Performance-based Wind Engineering Research Articles

Global vibration control of offshore wind turbines with a flexible monopile foundation using a pendulum-tuned mass damper: Risk mitigation and performance incrementation

This study investigates an optimized design approach for a passive-adaptive pendulum-tuned mass damper (PTMD). The PTMD is used to mitigate structural vibrations in offshore wind turbines (OWTs) with flexible monopile foundations considering Pile-Soil Interaction (PSI). The model OWT is based on the 5-MW design proposed by the National Renewable Energy Laboratory (NREL). The PSI incorporates a pile that is modeled as beam–column elements supported by nonlinear springs and accounts for lateral loads (p-y curves) and axial loads (t-z and Q-z curves) at nodal points. Wind and wave spectra estimation, as well as hydrodynamic and aerodynamic load analysis, are performed using a bespoke MATLAB® program operated in conjunction with an ANSYS® 3-D finite element global model. The resultant peak response at the OWT hub was evaluated through power spectral density (PSD) analysis. Optimal design choices for PTMD parameters are obtained via parametric analysis, which assesses the dynamic response in the along and across directions at the hub and stress at the tower base. A systematic representation considers the uncertainties stemming from the geometric and mechanical properties of the tower, environmental loads, and rotating blade dynamics. To address these uncertainties, a Monte Carlo simulation is employed to assess the structural risk via the Performance-Based Wind Engineering (PBWE) framework. Consequently, the probabilistic evaluation of structural response, foundation stresses, and power production assists in the optimal design process of PTMDs that mitigate the global structural vibrations of OWTs.

Performance-based wind engineering assessment of a telecommunication mast utilizing Bayesian extreme wind velocity model

A promising design concept, the performance-based wind engineering methodology is adopted, implementing a finite element model (FEM) to analyse the structural behaviour of a telecommunication steel lattice mast. The integration of site-specific wind loading models into the standardized FEM-based design can be a powerful tool for design engineers. The tower being investigated, located in Central Hungary, is equipped with sensors to measure wind velocity and strains in chord members. The stochastic modelling of the extreme wind velocity, i.e., the basic wind velocity is assessed using the peak-over-threshold approach with an automated threshold selection method. To enhance the accuracy of the analysis, Bayesian inference is employed, combining the information from a relatively short duration of measurements collected at the tower site with a more extensive dataset from measurement locations across the country. Numerical model of the telecommunication mast subjected to wind loading is developed in a general-purpose finite element software. The probabilistic design system module is applied for performing probabilistic calculations of both serviceability criterion and load-bearing capacity of the structure using Monte Carlo simulation with Latin hypercube method. Numerical results are compared and validated with measurement data. The accuracy of wind load assessment is examined in this study, considering both the standardized design method according to EN 1993-3-1 and wind tunnel testing. The main objective is to demonstrate the potential of integrating the Performance-based Wind Design framework with a monitoring system and a finite element model, highlighting their combined benefits.

Reliability of inelastic wind excited structures by dynamic shakedown and adaptive fast nonlinear analysis (AFNA)

The ever-growing interest in performance-based wind engineering has created a need for assessment frameworks that can efficiently deal with inelasticity. The computationally efficient strain-driven dynamic shakedown approach has provided a solution that is not only capable of identifying failure mechanisms that are potentially critical during extreme winds, e.g., low cycle fatigue and ratcheting, but also allows direct estimation of inelastic deformations. This approach, however, can only solve problems at dynamic shakedown, i.e., with limited nonlinearity, and is not capable of providing response time histories. To address these limitations, this paper presents an efficient framework for reliability assessment of inelastic structures at dynamic shakedown and beyond. To this end, a novel step-by-step integration algorithm is developed for rapid response time history analysis within the setting of dynamic shakedown. The method is based on advancing fast nonlinear analysis through introducing schemes for enabling at each time step the adaptive selection of the step size, number of modes to be included, and number of potentially nonlinear elements. Inelasticity is modeled as distributed at the level of the stress resultants through a return mapping scheme based on the Haar–Kàrmàn principle, therefore enabling the integrated estimation of the state of dynamic shakedown. The scheme is seen to preserve the efficiency of recently developed strain-driven dynamic shakedown algorithms while providing a full range of response time histories at and beyond the state of dynamic shakedown. To enable reliability analysis, the scheme is embedded in a general uncertainty propagation framework.

