Wind-resistant Design Research Articles

Full-scale monitoring of wind effects on a supertall structure during six tropical cyclones

Full-scale measurements under real wind conditions are viewed as the most reliable approach to investigating the wind effects on supertall structures. However, long-term monitoring on wind characteristics at the maximum atmospheric boundary layer height and the corresponding wind-induced responses of structures are very limited, especially under strong tropical cyclones. In this study, field monitoring of wind effects on a 600 m high supertall structure is obtained during 6 tropical cyclones by means of a sophisticated long-term structural health monitoring (SHM) system deployed on the structure. Wind characteristics (wind speed, direction, turbulence intensity, gust factor, power spectral density) of these tropical cyclones above 450 m height are presented and analyzed. The dynamic properties of the supertall structure are determined from the field measurements and compared with those stipulated in design. The damping ratios of the supertall structure are estimated by the virtual dynamic shaker (VDS) and the enhanced virtual dynamic shaker (EVDS) methods. In addition, the response amplitude-dependence of the structural natural frequencies and damping ratios is investigated. Finally, the comfort performance of the supertall structure during different tropical cyclones is assessed against four comfort criteria. The findings of this study would be beneficial to professionals and researchers engaged in wind-resistant design and practice of skyscrapers.

Research on Wind Field Characteristics Measured by Lidar in a U-Shaped Valley at a Bridge Site

Currently, research on wind fields of U-shaped valleys is rarely reported, and anemometers or wind observation towers are usually used for field measurement, but the measured position is limited and the cost is high. In order to study the wind characteristics in a mountainous U-shaped valley, a long-range, all-weather, high-precision Wind3D 6000 lidar was placed at a bridge site located in a U-shaped valley. Then, according to the data effective ratio and wind speed, nearly 6 months of original data ranging from 0 m to 810 m were analyzed statistically. It was found that the spatio-temporal distribution of wind speed and direction is obviously not uniform, and the wind parameters are correlated among different virtual wind towers (VWTs). By classification, the effective data of midspan position is taken as the research object, and the wind speed profile is divided into three categories. Type-1 shows disorderly characteristics; Type-2 shows a linear relationship; and Type-3 shows a nonlinear relationship. The wind direction is consistent with the main wind direction at the bridge site and the average wind direction of different VWTs has a high consistency. The concept of wind-direction deflection rate is put forward to describe the variation of wind direction with height. These measured wind parameters could be used as a reference for bridge wind-resistant design.

Field measurement study of wind characteristics in mountain terrain: Focusing on sudden intense winds

Due to the local terrain and temperature, various types of intense wind, such as sudden intense winds, thermally developed winds, and thunderstorms, will occur in mountainous areas of different regions and periods of time. The identification and separation of intense wind events into different families are key topics in wind engineering to study the characteristics of intense winds in mountainous areas, which are essential to investigate the wind-excited response of structures. This research presents a systematic field measurement study on intense wind events in a deep-cut canyon situated in a mountainous area of southwestern China and identifies a series of sudden intense wind events whose wind speed, direction, ambient temperature, and other characteristics change rapidly. To distinguish and isolate such events, an automatic classification method was proposed, and 11 sudden intense wind events were captured. Additionally, it was also found that the sudden intense wind had relatively strong nonstationary characteristics. Finally, the average and fluctuating wind characteristics of sudden intense winds were investigated, and the time-variant characteristics were discussed in detail. These varying characteristics at high wind speeds, which will make the loads acting on bridges more complex, should be considered in the wind-resistant design of long-span bridges.

Experimental investigation of wind loads on wind turbine blade under various turbulent flows

For investigation of the effects of turbulence intensity (TI) on the wind loads on wind turbine blade, a 1:20 scaled model of a typical 3D wind turbine blade is designed and used for the pressure measurement test in a wind tunnel. Five uniform flows with different turbulence intensities are simulated in the wind tunnel test. The mean and root-mean-square (RMS) wind pressure coefficients, base moment coefficients, and their power spectral densities are presented and discussed in detail. Combined with the dynamic properties of the blade structure, wind-induced displacements at the tip of the blade are calculated by the random vibration theory. The results show that the increasing of TI amplifies the aerodynamic loads on the blade in terms of RMS wind pressure coefficients and RMS bending moment coefficients. Large wind-induced displacement of the wind turbine blade may be stimulated by high TI even under the feathering condition. This article aims to further the understanding of wind loads on wind turbine blades and provide useful information for the wind-resistant design of wind farms established in regions with high turbulence levels.

