brief comparison of all the velocity power spectral density functions is also presented.
Canadian Journal of Civil Engineering, 2014
The aim of this study is to assess wind-induced torsional loads on low- and medium-rise buildings determined in accordance with the National Building Code of Canada (NBCC 2010). Two building models with the same horizontal dimensions but different gabled-roof angles (0° and 45°) were tested at different full-scale equivalent eave heights (6, 12, 20, 30, 40, 50, and 60 m) in open terrain exposure for several wind directions (every 15°). Wind-induced measured pressures were numerically integrated over all building surfaces and results were obtained for along-wind force, across-wind force, and torsional moment. Torsion load case (i.e., maximum torsion and corresponding shear) and shear load case (i.e., maximum shear and corresponding torsion) were evaluated to reflect the maximum actual wind load effects in the two horizontal directions (i.e., transverse and longitudinal). The evaluated torsion and shear load cases were also compared with the current torsion- and shear-related provisio...
Wind-induced motion of tall buildings
Engineering Structures, 1985
Modern buildings designed such that their lateral drifts under statically applied wind loads are less than some fraction of building height, may vibrate excessively during winds and cause occupant discomfort. Methods are presented for evaluating the vibration characteristics of buildings using random vibration theory to relate the fluctuating wind forces to structural response. These methods can be used to evaluate serviceability or to plan wind tunnel tests of buildings.