Stochastic Wind Loads Research Articles

Experimental study on characteristic curves of restoring forces of Populus alba var. pyramidalis

Static tests under cyclic loading were carried out on Populus alba var. pyramidalis to determine its characteristic curves of restoring forces. The results show that P. alba var. pyramidalis had good elastic performance. There was degradation of strength and stiffness under cyclic loading and unloading, where characteristic curves of restoring forces of P. alba var. pyramidalis assumed a “flat and contrary S-shape” form. Simultaneously, P. alba var. pyramidalis showed typical characteristics of brittle destruction under large high peak loading and unloading. Furthermore, dynamic tests were carried out under wind loads to obtain dynamic displacement curves and dynamic strain curves. P. alba var. pyramidalis reflected its stochastic dynamic performance in building up its resistance to the stochastic wind loads and its dynamically hysteretic properties. The dynamic response of this species was random and fuzzy under stochastic wind loads. This study has theoretical significance and reference value to research on the static characteristics and wind-induced dynamic performance of forests.

Fatigue Assessment of Slender Long-Span Bridges: Reliability Approach

It is well known that wind loads result in wind-induced buffeting of slender long-span bridges. Traffic also frequently exists on a slender long-span bridge simultaneously throughout its service life, which can affect the dynamic behavior of the slender structural systems. The nature of the vibration of a slender long-span bridge is further complicated by the dynamic coupling effects among the bridge, wind, and traffic. Fatigue damage is an important consideration in the serviceability performance of slender long-span bridges that typically experience cyclic or repetitive loads, such as those induced by wind and traffic. Stochastic wind and traffic loads, dynamic interaction, and fatigue accumulation for a slender long-span bridge essentially vary over time, with uncertainty contributions from each. Therefore, a reliability-based fatigue assessment model, which can rationally consider the combined load effects from wind and traffic as well as the associated uncertainties, is needed to provide an accurate estimate of reliability for fatigue. Initially, a scenario-based deterministic fatigue analysis model is developed. A typical year is categorized into several representative scenarios of traffic and wind conditions. After identifying the duration for each representative scenario in a typical year, a cumulative yearly fatigue damage factor can be predicted by superposing the cumulative hourly damage factors for all representative scenarios. On the basis of the scenario-based deterministic analytical model, the framework of the reliability-based fatigue damage assessment for a slender long-span bridge is further developed. Finally, an illustrative example for a prototype bridge is conducted.

On the performance of ground vehicles under the influence of stochastic wind loads

AbstractThe influence of aerodynamic loads on the performance of ground vehicles is an important economical, safety and comfort issue. For the safety and comfort matters, especially the crosswind behavior of the ground vehicles is of great interest, as strong lateral winds can cause major accidents or at least make the driver and the passengers feel very uncomfortable and insecure.Two different failure scenarios dominate the safety aspect. The most important one is the risk of overturning, which happens not very often but if it occurs it leads in most cases to serious personal damages and the second one is the sudden lane change of road vehicles and the associated driving instabilities because of unforeseen gusts.As most of the design and excitation parameters of the system are uncertain, they are recognized as stochastic variables. Taking the mentioned failure scenarios into account the probability of failure of a freight vehicle has been computed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wind-Induced Motion Control of 76-Story Benchmark Building Using the Hybrid Damper-TLCD System

The tuned liquid column damper (TLCD) has recently been advanced for vibration control of structures subjected to wind loading. The effectiveness of the semiactive TLCD system and the hybrid viscous fluid damper-TLCD control system recently proposed by the writers is investigated for control of wind-induced motion of high-rise buildings. Simulations are performed on a 76-story building benchmark control problem subjected to wind tunnel test data and stochastic wind loads. It is shown that the semiactive TLCD control system performs comparably to a sample active tuned mass damper (ATMD) system and thus is an attractive alternative to the ATMD system. More significantly, it is shown that the hybrid viscous fluid damper-TLCD system reduces the response of the building substantially more than the semiactive TLCD system at every natural frequency of the building. Furthermore, the hybrid damper-TLCD system is robust in terms of the stiffness modeling error for control of both displacement and acceleration responses. The simulation results show that the proposed hybrid viscous fluid damper-TLCD system can perform effectively under various wind loading conditions.