Design wind loads for local flexible cladding of structures based on wind tunnel tests

Damage and ultimate failure of cladding elements may play an important part in the wind-resistant performance of structural system. Particularly for those claddings made from lightweight and flexible materials, they are more sensitive and vulnerable to wind excitation. This study proposes an approach of reducing the design wind loads for the local flexible cladding of structures, where the significant geometric nonlinear effect of the cladding is considered. In the light of stress equivalence principle and finite element analysis, the equivalent design wind load for the local flexible cladding is presented with consideration of reducing extreme wind pressure which is usually used for the design of rigid cladding and resulted from statistical analysis of experimental pressure measurement. In view of characteristics of wind pressure distribution on local flexible cladding units, the reduction coefficient of extreme wind pressure at varying wind directions is also given to build wind load evaluation system for the flexible cladding. The effects of wind pressure gradient and correlation on determining the design wind loads are respectively quantified by fluctuating factor and synchronous factor in order to further explore their action mechanism. Moreover, a case study is performed to examine the effectiveness and reliability of this proposed approach in actual application, where the results of extreme wind pressure, reduction coefficient and relevant influencing parameters are analyzed. It proves that this evaluation system is not limited by the external geometry of structures, and can help to optimize the wind-resistant design of the cladding economically, especially for the local flexible cladding susceptible to variation of fluctuating wind pressures.

Wind tunnel study of wind effects on 90° helical and square tall buildings: A comparative study

Wind effects on a square model and a 90° helical model are investigated by both pressure measurement and aero-elastic model tests in a boundary layer wind tunnel. Based on the pressure measurement results, local wind force coefficients, base moment coefficients, vertical correlation coefficients and power spectral densities for the two models were analyzed and discussed in detail. The aerodynamic damping ratios were calculated by the random decrement technique (RDT) on the basis of the wind-induced acceleration obtained from the aero-elastic tests. Comparisons of wind loads and wind-induced accelerations were made for the square and helical models. The results shown that the aerodynamic damping should not be ignored, especially for across-wind direction. Moreover, the helical model has been proved to yield a better behavior in aerodynamic performance than square model. This study aims to provide useful information for wind-resistant design of helical building.

Wind Effect Analysis of a High-rise Ancient Wooden Tower with a Particular Architectural Profile via Wind Tunnel Test

ABSTRACT Wooden architectural heritage is a symbol of architectural heritage worldwide and has high historical, cultural, and scientific values in Asia countries (e.g., China, Japan, Korea, and Nepal). Wooden pagoda (a kind of tower with multiple eaves in East Asia) serving as one important member of wooden architectural heritages suffers from damages that are caused in various natural disasters such as windstorm, fire, and earthquake due to its long-time service and considerable size. Wind caused damage is one of the most common damages caused by natural disasters, making the structural safety of high-rise wooden pagodas under wind action a major concern in architectural heritage protection. This study analyzes the wind effects on the Yingxian wooden pagoda in China by a wind tunnel test and computes the wind loads on the wooden pagoda. The wind characteristics of wooden the pagoda in a wind tunnel test are presented and compared with modern buildings and other types of wooden architectural heritages. Additionally, this study attempts to analyze the difference of the computed wind loads from the wind tunnel test and from the full-scale measurement. The results reveal that the wind pressure distribution at certain locations are similar to those of modern buildings or other ancient wooden architectures. However, the wind pressure distribution at some locations are distinctive due to the complexity of the architectural profile (e.g., the boundary of the pagoda is an octagon in bird view). The wind load from wind tunnel test are in good agreement with those in full-scale measurement with less than 14% error. This study extends the understanding of the wind effects and structural safety assessment on the high-rise wooden pagoda, providing useful guidelines for structural design (e.g., wind-resistant design) and for structural health monitoring (e.g., service maintenance) to monitor not just the specific wooden pagoda but also other high-rise pagodas, especially the those with top views of octagonal shapes.

