Gust Loading Factor Research Articles

Wind-Induced Responses in Tall Buildings Using International Standards: A Review

Abstract: This study investigates the impact of international wind loading regulations on tall buildings by analyzing major codes from the United States (ASCE 7), Australia (AS/NZS 1170.2), Canada (NBC), and India (IS 875). The research reveals significant differences in the estimation of wind loads, attributed to variations in exposure categories, wind speed profiles, and calculation methodologies. Notably, the gust loading factor is commonly used across these standards. The parameters used to estimate wind loads by the international standards are also discussed. The findings underscore the necessity for global wind load limitations and emphasize the importance of considering local factors to ensure the structural safety and integrity of tall buildings under varying wind conditions.

Classification of equivalent static wind loads: Comparisons and applications

This paper reviews the basic ideas, developments, and codification practices of different calculation methods for equivalent static wind load (ESWL) in the past about sixty years. From the landmark work of Davenport's Gust Loading Factor (GLF), Kasperski's Load-Response-Correlation (LRC), and Katsumura, Tamura's Universal-ESWL (U-ESWL), the development thread of ESWL is clarified. The ESWLs are classified based on the number of target load effects (Single-target or Multiple-target) and on actuality (Realistic or Unrealistic). GLF is representative as a “Single-target Unrealistic” ESWL, which has been adopted in many international codes and standards for building design and is extended into many approaches considering different targets (e.g. base bending moment), and different components (along-wind, crosswind, torsional). The LRC method identifies a realistic wind load distribution that causes one target maximum/minimum load effect, is a representative of “Single-target Realistic” ESWL, is well adopted as a background component ESWL, and is further developed to consider the dynamic resonant effect. The U-ESWL simultaneously reproduces maximum/minimum load effects in multiple structural members with only two sets of load distributions, is a “Multiple-target Unrealistic” ESWL, and has also been developed and employed in a wind load code for roof structures.

Wind Load Effects and Gust Loading Factor for Cable-Suspended Photovoltaic Structures

The cable-suspended PV system has gained increasing popularity due to its large span and good site adaptability. However, this structure is quite sensitive to wind actions, and wind-induced module damage and structure failure have been frequently reported. Therefore, in this study, we carried out wind tunnel tests to study wind load effects on PV arrays with different lengths and widths. Considering the wind sheltering effects of upstream modules, reduction factors for the wind load were proposed in different array zones. Numerical simulations of wind-induced vibration and equivalent static analysis were conducted to yield gust loading factors for the PV array. This study showed that the maximum wind suction and pressure for the middle zone occurred at 0° and 180°, respectively, while those for the outermost zone appeared under oblique flows (e.g., 30° and 150°). For the PV modules beyond the windward fourth row, the reduction factors of the wind loads were 0.4 (maximum suction) and 0.2 (maximum pressure) for the middle zone and 0.5 (maximum suction) and 0.75 (maximum pressure) for the outermost zone. The gust loading factors for the typical wind directions of 0° and 180° varied from 2.2 to 2.7 for the middle zone and from 1.3 to 1.5 for the outermost zone.

Experimental investigation on wind-induced vibration of photovoltaic modules supported by suspension cables

Under the background of the global energy crisis and excessive carbon emissions, solar power stations have increased rapidly in number and size in recent years. To satisfy the construction needs on complex or special sites (e.g. intertidal zone, mountainous area, fishponds, etc.), a suspension cable supported photovoltaic (PV) module was developed recently and quickly aroused market interest; however, such cable-supported flexible PV systems are susceptible to wind loading and associated aerodynamic effects thereon remain unclear. Therefore, both aeroelastic and rigid model wind tunnel tests were conducted to investigate the wind-induced vibration (WIV) characteristics of a typical cable-supported PV module. The effects of module tilt angle, cable pre-tension, and wind speed on the vertical displacement response and the aerodynamic damping were evaluated. Based on wind pressure tests and finite element simulation, the three-dimensional WIV behavior of PV modules could be investigated. The non-dimensional gust loading factor representing the load dynamic amplification was presented based on multi-target equivalent static wind loads. Results show that wind-induced vertical vibration of the PV modules increased with tilt angle but reduced with increasing cable pretension. The fluctuating displacement shows a quasi-linear increase with the square of the wind speed. Negative aerodynamic damping was found for a tilt angle of 10° under high wind speeds. Compared to vertical vibration, horizontal and torsional responses were insignificant for the tested PV modules. The estimated gust loading factor for the PV module with tilt angle of 10° was between 1.1 and 2.5.

