Wind Load Estimation Research Articles

Real-time estimation of dynamic wind load on a structure

Real-time estimation of dynamic wind load on a structure

Universal Equivalent Static Wind Load Estimation for Spatial Structures Based on Wind-Induced Envelope Responses

Wind-resistant design for large-span spatial structures is complex and difficult in practice. Existing wind-resistant design methods were reviewed and the adaptation range of each method was discussed. Though the universal Equivalent Static Wind Loading (ESWL) method could produce a universal wind load distribution that simultaneously reproduces largest load effects for all structural members of cantilevered structures, it is found that the universal ESWL method is not applicable for general space structures, such as shell structures. In this paper, a practical approach to estimate the universal ESWL based on Wind-induced Envelope Responses (WER) is presented for this problem from the structural designer's point of view. Then, the efficiency of the presented approach is illuminated with a numerical example of cylinder single layered shell. Finally, the advantages and the disadvantages of existing approaches, as well as the presented one, are compared at many aspects, such as necessary information of wind load, efficiency, convenience in practice, and so on.

Wind loads for high-solidity open-frame structures

Open frame structures, such as those commonly found in industrial process facilities, are often densely occupied with process related equipment. This paper presents a method for estimating wind loads for high-solidity open frame structures that differs from current approaches, which accumulate wind load contributions from various individual structure components. The method considers the structure as a porous block of arbitrary plan dimension that is subject to wind from any direction. The proposed method compares favorably with wind tunnel test results for similar structures. The possibility of defining an upper bound force coefficient is also discussed.

태풍 내습 시 3-second gust를 이용한 피해액 산정

The most efficient measures to reduce damage from natural disasters include activities which prevent disasters in advance, decrease possibility of disasters and minimize the scale of damage. Therefore, developing of the risk assessment model is very important to reduce the natural disaster damage. This study estimated a typhoon damage which is the biggest damage scale among increased natural disasters in Korea along with climate change. The results of 3-second gust at the height of 10m level from the typhoon 'Maemi' which did considerable damage to Korean in 2003, using the wind data at the height of 700 hPa. September 12th 09 LST~13th 12 LST period by the time a typhoon Maemi approached to the Korean peninsula. This study estimate damage amount using 'Fragility curve' which is the damage probability curve about a certain wind speed of the each building component factors based on wind load estimation results by using 3-second gust. But the fragility curve is not to Korea. Therefore, we use the fragility curves to FPHLM(FDFS, 2005). The result of houses damage amount is about 11 trillion 5 million won. This values are limit the 1-story detached dwelling, of total area. Therefore, this process is possible application to other type houses.

Hurricane hazard modeling: The past, present, and future

Hurricane hazard modeling has become a commonly used tool for assessing hurricane risk. The type of hurricane risk considered varies with the user and can be an economic risk, as in the case of the insurance and banking industries, a wind exceedance risk, a flood risk, etc. The most common uses for hurricane hazard models today include: (i) Simulation of wind speed and direction for use with wind tunnel test data to estimate wind loads vs. return period for design of structural systems and cladding. (ii) Estimation of design wind speeds for use in buildings codes and standards. (iii) Coastal hazard risk modeling (e.g. storm surge elevations and wave heights vs. return period). (iv) Insurance loss estimation (e.g. probable maximum losses, average annual losses). This paper presents an overview of the past and present work in hurricane modeling. The wind model is the key input to each of the examples presented above and is the focus herein. We discuss the evolution and current state of wind field modeling, modeling uncertainties, and possible future directions of the hurricane risk modeling process.

FORMULA FOR ESTIMATING MAXIMUM ALONG-WIND LOAD ON A TOWER OF WIND TURBINE IN THE OPERATIONAL CONDITION

This paper describes equations for estimating maximum along-wind load on the structural design of a wind turbine tower in the operational condition. Some parameters are derived from field measurements and wind tunnel tests. Furthermore, the wind load estimation method is based on the gust effect factor method. First, the application terms and fundamental wind load estimation methods are shown. Second, the modeling of parameters of the equations is investigated. Lastly, the gust effect factors and maximum overturning moments are calculated using the suggested equations, and compared with field measurements. The estimated maximum along-wind loads agree with the field measurements, thus confirming the applicability of the equations.