The impact of parameter estimation uncertainty in extreme wind speed models

AbstractAll the available information and uncertainties should be taken into account in a model to give correct answer to a stated problem and evaluate the performance of a structure. This study deals with the impact of parameter estimation uncertainty in extreme wind speeds on the assessed reliability index using frequentist approach. The peak-over-threshold approach with an automated threshold selection method is applied and bootstrapping is used to determine the 95% confidence interval of the estimated reliability index. Based on the results practical recommendations, i.e., a framework of this procedure are derived on how to handle peak-over-threshold in extreme wind speed models for the application of the proposed performance-based wind engineering design.

Performance-based wind design for tall buildings: Review and comparative study

A brief review and state of the art for Performance-Based Wind Design (PBWD) has been presented to provide researchers with clear historic literature on the development of PBWD concepts. The literature clearly emphasizes the main differences between Performance-Based Seismic Design (PBSD) and Performance-Based Wind Design and the challenges incurred. The study presents a brief description of the current prescriptive approaches and the challenges and limitations to their use and the broad wide range of research areas in Performance-Based Design (PBD). It also highlights the nonlinear inelastic response studies for structures subjected to wind loads and the envelope performance for structures. Immense efforts have been made to develop the PBD concepts, and similar to PBSD, the PBWD approach has shown great potential, yet it has several uncertainties that need further investigation. Those PBWD approaches will have a tangible effect on the design concepts and consequently on the design of the fast-growing tall buildings for more resilient communities subjected to extreme wind events and accordingly, more economic designs. Wind tunnels and reliable Computational Fluid Dynamics (CFD) analysis can help in developing concepts and provide a dynamic load time history which will greatly help in Performance-Based Wind Engineering. The incorporation of field data on non-structural elements' performance during non-synoptic wind incidents (i.e., hurricane and thunderstorm events) into the simulation and analytical models is still under development and shows high potential and promising research outcomes that would help in developing more accurate damage evaluation and serviceability satisfaction. A comparative case study was also presented for the responses under wind and seismic forces. From the study, it can be concluded that PBWD has potential in some cases especially if the governing wind case is the across-wind case, where a significant reduction in base shear and moment values (∼50%) was observed when the building stiffness decreased. On the other hand, when the along-wind load is the governing load case, decreasing the building's stiffness has led to higher base forces (∼100% increase in the responses). However, further investigation is needed to study different aspect ratios and shapes and include more frequency ranges.

Wind-induced fragility of a monopole structure via Artificial Neural Network based surrogate analysis

Although brute-force Monte Carlo (BFMC) sampling has been commonly used in performance-based wind engineering (PBWE) due to its robustness and efficiency, the computing cost required by the considerable amounts of repetitious, stochastic realizations for situations that involve large structures and a multitude of uncertainties is still prohibitive. To alleviate the computational burden, this communication proposes a surrogate modeling approach, based on artificial neural networks (ANNs), to evaluate the probabilistic integral required to quantify wind-induced fragilities. The resultant ANN models form a computationally viable alternative between input and output variables, based on a database of observations obtained through BFMC stochastic simulations. A preliminary study is conducted to examine the fragility of a slender, monopole tower structure under the excitation of multidirectional, mixed-climate wind loads. The ANN-powered surrogate results show adequate accuracy while drastically reducing the computing time to less than 1% of the cost of BFMC approach. It is promising to incorporate the surrogate ANN modeling in a PBWE framework.