Torsional Stiffness Correction of the Split-Type Triple-Box Steel Box Girder Based on Refined Simulation

Split-type steel box girders are widely used in long-span bridges because of their good wind-resistance performance. In the design stage, a simple finite element model is usually established based on the beam element for wind-resistance design. However, since the irregular cross-beams and diaphragms in the split steel box girder cannot be virtually established, the stiffness of the girder will be underestimated. To improve the accuracy in simulating stiffness of the split-type triple-box steel box girder (STSBG) with the beam element model (BEM), a correction is made to the initial beam element model (IBEM) based on the result of a more refined finite element model. ANSYS is adopted to make a refined model (RM) of a bridge with STSBG as its girder and to calculate its aerostatic responses and dynamic characteristics in 3 typical construction states and 1 finished state. With the reference value, an objective function of the overall residual sum of squares is constructed for the torsion angle of the girder and the frequency of the bridge. Then, the beam element is used for conventional modelling of the bridge, and artificial bee colony (ABC) algorithm is adopted for the optimization and correction of structure parameters of the BEM of the girder. Finally, static and dynamic characteristics of the IBEM and the corrected beam element model (CBEM) are compared with values of the corresponding RM to evaluate the validity of the correction of the model. The results show that the aerostatic responses and dynamic characteristics of the CBEM are close to calculated values of the RM. In more detail, the relative error between the torsion angle of the girder in the middle span of the BEM and the corresponding reference value in the finished state is decreased from +61.71% to +4.94%, and the relative error of torsional fundamental frequency is decreased from −17.43% to +3.66%. According to the calculated value of the RM, ABC algorithm would satisfactorily improve the accuracy in simulating torsional stiffness of the STSBG with the IBEM. This research is expected to provide reference for beam element modelling, which is conducive to accurately simulating torsional stiffness of the STSBG.

Wind induced response of corner modified 'U' plan shaped tall building

In the present study, the well-adopted practice of minor aerodynamic modifications (chamfered corner and rounded corner) has been introduced on widely used irregular U plan shaped tall building to minimize the wind induced responses and also to give a good aesthetics. The necessary design inputs for a wind resistance design such as force coefficient and pressure coefficients have been well explored and illustrated graphically to provide a complete guideline to the designer. The randomness of wind directionality has a significant impact on tall structures, which is generally not detailed in existing design codes, is incorporated by considering wind directions ranging from 0° to 180° at an interval of 15°. Computational fluid dynamics (CFD) has been utilized to simulate wind flow using two turbulence models, i.e., k-epsilon and Shear Stress Transport. The model has been validated by comparing the results of a published research article on a U-shaped building without corner modification. The grid independence study has been done to check the reliability and accuracy of the analysis results. Since such study of wind directionality on corner modified U-shaped building is not observed in the existing literature, it constitutes the uniqueness of the present study. A significant reduction in force coefficient has been achieved by implementing modification, but the faces of those updated corners mostly been attracted by excessive pressure. This indicates the necessity of proper cladding configurations. The rounded corner buildings are turning out to be more effective when compared to the chamfered corner for reducing wind load.

Wind force of super high-rise buildings with hexagonal section

To study the wind force of super high-rise buildings with hexagonal section, a series of wind tunnel tests of synchronous pressure models were carried out. The alongwind force coefficient, as well as the power spectral density (PSD) and the RMS base moment of crosswind force were studied. Thereafter, the empirical formulae of wind force were established. Meanwhile, wind tunnel tests of multiple-degree-of-freedom (MDOF) aero-models were conducted to measure the crosswind responses. The aerodynamic damping ratios were identified by analyzing the time histories of measured responses. Finally, the aerodynamic damping ratios obtained from the aero-model test and the analytical model of wind force obtained from the synchronous pressure model were combined to calculate the crosswind dynamic response. The comparison between the wind induced response of calculation result and that of aero-model test shows that the wind force analytical model proposed in this paper is reliable. This study can provide references for the wind resistance design and standard improvement of super high-rise buildings with hexagonal section.

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.

Optimising the computational domain size in CFD simulations of tall buildings

Recently, there has been a growing interest in utilizing computational fluid dynamics (CFD) for wind resistant design of tall buildings. A key factor that influences the accuracy and computational expense of CFD simulations is the size of the computational domain. In this paper, the effect of the computational domain on CFD predictions of wind loads on tall buildings is investigated with a series of sensitivity studies. Four distinct sources of domain error are identified which include wind-blocking effects caused by short upstream length, flow recirculation due to insufficient downstream length, global venturi effects due to large blockage ratios, and local venturi effects caused by insufficient clearance between the building and top and lateral domain boundaries. Domains based on computational wind engineering guidelines are found to be overly conservative when applied to tall buildings, resulting in uneconomic grids with a large cell count. A framework for optimizing the computational domain is proposed which is based on monitoring sensitivity of key output metrics to variations in domain dimensions. The findings of this paper help inform modellers of potential issues when optimizing the computational domain size for tall building simulations.