A review of approaches to generate equivalent static and synthetic wind loads on tall buildings for the preliminary stage of design

The extraordinary urbanisation of cities in recent decades urges us to consider the efficient design of tall buildings. Because of the increased flexibility of slender buildings, wind loads are expected to dominate the design loads. Although there are widely accepted wind tunnel techniques for obtaining wind loads on tall buildings, they are time-consuming and may be inconvenient in the pre-concept design process, when structural engineers would like fast and low-priced methods to predict the wind loads over the height of tall buildings. This paper mainly reviews the gust loading factor including other semi-empirical approaches and mathematical approaches for generating equivalent static and synthetic wind loads on tall buildings. Although stochastic simulations and time series analysis methods have limited use in generating wind loads on tall buildings, they are also briefly examined. Based on the findings of this review the paper concludes that it is definitely viable for synthetic wind approaches to be used to speed up the preliminary design process when large numbers of structural systems need to be assessed rapidly.

Wind-induced responses and equivalent static design method of oval-shaped arch-supported membrane structure

This paper presents the wind-induced responses and wind resistant design method of arch-supported membrane structure. Series of rigid model wind tunnel tests are carried out to record wind pressure data on the roof surface of experimental models. Random vibration time history analysis is employed to get wind-induced responses. Geometric nonlinearity is taken into account in dynamic analysis. Effects of different factors such as wind velocity, wind direction, arch span, rise-span ratio, and membrane prestress on peak wind-induced responses are presented meticulously. Displacement, membrane stress, internal force of cable and abutment reaction are analyzed to study the peak responses of structure. This study considers the influence of boundary wall by conducting wind tunnel tests on both enclosed and open models. Results show that peak responses increase significantly as wind velocity and/or arch span increase. The performance of membrane structures can be enhanced by increasing membrane prestress, but the effect is quite small. Similarly, responses increase with rise-span ratio, but the rate of increment is not constant. Effect of the boundary wall depends significantly on wind direction and rise-span ratio. Additionally, this paper proposes the concept of equivalent static design method based on gust loading factor and nonlinear adjustment factor.

Analysis of wind-induced responses and GLF for super-large cooling towers

Based on wind tunnel tests, time-varying wind pressure distribution on the finite element model of a super-large hyperbolic cooling tower under group-tower environment were reconstructed by the radial basis function (RBF) method. The results were applied in time-domain calculations of wind-induced responses of the cooling tower. Then, the gust loading factor (GLF) method adopted in current engineering practice was analyzed. The results indicate that: due to some inevitable limitations, the existing GLF scheme, in which a unified amplification factor G is adopted to calculate the equivalent static wind loads, may not be applicable for super-large cooling towers.

Towards codification of thunderstorm/downburst using gust front factor: Model-based and data-driven perspectives

Winds associated with gust fronts originating from a thunderstorm/downburst exhibit rapid changes during a short time period which may be accompanied by changes in direction. For several decades, a number of studies have been focused on identifying the characteristics of such nonstationary gust front winds in a variety of manners such as experimental/numerical methods and full-scale measurements. Yet, beginning the dialogue on any guidelines for design practice has thus far not evolved, in part due to a limited consensus on such characteristics among studies in conjunction with paucity of available data needed for vetting and corroborating, which is further impacted by the presence of nonstationarity. In an effort to establishing a new design procedure for this type of wind load effect on structures, the gust front factor (GFF) framework has been proposed by authors that encapsulates both the kinematic and dynamic features of gust front induced wind effects on structures, which distinguish themselves from those experienced in conventional boundary layer flows. This study revisits the gust front factor framework seeking to take the next step toward a possible initial framework for codification of gust front winds from model-based and data-driven perspectives. A modular and extensible web-enabled framework to estimate gust front related wind load effects is envisaged to rationally and holistically quantify design loads. This would promote design practice to enhance disaster resilience of the built environment. In this context, a closed-form expression concerning nonstationary fluctuations for a case of a long pulse duration is derived to facilitate rapid evaluation of nonstationary turbulence effects. A preliminary uncertainty analysis is also carried out to assess the influence of uncertainties associated with the load effects of gust front winds and the reliability of GFF. In addition, a comparison of the model-based gust front factor with a recently introduced thunderstorm response spectrum technique to assess their relative performance is carried out. In view of the lessons learned from the history of the gust loading factor on codes and standards, a possible living codification concept through a learning and updating invoking the emerging “Design Thinking” approach is discussed.

