Wind Force Coefficients Research Articles

Study of Wind Force Coefficient on Four-flue Chimney Supported by Hexagon Shaped Steel Tower

Study of Wind Force Coefficient on Four-flue Chimney Supported by Hexagon Shaped Steel Tower

Interference effects of an adjacent tall building with various sizes on local wind forces acting on a tall building

This article focuses on variations of local wind forces along height levels of a tall building due to an adjacent tall building with various height and breadth ratios through huge wind tunnel experiments. It deals with the characteristics of local wind forces including root mean square local wind force coefficients, non-dimensional power spectra, and root coherences along height levels of a tall building with an adjacent tall building in critical locations. It is shown that increases of over 20% in interference factors ( MIFMD, RIFMD, and RIFML) for maximum mean and root mean square base overturning moment coefficients in along- and across-wind directions occur when the adjacent building is close to the principal building. Higher and wider adjacent buildings can cause not only higher mean wind loads but also higher dynamic wind loads in along- and across-wind directions, but the critical locations of an adjacent building with various height and breadth ratios are somewhat different. However, most critical locations of an adjacent building for wind-induced wind loads are within the region ( X/ B, Y/ B) = (1.5, 0–1.5).

Aerodynamic treatments for reduction of wind loads on high-rise buildings

For investigation of the effects of building corner modifications on reduction of wind loads on high-rise buildings, a benchmark square model and three corner modified models including recessed, chamfered and rounded are tested by pressure measurements in a boundary layer wind tunnel. Based on the experimental results, mean wind pressure coefficients, base moment coefficients, local wind force coefficients, power spectral densities and vertical correlation coefficients of the three corner modified models are discussed and compared with those of the square model to provide comprehensive evaluations of the effects of the aerodynamic treatments on reductions of the wind loads. This paper aims to provide useful information for the wind-resistant design of high-rise buildings.

INFLUENCE OF BASEBOARD HEIGHT ON WIND FORCE OF SCAFFOLDS AT BUILDING EDGE

When scaffolds are installed in construction sites, their resistance against wind force needs to be calculated. Japanese design guidelines require a specific scaffold resistance against wind force, but such rules and regulations are applicable solely to old-style scaffolds. A number of risks are inherent in the existing guidelines. First, new-style scaffolds are used in construction sites without practitioners knowing whether the design guidelines are appropriate for modern building components. Second, scaffolds are set near buildings, but workers are unaware of the effect of the wind force at the building edge. Finally, conventional designs feature the use of baseboards as scaffold components. While considering the aforementioned issues, a wind tunnel test was carried out as part of this study to examine the wind force exerted on scaffolds erected near a building edge. The parameters used in the test were baseboard height and the distance from the building edge. From the results, when the distances between the building’s center and the scaffold’s center are 180 mm, the wind force is high. Additionally, when the baseboard height is 130 mm, the wind force is high. This study examined the correction number for the wind force coefficient of scaffolds with baseboards that were positioned at building edge. Whenever the scaffolds were set near the building edge, we needed to revise the wind force coefficient of the scaffolds.

Effect of internal angles between limbs of cross plan shaped tall building under wind load

The present study revealed comparison the pressure distribution on the surfaces of regular cross plan shaped building with angular cross plan shaped building which is being transformed from basic cross plan shaped building through the variation of internal angles between limbs by 15 for various wind incidence angle from 0 to 180 at an interval of 30. In order to maintain the area same the limbs sizes are slightly increased accordingly. Numerical analysis has been carried out to generate similar nature of flow condition as per IS: 875 (Part –III):1987 (a mean wind velocity of 10 m/s) by using computational fluid dynamics (CFD) with help of ANSYS CFX (k-e model). The variation of mean pressure coefficients, pressure distribution over the surface, flow pattern and force coefficient are evaluated for each cases and represented graphically to understand extent of nonconformities due to such angular modifications in plan. Finally regular cross shaped building results are compared with wind tunnel results obtained from similar \'+\' shaped building study with similar flow condition. Reduction in along wind force coefficients for angular crossed shaped building, observed for various skew angles leads to develop lesser along wind force on building compared to regular crossed shaped building and square plan shaped building. Interference effect within the internal faces are observed in particular faces of building for both cases, considerably. Significant deviation is noticed in wind induced responses for angular cross building compared to regular cross shaped building for different direction wind flow.

