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Recent developments in pressure measurement technology, and unprecedented “big data” capabilities, have enabled the development of Database-Assisted Design (DAD), a powerful innovative approach to the design of tall buildings for wind. DAD eliminates unwieldy back-and-forth interactions between the wind and the structural engineer, needed in traditional practices if iterative designs are performed. Some structural engineers have shown interest in an alternative approach that uses equivalent static wind loads (ESWLs) in lieu of DAD. Such an approach is warranted if ESWLs induce in structural members demand-to-capacity indexes (DCIs) approximately equal to their peak counterparts obtained by DAD. This paper presents and assesses a simple procedure for calculating such ESWLs. The procedure uses an effective multiple points-in-time (MPIT) method for estimating combined peak wind effects, and accounts for wind directionality. A case study is presented that uses both the ESWL and DAD procedures, with the latter providing the requisite benchmark results. DCIs obtained from ESWLs based on the use of ten points-in-time (corresponding to 60 wind loading cases) were significantly closer to the benchmark DAD values than their counterparts based on the use of, e.g., four points-in-time (corresponding to 24 wind loading cases). For the building considered in this case study, ESWL-based design DCIs approximated to within approximately 3% the DCIs yielded by DAD. The approximation was found to be poorer for cases in which a single unfavorable wind direction is strongly dominant. The ESWL procedure is not applicable in its present form to structures with complex shapes. In all cases, the DAD procedure is the safest and most risk-consistent design option.

A 2004 Skidmore Owings and Merrill report (in Simiu E. (2011) Design of Buildings for Wind, Appendix 5, Wiley, Hoboken, NJ) notes that the ASCE 7 Standard (American Society of Civil Engineers (2002) ASCE 7–02, Reston, Va) is incomplete insofar as it provides no guidance on wind load factors appropriate for use with the Standard’s wind tunnel procedure. The purpose of this paper is to contribute to such guidance. Based on a classical definition of wind load factors as functions of uncertainties in the micrometeorological, wind climatological, aerodynamics and structural dynamics elements that determine wind loads, the paper presents a simple, straightforward approach that allows practitioners to use appropriate wind load factors applicable when those uncertainties are either the same as or different from those assumed in the development of the ASCE 7 Standard. Illustrations of the approach are presented for a variety of cases of practical interest. In estimating design wind loads, the various uncertainties should not be accounted for in isolation, for example by specifying peak pressure coefficients with percentage points higher than those corresponding to their expected values. Rather, to achieve risk-consistent designs, the uncertainties should be accounted for collectively, in terms of their joint effect on the design wind loading. The design wind effect is equal to the estimated expectation of the peak wind effect times a load factor that, in most cases, is not significantly different from the load factor explicitly or implicitly specified in the ASCE 7 Standard. Notably, the load factor is not affected significantly by errors associated with interpolations required in typical Database Assisted Design applications. However, if the available wind speed records are several times shorter than, say, 20 to 30 years, the wind load factors increase by amounts of the order of 15 %.

According to recent results of planetary boundary layer research relevant to the design of tall buildings subjected to large-scale synoptic storm winds, for elevations of up to at least 1 km, the longitudinal mean wind speeds are monotonically increasing with height. It is shown that, for this reason, to avoid the possible unconservative design of supertall buildings significantly affected aerodynamically by neighboring buildings, an explicit derogation from the ASCE 7 standard specification of the gradient heights z(g) is necessary for buildings with heights greater than z(g).

Characteristics of flow in the planetary boundary layer (PBL) strongly affect the design of tall structures. PBL modelling in building codes, based as it is on empirical data from the 1960s and 1970s, differs significantly from contemporary PBL models, which account for both “neutral” flows, and “conventionally neutral” flows. PBL heights estimated in these relatively sophisticated models are typically approximately half as large as those obtained using the classical asymptotic similarity approach, and are one order of magnitude larger than those specified in North American and Japanese building codes. A simple method is proposed for estimating the friction velocity and PBL height as functions of specified surface roughness and geostrophic wind speed. Based on published results, it is tentatively determined that, even at elevations as high as 800 m above the surface, the contribution to the resultant mean flow velocity of the component V normal to the surface stress is negligible and the veering angle is of the order of only 5\(^{\circ }\). This note aims to encourage dialogue between boundary-layer meteorologists and structural engineers.

