Wind Load Effects Research Articles

Adverse Effect of Wind Loads on the Cooling Capacity of an Evaporative Cooling Tower and a Device for its Reduction

An external wind has an adverse effect on the thermal efficiency of a cooling tower. At the top of the tower, the wind effect is manifested by the interaction of the incoming wind flow with the rising steam–air torch. Here a partial closing of the exit section of the cooling tower occurs, which reduces the free convective thrust and as a consequence reduces its cooling capacity. To reduce the adverse wind effect, a new aerodynamic method is developed for decreasing the negative wind impact on the thermal efficiency of the cooling tower through the use of its own kinetic energy. On the basis of the experimental studies on a laboratory model of the evaporative cooling tower, an optimal variant of a passive wind tip is created. Its optimal parameters under which the cooling capacity of the model with a wind load is maximum are determined.

Efficacy of Turkstra's combination rule for extremes of nonlinearly combined correlated wind load effects

The performance of Turkstra's combination rule for estimating the mean extremes of nonlinearly combined correlated responses is evaluated. The probability distribution of estimation from the Turkstra's rule is derived, which permits the assessment of its performance for various correlated responses as compared to existing combination rules. The performance of the Turkstra's rule is also examined using simulated response time histories of a high-rise building with coupled three-dimensional mode shapes. The results illustrate that the Turkstra's rule can give good estimations of the nonlinearly combined responses, while it is less accurate for linearly combined responses as pointed out in Chen (2015).

Study on Wind-Induced Vibration Behavior of Railway Catenary in Spatial Stochastic Wind Field Based on Nonlinear Finite Element Procedure

Due to its long-span structure and large flexibility, an electrified railway catenary is very sensitive to environmental wind load, especially the time-varying stochastic wind, which may lead to a strong forced vibration of contact line and deteriorate the current collection quality of the pantograph–catenary system. In this paper, in order to study the wind-induced vibration behavior of railway catenary, a nonlinear finite element procedure is implemented to construct the model of catenary, which can properly describe the large nonlinear deformation and the nonsmooth nonlinearity of dropper. The spatial stochastic wind field is developed considering the fluctuating winds in along-wind, vertical-wind, and cross-wind directions. Using the empirical spectra suggested by Kaimal, Panofsky, and Tieleman, the fluctuating wind velocities in three directions are generated considering the temporal and spatial correlations. Based on fluid-induced vibration theory, the model of fluctuating forces acting on catenary are developed considering the spatial characteristics of catenary. The time- and frequency-domain analyses are conducted to study the wind-induced vibration behavior with different angles of wind deflection, different angles of attack, as well as different geometries of catenary. The effect of spatial wind load on contact force of pantograph–catenary system is also investigated.

Interference effect and the working mechanism of wind loads in super-large cooling towers under typical four-tower arrangements

Group tower-related interference is one of the major causes of wind-induced damage of large cooling towers. The four-tower arrangements are the most common forms of the layout of group towers. In engineering practice, five arrangements are generally used, namely, single row, rectangular, rhombic, L-shaped, and oblique L-shaped. We performed wind tunnel tests on the rigid body to study the static, dynamic and extreme interference effects under these five arrangements. Then the computation formulas of interference factor that accounted for the wind directions under the five arrangements were proposed. The effects of four-tower arrangement on the distribution patterns of mean and pulsating wind pressures were discussed. The wind pressure signals at the typical measurement points of the cooling towers were subjected to decomposition and joint time-frequency analysis using mathematical statistics technique and Hilbert-Huang transform (HHT). The study shows that the maximum interference factors under the five arrangements were all higher than those under the layout of two towers. It is reasonable to use the extreme interference factor as the measure of the interference effects. The maximum positive pressure of the cooling towers was less affected by the interference effects related to four-towers, and the mean wind pressure were affected greatly in the regions of minimum negative wind pressure and leeward regions. The distribution patterns and values of pulsating wind pressures at the bottom and top of the cooling towers were significantly affected by the five arrangements of the cooling towers. Finally, based on comprehensive assessment of the interference effects of overall wind loads, arranging the four towers in a row was the best scheme, which was followed by the arrangements in oblique L-shaped pattern, L-shaped pattern, rhombic pattern and rectangular pattern successively.