An efficient stratified sampling scheme for the simultaneous estimation of small failure probabilities in wind engineering applications

With the advent of performance-based engineering frameworks for extreme winds, greater efficiency in the estimation of failure probabilities associated with multiple limit states at ultimate load levels, including collapse, is required. To meet this demand, an optimal stratified sampling-based simulation scheme is proposed that shares several meritorious characteristics of standard Monte Carlo simulation (MCS), including the capability to deal with high-dimensional uncertain spaces and multiple limit state functions. The optimality of the scheme is governed by the allocation of MCS samples among the strata as well as the strata division itself. A constrained optimization problem is formulated to address efficient sample allocation which is an extension of the Neyman allocation. Details for the practical implementation of the scheme within wind engineering reliability assessment applications are discussed. It is observed that the proposed methodology can reduce the variance by several orders of magnitude compared to MCS, which is illustrated on a wind-excited steel structure for the limit states of member/system first yield and collapse. The applicability of Latin hypercube sampling within stratified sampling-based simulation and the resulting efficiency gains are also critically studied. The results show promise in the wider applicability of the proposed scheme in performance-based wind engineering.

Wind fragility assessment and sensitivity analysis for a transmission tower-line system

Wind fragility is essential to performance-based wind engineering, risk, and resilience assessment for transmission towers. However, it has not been sufficiently studied due to the key issues in performance evaluation and uncertainty treatment for transmission towers. The performance of high-rise structures can be severely weakened by geometric imperfections, but these impacts have not been well addressed for transmission towers. Besides, the current uncertainty treatment only considers the tower itself although the transmission tower is part of an interconnected tower-line system that has complex interactions with wind environment. Therefore, this paper provides a systemic solution for geometric imperfections of transmission towers, where the users can clearly observe the effect of geometric imperfections on the capacity and failure positions of transmission towers. On this basis, a wind fragility framework that incorporates the uncertainties of each line component, wind environment, and aerodynamic parameters is proposed for transmission towers. Finally, sensitivity analysis was conducted to identify the significant uncertainty parameters for tower capacity and demand by sensitivity diagram. It is found that in addition to the uncertainties of the tower itself, the uncertainties of wind profile exponent, outer diameter and aerodynamic parameter of conductors have significant effects on the fragility of transmission towers.

Reliability-Based Collapse Assessment of Wind-Excited Steel Structures within Performance-Based Wind Engineering

As inelastic design for wind is embraced by the engineering community, there is an increasing demand for computational tools that enable the investigation of the nonlinear behavior of wind-excited structures and subsequent development of performance criteria. To address this need, a probabilistic collapse assessment framework for steel structures is proposed in this paper. The framework is based on the integration of a high-fidelity fiber-based nonlinear structural modeling environment with a wind-tunnel-informed stochastic wind load model to perform nonlinear time history analysis. General uncertainty is propagated using a stratified sampling scheme enabling the efficient estimation of reliabilities associated with rare events. The adopted models for simulating high-fidelity nonlinear structural behavior were found, in general, to be adequate for capturing phenomena, including progressive yielding, buckling, and low-cycle fatigue, that are essential for wind induced collapse analysis. In particular, the adopted fatigue model was found to be capable of predicting damage and potential fiber/section fracture associated with non–fully reversing stress-strain cycles that are characteristic of wind loading. Through illustration on a 45-story archetype steel building, critical discussions on the types of observed collapse mechanisms, the difference between along-wind and across-wind nonlinear behavior, reliabilities associated with first yield, and collapse are presented. A probabilistic description of the residual and peak story drifts is also provided through development of fragility functions.

