Design Wind Loads Research Articles

Design of Cantilevered Overhead Sign Supports

The AASHTO 2001 Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals include revised wind load provisions and new criteria for fatigue design. These provisions and criteria differ considerably from those in previous editions of the specifications, and their impact on the design of cantilevered overhead sign supports has not been fully studied. This study assesses the effect of these provisions and criteria on the design of cantilevered overhead sign support structures with the horizontal support composed of a four-chord truss. Wind and fatigue load design calculations of typical structures, located at sites across the United States, were performed with the design provisions of the 2001 supports specifications and compared with design in accordance with the previous edition of the specifications. The induced forces in the primary members of the cantilevered sign support structure were calculated, and corresponding member sizes and weights were estimated. The results of the study demonstrated the effect of the wind and fatigue load provisions on the design of cantilevered overhead sign support structures.

Correlation of dynamic characteristics of a super‐tall building from full‐scale measurements and numerical analysis with various finite element models

AbstractThe Di Wang Tower located in Shenzhen has 79 storeys and is about 325 m high. Field measurements have been conducted to investigate the dynamic characteristics of the super‐tall building. In parallel with the field measurements, seven finite element models have been established to model the multi‐outrigger‐braced tall building and to analyse the effects of various arrangements of outrigger belts and vertical bracings on the dynamic characteristics and responses of the Di Wang Tower under the design wind load and earthquake action. The distributions of shear forces in vertical structural components along the building height are also presented and discussed. The results from detailed modelling of group shear walls with several types of finite elements are addressed and compared to investigate various modelling assumptions. Finally, the performance of the finite element models is evaluated by correlating the natural frequencies and mode shapes from the numerical analysis with the finite element models and the field measurements. The results generated from this study are expected to be of interest to professionals and researchers involved with the design of tall buildings. Copyright © 2004 John Wiley & Sons, Ltd.

Accumulation of wind induced damage on bilinear SDOF systems

The evaluation of the accumulation of permanent set for inelastic structures due to wind action is important in establishing a criterion to select a reduced design wind load and in incorporating the beneficial ductile behaviour in wind engineering. A parametric study of the accumulation of the permanent set as well as the ductility demand for bilinear single-degree-of-freedom (SDOF) systems is presented in the present study. The dynamic analysis of the inelastic SDOF system is carried out using the method of Newmark for artificially generated time history of wind speed. Simulation results indicate that the mean of the normalized damage rate is highly dependent on the natural frequency of vibration. This mean value is relatively insensitive to the damping ratio if the damping ratio is larger than 5%. Thernscatter associated with the accumulation of the permanent set is very significant. The consideration of the postyield stiffness can significantly reduce the accumulation of the permanent set if the ratio of the yield strength to the expected peak response is small. The results also show that the ductility demand due to the wind action over a period of one hour for flexible structures can be much less than that for rigid structures or structures with larger damping ratio if the SDOF systems are designed with a reduced peak response caused by the fluctuating wind.

TROPICAL CYCLONE WINDS AT LANDFALL: The ASOS–C-MAN Wind Exposure Documentation Project

Photographs describing the wind exposure at automatic weather stations susceptible to tropical cyclones are now available on Web pages at the National Climatic Data Center and the National Data Buoy Center. Given the exposure for one of eight wind direction sectors, a user may estimate the aerodynamic roughness and correct mean wind measurements to an open-terrain exposure. The open-terrain exposure is consistent with the tropical cyclone advisories and forecasts issued by the National Weather Service, as well as building design wind load standards published by the American Society of Civil Engineers.

Reply to Discussion of “Specifications of the design wind load based on wind tunnel experiments” [J. Wind Eng. Ind. Aerodyn. 91 (2003) 527–541

Reply to Discussion of “Specifications of the design wind load based on wind tunnel experiments” [J. Wind Eng. Ind. Aerodyn. 91 (2003) 527–541

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)".

Directionality Reduction Effect of Design Wind Loads on Hong Kong Buildings

The extreme wind climate of Hong Kong has been estimated by using the wind data at Waglan. The 50 year return period wind speeds at 36 compass directions, and that without direction have been deter...

Determining Design Wind Loads for Work Zone Traffic-Control Devices

Proper traffic control and delineation are critical to achieving safety in work zones. In addition to being crashworthy, a barricade or temporary sign support should have the ability to withstand anticipated service loads. If a barricade or temporary sign support fails or overturns, it cannot perform its intended function and the safety of the work zone may be compromised. Currently, no guidance is provided on the service loads that should be used in the design of these work zone devices. Recommendations are provided for design wind loads for work zone traffic-control devices. The results from field trials indicate that truck-induced wind loading is not a critical design issue for barricades and barricades with signs. The recommendations are thus based on an analytical determination of design wind speeds associated with different recurrence intervals that correspond to the duration of work zone activities. Analytical case studies are presented for two common barricade designs, with consideration given to both structural capacity and overturn. Guidance on the amount of ballast required to prevent overturn is provided as a function of wind speed, barricade length, and sign mounting height.