07.23: Effect of loading rate on the pull‐through capacities of cold‐formed steel roof battens

ABSTRACTLocalised connection failure is the main shortcoming of cold‐formed steel roofing systems subjected to high wind suction loads. Pull‐through failure in the vicinity of roof batten to rafter connection is the major connection failure observed during recent high wind events. Both static and fatigue pull‐through failures occur based on the type of wind loads (static or cyclic loads). The loading rate to be used in the static and cyclic pull‐through failure tests is a moot point as the wind loading frequency can vary during wind events such as storms and cyclones. Therefore, it is necessary to understand the effect of wind loading frequency/rate on the pull‐through failures of steel roof battens. This paper investigates the influence of loading rate on both static and fatigue pull‐through capacities of steel roof battens by means of a series of static and cyclic tests conducted at various loading rates/frequencies. Initially, tests were conducted on roof battens made of two steel grades (G300 and G550) and two thicknesses (0.8 and 1 mm). The results showed a significant improvement in the pull‐through capacities during tests using higher loading rates. They also showed that the current static and cyclic pull‐through design rules/guidelines do not include the effect of loading rate. Secondly, to understand the influence of loading rate on the pull‐through capacity of battens, the effect of loading rate on the mechanical properties of steels was investigated using 40 tensile coupon tests. The effect of loading rate on both the tensile strength of steel used and the pull‐through capacity of roof batten was then compared. Using the results of comparison, the reasons for the increase in the static pull‐through capacity of roof battens with loading rate are discussed and, a recommendation is made in relation to the loading rate to be used with the new Low High Low (LHL) cyclic test. This paper presents the details and results of this study.

A Cyber-Based Data-Enabled Virtual Organization for Wind Load Effects on Civil Infrastructures: VORTEX-Winds

Despite many advances in the area of wind effects on structures in recent decades, research has been traditionally conducted within limited resources scattered geographically. With the trend toward increasingly complex designs of civil infrastructure combined with the escalating potential for losses by extreme wind events, a new culture of research needs to be established based on innovative and collaborative solutions for better management of the impact of extreme wind events. To address this change, this paper presents a new paradigm of a multi-scale cyber based laboratory framework for the analysis/design, modeling and simulation of wind load effects based on an ongoing collaborative cyberinfrastructure based platform, VORTEX-Winds: Virtual Organization for Reducing the Toll of EXtreme Winds (https://vortex-winds.org), and discusses its current status since its inception in 2007 and ongoing developments. This collaborative framework as it evolves would enable a paradigm shift by offering advanced cyber-enabled modules (e-modules) for accelerating advances in research and education to achieve improved understanding and better modeling of wind effects on structures. Accordingly, it will enhance wind community’s analysis and design capabilities to address next generation challenges posed by wind. Through empowering those without computational or experimental resources, the e-modules will encompass a large set of subject areas and topics categorized as Database-enabled design, Full-scale/Field site data repository, Statistical/Stochastic toolboxes, Tele-experimentation, Uncertainty modeling, Damage assessment, and Computational platforms. This prototype will allow access to the individual e-module, while it is envisaged that next level of development in VORTEX-Winds will have the capability for an automated and integrated analysis/design through a nexus of e-modules. A highlight of the e-modules currently completed or in development is presented not only to show the efficacy of the framework to enhance and supplement the limitation of traditional off-line approaches, but also to describe architecture and features of e-modules to promote additional cyber-enabled data-driven developments in the field.

A refined analysis of thunderstorm outflow characteristics relevant to the wind loading of structures

The study of thunderstorm outflows and their loading and response of structures is a key topic in modern wind engineering. This paper provides a new contribution to this research by analyzing a wide dataset of 277 wind velocity records characterized by strong transient properties and labeled by thunderstorm outflow. These records have been detected for up to 6 years by 14 anemometers belonging to an extensive in-site monitoring network distributed in the Northern Mediterranean ports. Analyses are carried out in order to extract the parameters of major interest for evaluating the wind loading effects of structures and furnishing a comprehensive statistical characterization of the huge amount of data recorded. Results lead to a novel classification of thunderstorm outflows with reference to the time scale of the gust front passage and their intensity; a refined interpretation of the differences involved by the turbulence intensity, the integral length scale and the gust factor of mesoscale downbursts and synoptic low-pressure systems; a confirmation of the substantial independence of these quantities with respect to the ratio between the height above ground of the sensor and the roughness length of the terrain, together with their correlation with the wind velocity; a new parameterization of the harmonic content of the turbulent fluctuations.