Prediction of nonlinear structural response under wind loads using deep learning techniques

The wind actions on buildings are continuous in nature and could range from a few minutes to more than hours. Such long duration high intensity winds can push the structure to enter post elastic structural range and cause nonlinear behavior. Therefore, unlike performance-based earthquake engineering, where the structural simulations require seismic loads acting for a few seconds, the simulations for performance-based wind engineering (PBWE) requires wind load models acting for much longer durations. However, the nonlinear 3D model of a tall building will contain thousands of connections and structural members making it a complex finite element model. Dynamic time history analysis of such a model under loads lasting for hours can be tedious and often fail to achieve convergence. Using data-driven techniques that utilizes limited numerical and field data to obtain accurate structural responses under long duration loads is an exciting alternative. Deep learning techniques have been extensively used in the studies for structural health monitoring and earthquake engineering. However, the implementation of such data-driven techniques is very limited and has the potential for exploration in problems related to wind dynamics on tall buildings. This paper aims to predict the nonlinear structural response of tall buildings under sustained durations of wind loads using deep learning models. A Long Short-term Memory (LSTM) architecture is used to assess the efficiency of data-driven methods to replace computationally intensive 3D finite element analyses. The architecture will be tested on a 150 m tall building for response predictions under long duration wind loads. The robustness of the architecture will be further evaluated with predicting the acceleration response history of a scaled aeroelastic model based on experimental studies conducted at the Wind Simulation and Testing Laboratory (WiST) at Iowa State University.

Risk assessment of rehabilitation strategies for steel lattice telecommunication towers of Greece under extreme wind hazard

The risk and losses associated with the wind-induced failure of existing steel lattice telecommunication towers are assessed for a number of upgrade/replace/redesign schemes. Specifically, a performance-based wind engineering framework is employed for assessing a typical tower topology used by EU telecommunication network operators over four different cases: a conventional design, its corroded version after 60 years, a strengthened version of the corroded tower by applying fibre-reinforced polymer plates, and a redesign with high-strength steel. Multiple potential sites of installation were considered throughout coastal and mainland Greece, comprising two different groups of design wind speed. Mischaracterization of the site-specific wind distribution is by far the most important risk factor, with corrosion coming right behind. Still, selecting a rehabilitation approach does not depend only on site and tower characteristics, but also on the projected direct and indirect losses. By considering service to different populations, even after 60 years of corrosion, the “Do Nothing” approach may still be competitive when serving few residents and for short projected lifetime, while an upgrade is considered optimal for larger towns, or wherever higher revenue is on the line.

Next generation PBWE: Extension of the SAC-FEMA method to high-rise buildings under wind hazards

This paper proposes a method for the Performance-Based Wind Engineering (PBWE) of buildings by extending the well-established SAC-FEMA method originally implemented in seismic engineering for the evaluation of the mean annual frequency (MAF) of pertinent structural Limit States (LSs) in frame buildings. The development of such a method, that we will call the “SAC-FEMA WIND” method, implies the consideration of specific wind engineering peculiarities, like the classification of the across-wind response in two distinct regimes due to buffeting and vortex shedding phenomena, with the consequent adaption of the analysis procedures already defined for earthquakes to these two regimes. The method is then applied for the MAF evaluation of the occupants’ comfort LS for a high-rise steel building: the SAC-FEMA WIND is calibrated by comparing the obtained results with those coming from a Monte Carlo numerical analysis. This allows the definition of appropriate analysis procedures and shows the reliability of the SAC-FEMA WIND in evaluating MAFs. The SAC-FEMA WIND can be viewed as a “next generation” method for PBWE, in the sense that, after years of developments of the PBWE in research, now simplified methods like the SAC-FEMA WIND are needed for the implementation in Standards and in the design practice of explicit probabilistic PBWE approaches.

Performance-Based Wind Engineering: Background and State of the Art

This paper surveys the rapidly growing field of performance-based wind engineering (PBWE) of engineered systems, with focus on not only how PBWE has evolved since its early incarnations inspired by performance-based seismic engineering, but also the unique challenges of PBWE and the research that continues to emerge to tackle them. The limitations of traditional prescriptive wind design approaches are discussed with the aim of illustrating how such approaches are inadequate for providing acceptable building performance during extreme wind events, thus motivating why performance-based strategies for wind engineering are gaining traction and are poised to complement, if not replace, current approaches to wind design. In this respect, the current state of knowledge on the factors that affect building performance via extreme structural response, damage to the envelope system, and nonstructural components, is reviewed and challenges are identified. Lastly, the potential benefit of integrating optimization methods is identified while acknowledging the computational difficulty associated with such approaches.