This paper illustrates the application of the database-assisted design (DAD) method to the wind design of high-rise buildings. The paper uses publicly available wind tunnel data and DAD procedures to compare responses to (1) corner winds and (2) face winds of a high-rise building of square cross-section supported by a central core column and four mid-side legs. The responses being considered consist of overturning moments, and of demand-to-capacity indexes (DCIs) of selected members, including multistory chevron braces. The analysis accounts for structural dynamics and second-order load-deformation effects. The results show that corner winds are less demanding than face winds, both globally (overturning moments) and locally (DCIs). The along-wind and across-wind overturning moments in the corner wind case are about 20% and 50% lower, respectively, than their counterparts in the face-wind case. The peak axial forces in the legs (peak refers to absolute value) and the peak DCIs in the mid-side mast columns (continuation of the legs) induced by corner winds are lower by 20%–30% than their counterparts due to face winds. The investigation confirms that the building code of the City of New York in effect in the early 1970s can be interpreted as meaning that the design for wind of structures with a square shape in plan may be performed by assuming the wind loads to act normal to a face of the building. The building analyzed in this paper is similar to the Citicorp Building (completed in 1977, later renamed Citigroup Center, now called 601 Lexington) and the results of the analyses presented herein suggest that a re-examination of the history of the Citicorp Building design and retrofit may be warranted.

In this report, high-Reynolds number turbulent flow around an axisymmetric hill is studied using large eddy and unsteady Reynolds averaged Navier-Stokes simulations and the results are extensively validated against experiment. The boundary-layer thickness of the incoming flow is about half of the height of the hill. In the process, the dynamic Smagorinsky sub-grid scale eddy-viscosity model and a precursor forcing technique to match the experimental mean velocity profile is implemented in the computational toolbox for wind engineering, windOF which is based on the open source computational fluid dynamic solver OpenFOAM. The results show that the windOF is capable of producing reliable results with LES for this complex flow which includes complicated flow topography due to smooth-wall separation, lee-side separation, reattachment and recovery behind the hill, etc. However, URANS predictions demonstrate significant discrepancies in several flow features, specifically in the lee-side separation and recovery that are characteristic of the RANS models which only consider much smaller scale turbulence compared to the mean flow distortion scales relevant to this flow.

Integral length scales of atmospheric boundary layer (ABL) flows, as well as mean velocities and turbulence intensities, play an important role in determining the response of structures subjected to wind loads. For tall building design, however, sufficient relevant data at high elevations are currently not available from experimental/field measurement data or in building standards. This study uses Large Eddy Simulation (LES) with a constant horizontal pressure gradient and streamwise periodic boundary conditions to develop horizontally homogeneous neutral ABL flow. Based on two-point velocity correlation functions ( ρ u x , ρ u y , ρ u z , ρ v y , ρ w z ), the corresponding integral length scales ( L u x , L u y , L u z , L v y , L w z ) are presented at heights across the ABL depth for better characterization of the energetic turbulent eddies. In particular, this study addresses numerical artifacts inherent in the CFD simulations, which are due to insufficient longitudinal domain lengths and streamwise periodic boundary conditions, frequently used in computational studies, that affect the estimation of longitudinal correlation function in the streamwise direction, ρ u x , and the corresponding integral length scale, L u x . An analytical expression for ρ u x is proposed and calibrated using simulations with various longitudinal domain lengths, to obtain domain-independent L u x estimates across the ABL depth. The results clearly show that the turbulent eddy structures are highly elongated (streamwise) in the near-ground region, and become shorter in the outer region of the ABL. Estimates of the integral length scales are provided at heights much greater than the upper limit of standards like ASCE 7–16. This study provides an insight into the three-dimensional coherent structures of flows throughout the ABL depth and presents data on modeling approach flows in wind tunnel tests, in numerical simulations, and in associated standard provisions.