Discussion of “Specification of the design wind load based on wind tunnel experiments” [J. Wind. Eng. Ind. Aerodyn. 91 (2003) 527–541

Discussion of “Specification of the design wind load based on wind tunnel experiments” [J. Wind. Eng. Ind. Aerodyn. 91 (2003) 527–541

Effect of building length on wind loads on low-rise buildings with a steep roof pitch

A wind tunnel model study was carried out on long, low-rise buildings with a steep roof pitch to determine the effect of the length-to-span aspect ratio on the external wind pressure distributions. The study showed a significant increase in the magnitude of the negative pressure coefficients on the leeward roof and wall, with an increase in aspect ratio, for oblique approach winds. These large suction pressures also generate large design wind load effects on the frames near the gable-end. The 1989 edition of the Australian standard for wind loads, AS 1170.2-1989 was found to underestimate the wind loads on steep pitch gable-roof buildings of aspect ratio greater than 3, on areas near the windward gable-end, and hence the critical bending moments in the supporting structural frames. The current Australian/New Zealand wind load standard, AS/NZS 1170.2-2002 specifies increased negative pressure coefficients on the leeward half of high pitch roof buildings, and critical bending moments in the supporting frames calculated from these distributions agree quite well with values obtained from the wind tunnel study. However, other major standards severely underestimate the critical bending moments, and the effective pressure coefficients producing those bending moments, especially on the leeward roof slope.

矩形平面を持つ陸屋根の構造骨組用風荷重(構造)

The primary purpose of this study is to provide simple formulas for estimating the design wind loads for the structural frames of rectangular flat roofs considering the dynamic response to turbulent wind forces. Two types of structural systems are considered here ; that is, (i) a series of simple beams arranged in parallel, and (ii) a structurally integrated type, which acts like an elastic plate, such as space truss. The characteristics of the first modal force are investigated, using a model of the pressure field on the roof. Based on the results, the gust effect factors for estimating the design wind loads are formulated as a function of the geometric and structural parameters of the roof and the turbulence intensity of approach flow. The formulas are verified by comparing the results on the load effects predicted by the formulas with those computed by using the experimental results for the modal force. The results of this study will be used for updating the specifications of roof wind loads in the AIJ Recommendations for Loads on Buildings.

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.

Wind-induced dynamic response and its load estimation for structural frames of single-layer latticed domes with long spans

The main purpose of this study is to discuss the design wind loads for the structural frames of single-layer latticed domes with long spans. First, wind pressures are measured simultaneously at many points on dome models in a wind tunnel. Then, the dynamic response of several models is analyzed in the time domain, using the pressure data obtained from the wind tunnel experiment. The nodal displacements and the resultant member stresses are computed at each time step. The results indicate that the dome`s dynamic response is generally dominated by such vibration modes that contribute to the static response significantly. Furthermore, the dynamic response is found to be almost quasi-static. Then, a series of quasi-static analyses, in which the inertia and damping terms are neglected, is made for a wide range of the dome`s geometry. Based on the results, a discussion is made of the design wind load. It is found that a gust effect factor approach can be used for the load estimation. Finally, an empirical formula for the gust effect factor and a simple model of the pressure coefficient distribution are provided.

Specification of the design wind load based on wind tunnel experiments

Once a high-quality wind tunnel experiment with no major flaws on the experimental side has been performed and the data have been processed/translated appropriately to the design-decisive variable, the final step is to estimate the appropriate load or load effect coefficient for the specification of the design wind load. Four questions arise: what is the appropriate length of a single run in the wind tunnel, what is the appropriate fractile of the observed extreme coefficients, how many independent experiments are required to estimate this fractile and what should be the target confidence interval. The paper tries to give some answers to these questions and discusses the findings in regard to some wind load codes.

Wind Performance of Short Utility Pole Structures

Most utility engineers in the United States use the National Electrical Safety Code (NESC) to determine minimum structural loading requirements for the design of transmission and distribution pole structures. The NESC specifies two weather loadings—combined ice and wind loading (rule 250B) and extreme wind loading (rule 250C). However, the current NESC excludes poles with heights above ground of 60 ft or less from the extreme wind loading (rule 250C) design requirement. ASCE 7-98 prescribes extreme wind load requirements for the design of buildings and other structures and contains no extreme wind load exclusion provision for short structures. This paper reviews the adequacy of the current NESC 60 ft exclusion provision for the design of poles located in the 90–140 mph 3 s gust wind speed based on ASCE 7-98.