A framework for the efficient reliability assessment of inelastic wind excited structures at dynamic shakedown

The introduction of performance-based wind engineering has opened the door to the potential of designing wind excited structural systems with controlled inelasticity. The possibility of adopting the state of dynamic shakedown as a target system-level limit state is attracting growing interest. However, there is a lack of frameworks that enable the efficient assessment of the reliability of structural systems at dynamic shakedown. To overcome this limitation, a stochastic simulation-based reliability assessment framework is presented in this paper, in which the dynamic shakedown problem is formulated within the setting of distributed stress-resultant plasticity. In addition, the framework allows the estimation of traditional component-level first yield limit states therefore enabling direct comparison between reliabilities associated with system-level inelastic limit states and those aligned with current design practices. A full scale archetype is studied, from which it is seen that the limit state of dynamic shakedown occurs at load levels far beyond those inducing first yield, resulting in significant increases in reliability at dynamic shakedown as compared to component and system first yield. The straightforward estimation of the reliabilities through the proposed framework illustrated the potential of adopting dynamic shakedown as a target system-level limit state for design with controlled inelasticity.

A Performance-Based Wind Engineering Framework for Engineered Building Systems Subject to Hurricanes

Over the past decade, significant research efforts have been dedicated to the development of performance-based wind engineering (PBWE). Notwithstanding these efforts, frameworks that integrate the damage assessment of the structural and envelope system are still lacking. In response to this need, the authors have recently proposed a PBWE framework that holistically treats envelope and structural damages through progressive multi-demand fragility models that capture the inherent coupling in the demands and damages. Similar to other PBWE methodologies, this framework is based on describing the hurricane hazard through a nominal straight and stationary wind event with constant rainfall and one-hour duration. This study aims to develop a PBWE framework based on a full description of the hurricane hazard in which the entire evolution of the storm track and time-dependent wind/rain fields is simulated. Hurricane-induced pressures impacting the building envelope are captured through the introduction of a non-stationary/-straight/-Gaussian wind pressure model. Time-dependent wind-driven rain is modeled through a computational fluid dynamics Eulerian multiphase framework with interpolation schemes for the rapid computation of wind-driven rain intensities over the building surface. Through the development of a conditional stochastic simulation algorithm, the envelope performance is efficiently characterized through probabilistic metrics associated with rare events of design interest. The framework is demonstrated through analyzing a 45-story archetype building located in Miami, FL, for which the envelope performance is estimated in terms of a suite of probabilistic damage and loss metrics. A comparative study is carried out in order to provide insights into the differences that can occur due to the use of nominal hurricane models.

Life-cycle cost assessment of vertical structures under nonstationary winds: Downburst vs. tornado loads

The continued development of performance-based wind engineering (PBWE) has led to the application of life-cycle cost assessment (LCCA) as a means to evaluate the risks and consequential losses over a structure’s lifetime from damages caused by large-scale wind phenomena, such as synoptic storms and hurricanes. However, the advancement of this analytical tool with regard to non-synoptic, nonstationary windstorms such as downbursts and tornadoes has so far been lacking due to incomplete knowledge of either the wind fields or their induced fluid-structure forces. In this study, a methodology is proposed that extends PBWE and LCCA to characterize structural damages with respect to hazard parameters, describing these wind phenomena, and subsequently to quantify and compare the relative monetary losses that are incurred. The dynamics of two vertical structures subjected to wind loads of various intensities using multiple downburst and tornado wind field models and data from wind tunnel experiments will be analyzed. Key components of the methodology are tailored in the holistic framework to consider the risks and consequences posed by these nonstationary windstorms.