Comparative assessment of validity of gradient wind models for a translating tropical cyclone

Accurate and conservative evaluations of the gradient wind in the free atmosphere are needed to account for high-wind hazards when designing wind resistance for critical infrastructure. This paper compared the validity of three existing gradient wind models to select an appropriate evaluation model, which enables us to accurately compute the asymmetric gradient wind field of a translating tropical cyclone under the condition of a symmetric pressure distribution and a constant translation velocity. The validity of the three models was assessed by evaluating the residuals in momentum conservation equations for the gradient wind under a specific tropical cyclone condition. The magnitude of the residuals was considered to be the measure of error in the gradient wind derived from each model. The results showed that the most frequently used model yielded the largest magnitude of residuals with the lowest maximum wind speed among the three models. The wind characteristics of the three models were validated using archived observation data of hurricanes. The physical reason for the difference in maximum wind speed among the three models was explained by the difference in the streamline feature of the gradient wind field. It was also revealed that the differences in maximum wind speed and magnitude of residuals became more pronounced as the translation speed and the intensity of a tropical cyclone increased. The comparative assessment of the three gradient wind models allowed us to identify the best model for use in conservative wind-resistant design and high-wind risk estimates.

Wind-induced vibrations and suppression measures of the Hong Kong-Zhuhai-Macao Bridge

A series of wind tunnel tests, including 1:50 sectional model tests, 1:50 free-standing bridge tower tests and 1:70 full-bridge aeroelastic model tests were carried out to systematically investigate the aerodynamic performance of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The test result indicates that there are three wind-resistant safety issues the HZMB encounters, including unacceptable low flutter critical wind speed, vertical vortex-induced vibration (VIV) of the main girder and galloping of the bridge tower in across-wind direction. Wind-induced vibration of HZMB can be effectively suppressed by the application of aerodynamic and mechanical measures. Acceptable flutter critical wind speed is achieved by optimizing the main girder form (before: large cantilever steel box girder, after: streamlined steel box girder) and cable type (before: central cable, after: double cable); The installations of wind fairing, guide plates and increasing structural damping are proved to be useful in suppressing the VIV of the HZMB; The galloping can be effectively suppressed by optimizing the interior angle on the windward side of the bridge tower. The present works provide scientific basis and guidance for wind resistance design of the HZMB.

Evaluation of full-order method for extreme wind effect estimation considering directionality

The estimation of the extreme wind load (effect) under a mean recurrence interval (MRI) is an important task in the wind-resistant design for the structure. It can be predicted by either first-order method or full-order method, depending on the accuracy and complexity requirement. Although the first-order method with the consideration of wind directionality has been proposed, less work has been done on the full-order method, especially with the wind directionality. In this study, the full-order method considering the wind directionality is proposed based on multivariate joint probability distribution. Meanwhile, considering two wind directions, the difference of the corresponding results based on the first-order method and full-order method is analyzed. Finally, based on the measured wind speed data, the discrepancy between these two methods is investigated. Results show that the difference between two approaches is not obvious under larger MRIs while the underestimation caused by the first-order method can be larger than 15% under smaller MRIs. Overall, the first-order method is sufficient to estimate the extreme wind load (effect).

Dependence of wind load on air density for highrise buildings

Accurate determination of wind load is of great importance for the wind-resistant design of building structures. Despite the fact that air density varies systematically with altitude, and somewhat less so with barometric pressure, air temperature, and latitude, there is a lack of studies on the dependence of wind load on air density especially for highrise buildings. This article presents a special study on this topic. The dependence of air density on latitude, season and altitude is investigated first, based on meteorological records at several national stations in China. The height-dependence of air density in the inner region of a tropical cyclone (TC) is highlighted, since there is a fast development of highrise buildings in TC-prone areas and TC wind load dominates the design wind loads for such slender wind-sensitive structures. A data-driven model for the height-dependence of TC air density is established. It is shown that the measured TC air density is reduced by 8%–10% compared with the values recommended in the wind load codes. The dependence of wind load and wind-induced structural response on air density for a supertall building is then analyzed through a combined usage of the proposed TC air density model and wind tunnel testing. Results suggest that the wind load and wind-induced response of the building obtained by considering the height-dependence of air density can be decreased by as much as ~12% compared with those without considering such effects. Thus, more economic wind-resistant designs for highrise buildings may be achieved by taking into account the height-dependence of air density.