Estimates of wind effects on rigid buildings by database-assisted design (DAD) methods can be far more accurate than those based on information available in standards. An upgraded version of DAD is presented that streamlines the wind engineering/structural engineering components of the design process by allowing the direct computation of Demand-to-Capacity Indexes (DCIs). The computation achieves the rigorous combination of imperfectly correlated time series of wind forces and effects, thus eliminating errors due to subjective estimates of combined effects. The basic approach being presented is applicable to any rigid building. This paper focuses on simple buildings with gable roofs, portal frames, and bracing parallel to the ridge. Useful features of this work include: the capability to use the two largest building aerodynamics databases available worldwide; the use of large simulated extreme wind databases for hurricane- and non-hurricane-prone regions; a novel interpolation scheme allowing the design of buildings with dimensions not represented in the databases; an effective multiple-points-in-time algorithm for estimating peaks; and parameter-free methods for estimating DCIs with specified mean recurrence intervals. Case studies indicated that the proposed interpolation scheme was satisfactory. The results obtained confirm: (i) published results which show that the ASCE 7-10 envelope procedure can significantly underestimate wind effects; (ii) the mutual consistency for practical purposes of the two aerodynamic databases being used; and (iii) DAD’s potential for practical use in structural design. The software developed for the implementation of the procedure is available at http://www.itl.nist.gov/div898/winds/iterative_design/wind_design.htm . A user’s manual is available at http://nvlpubs.nist.gov/nistpubs/TechnicalNotes/NIST.TN.1908.pdf .

We perform Computational Fluid Dynamics (CFD) analyses of a low-rise building immersed in a turbulent boundary layer. The Silsoe 6 m cube is chosen as the main case study aiming at representing the key features of the typical wind conditions experienced by low-rise buildings. The turbulent inflow condition is generated by employing a precursor technique. A sensitivity study is conducted to investigate the effects of eight subgrid-scale (SGS) models on the flow around the cube. The incoming turbulence intensity and mesh sizing for each of the SGS models are also explored. The results in terms of time-averaged pressure fields for relatively well-resolved simulations are well compliant with available experimental data and insensitive to the selection of the SGS model. We demonstrate that, while the effect of the aforementioned factors has a limited impact on the first-order statistics of the pressure coefficients, their influence becomes much more pronounced when analysing higher-order statistics (i.e. variance, skewness and kurtosis) and extreme values. The extent of their relative importance depends on the location of the point under investigation and the quantity of interest. The current study provides guidelines on the choice of factors which can strongly affect the results obtained employing CFD simulations when the local peak pressures are of interest, for example, as in the case of cladding design.

This paper briefly reviews recent and current National Institute of Standards and Technology (NIST) research aimed at improving standard provisions and advancing structural design practice for wind loads. The research covers: (i) New wind speed maps for the conterminous United States; (ii) Risk-consistent estimation of wind load factors for use with the wind tunnel procedure; (iii) Modern peaks-over-threshold approaches to estimation of peak wind effects; (iv) User-friendly procedures for the database-assisted design of rigid and flexible structures; (v) Novel approaches to codification of pressures on cladding and components; (vi) Modern modeling of synoptic storm planetary boundary layers and its implications for super-tall building design; (vii) Computational Wind Engineering (CWE); (viii) Tornado climatology and development of tornado-resistant design methodologies; (ix) Joint climatology of wind speeds, storm surge and waves heights, and estimates of their combined effects on structures.

This paper investigates second-order effects on wind-induced structural dynamic behavior of a 60-story high-rise steel structure known as the Commonwealth Advisory Aeronautical Research Cou...

This paper presents large eddy simulations (LES) of model-scaled neutrally stratified atmospheric boundary layer (ABL) flows for structural engineering applications and examines their stati...

