External Wind Load Research Articles

A framework for design wind loads on air-permeable multilayer cladding systems

Air-permeable multilayer cladding (vinyl siding, roof pavers, discontinuous metal roofing, solar panels, etc.) are one of the most common types of building components in North America. Their defining aerodynamic feature is that they have an air cavity separating the component from the sheathing, studs, or interior layer. Due to air-permeability, external wind loads can transfer into the air cavity between the layers. Although these cladding systems have similar geometries in many ways, design loads are not generally available for such systems. This study aims to synthesize the available literature on the pressure equalization factor, which is the proportion of external load acting on the cladding and provide a framework for design wind loads on air-permeable multilayer cladding systems. To accomplish this, the many factors that affect the pressure equalization factor, such as the gap-to-cavity-depth ratio, panel size, and exposure are discussed. Then, the pressure equalization factors from multiple studies are combined to examine the effect of effective area on the pressure equalization factor. Finally, recommendations for implementing these guidelines into design standards are provided.

Response and reliability of suspension system under stochastic and periodic track excitations by path integral method

Considering that maglev trains are affected by factors such as track irregularities, variations in load, external wind loads, and track materials, this paper establishes a suspension system model that takes into account the combined action of periodic and stochastic excitation. It then examines the response and reliability of the suspension system from the perspective of stochastic dynamics. The path integral method is introduced to address the challenges posed by periodic excitation. Expressions for the path integral solutions of the probability density function for the responses and the reliability density function are derived directly from the suspension system. The reliability function and the mean first-passage time are then further derived. Using the path integral solutions, we investigate the effects of stochastic excitation, periodic excitation of the track, and safety domain on the suspension system. Research shows that as the intensity of stochastic excitation increases, the oscillation amplitude of the response also increases, while the reliability of the system decreases. The effect of periodic excitation on the response and reliability of the system is more complex. The most intriguing discovery is that the reliability of the suspension system weakens when the angular frequency of the periodic excitation is close to the system’s natural frequency.

Finite-time suspension control based on GFTSM and RBFNN for low-wind-speed MVAWT

For low-wind-speed maglev vertical axis wind turbine (MVAWT), this paper proposes a finite-time suspension control strategy based on global fast terminal sliding mode (GFTSM) and adaptive RBF neural network (RBFNN). Due to the randomness of wind speed and wind direction, the actual working conditions of low-wind-speed wind farms are very complex. In order to ensure the stability of the maglev system in MVAWT and improve its anti-disturbance ability, a finite-time GFTSM controller with small chattering is firstly designed based on the dynamic suspension model considering external wind load disturbance. Secondly, the RBFNN is adopted to approximate system uncertainties and external disturbance, its network weight is adjusted according to the adaptive law, and the finite-time global fast convergence characteristic of GFTSM is also introduced into the adaptive law to improve the convergence speed of the RBFNN. Furthermore, in order to obtain the derivatives of input signals of controller and mitigate the effect of sensors’ noise, a finite-time differentiator is introduced. According to Lyapunov stability theory, the stability and finite-time convergence characteristics of the proposed control strategy are proved. Finally, simulation and experiment results show that the proposed strategy has faster dynamic response speed and stronger anti-disturbance ability.

An improved derivation and comprehensive understanding of the equivalent static wind loads of high‐rise buildings with structural eccentricities

SummaryThe trend of constructing high‐rise buildings with irregular structural configurations results in buildings with complicated external wind loads and eccentricities between the mass and stiffness centers, which complicate the assessment of buildings' 3D equivalent static wind load (ESWL). This paper develops an improved method to determine the 3D ESWLs for high‐rise buildings with structural eccentricities. First, the derivation process of each floor's 3D internal force‐based ESWLs, including the mean, background, and resonant components, is described in detail. Then, three typical high‐rise buildings, each with 15 eccentricity cases, are used to demonstrate the proposed method's advantage in the wind resistance design of high‐rise buildings with structural eccentricities, especially in providing reliable along‐height distribution of ESWLs. Finally, systematic analyses are conducted to examine the effects of load‐correlation, structural eccentricity ratio, and building side ratio on the derived 3D ESWLs. The results show that the proposed method provides a reliable along‐height distribution, which helps give an adequate understanding of the ESWLs of high‐rise buildings with structural eccentricities. Some concluding remarks are extracted from the results to show how the load‐correlation, structural eccentricity ratio, and building side ratio affect the ESWLs of high‐rise buildings. The conclusions are valuable references for the wind‐resistant design of high‐rise buildings with structural eccentricities.