Optimization design of large span portal-rigid steel frame with tapered sections under wind-induced drift constraint

Large span portal-rigid frames with tapered sections in low-rise metal building system are often used in industrial and commercial buildings. The drift of such portal-rigid frames induced by the wind load needs to be smaller than a prescribed limit, and at the same time the frames should be as light as possible for cost-effectiveness. To this end, structural optimization of such portal-rigid frames subjected to the wind-induced drift constraint is required. However, little research for optimization of the large span portal-rigid frame with tapered sections has been reported. This paper proposed a procedure for structural optimization of such portal-rigid frames by adopting the Optimality Criteria (OC) method. Based on an aerodynamic database of the measured wind pressure from a wind tunnel test, several forms of the Equivalent Static Wind Load (ESWL) acting on a large-span portal-rigid frame were evaluated by the Gust Loading Factor (GLF), Load Response Correlation (LRC) and Proper Orthogonal Decomposition (POD) method. The method of virtual-work was utilized to construct the wind-induced drift or displacement. An effective iteration algorithm was derived for the minimum weight optimization of the frame while all wind-induced drift constraints were satisfied. The wind resistant structural optimization for the large-span rigid frame with taped section were conducted when it was bore by different forms of ESWL (GLF based, single objective and multiple objective ESWLs), and their optimized results were multi-compared in the form of the optimized total weight and the height of the optimized structural members. The effects of the connection stiffness at semi-rigid joints and the stiffness of support restraints on the optimized results are also investigated. Finally the global optimality property of the proposed OC method adopted for the optimized case in this paper was also discussed and verified. Optimized results show that the OC optimization procedure proposed in this paper is very effective for the optimization design of large-span portal-rigid steel frames with tapered sections under wind-induced drift constraints.

Characteristics of wind-induced displacement of super-large cooling tower based-on continuous medium model wind tunnel test

A cooling tower is a wind-sensitive structure, and wind loading is used as the control load for its design. In this study, the displacement characteristics of a large concrete cooling tower with respect to a turbulent wind is investigated by using a continuous medium model wind tunnel test. Firstly, based on the similarity relations of the continuous medium model for the cooling tower, which were derived and verified in the present study, a continuous medium model with a geometrical scale of 1:400 is designed and processed for a 200 m high cooling tower at a nuclear power plant in China. Subsequently, wind tunnel tests are carried out to measure the wind-induced displacement using a high-precision laser displacement sensor. Based on the results, the displacement and characteristics of the power spectra of some typical measurement points are analyzed. The analysis result indicates that the continuous medium model can accurately simulate the similarity relations of mass, stiffness, and damping. It is also found that the maximum displacement occurs in the windward side of the throat, and the size is about 20% of the throat thickness. In addition, background response plays a major role in the total displacement response, and the dynamic amplification effect is not obvious. The mean dynamic amplification coefficient is 1.02, which is slightly less than the value of 1.05 specified in VGB-R 610Ue, 2010. At the same time, the test result shows that gust loading factor decreases with increase in height, which is consistent with VGB-R 610Ue, 2010, and the mean value is slightly less than the specified value.

Examination of Derived Gust Velocities from a Fleet of Aerial Supervision Module/Lead Aircraft

Flight data collected from a fleet of Beechcraft King Air airframes have been analyzed. The data consisted of information from 3094 flights in various missions flown for the U.S. Forest Service. The missions consisted of those in support of aerial firefighting as well as passenger and ferry operations. The 2 s rule for separation of gust and maneuver load factors has been examined and deemed adequate. Gust and maneuver loads spectra for ground–air–ground are shown to correlate better with altitude above ground than with altitude relative to mean sea level. The flights are separated into six specific phases, some of which are unique for firefighting missions. The incremental vertical gust loads are then used to find derived gust velocities for each flight phase and for the entire flight. The derived gust velocity spectra are shown to be independent of the flight phase and depend only on altitude. It is concluded that the development of such spectra for individual flight phases is unnecessary and that a single spectrum, showing altitude dependence, is equally applicable to all phases of flight.