INFLUENCE OF BASEBOARD HEIGHT ON RESISTANCE TO WIND FORCE OF SCAFFOLDS AT WINDWARD SIDE OF BUILDINGS

The Japanese Industrial Safety and Health Law was revised in March 2009 to introduce new measures by which to prevent accidental falls in the construction industry. As part of this revision, regulations on the installation of guard rails, toe boards, mesh sheets, and other components in appropriate positions on scaffolds were established. When scaffolds are installed in construction sites, their resistance against wind force needs to be calculated. Japanese design guidelines stipulate a specific scaffold resistance against wind force, but such regulations are applicable to conventional scaffolds. The problem with outdated regulations is that scaffolds are used during building construction without practitioners knowing whether the existing guidelines are suitable for new-style scaffolds. Accordingly, this study was conducted a wind tunnel test to examine the wind force exerted on building scaffolds, with the parameters being baseboard height and distance between scaffolds and a building. The relationship between the wind force coefficient of the scaffolds and baseboard height was proportional only on the scaffolds. As the distance between the scaffolds and the building lengthened, however, the relationship between the parameters reflected a steeper curve as baseboard height increased. Whenever the scaffolds were set near the building, negative pressure acted on the scaffolds as a consequence of the downwind structure. This study was examined the correction factor of the wind force coefficient of the scaffolds.

Extreme Learning Machine for Prediction of Wind Force and Moment Coefficients on Marine Vessels

Background/Objectives: To develop a universal method for wind force and moment coefficient prediction on marine vessels independent of ship types. The marine vessels’ equation of motion includes hydrodynamics forces, moments and environmental disturbances. One of the environmental forces and moment acting on the ship originate from wind and play a vital role in offshore operations. Till date, wind loads are determined by statistical and regression analysis. In this paper, an extreme learning machine is used as a technique to predict the wind force and moment coefficients. Findings: This approach is novel and is common for any ship shapes. The performance of the proposed method is much more accurate and simplified compared with the existing tools. The result matches precisely with the experimental data. Applications/ Improvement: This method shall be an effective tool in calculation of wind loads on marine structures which is extremely critical in marine operations and ship maneuvering and positioning.

WIND TUNNEL TEST OF SCAFFOLDS SET WITH WALL CONNECTERS WITH BASEBOARD HEIGHT AS A PARAMETER

The Japanese Industrial Safety and Health Law were revised in March 2009 to introduce new measures by which to prevent accidental falls in the construction industry. As part of this revision, authorities established regulations on the provision of guard rails, toe boards, mesh sheets, and other components in appropriate positions on scaffolds. When scaffolds are set in construction sites, their strength against wind force needs to be calculated. Japanese design guidelines regulate the strength of scaffolds against wind force; however, the design guidelines were written with old-style scaffolds in mind. It is not known whether the design guidelines are appropriate for new-style scaffolds. At the construction sites, the scaffolds connect to structures through the use of wall connecter, to keep scaffolds from falling down. The wind load that acts on the scaffolds was supported by the wall connecter at the construction sites. On the other hand, in conventional designs, a baseboard is used on construction sites. In this study, to set scaffolds at construction sites while using baseboard height as a parameter, we performed a wind tunnel test to examine the wind load that acts on scaffolds that have been set with wall connecters. The wind tunnel device has a total length 74,900 mm, while the device interior is 2,300 mm wide and 2,000 mm high. The load sell to set the wall connecter was used to measure wind load. The models, each of which was 1/10 in size, were used on scaffolds at general construction sites. The scaffolds were three stories high and one span wide. A baseboard was situated on one side of the long face of the scaffolds. The wind speed was set at a uniform flow of 10 m/s, because the wind force coefficient of a cylinder is stable at this speed. The characteristic length was positioned 5 mm along the diameter of a leg member. The Reynolds number was approximately 3.5 × 103. From our results, the wind force coefficient was found to increase as the baseboard height increased. With regard to efficient scaffold design, calculations of the wind force coefficient should therefore consider baseboard height.

屋上広告板に作用する風力特性および外装材用設計風力係数の提案

屋上広告板に作用する風力特性および外装材用設計風力係数の提案

Wind tunnel and full-scale study of wind effects on a super-tall building

This paper presents the analyzed results from a combined wind tunnel and full-scale study of the wind effects on a super-tall building with a height of 420m in Hong Kong. In wind tunnel tests, mean and fluctuating forces and pressures on the building models for the cases of an isolated building and the building with the existing surrounding condition are measured by the high-frequency force balance technique and synchronous multi-pressure sensing system under two typical boundary layer wind flow fields. Global and local wind force coefficients and structural responses are presented and discussed. A detailed study is conducted to investigate the influences of incident wind direction, upstream terrain conditions and interferences from the surroundings on the wind loads and responses of the high-rise structure. On the other hand, full-scale measurements of the wind effects on the super-tall building have been performed under typhoon conditions. The field data, such as wind speed, wind direction, structural acceleration and displacement responses have been simultaneously and continuously recorded during the passage of 12 typhoons since 2008. Analysis of the field measured data is carried out to investigate the typhoon effects on the super-tall building. Finally, the model test results are compared with the full-scale measurements for verification of the wind tunnel test techniques. The comparative study shows that the wind tunnel testing can provide reasonable predictions of the structural resonant responses. The resonant displacement responses are comparable to the background displacement responses so that the contribution of the background responses to the total displacement responses should not be underestimated. The outcome of the combined wind tunnel and full-scale study is expected to be useful to engineers and researchers involved in the wind-resistant design of super-tall buildings.