We propose a simple but effective tracking-by-segmentation algorithm using Absorbing Markov Chain (AMC) on superpixel segmentation, where target state is estimated by a combination of bottom-up and top-down approaches, and target segmentation is propagated to subsequent frames in a recursive manner. Our algorithm constructs a graph for AMC using the superpixels identified in two consecutive frames, where background superpixels in the previous frame correspond to absorbing vertices while all other superpixels create transient ones. The weight of each edge depends on the similarity of scores in the end superpixels, which are learned by support vector regression. Once graph construction is completed, target segmentation is estimated using the absorption time of each superpixel. The proposed tracking algorithm achieves substantially improved performance compared to the state-of-the-art segmentation-based tracking techniques in multiple challenging datasets.

The purpose of this paper is to discuss issues associated with ASCE 7-10 standard methods for determining wind loads on buildings and other structures that warrant comment, correction, or improvement. The assessment is intended to serve as a resource in the development of a new version of the ASCE 7 standard and to stimulate a wider participation in that development by the structural engineering community. Issues discussed in the paper include: wind speeds in nonhurricane regions; alternative analytical methods for determining wind loads and wind effects on main wind force resisting systems and components and/or cladding; aerodynamic pressure coefficients; pressures on rooftop equipment; component and cladding pressures on arched roofs; and the wind tunnel procedure. It is noted that the ASCE 49 standard essentially covers wind tunnel testing, rather than the wind tunnel procedure, of which wind tunnel testing is only a part.

The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as hasbeenshownbythelargediscrepanciesamongresultsobtainedindifferentwindtunnelfacilitiesoreveninthesamewindtunnel.Twomajor causes of the discrepancies are the difficulty of simulating large-scale, low-frequency turbulent fluctuations uniformly across laboratories and the small scale of models in typical civil engineering wind tunnels. To address these issues, it was proposed that a simplified flow be used in laboratory simulations,rather thana conventionalABL flow.In thesimplified flowthe referencemeanwind speedislarger thanthemean wind speed of the ABL flow, and the low-frequency fluctuations present in the ABL flow are suppressed; that is, the peak energy of the missing low- frequency fluctuations is supplied in the simplified flow by the increment in the mean wind speed, which may be regarded as a flow fluctuation with zero frequency. High-frequency turbulent fluctuations, which typically affect flow reattachment, are approximately the same in the ABL and the simplified flow. Because, over small distances, low-frequency fluctuations are highly coherent spatially for small low-rise buildings with dimensions of up to approximately 20 m (e.g., single-family residential homes), the peak aerodynamic effects of the two flows may be hypothesized to be approximately the same. Preliminary experimental results obtained in University of Western Ontario's ABL wind tunnel facility and Florida International University's small-scale Wall of Wind facility are shown to support this hypothesis. The use of the proposed simplified flow is currently being tested by the authors for application to computational wind engineering (CWE) applications. Such use eliminatestheneedtosimulatethelowerfrequency fluctuationsoftheboundarylayer flowandthusmakesitpossibletoachievepracticalCWE calculations, and it is advantageous in experiments from the points of view of measurement accuracy, model scaling, repeatability of the simulations, and computational efficiency. DOI: 10.1061/(ASCE)EM.1943-7889.0000508. © 2013 American Society of Civil Engineers. CE Database subject headings: Boundary layers; Wind loads; Low-rise buildings; Wind tunnels. Author keywords: Atmospheric boundary layer; Computational wind engineering; Flow modeling; Low-rise buildings; Wind engineering; Wind tunnel tests.