Roof Damage in New Homes Caused by Hurricane Charley

Hurricane Charley was the first Category 4 hurricane to strike Florida after 1992. This paper presents results of a study to investigate the performance of 425 of 747 roofs of new homes in Punta Gorda Isles, a subdivision of Punta Gorda that was directly in the path of Hurricane Charley shortly after it made landfall. The homes examined were larger, concrete/clay tiled roof homes having irregular floor plans and complex roof configurations not explicitly addressed by prevailing wind load codes. Roof damage was evaluated using images from aerial photographs taken at an elevation of approximately 762m(2,500ft.) Specialized software was used to quantify damage. Damage was classified based on tile loss area. The study showed that the vast majority of the roofs were either undamaged or sustained minor damage. Fewer than 14% were classified as damaged. The most common observed tile loss was along ridges, corners, or in the hip zone where negative uplift pressures are recognized to be the highest. Given the modest observed damage, prevailing methods for estimating wind loads for irregular buildings specified in codes may be adequate. Problems encountered may be best resolved through new details for attaching tiles on ridges, corners, and hip zone.

Measurement of extreme aerodynamic interference forces acting on circular cylinders in turbulent boundary layers

Extreme interference wind loads on circular cylinders are investigated in wind tunnel simulations of atmospheric boundary layers with high turbulence levels. Since for circular cylinders interference effects caused by vortex shedding are pronounced, the present work tries to clarify to which extent turbulence effects are reducing the interference in this case. Aerodynamic forces and moments were measured with a piezoelectric six-component wind tunnel balance. The balance is distinguished by a large dynamic range, low interferences and a high natural frequency. The numerous results include comparisons of mean values, r.m.s. values and extreme values of force coefficients with and without interference with reference to the velocity profiles and the turbulence levels in two different boundary layer simulations. Conclusions are drawn with regard to the application of the results in estimating wind loads on cylindrical structures.

Theoretically estimated peak wind loads

Current estimation of peak pressure coefficients and peak wind loads on structures in the ASCE 7 Standard [American Society of Civil Engineers, ASCE Standard, Minimum Design Loads for Buildings and Structures, ASCE 7-02, ASCE, Reston, VA, USA, 2002] is based on the assumption that they are distributed normally. However, this assumption is erroneous in the case of low-rise structures because the time varying pressures and loads along roof edges and ridges have been observed to be generally non-Gaussian [H.W. Tieleman, Z. Ge, M.R. Hajj, T.A. Reinhold, Pressures on a surface-mounted rectangular prism under varying incident turbulence, J. Wind Eng. Ind. Aerodyn. 91 (2003) 1095–1115]. In this article, a new procedure is used to evaluate from one individual non-Gaussian sample record statistics of peak pressure or peak load coefficients. The initial step for the analysis requires the identification and evaluation of the appropriate marginal probability distribution. The results reveal that the distribution of the time histories of surface pressure and load coefficients is well represented by the gamma distribution, whose parameters can be adequately evaluated from the theoretical moment estimators. The corresponding distribution of the peaks of the sample records that represents either the pressure coefficients or the load coefficients, can then be obtained using a standard translation process approach. This information yields the mean and the standard deviation of the sample peaks, which are then used to determine the extreme coefficients associated at any selected probability level of non-exceedence. This latter step can be made by assuming that the distribution of the peaks follows the Extreme Value Type I (Gumbel) distribution. The analysis is applied to pressure measurements on the 1:50 scale model of the experimental building at the Wind Engineering Research Field Laboratory (WERFL), and executed in the Clemson boundary-layer wind tunnel over a range of incident turbulence intensities.

Equivalent static wind load estimation in wind-resistant design of single-layer reticulated shells

Wind loading is very important, even dominant in some cases, to large-span single-layer reticulated shells. At present, usually equivalent static methods based on quasi-steady assumption, as the same as the wind-resistant design of low-rise buildings, are used in the structural design. However, it is not easy to estimate a suitable equivalent static wind load so that the effects of fluctuating component of wind on the structural behaviors, especially on structural stability, can be well considered. In this paper, the effects of fluctuating component of wind load on the stability of a single-layer reticulated spherical shell model are investigated based on wind pressure distribution measured simultaneously in the wind tunnel. Several methods used to estimate the equivalent static wind load distribution for equivalent static wind-resistant design are reviewed. A new simple method from the stability point of view is presented to estimate the most unfavorable wind load distribution considering the effects of fluctuating component on the stability of shells. Finally, with comparisive analyses using different methods, the efficiency of the presented method for wind-resistant analysis of single-layer reticulated shells is established.