Database-assisted design for wind: basic concepts and software development

Standard provisions for wind loads on buildings have traditionally been based on summary tables and/or plots suitable for slide-rule calculations. The accuracy in the definition of wind loads inherent in such tables and plots is far lower than that inherent in current methods for stress computation. Advances in computational power now make it possible to reduce this discrepancy and achieve structural designs for wind that are significantly safer and more economical than current designs. This is true both for routine, low-rise structures and for flexible structures experiencing significant dynamic effects. In this paper, we present the concept of database-assisted design (DAD) along with a discussion of the application software Wind Load Design Environment, a user-friendly tool for designers and code writers that employs the DAD approach. The DAD approach entails the use of large databases of aerodynamic pressures, the optional use of databases of directional extreme wind speeds, and the use of structural information needed for the description of linear or nonlinear structural behavior. We present progress achieved to date, describe current efforts and future needs, and discuss the implications of DAD for reliability-based design and performance-based standards development.

Wind-induced dynamic response and its load estimation for structural frames of circular flat roofs with long spans

This paper describes a simple method for evaluating the design wind loads for the structural frames of circular flat roofs with long spans. The dynamic response of several roof models were numerically analyzed in the time domain as well as in the frequency domain by using wind pressure data obtained from a wind tunnel experiment. The instantaneous displacement and bending moment of the roof were computed, and the maximum load effects were evaluated. The results indicate that the wind-induced oscillation of the roof is generally dominated by the first mode and the gust effect factor approach can be applied to the evaluation of the maximum load effects. That is, the design wind load can be represented by the time-averaged wind pressure multiplied by the gust effect factor for the first mode. Based on the experimental results for the first modal force, an empirical formula for the gust effect factor is provided as a function of the geometric and structural parameters of the roof and the turbulence intensity of the approach flow. The equivalent design pressure coefficients, which reproduce the maximum load effects, are also discussed. A simplified model of the pressure coefficient distribution is presented.

Generation of local wind pressure coefficients for the design of low building roofs

This paper presents recent research on the experimental evaluation of wind loads on low buildings and the recommendations provided in the form of traditional codification. These mainly include the wind loads on buildings with geometries different from those examined in previous studies. This is followed by the evaluation of simulated wind loads on low building roofs. The overall application of a recently proposed simulation methodology for codification purposes is discussed in detail. The traditional codification provides for a group of roof geometries a single peak design pressure coefficient for each roof zone considering a nominal worst-case scenario; this may often lead to uneconomical loads. Alternatively, thernpresented methodology is capable of providing peak pressure coefficients corresponding to specific roof geometries and according to risk levels; this can generate risk consistent and more economical design wind loads for specific roof configurations taking into account, for instance, directional design conditionsrnand upstream roughnesses.

Wind-induced dynamic behavior and its load estimation of a single-layer latticed dome with a long span

This paper describes the results of some basic investigations on the wind-induced dynamic behavior and the resultant load estimation of a single-layer latticed dome with a long span. The wind pressures at many locations on dome models were measured simultaneously in a wind tunnel. The dynamic response of several dome models was analyzed in the time domain by using a finite element method. For generating a time history of the wind load vector, which consisted of concentrated loads at all internal nodes, the proper orthogonal decomposition (POD) technique was applied to the wind pressure data obtained from the wind tunnel experiment. The nodal displacements and the resultant member stresses, both axial and bending, were computed at each time step. Based on the results, the characteristics of the wind-induced dynamic response of the dome are discussed. In the analysis, special attention is paid to the vibration modes that dominate the dynamic response. Furthermore, a brief discussion is made of the load estimation for the dome. A simple model for estimating the design wind load, expressed as an effective load, is proposed.

Performance based design extreme wind loads on a tall building

AbstractThis paper presents a procedure for the calculation of wind loads on a proposed 385 ft tall building located in strong wind and mixed strong wind and hurricane wind regions. The procedure for the computation of design wind loads uses mixed distribution and Monte Carlo simulation. The results of a probabilistic analysis of hurricane wind speeds are combined with the probability distribution of recorded extreme wind speeds (excluding hurricane data) at the site. A 50‐year sample of extreme wind speeds is created and the maximum 50‐year wind (from the hurricane and the recorded data) is noted. The simulation is repeated for a large number of samples (>10000) and the probability distribution of the 50‐year wind speed is computed for use in establishing the design wind speed Copyright © 2001 John Wiley & Sons, Ltd.