One of the problems encountered in the estimation of wind effects on high-rise structures is the development of combinations of wind-induced translational responses in possible conjunction with rotational responses and/or of forces and moments that contribute to the wind-induced demand at various cross sections of individual structural members. In current wind engineering practice such combinations are developed in large part intuitively because phase information on the effects being combined is not readily available from frequency domain analyses. In contrast, full time series analyses can produce estimates of combined wind effects because they preserve phase information; however, such analyses can be overly time-consuming. In current wind engineering practice it is common to use the empirical point-in- time (PIT) procedure for the estimation of peaks of combined stationary stochastic processes. The procedure is applied to pairs of such pro- cesses, and consists of adding an estimate of the peak value of one of the processes to the estimated value of the second process at the time of the occurrence of that peak. Even if the full time histories of the two stochastic processes are used, errors inherent in PIT can be in some casesashighas20%ontheunconservativeside.Thepurposeofthispaperistopresenttheempiricalmultiplepoints-in-time(MPIT)procedure, which improves significantly upon the PIT approach. The MPIT procedure is illustrated by an application to a 60-story reinforced concrete structure. Results show that the MPIT approach produces remarkably accurate estimates of the peak combined wind effects by using a limited number of peaks from the time histories of the individual wind effects being combined. Those estimates are obtained far more economically in terms of computational time than conventional time domain estimates that use full time histories. DOI: 10.1061/(ASCE)ST.1943- 541X.0000649. © 2013 American Society of Civil Engineers.

We propose a novel algorithm for weakly supervised semantic segmentation based on image-level class labels only. In weakly supervised setting, it is commonly observed that trained model overly focuses on discriminative parts rather than the entire object area. Our goal is to overcome this limitation with no additional human intervention by retrieving videos relevant to target class labels from web repository, and generating segmentation labels from the retrieved videos to simulate strong supervision for semantic segmentation. During this process, we take advantage of image classification with discriminative localization technique to reject false alarms in retrieved videos and identify relevant spatio-temporal volumes within retrieved videos. Although the entire procedure does not require any additional supervision, the segmentation annotations obtained from videos are sufficiently strong to learn a model for semantic segmentation. The proposed algorithm substantially outperforms existing methods based on the same level of supervision and is even as competitive as the approaches relying on extra annotations., CVPR 2017 (Spotlight)

Atmospheric boundary layer winds experience two types of effects due to friction at the ground surface. One effect is the increase of the wind speeds with height above the surface. The second effect, called the Ekman layer effect, entails veering - the change of the wind speed direction as a function of height above the surface. In this study a practical procedure is developed within a database- assisted design (DAD) framework that accounts approximately for veering effects on tall building design. The procedure was applied in a case study of a 60-story reinforced concrete building, which also considered the dependence of veering effects on the orientation of the building. Comparisons are presented between response estimates that do not account for veering, and account for veering conservatively. For the case studied in this paper veering effects were found to be small.

Large-amplitude vibrations of stay cables in cable-stayed bridges are an aeroelastic phenomenon caused by an interaction between wind and motion of the cables that is not yet fully explained. Understanding how flow around and the associated forces on an oscillating cable in the across-flow direction are developed interactively is essential to describe the mechanism of cable vibrations. This can ultimately lead to effective mitigation strategies for the large-amplitude vibrations. In this numerical study, using three-dimensional detached eddy simulation (DES), we considered vertically oscillating incoming flow over a stationary, yawed horizontal circular cylinder to investigate the effects of oscillation frequency on flow around and forces on the cylinder. The flow patterns and forces indicate that the incoming and around-cylinder oscillating flows interact significantly. Results showed that the flow around a yawed cylinder develops in different ways depending on the frequency of the incoming flow oscillation, resulting in changed characteristics of flow-induced forces. When incoming flow oscillated at frequencies similar to those of forces generated on the cylinder under uniform incoming flow, along-span flow that generated the low-frequency forces was intensified, i.e., the associated forces were strengthened while preserving their low frequency. However, when the incoming flow oscillated at a frequency close to that of Karman vortex shedding, the along-span flow was suppressed while the Karman vortex shedding phenomenon was strengthened over the whole cylinder length. This study suggests that when an oblique cable oscillates at a low frequency due to oblique wind-induced aerodynamic forces, those forces play an important role in initiating and increasing the vibration at the low frequency. A fluid-structure interaction analysis is planned that will shed more light on the phenomenon studied in this work by considering only the fluid motion.