Wind-induced response of large offshore oil platform

In connection with wind sensitivity for the towering and hollowed-out structures (drilling derrick, crane, etc) of large offshore oil platform, the wind-induced response of towering structure was studied. By the similarity criteria, high frequency force balance tests for the large offshore oil platform under 0–360° wind directions were carried out, and the spatial distribution model of fluctuating wind load acting on platform was presented. Also, the characteristics of wind-induced vibration and the changing rule of gust loading factors were obtained precisely through wind-induced assessment in all directions. The results show that: the RMS (Root Mean Square) of the fluctuating across-wind load is about 10% of the fluctuating along-wind load on the platform; the vibration is mainly focused on the towering and hollowed-out structure like derrick, and the RMS of the across-wind acceleration is about 55% of the along-wind acceleration; the towering derrick has a big dynamic magnification of fluctuating across-wind load. The across-wind load can not be neglected in wind resistance design of large offshore oil platform, also the wind-induced response on the top/bottom of derrick and the magnification of fluctuating across-wind load of towering structure should be mainly considered.

Preliminary Investigation of Flight Loads of Single-Engine Air Tankers

Operational data recorded from five agricultural aircraft are used to compare their flight loads. Four of the airframes were used as single-engine air tankers, whereas the fifth was flown exclusively for agricultural applications. The data collectively consisted of 454 h of flight time from firefighting and 100 h from the agricultural operation. Gust and maneuver vertical load factors are separated using the two-second rule, and their cumulative occurrences are presented per 1000 h. The flight load spectra are presented for the overall flight and for individual phases. Gust loads are shown to behave similarly for all missions. Air tankers are shown to be subject to a large load factor during the drop phase, which occurs once or twice per flight. In the case of agricultural missions, the positive load factors do not reach very high values but occur at much larger frequencies. It is also shown that the load factor alone is not a sufficient indicator of the stresses exerted on the structure due to the large changes in the aircraft weight.

Turbulence Integral Scale Corrections to Experimental Results of Aeroelastic Models with Large Geometric Scales: Application to Gust Loading Factor of a Transmission Line Tower

Full aeroelastic model tests are often carried out to investigate the buffeting responses and the corresponding gust loading factor (GLF) of flexible structures. The geometric model scale for complicated structures may sometimes be excessively large in comparison with the ratio between turbulence integral scales measured in wind tunnel and in real atmospheric environments. This inconsistency in scale modeling leads to severe distortions of turbulence integral scale similarity whose influence manifests itself by modifications in resonant component of buffeting response and in resulting GLF as well, and numerical correction is needed when these testing results are converted to full-scale. This paper presents a correction procedure in terms of correction factors for experimental GLF obtained from full aeroelastic model tests to account for the inconsistency in scale modeling. The correction is simply made on analyzing the prototype in two air flows with different turbulence integral scales, namely the nominal value in the real atmosphere environment and the full-scale value correspondent to aeroelastic model test. The correction procedure is applied to the full aeroelastic model experiments of a transmission line tower with an unusually large geometric scale of 1/40 in order to examine the effect of turbulence integral scale on GLF. An appreciable effect is observed. It is found that the GLF obtained from wind tunnel experiments tends to be conservative for most structures and becomes unsafe for structures with extremely low modal frequencies when disregarding the correction. Correction factors are then derived to accommodate the inconsistency in modeling turbulence integral lengths. As a first generalization, a set of more general correction factors defined in terms of modal damping ratio and frequency ratio, the ratio between modal frequency and the dominant frequency in wind power spectra, are further developed through parametric analysis. The correction factors decrease with the augment of modal damping ratio and frequency ratio.

Comparison of the Flight Loads Spectra of Two Business Jets

Abstract Operational flight loads have been analyzed from two business jets, a Global 5000 and a Global Express XRS. It is shown that both airframes were subjected to nearly the same number of ground-air-ground cycles, even though the flight times were much different. Flights have been divided into various phases, and loads and turbulence data have been categorized by altitude bands within each phase. Cumulative occurrences of incremental vertical gust load factors have been compared and shown to be comparable for the two airframes. Maneuver load factors have been shown to spread over a wider range of values for the 5000 in every phase. This has been confirmed through comparison of combined loads with those from a CRJ100 and an ERJ-145XR. Derived gust velocities, obtained from the load factors are presented in the form of exceedance spectra. These results from both aircraft are shown to agree well