Optimization of woven jute/glass fibre-reinforced polyester hybrid composite solar parabolic trough collector

In the present work, structural analysis of 5.77m × 4m woven jute (J)/glass (G) fibre-reinforced polyester hybrid composite solar parabolic trough is carried out based on trough parameters to obtain the minimum RMS local slope deviation, termed as SDx value under gravity loading. The optimization is done by varying parameters viz. direction and size of reinforced conduits, stacking number and sequence of hybrid trough laminate at fibre orientation of Δθ=45° and Δθ=60° amongst the layers at 0° collector angle. The analysis revealed that the configuration in which the conduits are placed in both X and Y directions is preferred over other configurations to scale down the effect of wind loads. Furthermore it has been observed that laminate of the order [0°G/45°G/-45°J/90°J]s undergoes minimum surface deformation amongst all the other configurations at conduit reinforcement in both X and Y directions for a conduit thickness of 0.75 mm and radius of 10 mm and obtains the overall SDx value of 1.3492 mrad. The results shows that proposed trough model is very promising and evolves a cost effective system.

Wind loads and structural response: Benchmarking LES on a low-rise building

The correct and safe design of structures subjected to the wind actions requires a realistic estimate of the wind effects on their resisting systems. In this context, the present paper proposes a complete numerical study that, starting from Large Eddy Simulation of the turbulent flow around a low-rise building, arrives to the assessment of the wind loading effects, that is the evaluation of design forces in all structural elements. Since it is well known that a realistic representation of the turbulent features found in the lower part of the atmospheric boundary layer is required in order to obtain accurate predictions of the structural response, firstly, the incoming flow turbulence is synthetically generated by means of the Modified Discretizing and Synthesizing Random Flow Generator technique. Then, the obtained synthetic fluctuation field is used as inflow condition for the subsequent Large Eddy Simulations taking into consideration different angles of attack. Results in terms of pressure distributions statistics are analyzed and systematically compared to experimental data. Finally, starting from both simulated and experimental pressure fields, dynamic structural analyses are performed and results directly compared in terms of design forces in the structural elements.

Typhoon- and temperature-induced quasi-static responses of a supertall structure

Wind loads and the associated load effects on supertall structures are key factors in structural design. In practice, typhoon-induced quasi-static responses measured from the field mix with temperature-induced responses because temperature varies significantly during a typhoon event. The mixed responses complicate the assessment of the wind loading effects and the separation of the two load effects is difficult in practice. In this study, the wind- and temperature-induced quasi-static responses of the 600m-tall Canton Tower are investigated using a comprehensive long-term structural monitoring system installed on the structure. The structural responses (stresses and displacement) obtained from the field monitoring system during a strong typhoon are presented. The temperature-induced responses are calculated by applying a temperature loading model to the finite element model of the structure. The purely typhoon-induced quasi-static responses are then separated from the total measured responses by subtracting the temperature-induced ones. It shows that the typhoon-induced quasi-static responses of the supertall structure are slightly smaller than the temperature-induced responses in a typical sunny day. The typhoon-induced quasi-static displacement obtained from the field is also compared with the counterpart from the wind tunnel test on an aeroelastic model of the full tower.

Performance-based Design of Tall Building Envelopes using Competing Wind Load and Wind Flow Criteria

This paper investigates performance-based tall building design and the development of a combined architectural-urban design method focusing on the effects of wind loads on- and wind flows around tall buildings. The paper provides an overview of related buildings codes and city development design guidelines that define requirements for structural façade wind loading and urban ventilation. A review of performance-based design methods for the generation, analysis and optimization of buildings is also presented. Within this frame, an approach to performance-based tall building envelope design is proposed. The approach is aimed at addressing wind loading and wind impact requirements based on generative parametric modelling and performance analysis that integrates physical parameters at the architectural and urban scales and performance criteria can support filtering and optimization relative to prevailing wind conditions.

A substructure approach for fatigue assessment on wind turbine support structures using output-only measurements

Fatigue constitutes a major and highly-uncertain safety-related factor for wind turbines. In order to ensure a reliable fatigue assessment of such structures, it is essential that stress predictions be based on the actual structural behaviour. The response identification of operational wind turbines in a global framework constitutes a challenging problem due to the uncertainties associated with the variability of the wind loading and the dynamics of the rotor. In reducing these uncertainties, this study proposes a substructuring approach, which abolishes the need for modelling the intricate and time-varying dynamics of the rotor. Instead, response prediction is performed on a substructure model of the tower and the effect of wind loads and servo dynamics is accounted for via the estimated interface forces at the top of the support structure. The application is based on synthetic vibration data generated via the FAST software and an output-only Bayesian filter employing the structural model of the support structure. The effectiveness of the proposed framework is presented in terms of fatigue damage estimates at different locations on the tower.