Wind loads on low-rise buildings in general and residential homes in particular can differ significantly depending upon the laboratory in which they were measured. The differences are due in large part to inadequate simulations of the low-frequency content of atmospheric velocity fluctuations in the laboratory and to the small scale of the models used for the measurements. The imperfect spatial coherence of the low frequency velocity fluctuations results in reductions of the overall wind effects with respect to the case of perfectly coherent flows. For large buildings those reductions are significant. However, for buildings with sufficiently small dimensions (e.g., residential homes) the reductions are relatively small. A technique is proposed for simulating the effect of low-frequency flow fluctuations on such buildings more effectively from the point of view of testing accuracy and repeatability than is currently the case. Experimental results are presented that validate the proposed technique. The technique eliminates a major cause of discrepancies among measurements conducted in different laboratories. In addition, the technique allows the use of considerably larger model scales than are possible in conventional testing. This makes it possible to model architectural details, and improves Reynolds number similarity. The technique is applicable to wind tunnels and large scale open jet facilities, and can help to standardize flow simulations for testing residential homes as well as significantly improving testing accuracy and repeatability. The work reported in this paper is a first step in developing the proposed technique. Additional tests are planned to further refine the technique and test the range of its applicability.

Aerodynamic testing of low-rise structures is fraught with difficulties that can be the cause of large measurement errors, resulting in the underestimation of aerodynamic pressures by a factor of as much as two. The errors are primarily attributable to the inadequate knowledge and simulation of wind flows affecting low-rise buildings, especially residential homes in suburban environments. A type of aerodynamic testing of sufficiently small low-rise structures is explored that does not entail the simulation of the turbulence intensity and integral turbulence scales. That type of testing would offer several advantages: eliminating a major cause of discrepancies among measurements conducted in different laboratories, allowing the use of larger model scales, and allowing testing in both typical commercial wind tunnels and in open jet facilities of the Wall of Wind (WoW) type. Preliminary tests based on data obtained at the University of Western Ontario wind tunnel and the Florida International University large-scale six-fan WoW facility suggest that the proposed type of testing yields systematically conservative results for the specialized type of measurements considered herein. In most cases, but not all, the degree of conservatism is modest. The results appear to be of sufficient interest to warrant additional research.

Advances in wind pressure measurement and computer technology have made time-domain analyses of wind effects on high-rise structures possible in recent years. Time-domain solutions use aerodynamic and wind climatological databases and provide full phase information on wind-induced response that is lost in the frequency-domain approach; therefore, they can account rigorously for the superposed effects of any number of modes of vibration of any shape; for mode coupling; for wind directionality effects; and for the joint contributions of axial forces, bending moments, and shear forces in interaction equations used for structural design. Unlike the frequency-domain approach, in the time-domain approach, the process of determining wind effects and the structural design process, referred to jointly as database-assisted design (DAD), are integrated, transparent, and fully auditable. The objective of this study is to present the DAD approach as applied to high-rise reinforced concrete (RC) buildings. Given the ti...