Generalized gust-front factor: A computational framework for wind load effects

This paper presents a unified framework of a generalized gust-front factor for modeling winds in gust-fronts and their attendant load effects on structures. This is analogous to the gust loading factor, a widely recognized format used world-wide in codes and standards, for the treatment of gusts in conventional boundary layer winds. The generalized gust-front factor encapsulates dynamic features inherent in wind load effects in gust-fronts originating from winds in downbursts/thunderstorms. In view of the computational complexity of the formulation and the need to promote the usage of such a framework, a web-based portal is provided. The portal at http://gff.ce.nd.edu can be conveniently utilized to evaluate the generalized gust-front factor in conjunction with international standards. The proposed generalized gust-front factor reduces to conventional gust loading factor in the case of boundary layer winds, thus, it represents a most generalized dynamic wind load effects modeling framework on structures that is compatible with the format used in ASCE 7 or any other international standard.

Wind-Induced Vibration Analysis of Wind Fence Structure

As a new wind-break and dust-control technology, the wind fence is widely used at storage yards in factories and ports. The wind fence structure is a new high-rise wind-resistant structure with light damp and very heavy wind load, and the wind-induced vibration response is unknown and equivalent static wind load is hard to determine in design. Based on the Davenport spectrum, wind-induced vibration of the plane frame structure was analyzed with frequency domain method and the response spectrum of displacement and acceleration were obtained. The equivalent static wind load was studied and the wind-induced vibration coefficient and gust loading factor were gained. The results show that the wind-induced vibration response of the structure is significant, and it should be taken into consideration in structural design.

Dynamic Wind Load on an Internal Partition Wall inside a Compartmentalized Building with an External Dominant Opening

AbstractA theoretical and experimental investigation of the net dynamic load on the partition wall resulting from the internal pressure in a compartmentalized building with and without an internal opening is reported in this paper for a building with an external opening. An increase in the mean and net dynamic load on the partition wall with decrease in the size of the internal opening as predicted by the set of theoretical equations is backed by wind tunnel tests. In particular, a good agreement between the theoretical and measured admittance function of net wall partition load to ridge height dynamic pressure is observed for a loss coefficient value of 2.78. While the mean load on the partition wall with an internal opening is found to be predictably low from pressure equalization on either side of the wall, gust load factors of 2–3 in combination with Helmholtz resonance of internal pressure observed in the study can have severe implications on the direct and fatigue wind loads on partition walls, whic...

Experimental and computational simulation for wind effects on the Zhoushan transmission towers

Long-span transmission tower and conductor line systems become important infrastructures in modern societies. The analysis of wind-induced dynamic responses of transmission towers is an essential task in the design of spatial lattice tower structures. Wind effects on the world's tallest transmission tower are presented in this paper. The tower with a total height of 370 metres, part of the Zhoushan long-span transmission project, enables high voltage conductor lines to span as long as 2750 metres over the typhoon-prone sea strait. A multi-DOF aeroelastic model test with and without conductor lines was carried out to investigate the dynamic performances of Zhoushan tower during typhoon events. Using the response measurement results in the wind tunnel, the inertial force based gust loading factors (GLFs) are applied to represent dynamic wind load effects on the tower for structural design purposes. Time domain computational simulation approach is also employed to predict dynamic responses of the transmission tower and the displacement based gust response factors (GRFs). The fair comparison of GLFs or GRFs are made between the results of the experimental approach and the computational simulation approach, which is an effective alternative way for quickly assessing dynamic wind load effects on high-rise and complex tower structures.

Gust-front loading effects on wind turbine tower systems

With an increasing focus on the issues of extreme wind events, particularly thunderstorms and downbursts, it is important not to lose sight of their impact with regards to other industrial structures, which are themselves sensitive even to typical flow fields. For the treatment of conventional boundary layer winds, a gust loading factor approach has been widely adapted in most international codes and standards for the design of buildings. Wind turbine towers, though fundamentally different from buildings when viewed as a multi-body system featuring a tower/nacelle and blades, may be treated much in the same way with modified gust loading factors. This paper introduces a possible approach to mesh conventional treatments of gust loading factors with those of newly introduced gust-front factors on wind turbine towers. Much like gust-front factors for buildings, this approach encapsulates many of the varied kinematic and dynamic changes associated with nonstationary characteristics of gust-fronts originating from thunderstorms/downbursts and the changing aerodynamics on wind turbine towers. From an example of a wind turbine tower system, gust-front loading effects as compared to those of boundary layer winds are investigated.