Active vibration suppression of wind turbine blades integrated with piezoelectric sensors

Abstract As the wind turbine size gets larger, the optimal design of blades, which is a major source of energy for the wind turbines and also the cause of loads, is becoming more important than anything else. Therefore, reducing the load on the blade should be the top priority in designing a blade. In this article, we studied the vibration control of the stiffened wind blades subjected to a wind load with piezoelectric sensors and actuators to mitigate fluctuations in loading and adding damping to the blade. The model is a laminated composite blade with a shear web and the PZT piezomaterial layers embedded on the top and bottom surfaces act as a sensor and actuator, respectively. A uniformly distributed external wind load is assumed over the entire plate surface for simplicity. The first-order shear deformation (FSDT) theory is adopted, and Hamilton’s principle is used to derive the finite element equation of motion. The modal superposition technique and the Newmark- β \beta method are used in numerical analysis to calculate the dynamic response. Using the constant gain negative velocity feedback control algorithm, vibration characteristics and transient responses are compared. Furthermore, vibration control at various locations of the shear webs subjected to an external load is discussed in detail. Through various calculation results performed in this study, this article proposes a method of designing a blade that can reduce the load by actively responding to the external load acting on the wind turbine blade.

Coupled deformation behavior analysis for the glass panel in unitized hidden-frame supported glass curtain wall system

As a kind of building envelope, glass panel has been emerging and widely employed in unitized hidden-frame supported (UHFS) glass curtain wall system in modern construction engineering. In practical service conditions, the large area of glass panels involved in the all-glass facades of UHFS glass curtain wall system usually expose to external wind loads, thus it is quite essential to focus on the coupled deformation of the glass panel caused by complex boundary constraints stemming from connected components and their interactions in UHFS glass curtain wall system. In this paper, the optical measurement system associated with the standard air-tight test chamber of UHFS glass curtain wall samples for DIC analysis of the glass panel was first established based on the theory of stereo vision and digital image correlation. Then, the conventional digital indicators and finite element analysis (FEA) models were employed to provide the actual and theoretical deformation information of the panel, which were used to demonstrate that the adopted DIC method had the unique advantage of characterizing full-field coupled deformation behavior of the glass panel affected by complicated boundary conditions. Consequently, the spatiotemporal deformation behavior of the glass panel in practical service conditions was investigated and thus the principal strain, maximum relative deflection (MRD) as well as strain energy density on the panel surface were accordingly evaluated. The above metrics could be used for failure risk evaluation and providing safety design suggestions for the glass panel in UHFS curtain wall system.

Aerodynamics of air-permeable multilayer roof cladding

Currently, design approaches to determine loads on different types of building cladding elements can vary significantly by product type, even though they may have similar geometries. Using the full-scale wind tunnel at the Insurance Institute for Business & Home Safety, external and net wind loads on two discontinuous metal roof systems were measured. The results indicate that cavity pressures in air-permeable multilayer cladding, such as discontinuous metal roofs are approximately uniform across individual panels and closely related across multiple panels which share the same cavity. The testing also showed that peak net loads tend to occur slightly after the peak spatial gradient of the external pressure across the cladding elements. The two types of discontinuous metal roofing products, which have significantly different cavity geometries, have similar ratios between the net and external wind loads with metal shingles having a Ceq value of 0.55 and metal panels having a Ceq value of 0.67. Overall, these experimental results indicate that the peak pressure equalization factor is dependent on the external pressure difference across the cladding, the geometry of the cladding, and the fluid inertia of the cavity flow. The experimental results also show that the peak pressure equalization factor is not dependent on location and wind direction, for panels that are not adjacent to the edges.

Analysis on dynamic interaction between flexible bodies of large-sized wind turbine and its response to random wind loads

Analysis of structural dynamic response of wind turbine is one of important issues to assess its structural integrity and safety during operation process. As the output power of wind turbine increasingly gets larger, the structural flexibility of the elastic components, such as rotor blades and supporting tower, of wind turbine gets larger owing to larger structural size, and, consequently, the dynamic interaction between these flexible bodies become more profound or, even, may have a significant impact on the dynamic response of the wind turbine. In this study, the integrated finite element model of a 5-MW wind turbine is developed so as to carry out dynamic response analysis, in terms of both time history and frequency spectrum, of the large wind turbine including multiple elastic bodies and their dynamic interactions. In order to have a deeper insight into the impact and mechanism of the dynamic interaction, the load transmission along its transmitting route and mechanical energy distribution during dynamic response under random wind loads are studied. And, the influences of the stiffness and motion of the supporting tower on the integrated system response are discussed.Our numerical results show that the dynamic interaction between the elastic bodies may be significant during dynamic response. The response of the tower top becomes around 15% larger than that of the simplified model mainly due to the elastic deformation and dynamic vibration (called inertial-elastic effect) of the flexible blade; On the other hand, the elastic deformation may additionally consume around 10% energy (called energy-consuming effect) coming from external wind load, and, consequently, it could decrease the displacement of the tower. Therefore, there is a competition between the energy-consuming effect and inertial-elastic effect of the flexible blade on the overall dynamic response of the wind turbine. As for the blade response, the displacement of the blades gets up to 20% larger than that without blade-tower interaction, because the elastic-dynamic behaviors of the tower principally provides a more flexible and vibrating supporting base, which can significantly change the natural mode shape of the integrated wind turbine and can decrease the natural frequency of the blade.