Large-amplitude vibrations of stay cables in cable-stayed bridges can threaten the safety and serviceability of the structures. Understanding of the excitation mechanism is necessary to mitigate such vibrations effectively and efficiently. Experimental research has investigated the mechanism of oscillation using flow oblique to a cylinder; however, since the aspect ratio of the cylinder is much lower than that of a real stay cable in bridges, the results might not reliably describe the real phenomenon. The aim of this study is (1) to provide better understanding of aspect ratio effects of a circular cylinder on aerodynamic characteristics of the cylinder oblique to flow associated with the large-amplitude cable vibrations and (2) to provide the experimentalists suggestions of a requisite aspect ratio and appropriate pressure-measuring positions of a cylinder for fully developed flow around the cylinder. To this end, the current work applied three-dimensional detached eddy simulations (DES) to flow around a yawed and inclined cylinder to investigate the importance of the aspect ratio of the cylinder when flow oblique to the cylinder develops fully along its spanwise axis. The Reynolds number is 1.4 × 105 based on the incoming flow velocity and the diameter of the cylinder. Three aspect ratios (L/D=10, 20, and 30; L: a cylinder length; D: a cylinder diameter) and two numerical conditions (slip and periodic) on spanwise boundaries were employed. Results showed that three-dimensional flow and the associated forces on a yawed and inclined cylinder are significantly influenced by the spanwise aspect ratios and spanwise boundary conditions. This study suggests that when a wind tunnel experiment investigates flow oblique to a very slender cylinder, such as attempting to model a stay cable, experimentalists should use a sufficiently high spanwise aspect ratio of the cylinder. For the case of the 30° yaw and 45° inclined cylinder, the requisite ratio would be approximately 60 or higher and appropriate pressure-measuring positions of a half to two-thirds of the cylinder length from its upper/upstream end in order to accurately model inherently three-dimensional characteristics of the flow.

As the world struggles to reduce energy consumption and greenhouse gas emissions, much attention is focused on making buildings operate more efficiently. However, there is another, less recognized aspect of the built environment: the embodied energy of buildings, which represents the energy consumed in construction, including the entire life cycle of materials used. Architects and structural engineers extensively perform designs of buildings with steel and reinforced concrete–materials that, to different degrees, are energy intensive. This presents an opportunity to use structural optimization techniques, which have traditionally been employed to minimize the total cost or total weight of a structure, to minimize the embodied energy. With this in mind, an analysis is carried out to determine the implications, from the point of view of cost, of optimizing a simple reinforced concrete structural member, in this case a rectangular beam of fixed moment and shear strengths, such that embodied energy is minimized. For the embodied energy and cost values assumed, results indicate a reduction on the order of 10% in embodied energy for an increase on the order of 5% in costs.

Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Karman vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10 5 . Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.

A three-dimensional detached eddy simulation (DES) study was conducted to investigate the three-dimensional characteristics of the fully developed flow past a yawed and inclined circular cylinder. Flow at Reynolds number ( Re ) of 1.4×10 5 (based on freestream velocity U and the diameter of the cylinder D ) over a cylinder with axial lengths of 10 D , 20 D and 30 D was simulated. Spanwise wall boundary conditions were also studied to examine their effect on the flow field. The simulation shows that the flow is highly three-dimensional. The swirling flow with low pressure on the cylinder plays an important role in generating multiple moving forces, which can produce low-frequency loadings. The mechanism of generation of forces on the cylinder provides fundamental information necessary for the understanding of the oscillation of a yawed and inclined circular cylinder.

Filmon Habte; Arindam Gan Chowdhury, M.ASCE; DongHun Yeo, M.ASCE; and Emil Simiu, F.ASCE Graduate Student, Dept. of Civil and Environmental Engineering, Florida International Univ., Miami, FL 33199. E-mail: fhabt003@fiu.edu Associate Professor, Dept. of Civil and Environmental Engineering, Florida International Univ., Miami, FL 33199. E-mail: chowdhur@fiu.edu Research Structural Engineer, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 (corresponding author). E-mail: donghun.yeo@nist.gov NIST Fellow, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899. E-mail: emil.simiu@nist.gov

The wind directionality factor, Kd, is a nondimensional quantity smaller than unity that reflects the fact that the climatologically and aerodynamically or dynamically most unfavorable wind directions typically do not coincide. The ASCE 7-10 standard specifies for buildings a directionality factor Kd=0.85, although no justification appears to have been adduced for this value in the literature. This paper presents a more informed discussion of this topic by the engineering and codification communities. The results of this work show that the directional factor Kd varies as a function of type of wind storm, geographical location within an area with a given type of wind climate, type of wind effect (e.g., local pressures, internal forces in members of wind force resisting systems, global shear or torsion), and position of the wind effect being considered in the structure. These results suggest that, in most if not all cases, the dependence of the directionality factor on mean recurrence interval of wi...