A Modified Logarithmic Law for Neutrally Stratified Flow over Low-Sloped Hills

AbstractThe study of the atmospheric boundary layer flow over two-dimensional low-sloped hills under a neutral atmosphere finds numerous applications in meteorology and engineering, such as the development of large-scale atmospheric models, the siting of wind turbines, and the estimation of wind loads on transmission towers and antennas. In this paper, the intermediate variable technique is applied to the momentum equations in streamline coordinates to divide the flow into regions, with each characterized by the dominance of different terms. Using a simple mixing-length turbulence closure, a simplified form of the x momentum equation is solved for the fully turbulent region, resulting in a modified logarithmic law. The solution is expressed as a power series correction to the classical logarithmic law that is valid for flat terrain. A new parameter appears: the effective radius of curvature of the hill. The modified logarithmic law is used to obtain new equations for the speedup, the relative speedup, the maximum speedup, and the height at which it occurs. A new speedup ratio is proposed to calculate the relative speedup at specific heights. The results are in very good agreement with the Askervein and Black Mountain field data.

Studies on Wind Resistant Design Using the Directional Basic Wind Speed

Transmission towers are considered to be designed with enough wind-resistant performance, however, it is necessary to re-examine the current estimation methods from both points of design wind speed and wind load to rationalize the tower design and to improve the structural integrity. Wind resistant rationalization committee (FY1999-FY2001), organized by Central Research Institute of Electric Power Industry (CRIEPI), promoted the studies on directional basic wind speed and equivalent static wind load estimation following the previous committee on wind resistant design method for local winds effected by topography (FY1992-FY1998). The purpose of this paper is to describe the summary of the investigation results of the wind resistant rationalization committee and to show the outline of "Recommendations for wind loads on transmission towers - a draft (2002)".

円形平面を持つ陸屋根に作用する風圧のモデル化と風荷重評価への応用(構造)

The characteristics of wind pressures acting on a circular flat roof have been investigated, based on the data obtained from a wind tunnel experiment. A simple model of the pressure field is provided as a function of the geometric parameters of the building as well as of the turbulence parameters of the approach flow. A discussion is made of the application of the pressure field model to the wind load estimation, based on the gust effect factor approach and the LRC method. The gust effect factor and the equivalent static load distribution derived from the pressure field model are compared with those obtained from the time history of the pressures. The results indicate the validity of the pressure model.

Geometrical and structural characteristics and wind resistant design method of spatial structures constructed in Japan

The geometry, structural characteristics and wind resistant design method of spatial structures constructed in Japan in the last two decades have been investigated, based on a literature survey as well as on a questionnaire answered by structural engineers at some construction companies. Regarding the wind resistant design, focus is on the method of wind load estimation used in the practical design. The results indicate that the structural characteristics, such as the first natural frequency and damping factor, depend not only on the geometry of the structure but also on the structural system. Various methods were used for estimating the design wind load. In many cases, however, the gust effect factor approach has been used, particularly since the AIJ Recommendations for Loads on Buildings was revised in 1993 and the specification of gust effect factor was provided for beams supporting flat roofs.

TURBULENT CHARACTERISTICS OF SEA WIND AND NUMERICAL SIMULATION OF FLOW AROUND A FLOATING BODY

This research is concerned with the characteristics of wind velocity on through the measurement of wind velocity of nearby sea surfacec ontinuously by using a multichannel anemomaster.The main conclusion from this study is as follows; t he coefficient of friction calculated by assuming Karman constant as 0.4 ranges between 0.01 and 0.07. Furthermore, there is linear relation between roughness parameter and the coefficient of friction.Wind velocity fluctuation spectra showed that it differs depending upon the height from sea level. A strong eddy occurs at the back of a floating body when the wind velocity measured used in numerical modelling the response of the floating body, which implies that this fact must be taken into account in wind load estimation.