ANALYSIS OF JIAYUGUAN [嘉峪关] PAVILIONS' DEFORMATION AND ITS INFLUENCE FACTORS WITH THE APPLICATION OF COMPREHENSIVE TECHNOLOGY

Abstract. In the case study of Guanghua Pavilion [光化楼] located in Jiayuguan [嘉峪关] City, Gansu province in China, the 3D laser scanning technology and leveling technology are used to analyze overall tilt, columns tilt and uneven settlement of the pavilion. It is found that Guanghua Pavilion [光化楼] tilted to the southeast; most of the columns from the first floor to the third floor tilted to the northeast and east directions, and all the tilted distance of the columns is within 100 mm.; a certain amount of uneven settlement happened on Guanghua Pavilion [光化楼], in which the east side sinks more obviously. In the process of analyzing the influencing factors of deformation, numerical wind tunnel simulation and Midas Gen modeling methods are used. It is concluded that the external wind load is the main cause of Jiayuguan [嘉峪关] pavilions’ deformation.

Investigation of the thermal response and breakage mechanism of point-supported glass facade under wind load

Glass façade has gradually become main external wall material in high-rise buildings due to its multi-functionalization and diversification. Nevertheless, glass is relatively fragile and prone to fracture when subjected to the coupling effect of fire and external wind load that inevitably significant influences the mechanical property of glass facades in high-rise buildings. Newly formed vents caused through glass breakage are especially vital for the growth of ventilated controlled enclosure fire and play a crucial role in interactive-external tridimensional fire development. Therefore, it is necessary to explore the mechanism of thermal fracture of glass façades under wind load. In the present study, a total of nine tests were performed to investigate the fracture mechanism of point-supported glass facades under various wind speeds combined with fire. Measurements were conducted for the first breakage time, glass surface temperature, and crack initiation and propagation. Numerical simulation, based on finite element method (FEM) was conducted to predict the temperature variation at the ambient side surface of glass panel. The results have implications concerning fire resistance designs for point-supported glazing assemblies in high-rise buildings.

An efficient method for universal equivalent static wind loads on long-span roof structures

Wind-induced response behavior of long-span roof structures is very complicated, showing significant contributions of multiple vibration modes. The largest load effects in a huge number of members should be considered for the sake of the equivalent static wind loads (ESWLs). Studies on essential matters and necessary conditions of the universal ESWLs are discussed. An efficient method for universal ESWLs on long-span roof structures is proposed. The generalized resuming forces including both the external wind loads and inertial forces are defined. Then, the universal ESWLs are given by a combination of eigenmodes calculated by proper orthogonal decomposition (POD) analysis. Firstly, the least squares method is applied to a matrix of eigenmodes by using the influence function. Then, the universal ESWLs distribution is obtained which reproduces the largest load effects simultaneously. Secondly, by choosing the eigenmodes of generalized resuming forces as the basic loading distribution vectors, this method becomes efficient. Meanwhile, by using the constraint equations, the universal ESWLs becomes reasonable. Finally, reproduced largest load effects by load-response-correlation (LRC) ESWLs and universal ESWLs are compared with the actual largest load effects obtained by the time domain response analysis for a long-span roof structure. The results demonstrate the feasibility and usefulness of the proposed universal ESWLs method.

Coupled wind-induced responses and equivalent static wind loads on long-span roof structures with the consistent load–response–correlation method

Long-span roof structures with multiple vibration modes may undergo coupled motions when exposed to spatiotemporally varying dynamic wind loads. This article presents a framework for the analysis of coupled wind-induced responses and equivalent static wind loads on long-span roof structures. This framework takes into account the inter-modal coupling of modal response components and cross correlation between the background and resonance. The load–response–correlation method is widely used for the background equivalent static wind loads of rigid structures. Also, the concept of load–response–correlation was extended for the correct estimation of equivalent static wind loads by considering the correlation between the load and exact total responses. However, there is no detailed study for the correct estimation of equivalent static wind loads on the component of background, resonance, and their cross response using load–response–correlation method. In this article, a consistent load–response–correlation method for equivalent static wind loads is presented in a unified framework which contains the background, resonance, and modal coupling. First, the accuracy of wind-induced responses is ensured by considering the modal coupling. Meanwhile, the efficiency is improved by decomposing the covariance matrix of the generalized resuming forces. Second, several effects of the wind-induced responses are discussed in detail, such as the effect of the modal coupling, the effect of the modal participations to resonant responses, and the effect of the cross correlation between the background and resonance. Finally, the proposed equivalent static wind loads are represented by the composition of the external wind loads and inertial forces, which are both the most probable load distributions. Accordingly, the equivalent static wind load distribution and the responses by equivalent static wind loads are reasonable.