Efforts are being made to achieve more efficient operation of buildings, with the goal of reducing the construction industry’s contribution to energy consumption and greenhouse gas emissions. That contribution also includes the energy embodied in structures; that is, the energy consumed in the processes of extracting, manufacturing, transporting, and installing construction materials (including recycled materials) and elements. In particular, in spite of the use of additives such as fly ash, reinforced concrete (RC) structures, which are large consumers of cement, are responsible for a sizable proportion of worldwide carbon emissions. These emissions can be reduced significantly through the more efficient use of both concrete and steel that can be achieved by optimization. Modern optimization tools are now available that make it possible to perform large volumes of calculations efficiently that are applicable to a wide variety of structural engineering problems. This study presents an optimization...

Database-assisted design (DAD) is an integrated methodology that calculates wind loadings and wind-induced internal forces. It can also calculate demand-to-capacity indexes for each structural member, and by checking whether they differ significantly from unity, determine the adequacy of the members’ structural design. Its practical usefulness depends on the availability of comprehensive aerodynamic databases. A public domain aerodynamic database produced in 2003 by the University of Western Ontario (UWO) is not sufficiently extensive to satisfy design needs generally encountered in practice. For this reason, the Tokyo Polytechnic University (TPU) recently developed comprehensive sets of aerodynamic databases that are publicly available and would fill large voids present in the UWO database. This paper presents comparisons of aerodynamic pressures and forces based on TPU and UWO data for low-rise buildings to help assess the extent to which the respective aerodynamic pressure measurements are comp...

For structures sensitive to wind directionality, methods for the estimation of wind effects require the use of time series of directional wind speeds that cover time periods exceeding the length of the mean recurrence interval (MRI) of interest to the design. This study proposes a procedure for generating such time series from relatively short wind data sets. First, an algorithm is developed for estimating the parameters of the distributions of the directional wind speeds, given that the size of the data sample within one or more directional sectors can in some instances be too small for statistical inference purposes. Once the distribution parameters are estimated, a simple Monte Carlo procedure is used for data generation. The wind speed data being generated can be used within the framework of the database-assisted design approach to determine wind effects on buildings by accounting for wind directionality.

A procedure is presented for estimating parametric probabilistic models of hurricane wind speeds from existing information on state-of-the-art estimates of wind speeds with various mean recurrence intervals (MRIs). Such models may be needed, for example, for the estimation of hurricane wind speeds with long MRIs required for the performance-based design of structures susceptible of experiencing nonlinear behavior. First, the procedure is applied to the case where that information is obtained from ASCE 7-10 wind maps, and examples are provided of its application to a number of coastal mileposts on the Gulf and Atlantic coasts. Next, the procedure is applied by using, in addition to the ASCE 7-10 information, hurricane wind speeds with 1,000,000- and 10,000,000-year MRIs estimated in a 2011 Nuclear Regulatory Commission (NRC) report. It is then argued that ASCE 7-10 Standard basic wind speeds for New York City are not conservative with respect to their counterparts specified in the standard for othe...

The paper summarizes recent research and development of computer-aided and computational methods in wind engineering at the National Institute of Standards and Technology (NIST). Specific topics to be covered include: 1. Time-domain database-assisted design of tall, flexible structures excited by turbulent winds inducing dynamic structural responses. 2. Computational Fluid Dynamics (CFD) estimates of aerodynamic pressure on low-rise buildings with geometrical dimensions comparable to the acrosswind integral turbulence length scale. 3. Development of synthetic directional wind speed databases covering on the order of 10,000 years, from measured wind speeds over periods of approximately 30 years. 4. Probability distributions of hurricane wind speeds, Gulf and Atlantic coasts. 5. Extreme wind speeds in non-hurricane prone conterminous United States. 6. Estimates of hurricane-borne missile speeds. 7. Disaster and Failure Events Repository – a new research tool for archival and analysis of post-disaster information and data.