Wind loads on marine structures

A review of the available methods for the calculation of wind loads on ships and offshore structures is presented. Based on the review, four methods were selected and implemented in order to carry out a comparative study of the wind loads on ships. Namely, the ahead force, the side force and the yawing moment were calculated and compared. A large tanker both in the loaded and ballast conditions was analysed using the four methods. In the second part, an expression for the estimation of wind loads on ships is proposed and compared with the experimental data. A neural network technique was used to obtain this expression.

Response of untethered-span-wire signal poles to wind loads

Abstract A study was undertaken to examine design procedures used in calculating loads on poles supporting traffic signals suspended from untethered span wires. Procedures used by New York State were first examined for their appropriateness and compliance with AASHTO specifications. A traffic-signal pole was then instrumented with load cells and a wind-speed monitor. Load transferred to the pole from the span wire and associated wind speeds were recorded over several months. These data were compared with corresponding loads calculated using methods specified by AASHTO, and with the current design method used by the State. The results indicate that the field data are about 90% of those calculated using the AASHTO procedure in the measured wind-velocity range, assuming no pole deflection. Extrapolated data at design speeds showed AASHTO method to be conservative in estimating wind loads on untethered span-wire signal poles. This paper summarizes the study and its results.

The use of aerodynamic databases for the effective estimation of wind effects in main wind-force resisting systems:

Abstract As a part of the ongoing National Institute of Standards and Technology research on the development of a new generation of standard provisions for wind loads, we present results of a pilot project on the estimation of wind effects in low-rise building frames. We use records of wind pressure time histories measured at a large number of taps on the building surface in the boundary layer wind tunnel of the University of Western Ontario. Time histories of bending moments in a frame are obtained by adding pressures at all taps tributary to that frame multiplied by the respective tributary areas and influence coefficients. The latter were obtained from the frame designs provided by CECO Building Systems. We compare results obtained by using the pressure time history records with results based on ASCE 7 standard provisions. The comparison suggests that provisions which use aerodynamic databases containing the type of data described in this work can result in designs that are significantly more risk-consistent as well as both safer and more economical than designs based on conventional standard provisions. We outline future research on improved design methodologies made possible by the proposed approach to the estimation of wind effects. We note that the use of the proposed methodologies is fully consistent with the ASCE 7 Standards insofar as these allow the use of wind-tunnel data for estimating wind load effects. Finally, We note that the proposed methodologies may be used for damage assessment for insurance purposes.

Wind direction and hurricane-induced ultimate wind loads

A consensus on the wind directionality issue is needed for the validation by building officials of the wind-tunnel procedure allowed by the ASCE 7-95 Standard, and for the development of provisions for wind loads that use large aerodynamic and climatological databases. As a contribution to the debate needed to achieve such a consensus, we describe an updated method for estimating wind loads that takes into account the directional dependence of the aerodynamic coefficients and the extreme wind climate, and uses the `peaks over threshold' approach for the estimation of extremes. For hurricane-prone regions, assuming epistemic uncertainties are negligible, we estimate mean recurrence intervals (MRIs) of wind loads inducing the design strength, obtained from 50 yr loads via multiplication by a factor specified by the ASCE 7-95 Standard. For typical aerodynamic coefficients with strong directional preference, depending upon location and building orientation those estimated MRIs varied between less than 1000 to more than 10 000 yr. If epistemic uncertainties were taken into account the estimated MRIs would be shorter. We also found that for loads with very large MRIs the common practice of disregarding direction effects is not necessarily conservative from a structural engineering viewpoint.

Estimation of Lift Forces on Offshore Structures with Deck Supported by Substructures

On the Estimation of wind loads on offshore structures which have the deck supported by substructures, it is clear through previous studies that lift force of deck is caused by asymmetry of upper and lower surfaces of deck and that it may be much larger than drag force in case of large waves. Therefore, wind-wave tank experiments on such structures under progressive wave conditions were conducted and the effect of progressive wave on lift force was investigated. Lift forces were measured as a function of substructure, unit number, and wave height. The Experimental results showed that the lift force is significant, especially on leading edge of deck. The study also showed that the fluctuating lift force can be comparable in magnitude to the mean lift force in case of large waves. Further estimation method is provided to help define the nature of lift forces on such structures.