Mode acceleration approach for rotating wind turbine blades

This paper presents a time-domain analytical approach for evaluating the displacement response in the flapping direction of rotating wind turbine blades subjected to stationary stochastic wind loading. This approach includes the effects of rotational sampling of the wind spectra on the blades. The blades are modelled as discrete multi-degree-of-freedom systems, consisting of tapered beams of rectangular hollow cross-section built using the finite element software code ANSYS. ANSYS is used to obtain the stiffness matrices of the blades, allowing the free vibration characteristics of the rotating blades to be determined by analytical formulation. A geometric stiffness matrix is included in the free vibration solution allowing for the centrifugal stiffening effects experienced by the blades to be included. Once the natural frequencies and mode shapes are obtained, the mode acceleration technique is employed to predict nodal responses to the prescribed wind loading. Nodal wind loading is obtained by generating artificial drag force time-histories, which have elevated energy at frequencies corresponding to integer multiples of the blade rotational frequency, in order to replicate realistic blade loading conditions. Blade nodal displacements based on rotationally sampled and nonrotationally sampled spectra are obtained for varying rotational frequencies. Blade response is also obtained in the frequency domain and used to verify the time-domain results.

Application of Wavelet Approach for ASCE Structural Health Monitoring Benchmark Studies

This paper presents an application of wavelet analysis for damage detection and locating damage region(s) for the ASCE structural health monitoring benchmark data. The response simulation data were generated basically by a FEM program provided by the ASCE Task Group on Health Monitoring for a four-story prototype building structure subjected to simulated stochastic wind loading. Damage was introduced in the middle of response by breaking one or more structure elements such as interstory braces. Wavelets were used to analyze the simulation data. It was found that structural damage due to sudden breakage of structural elements and the time when it occurred can be clearly detected by spikes in the wavelet details. The damaged region can be determined by the spatial distribution pattern of the observed spikes. The effects of measurement noise and the severity of damage were investigated. The results in this paper illustrate a great promise of wavelet analysis for structural health monitoring, especially for an on-line application.

Experimental test on bridge jointed twin-towered buildings to stochastic wind loads

This paper presents results of a study on wind loads and wind induced dynamic response of bridge jointed twin-towered buildings. Utilizing the high-frequency force balance technique, the drag and moment coefficients measured in wind tunnel tests, and the maximum acceleration rms values on the top floor of towers, are analyzed to examine the influence of building's plan shapes and of intervals between towers. The alongwind, acrosswind and torsional modal force spectra are investigated for generic bridge jointed twin-towered building models which cover twin squares, twin rhombuses, twin triangles, twin triangles with sharp corners cut off, twin rectangles and individual rectangle with the same outline aspect ratio as the twin rectangles. The analysis of the statistical correlation among three components of the aerodynamic force corroborated that the correlation between acrosswind and torsional forces is significant for bridge jointed twin-towered buildings.

Optimal placement of output feedback controllers on slender civil structures at discrete locations

The dynamic responses of tall civil structures due to high winds and earthquakes are very important to the civil engineer. These dynamic responses can produce situations that can range from uncomfortable to unsafe. In recent years classical control theory has been used in civil engineering to reduce the dynamic response of tall civil structures. Many optimal control algorithms for civil structures involve full state feedback control. This method of control requires good estimates of the velocity and displacements throughout the structure. However, there are several important advantages of output feedback control: it takes less computational effort and it has the robustness of passive systems. In this paper, control algorithms are formulated for the selection of feedback gains and controller placement for flexible structures. In some cases, it is necessary to place controllers at discrete locations. For instance, for a tower there might be only several locations that are able to support the equipment needed for a feedback controller. For the placement of controllers at discrete locations in flexible structures, a method is proposed to select gains and placement simultaneously. The effectiveness of this algorithm is demonstrated for stochastic wind loads in the frequency domain.

Evaluation of Wind-Induced Vibration Of Tall Buildings and Reliability Analysis: A Case Study

The alongwind, crosswind and torsional components of wind forces are simultaneously measured during a wind tunnel test of a rigid model of a tall building. The three components of wind-induced responses of the tall building are thus estimated and investigated by structural dynamic analysis. A reliability assessment procedure is presented in terms of upcrossing prababilities of wind-induced response and provides a convenient checking procedure for serviceability performance evaluation of tall buildings under stochastic wind loads.

Actuator and Sensor Placement for Multiobjective Control of Structures

A simple algorithm for multiobjective linear quadratic Gaussian control that can be used for various structural control applications is presented. This algorithm synthesizes Pareto optimal trade-off curves, which are plots of one performance variable constraint versus another. These curves separate the regions of feasible and infeasible constraints and enable the control designer to minimize one regulated output, such as control force, a structural displacement, or an acceleration, while keeping others within specified constraints. Pareto optimal curves are compared with each other to determine preferred locations for actuators and/or sensors. To illustrate the proposed methodology, numerical examples of simple lumped-mass shear-beam building models subjected to stochastic wind and earthquake loads are considered. Control is presumably through one or more active tendons placed on various floors of the structure. The numerical results presented demonstrate the applicability and feasibility for developing optimal multiobjective controllers for civil structures.