Layered Stochastic Approximation Monte-Carlo method for tall building and tower fragility in mixed wind load climates

Performance-based wind engineering has emerged as an active research field due to potential applications into design standards [e.g., by the American Society of Civil Engineers (ASCE) in the United States of America]. Therefore, novel and accurate methodologies are necessary to successfully implement practice-oriented guidelines. This study will systematically examine the use of the Layered Stochastic-Approximation Monte-Carlo method, recently explored to assess of wind-induced structural dynamic analysis of vertical structures. The study will utilize a standard tall building and a monopole tower structure to investigate maximum response in terms of lateral displacement and acceleration, and the behavior of a structural member in terms of demand-to-capacity index. Both serviceability and ultimate limit states will be considered. The proposed method will be verified against standard Monte-Carlo sampling to assess its adequacy, accuracy and potential limitations. Particular consideration will be devoted to the study of wind loads and response in mixed wind climates, characterized by the presence of both tropical cyclones (hurricanes) and extra-tropical depressions.

Performance-based Bi-objective optimization of structural systems subject to stochastic wind excitation

This paper outlines the development of a stochastic simulation-based design optimization approach for dynamic wind excited structures in which correlations between component damages and losses are explicitly treated. The proposed approach integrates a bi-objective design optimization scheme with a probabilistic performance-based wind engineering methodology which systematically accounts for the various sources of uncertainties involved in system loss estimation. Through the ∊-constraint technique, the bi-objective optimization problem is transformed into a series of single-objective stochastic optimization problems. To solve each ∊-constraint optimization problem, a pseudo-simulation scheme is proposed that allows for the formulation of an approximate sub-problem that can be solved sequentially to identify solutions that define a set of Pareto optimal designs. In the proposed scheme, samples of engineering demands are approximated in terms of auxiliary variable vectors, which are by-products of an augmented simulation carried out in a fixed design point. Analytical expressions are derived that relate the engineering demand samples to the second-order statistics of wind-induced losses based on the concept of fragility. Potential correlations between the component capacities and component losses are explicitly treated. The effectiveness of the proposed approach and its scalability to high-dimensional problems are illustrated through optimal designs of moment-resisting frames subject to stochastic wind loads.

Perfomance-based wind engineering assessment of critical telecommunication infrastructure subjected to bora wind

Wind phenomena present significant societal risks in many regions of the world due to, among others, economic losses resulting from damages to the built environment, discomfort to people, and disturbances in marine, air, and road traffic. These risks have motivated the development of performance-based design methodologies to support the decision makers in making rational and optimal measures to mitigate those risks. This paper investigates the application of the Performance-Based Wind Engineering (PBWE) methodology to the risk assessment to the critical telecommunication infrastructure subjected to wind hazard. Motivated by failures of telecommunication infrastructure due to wind load, the focus of the study is on the implementation of the PBWE methodology to estimate the expected annual losses to typical lattice frame steel telecommunication towers subjected to the Bora wind along the Croatian coastline. The statistical description of the wind hazards is based on long-term meteorological measurements available at several locations to capture the local variations characteristic for the Bora wind. The uncertainties in the wind hazard and the structural parameters were propagated to the structural response (e.g., displacements, internal forces) through a set of Monte Carlo analyses. The analyses provided a basis to estimate the probabilities of exceeding the serviceability and ultimate limit states. The resulting probabilities were used as an input to the loss function that evaluates risks from the wind hazard. The risk estimates provide valuable information to the stakeholders and decision makers that enable improved strategies for managing risks from wind hazard.

Performance-Based Assessment and Structural Response of 20-Story SAC Building under Wind Hazards through Collapse

AbstractWith the increasing occurrence of extreme wind events (e.g., hurricanes) and growing interest in performance-based wind engineering, a better understanding of the structural response and co...