Natural characteristics of long span bridge under initial load: a case study of Minpu bridge

Natural frequencies and modes of bridges are very important for wind-resistant design, seismic design and damage test. Natural characteristics of existing bridge in design stage cannot consider the initial complex stress conditions. Actually, the bridge bears the complex initial load (Gravity load, Vehicle load, etc.) in the operation stage, which will cause a certain initial deflection, especially for long span bridges. So, the natural characteristics of bridge get changed. According to the design data of Minpu bridge, the three-dimensional finite element model of Minpu bridge is established by using frame element system based on SAP2000. Result shows that the first and second natural frequencies of the Minpu bridge in design stage are 0.12 Hz and 0.33 Hz respectively. Natural characteristics of Minpu bridge in the operation state are tested by using the microtremor measurement, and the first and second natural frequencies and modes of it are obtained. Result shows that the first natural frequency is 0.39 Hz. The second natural frequency is not uniform, which is within 2.34 ∼ 3.70 Hz. The results reflect that the first and second natural frequencies of the Minpu bridge in operation stage increased greatly, which show that the initial loading state will have a great impact on the natural characteristics of long span bridges.

A fast partition method for wind pressure coefficient of large-span roof based on modified GK clustering

Structures with large-span roofs are particularly vulnerable to wind action, and evidences have shown that wind-induced damage of large-span roofs occurs mostly on edges and corners. This implies that different regions of large-span roofs may exhibit different degree of sensitivity to wind. It is therefore of substantial importance to partition the roof surface into different regions based on their respective vulnerability, which allows a better wind-resistant design. In this study, the concept of cluster analysis was extended for wind pressure coefficient (WPC) partitioning of large-span roofs, in which a fast partition method based on the modified GK clustering algorithm was employed to partition the WPC on two engineering cases, i.e., a cantilever flat roof and a curved roof. Its reliability was examined via comparative analysis of WPC distribution and the optimal zoning of WPC derived by cluster analysis. The optimal number of clusters was identified using clustering validity indices. The comparisons were overall satisfactory, both in quantitative and qualitative sense. The optimal zoning results of WPC reflect well the characteristics of WPC distribution. It is expected that the methodology applied in this study can be well used to aid the wind-resistant design of other similar structure systems.

Wind-induced vibration response analysis of Chinese solar greenhouses

Chinese solar greenhouses (CSG) are widely used in agricultural and horticultural industries in China. With the characteristics of lightweight, small stiffness and high flexibility, CSG are sensitive to wind loads. In this study, based on Davenport wind spectrum, the fluctuating wind speed time histories were simulated by harmony superposition method. The wind-induced vibration response of a 12 m span CSG was investigated by using ANSYS in time domain. The time histories of stress and displacement were obtained. The results show that both the stress and displacement under instantaneous wind loads are obviously larger than those under the corresponding mean wind loads. The most dangerous section appears near the front foot of the CSG structure. The critical wind speeds for dynamic and static instability are 38.7 and 58.5 m/s, respectively. Finally, a recommended nodal displacement wind vibration coefficient is given for practical structures. The analytical results can provide a reference for dynamic analysis and wind resistance design of CSG structures in the future.

Combination coefficient of ESWLs of a high-rise building with an elliptical cross-section

As the height and flexibility of high-rise buildings increase, the wind loads become more dominant and the combination coefficient of Equivalent Static Wind Loads (ESWLs) should be considered when they are used in the structural design. In the first phase of the study, a brief introduction to the theory on the combination coefficient for high-rise buildings was given and then the time history of wind-induced responses of a 208-meter high-rise building with an elliptical cross-section was presented based on the wind tunnel test results for pressure measurement. The correlation between wind-induced responses was analyzed and the combination coefficients of ESWLs of the high-rise buildings using Turkstra's rule, and Asami's method, were calculated and compared with related design codes, e.g., AIJ-RLB, ASCE 7-10, and China Load Code for structural design. The results of the study showed that the combination coefficients from Asami's method are conservative compared with the other three methods. The results of this paper would be helpful to the wind-resistant design of high-rise buildings with elliptical crosssection.