Equivalent static wind loads analysis of tall television towers considering terrain factors of hilltops based on force measurement experiment

Wind field in mountainous regions demonstrates unique distribution characteristic as compared with the wind field of the flat area, wind load and wind effect are the key considerations in structural design of television towers situated in mountainous regions. The television tower to be constructed is located at the top of Xiushan Mountain in Nanjing, China. In order to investigate the impact of terrain factors of hilltops on wind loads, firstly a wind tunnel test was performed for the mountainous area within 800m from the television tower. Then the tower basal forces such as bending moments and shear strength were obtained based on high frequency force balance (HFFB) test. Based on the experiments, the improved method for determining the load combinations was applied to extract the response distribution patterns of foundation internal force and peak acceleration of the tower top, then the equivalent static wind loads were computed under different wind angles, load conditions and equivalent goals. The impact of terrain factors, damping ratio and equivalent goals on the wind load distribution of a television tower was discussed. Finally the equivalent static wind loads of the television tower under the 5 most adverse wind angles and 5 most adverse load conditions were computed. The experimental method, computations and research findings provide important references for the anti-wind design of high-rise structure built on hilltops.

Effect of Wind on Multi Storey Buildings of Different Shapes

Objective of the Study: To study and analyse the effect of wind load on different shape of the building and asses the most structurally stable shape of a multi storey structure. Method: The present study deals with the buildings of seven different shapes: Rectangular; L; U; T; I; Plus and Non-uniform IS: 875 (Part 3)-1987 is the standard code of practice for design loads of buildings and structures which was used to calculate the gust factor. Further, all these shapes were analyzed using Staad. Pro 2007 software. Each building is a 50 storied building with storey height as 3m summing upto a total height of 150m.For, the purpose of analysis the plan area and stiffness of the columns were kept equal. Dead loads and Live loads were calculated by using the code IS: 875-1987 (Part 1, 2) respectively. By using the Indian standard codes the combinations of loads were taken. Parameters like Storey drift, Joint displacement, Intensity, Bending moment are used for the assessment.Based on this study it can be established that the shape of structure plays a very important role in resisting wind loads Findings: Plus Shape and Non uniform shape were the most stable shapes whereas L-shape and U-shape was the least stable of all the shapes. More the stiffness of the building more will be its stability. Storey drift and joint displacement increases with increase in height. A reduction in Shear force and bending moment was detected with the increase of height. Application: With the increase in population and shortage of land, it has become necessary to construct high rise buildings. Wind load plays an important role in tall structures while designing buildings. Thus, to understand and analyse the wind effect on structures.

Wind loading on catenary vault structures

Catenary vault structures are increasingly being utilised as an efficient alternative to the traditional circular vault. However, little is known regarding wind loading effects, in particular the pressure distribution, over these forms. Consequently, applicability of the data given for circular vaults used for the design of catenary vaults is also uncertain. In this paper the results of a wind-tunnel investigation and their implications on the design of catenary vaults are discussed. A series of tests were undertaken to assess the effects of variation in vault geometry and wind orientation on surface pressures measured over these structures. These parameters are evaluated to clarify their influence on the loading on catenary vaults. Only the results relating to mean and root-mean-square pressure coefficients are reported, in line with wind loading standardisation practice (if localised pressures are relevant, the designer is referred to expert advice or an adoption of the data from similar geometrical forms). The primary focus of the investigation is to examine the applicability of the design data given in SANS 10160-3:2011 (SANS 2011b) (referring to circular and duo-pitched roofs) to catenary structures. Subsequently, the merit of developing a set of exclusive design coefficients relating to catenary vaults is considered.

Movements of the Quebec Bridge’s Suspended Span Measured by GNSS Technology

The Quebec Bridge was completed in 1917 and it is still the longest cantilever bridge in the world. Overall, the actual movements of its suspended span, as detected by GNSS (between 2012 and 2013), are in fair agreement with the original design calculations: for the train loading effect on the vertical movement (17 cm for one freight train); the transversal wind load effect on the transversal movement (32 cm for a wind speed of 170 km/h); and the temperature loading effect on the ver ti cal movement of the suspended span (3.2 cm for a 50°C temperature variation). Further movements have been detected by GNSS technology, namely: the transversal and longitudinal movements of the suspended bridge span due to train passages (11 cm transversally, at the top of the suspended span, and 1 cm longitudinally); the transversal movement of the bridge caused by solar radiation (differential) conditions on both sides of the bridge (5 cm for high solar radiation values); and the longitudinal movement of the suspended span of the Quebec Bridge at temperatures lower than 6°C (7 cm to −25°C).