Control of Wind-Induced Vibration of Transmission Tower-Line System by Using a Spring Pendulum

The high-voltage power transmission tower-line system, which is a high flexible structure, is very susceptible to the wind-induced vibrations. This paper proposes the utilization of the internal resonance feature of the spring pendulum to reduce the wind-induced vibration of a transmission tower. The kinetic expression of the spring pendulum system is obtained through Lagrangian equation. The condition of the internal resonance is verified to beλ = 2, in whichλis the ratio of the spring mode frequency over the pendulum mode frequency. A 55 m tower in the Liaoning province is established in SAP2000 to numerically verify the effectiveness of the proposed device. The spring pendulum is modeled using Link element. The wind speed history is generated based on Kaimal spectrum using harmonic superposition method. Results show that, (1) compared with the suspended mass pendulum, the spring pendulum absorbs more energy and reduces the oscillation more effectively and (2) the vibration control performance of the proposed spring pendulum improves as the external wind load increases.

The influence of self-excited forces on wind loads and wind effects for super-large cooling towers

The self-excited force induced by the interaction between the structure and airflow has been technically ignored in previous studies conducted on wind loads and wind effects for super-large cooling towers. Moreover, no criteria could be used for qualitative and quantitative studies of the effects resulting from the self-excited force. In this study, by taking a Chinese super-large cooling tower for nuclear power with a height of 215m as an example, the wind tunnel test of cooling tower aero-elastic model with simultaneous pressure and vibration measurement through a modified equivalent beam-net design method was firstly carried out, in which external wind loads of super-large cooling towers were obtained with the presence of the self-excited force. Firstly, the effects of self-excited force on distribution characteristics of external mean and fluctuating wind pressures were analyzed. Through the refined frequency-domain algorithm of wind-induced responses from our previous studies, wind-induced responses of super-large cooling towers were calculated by considering two cases of wind tunnel tests with or without self-excited force. Subsequently, the effects of self-excited force on wind-induced responses and Gust Response factors of super-large cooling towers were discussed. The results showed that the self-excited force had weak influence on the distribution of external mean wind pressure of the super-large cooling tower, while it significantly affected distribution and values of fluctuating wind pressure. Moreover, the effects of self-excited force on wind-induced mean response were negligible for the super-large cooling tower. The response differences calculated using two aerodynamic parameters were mostly below 5%, and regardless of whether or not to consider the influence induced by self-excited force. The excitation mode of wind-induced resonant response was consistent even at the maximum error (i.e. 10%). Furthermore, this study indicated that the influence of self-excited force on wind effects was advantageous to majority of regional structures. To overcome the problems existing in aero-elastic model, e.g., accuracy, accessibility and cost of test, this study suggested that external wind load model without self-excited forces obtained by pressure test of rigid body could be used to calculate the wind-induced responses of super-large cooling towers, in which the differences were within an acceptable range.

Semiactive Control System based on MR Damper for Suppressing Vibration of Stay Cable under Wind Load

This paper investigates the performance of the semiactive control system based on magnetorheological fluid (MR) dampers for suppressing excessive vibration of stay cable installed in cable-stayed bridges under wind load. The cable model is extracted from a 156.3 m long stay cable with high tension. The external wind load is generated from the widely used wind load spectrum such as the Kaimal spectrum. Several semiactive control algorithms such as the Lyapunov stability theory-based control, the maximum energy dissipation and the clipped-optimal control are considered to find the appropriate control strategy for the cable-damper system employing MR dampers. Numerical simulations are carried out to demonstrate the effectiveness of the semiactive control systems based on MR dampers and their control performances are compared with those of passively operated control systems.

Aerodynamic Model Tests of Tall Buildings

The theory of the dynamic-balance wind-tunnel test is reviewed to identify sources of error that arise when the mode shapes of a structure are non-ideal. A systematic process of applying corrections is developed, which results in two adjustment factors—one applicable to displacements and accelerations, and a second applicable to equivalent static loads. The factors are separated into unknown random effects arising from the external wind load distribution, and a deterministic effect arising from the structure’s mode shape and mass distribution. A simplified assumption on the former is made to evaluate the sensitivity of the correction factors, mode shape and external distribution and to compare them with previous results in the literature. Certain of those results are seen to be misleading in implying that torsional loads should be reduced by a significant, but inappropriate, factor. A simple means of distributing static-equivalent loads over the height of the structure, while accounting for resonant and background response contributing is also given.