Mesh-adaptive LES for wind load estimation of a high-rise building in a city

This paper discusses the applicability of large eddy simulation (LES) to the wind-resistant design of buildings in cities. In order to accurately predict wind pressures and forces on actual buildings with complicated shapes, we partially introduce the unstructured grid system, which is formulated on the open-source CFD code. Applying the LES method for modeling the urban flow, where a specified high-rise building focuses on safety under wind loading, the combined model is employed to investigate aerodynamic characteristics. This model uses overset grids, consisting of the Cartesian grid and the unstructured-grids. According to previous studies, the Cartesian grid method can accurately generate the turbulent structures in the urban canopy, whereas the unstructured grid method can reproduce detailed patterns of the near-wake flows around a specified building inside a densely built-up area. In this study, we have applied the combined model consisting of the Cartesian grid and unstructured grid for wind load estimation of a high-rise building in a city. Particularly, at inclined wind direction to the main streets, there is a presumption of different effects of wind impact at each vertical level of a high-rise building along the street. Accordingly, relatively a large torsional force tends to be present. On the basis of the results obtained, their accuracy is checked in comparison with the previous data by wind tunnel experiment, and wind pressure distributions on the surfaces as well as wind force coefficients of a high-rise building are estimated and discussed in view of structural safety.

Design wind loads for open-topped storage tanks in various arrangements

The present article proposes a model of wind force coefficient for designing open-topped storage tanks in various arrangements; main focus is on oil storage tanks. In our previous paper, we discussed the design wind force coefficients for isolated tanks, based on wind tunnel experiments of wind pressure distributions and buckling as well as on a finite element analysis of buckling under static wind loading. In practice, however, more than two tanks are constructed in various arrangements in a site. In such cases, the wind force distribution and the resultant buckling behavior of tanks may be affected by the arrangement significantly. Therefore, the present article focuses on the grouping effect on the wind force distribution and the buckling behavior. First, the wind pressures are measured simultaneously at many points both on the external and internal surfaces of a rigid model for various arrangements of two to four tanks in a turbulent boundary layer. The effects of arrangement pattern and gap spacing of tanks on the pressure distributions are discussed. Then, the buckling of tanks under static wind loading for various arrangements is analyzed by using a non-linear finite element method. The results indicate that the distribution of positive wind force coefficient in the windward area affects the buckling behavior significantly. Finally, based on the results obtained, we propose a model of wind force coefficient on tanks in various arrangements by modifying the model for isolated tanks that we proposed in our previous paper. For evaluating the design wind loads a gust effect factor approach is employed. The wind load evaluation is based on the quasi-steady principle and therefore the resonant effect is not taken into account.

低層住宅に設置される太陽電池モジュールの設計用風力係数に関する検討

The wind pressures on the upper and lower surfaces of the modules indicate negative values where photovoltaic modules are installed on the roof of buildings. Therefore the mean wind forces on the modules are relatively weak. On the other hand, the peak wind forces on the modules become severe due to the differences of fluctuating wind pressures on the upper and lower surfaces. This paper presents the design wind force coefficients for photovoltaic modules installed on the gable roof of low-rise buildings, based on the peak wind force coefficients which are measured the wind tunnel experiments.

Wind force coefficients on hexagonal free form shell

This paper presents the wind force coefficients on non-conventional building of the free form shell structure generated by the simulation of a membrane initially in the horizontal plane surface with hexagonal plant, under the action of self-weight and supported on six corners. Initially is presented the computational model for free form shells generation, the model generated and the correspondent construction of the hexagonal free form shell scale model in fiberglass by a CAD/CAM system. Following is presented the wind tunnel of atmospheric boundary layer and the scale model used to perform the tests to obtain the wind force coefficients. Finally are presented the numerical analysis of the scale model of free form shell structure by the computational fluid dynamics software ANSYS-CFX. The wind force coefficients for the free form shell obtained by the wind tunnel tests and ANSYS-CFX software are compared. The results demonstrates the possibilities to apply the computational fluid dynamic analysis for future applications to analyze other free form shells in order to obtain wind force coefficients.