Design of a mega-sub-controlled building system under stochastic wind loads

Vibration control of high-rise buildings under wind loads with application of the mega-sub-control method is studied in this paper. A building with a megasub-configuration consists of two major structural components - a megastructure as the main structural frame and several sub-structures for residential and/or commercial usage. The authors have previously proposed a ‘megasub-control method’ in which the sub-structures are designed to serve as vibration control dampers. The control objective is to suppress certain critical building responses such as inter-story drifts of the mega-structure for the purpose of structural safety and acceleration response of the sub-structures for the purpose of protecting contents and improving human comfort. The feasibility of this method has been explored by the authors in previous publications. In this study, the procedure of optimally designing dynamic parameters of a megasub-controlled building under stochastic wind loads is developed, together with two possible structural configurations which provide a mega-sub-control mechanism. The mega-structure of a mega-sub-building is modeled as a cantilever beam to retain the dominant bending mode characteristics of highrise buildings, and the sub-structure as a shear building to retain the shear mode. The fluctuating wind speed is modeled as a non-white random process in both time and space domains. The power spectral density (PSD) of critical building responses is obtained using the random vibration theory. The mean square value (MSV) of those responses, as functions of the dynamic parameters including the stiffness and damping ratio of the sub-structures, are evaluated from their PSD by numerical integration in the frequency domain. The optimal values of the dynamic parameters are determined by minimizing the MSV of certain critical building responses. An example building is used to demonstrate the design procedure and the numerical simulation of the response quantities in the time domain is carried out to verify the MSV of the building responses obtained from the random vibration theory in the frequency domain. The results show that the proposed design procedure is suitable to apply to a mega-sub-building with different sub-structural configurations. The MSV obtained from the random vibration theory in the frequency domain and from the numerical simulation in the time domain exhibit an excellent agreement. It is also found that the megasub-control method is robust in the sense that slight change in the dynamic parameters affects the building's performance very little. With the design procedure developed, and the corresponding favorable building response demonstrated, this paper has enhanced the feasibility of application of the mega-sub-control method to actual high-rise buildings for wind vibration suppression.

Dynamic response of high-rise buildings to stochastic wind loads

This paper presents results of a recent study addressing issues concerning the dynamic response of high-rise buildings. Utilizing a high-frequency base-balance, the alongwind, acrosswind and torsional components of aerodynamic loads and their statistical correlations for a wide range of generic building shapes of different aspect ratios in two approach flow conditions are quantified. A random-vibration-based procedure for estimating response of high-rise buildings is outlined. A checking procedure for building serviceability is presented for enabling designers to assess the building serviceability performance. The methodology presented here will enable designers in the preliminary design stages to assess the serviceability of buildings, the need for a detailed wind tunnel test and to evaluate the merit of design modifications that may include a choice of an auxiliary damping system.

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

A numerical model for simulating the nonlinear dynamic response of natural draught cooling towers to wind loading is introduced. Geometrical and physical nonlinearities are considered in the F.E. modeling of the doubly-curved thin shell structure. An original simulation procedure of the artificial wind loading is used, generating directly the multi-correlated field of the (stochastic) time series of the external pressures. The effective correlation structure of the fluctuating pressure is imposed from the experimental data obtained by wind tunnel tests. Some preliminary analyses, carried out for checking the performance and reliability of the model, are finally reported.

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Nonlinear dynamic analysis of cooling towers under stochastic wind loading

Dynamic Response of Tall Buildings to Stochastic Wind Load

A random vibration‐based procedure is used to estimate the dynamic responses of symmetric tall buildings (coincident centers of mass, rigidity, and geometry) subjected to the effects of wind. The along‐wind, across‐wind, and torsional components of wind force were obtained from a time‐series analysis of surface pressures measured during a wind‐tunnel test of a rigid model. The structural response analysis takes the statistical correlation among these three components of aerodynamic force into account. The contributions of the first and second translational and torsional modes to the response are investigated. The across‐wind and torsional accelerations are the major contributors to building acceleration. A simple approach is developed for evaluating the response statistics that are important for building serviceability. This approach can be used in the preliminary design stage to assess the possibility of unserviceability and the need for more detailed and expensive wind‐tunnel model tests.

Active Tendon Control of Structures

A method is developed for the analysis of a continuous structure implemented by an active tendon control under the action of stochastic wind loads. The transfer matrix technique is employed to obtain the frequency response function, in a closed form, of the actively controlled structure. This permits an examination of the behavior of all the vibrational modes in the frequency domain with respect to the variation of control parameters. It is shown that both the displacement and the acceleration of the structure can be reduced significantly in the entire frequency domain only if the feedback control parameters are designed appropriately. It is further shown that although some vibrational modes can be suppressed completely by the active control devices, other vibrational modes may be magnified if the feedback control parameters are not designed carefully.