The Effects of the Foldable Dome of KDUST on the Observation Based on CFD Method at Dome A

For modern telescopes with the strict requirement of high-resolution image quality, the influence of wind load cannot be ignored. KDUST is a 2.5 m optical telescope and will be installed at Dome A. To study the effects of wind load on KDUST, the low-frequency wind speed data observed by KL-AWS-2G weather station at Dome A are transformed into high frequency based on the theory of wind speed fluctuation spectrum; then, the numerical wind tunnel simulation is conducted under the conditions of different dominant wind directions, different dome opening angles, and the elevation angles of KDUST. The results show that different wind directions mainly affect the wind velocity and turbulence kinetic energy around the telescope; the optical path difference increases along with the increase of the dome opening angle, but decreases with the increase of the elevation angle of KDUST; the dome seeing decreases with the increase of both the dome opening angle and elevation angle. This simulation will provide a useful reference for the future design and construction of KDUST and its foldable dome.

The Breakage of Float Glass with Four-Edge Shading Under the Combined Effect of Wind Loading and Thermal Loading

The glass breakage in high-rise building fires may be significantly influenced by both the compartment fire and the environmental wind. In this work, float glass panes supported by the frame with a dimension of 600 × 600 × 6 mm3 were employed to study the glass breakage under the combination of wind and fire effects. The first breaking time, glass temperature, crack patterns, and fallout were obtained. With an increase of wind speed, the average value of temperature difference between the mean temperature at the heated exposed side and that at the ambient shaded side decreased gradually when crack initiated. The average time to first crack was maximum without wind loading and decreased gradually as the wind speed increased. Comparing with the glass breakage only under thermal radiation, the combination of environmental wind accelerated the glass breaking. The present results suggest that the wind effect should be considered for building fire protection in the window glass design.

Estimation of Wind Load Effects with Various Mean Recurrence Intervals with a Closed-Form Formulation

This study introduces closed-form formulation for estimating wind load effects with various mean recurrence intervals (MRIs), which was originally derived for assessing probabilistic seismic performance of structures, but has not been adopted in wind engineering community. The accuracy of the closed-form formulation is verified by comparing its estimations with those from traditional numerical integration for a wide range of probabilistic responses of both rigid and flexible structures. The closed-form formulation sheds more physical insights regarding the influence of uncertainties in wind speed and extreme response coefficient. It results in a more convenient and accurate definition of design response for a target MRI over the widely used Cook–Mayne coefficient in wind engineering. With this closed-form framework, the influence of epistemic uncertainties attributed to limited knowledge and data is also quantified in terms of confidence interval of estimation in closed-form formulation.

Investigation of the VIMs of a spar-type FOWT using a model test method

This article presents the research findings of an extensive model test investigation of the dynamic response to vortex-induced motions (VIMs) of the OC3 spar-type floating offshore wind turbine (FOWT). Particulars of this research are to investigate the unique and crucial effects of wind load on the spar-type FOWT, which differs considerably from other traditional spar-type floating systems utilized in the gas and oil industry, on the VIMs. The model test was performed with a sequence of current, wind, and irregular wave sea states to analyze the nature of the coupled dynamic response behavior of VIMs. Many unique characteristics were found and analyzed. The lock-in phenomenon of sway in the cross flow (CF) direction was found to occur first, followed by the lock-in phenomenon of surge in the in-line (IL) direction. For the current-only case, the remaining responses, including the other 4-degree-of-freedom motions, mooring tensions, and turbine bearing loads, were found to be coupled by sway/surge VIMs. Moreover, the oscillation amplitudes of all of the responses increased significantly with increasing current velocity, particularly after locking-in. Furthermore, the wind load had a clear suppression effect on the CF and IL VIM responses. The experimental measurements demonstrated that the wave load excites wave-induced oscillations for some CF responses and all IL responses, and it further restrains the VIM oscillation amplitudes on the foundation of the wind suppression effect. In particular, when a wind load is involved, the influence of current or wave is limited to the yaw and IL tower-top bending moment.