WIND TUNNEL TEST FOR CALCULATING WIND FORCES ON SCAFFOLDS WITH BASEBOARD HEIGHT AS A PARAMETER

The Japanese Industrial Safety and Health Law was revised in March 2009 to introduce new measures concerning accidental falls in the construction industry. This revision mandates the use of guard rails, handrails, and other scaffold components. The wind load criteria and structural specifications of scaffolds are regulated by current design codes. Nevertheless, these provisions do not necessarily comply with the newly incorporated legal requirements because they apply to old-style scaffolds. This study examined the wind force on scaffolds by wind tunnel test, with baseboard height used as a parameter. The wind force coefficient of one story of scaffolds was calculated. Wind force coefficient increased as baseboard height increased. The wind force on the scaffolds equipped with baseboards is 9.2 times that on the scaffolds without baseboards. The baseboard must be greater than or equal to 15 cm to satisfy regulation requirements. The wind force coefficient of scaffolds with a 15 cm baseboard is 1.5 times that of the scaffolds without a baseboard. In scaffold design, baseboard height should be considered to guarantee a suitable wind force coefficient.

WIND LOADS AND WIND-INDUCED BUCKLING OF OPEN-TOPPED OIL-STORAGE TANKS IN VARIOUS ARRANGEMENTS

Wind force coefficients for designing open-topped oil-storage tanks in various arrangements have been investigated under experiments involving a wind tunnel and a buckling analysis of the tanks. In the wind tunnel experiment, the wind pressures were measured simultaneously at many points both on the external and internal surfaces of a rigid model for various arrangements of two to four tanks. The effects of arrangement and gap spacing of tanks on the pressure distribution are investigated. The buckling of tanks under static wind loading is analyzed by using a non-linear finite element method. A discussion of the effect of wind force distribution on the buckling behavior follows. The authors provided a model of circumferential distribution of wind force coefficient on isolated open-topped tanks in their previous paper. This paper proposes a model of wind-force coefficient for plural tanks in various configurations by modifying the model for isolated tanks.

Wind Loading on a Hyperbolic Paraboloid Free Roof

Wind loading on an H.P. (hyperbolic paraboloid) free roof has been investigated on the basis of a wind tunnel experiment. The roof models of 1 mm thickness were made of nylon resin using laser lithography. The parameters under consideration are the rise to span ratio and slope of the roof. The overall aerodynamic forces and moments were measured by a six-component force balance in a turbulent boundary layer. Based on a combination of the lift and moment coefficients, the design wind force coefficients, CNW * and CNL * , on the windward and leeward halves of the roof are proposed. Focus is on the column axial forces induced by wind loading as the load effect for discussing the design wind loads, assuming that the roof is rigid and supported by four corner columns. Indeed, two pairs of CNW * and CNL * , generating the maximum tension and compression in the columns, are provided for each of the two or three wind directions parallel to the roof's diagonal lines. The proposed values of the wind force coefficients are compared with the specified values in the Australia/New-Zealand Standard for a limited range of rise to span ratio.

Design wind force coefficients for open-topped oil storage tanks focusing on the wind-induced buckling

Wind force coefficients for designing open-topped oil storage tanks have been investigated both experimentally and analytically. First, simultaneous pressure measurements were carried out at many points both on the outside and inside of the wall of a rigid model in a turbulent boundary layer. A conditional sampling of pressures was made for investigating the pressure distribution at an instant when the external pressure at a reference point, roughly corresponding to the windward stagnation point, became the maximum peak value. The instantaneous distribution of wind force coefficients, or the pressure difference coefficients at this moment was found to be similar to that of the mean wind force coefficients. Then, the buckling behavior of thin cylindrical shells was investigated based on a wind tunnel experiment with elastic cylinders. Furthermore, a finite element analysis of the buckling behavior under static wind loading was carried out. The results indicate that the buckling behavior is mainly affected by the magnitude and extent of positive wind force coefficient on the windward area of the cylinder. Finally, a discussion is made of the wind force coefficients to be used for the design of open-topped oil storage tanks, based on the above-mentioned wind tunnel experiments and finite element analysis.

Local and overall wind pressure and force coefficients for solar panels

This paper reports on an experimental study carried out to better understand the wind pressure distribution on stand-alone panel surfaces and panels attached to flat building roofs. A complex model capable to incorporate solar panels at different locations and various inclinations was constructed at a 1:200 geometric scale. Three model panels equipped with pressure taps on both surfaces (36 in total) for point and area-averaged pressure measurements were used. Pressure and force coefficients were computed for every pressure tap and for all the panels. Different configurations were tested under similar conditions in order to examine the effect of various parameters on the experimental results. A minimal gap occurred between the solar panels and the roof of the model. The study found that the net values of pressure coefficients corresponding to different configurations are affected by the panel inclination for the critical 135° wind direction, for which panels on the back location undergo higher suctions in comparison to those in the front. The effect of building height on the solar collector total load is minimal, whereas corner panels are subjected to higher net loads for critical azimuths. Simplified net pressure coefficients for the design of solar panels are provided.

The influence of photovoltaic array arrangement placed pararell to the predominant wind direction on wind force coefficients

The influence of photovoltaic array arrangement placed pararell to the predominant wind direction on wind force coefficients