Wind-induced Fatigue Damage Research Articles

Fragility Analysis of a Transmission Tower-Line System Subjected to Wind and Ice Loads Considering Fatigue Damage

Disasters such as ice and wind can pose a serious threat to the normal operation of power transmission lines. Wind-induced fatigue damage can further reduce the load-carrying capacity of transmission towers, increasing their fragility to ice and wind disasters. To assess the comprehensive capability of transmission towers to resist extreme ice and wind disasters, this paper proposes a failure probability evaluation framework for transmission towers considering wind-induced fatigue damage under the coupled effect of ice and wind. Taking a certain transmission line in Hunan as an example, the failure probability caused by ice and wind disasters is calculated for different years of service. First, based on the historical meteorological data in three cities in Hunan, a joint probability model of wind speed and wind direction considering their correlation is established using the copula function. Then, based on this probability model, the wind-induced fatigue damage of transmission towers is calculated using the Miner linear damage theory and the S-N curve. Subsequently, the fragility of the tower under the coupled load of ice and wind is calculated for different years of service. Finally, by combining the structural fragility function with the joint probability distribution model of ice thickness and wind speed, the collapse probability of the transmission tower under the action of ice and wind disasters is calculated. The results indicate that the influence of wind-induced fatigue damage cannot be ignored when transmission towers encounter ice and wind disasters. With increasing service time, the ability of transmission towers to resist ice and wind disasters gradually decreases, and the failure probability also increases under extreme ice and wind conditions.

Study on wind-induced fatigue performance of large-span transmission tower-line system considering the combined distribution probability of wind direction and speed

To accurately evaluate the fatigue life of transmission line structures under wind loads, this study proposes a multivariate member fatigue damage analysis method for investigating the wind-induced fatigue performance of a large-span transmission tower-line with full consideration of the combined distribution effects of wind direction and speed in the actual wind field. With the background of in-service transmission line project, a refined finite element model of the large-span transmission tower-line system is established, and the wind load is simulated and generated based on the linear filtering method. According to the meteorological statistics of the project site in the past 50 years, the wind-induced fatigue sensitivity analysis of the tower-line system is performed through considering the combined distribution probability of wind direction and speed. The wind-induced fatigue damage of the tower-line system is calculated based on the rain-fall counting method and Miner's fatigue cumulative damage theory, and its wind-induced fatigue life is further analyzed. The analysis results show that the sensitive members of the tower-line system are mainly distributed in the 2nd, 6th, 8th and 9th segments by combining the effects of wind attack angle and wind speed. The fatigue damage of the sensitive members decreases gradually with the increase of wind attack angle (0° wind attack angle damage is the largest), and the effect of wind speed on the vertical main member is larger than that of the crossarm upper chord member. Moreover, the fatigue damage at the end of the member is significantly larger than that in the center, and even at small wind speeds, the member's end can produce a stress amplitude larger than the fatigue cut-off limit. The fatigue life of crossarm upper chord members is 72.89 years, and that of the vertical main member is 77.60 years. In particular, the vertical main member should be employed as the control member for the structural fatigue life when considering extreme wind loads.

Fracture failure analysis of a lightning rod on a substation frame considering residual thermal stress

The collapse of a typical lightning rod on a 500-kV high-voltage substation frame in central China is investigated to identify the mechanism of fracture. Comprehensive analyses are performed on the fracture morphology, metallurgical structure, chemical composition and mechanical properties of the materials at the fracture site. A finite element (FE) model of a typical lightning rod structure with an intersecting joint weld is developed and verified using experimental results. Based on the FE results and wind tunnel tests, the fatigue life is estimated for the lightning rod structure at the accident site considering residual stress. The results indicate that the fracture failure of the typical lightning rod structure is mainly caused by wind-induced fatigue damage in the weld area of the intersecting joint of the rod base and the frame beam. The welding residual stress has a severe impact on the fatigue life of the structure. Regardless of the welding residual stress, the actual fatigue life of the typical lightning rod structure under a long-term wind load is lower than the design service life. Therefore, complete analysis of the structure under complex wind-induced dynamic effects is needed in engineering design. Additionally, attention should be given to the quality control of the welding, and measures should be adopted to reduce residual stresses during manufacturing and installation.

Lifetime multi-hazard fragility analysis of transmission towers under earthquake and wind considering wind-induced fatigue effect

Wind-induced fatigue damage is a predominant factor eventuating in structural performance degradation of transmission towers exposed to long-term environmental wind. Moreover, transmission towers may suffer from multiple extreme natural hazards (such as earthquake and strong wind) during their service lives. However, these phenomena have not been well accounted for in current design specifications and previous studies for transmission towers. To this end, this paper proposes a comprehensive probabilistic analysis framework for achieving the lifetime multi-hazard fragility evaluation by considering the wind-induced fatigue, which is applied in a 1000 kV steel tubular transmission tower. Firstly, based on the field wind data measured at the meteorological station of Qingdao city, China, from Jan. 1, 1971 to Dec. 31, 2020, a fatigue analysis is performed on an actual transmission tower constructed in this region to compute the annual mean fatigue damage. Secondly, a series of time-dependent uncertain numerical models of the tower are established by integrating the accumulated fatigue damage and material deterioration model, and nonlinear time history analyses are imposed on these models to examine the effect of fatigue damage on lifetime responses under combined earthquake and wind loads. Analogously, the time-dependent probabilistic multi-hazard demand models are derived via the dynamic analyses and statistical regression, and these demand models are employed to further develop the lifetime multi-hazard fragility surfaces of the tower. Finally, a fast lifetime safety assessment method, i.e. the critical safety surface, is proposed to efficiently judge the collapse state of the transmission tower at various wind speeds, PGAs and service times. Numerical results indicate that the structural capacity of the transmission tower will experience significant deterioration due to wind-induced fatigue damage; the multi-hazard induced structural responses and fragilities will considerably increase with the service life although the tower is initially well-designed. The proposed analysis framework will be beneficial for the design and maintenance of transmission towers subjected to both earthquake and wind hazards for designers and decision-makers.

Creating an asset management plan for traffic signal structures through interactive explorations of wind induced fatigue damage

This paper presents an asset management framework for remote monitoring of traffic signal structures for fatigue damage under wind loads, using historical wind measurements from nearby weather stations. Estimate wind profiles developed from the wind data are used to calculate fatigue damage at welded connections for a wide variety of common traffic pole configurations. The analysis is embedded within a novel remote monitoring application that performs the fatigue life analysis in real time for a user defined location and traffic pole configuration. Such a framework is the first of its kind that allows operators to make real time asset management decisions though interactive explorations of the relationship between traffic pole configuration and fatigue life due to local wind conditions. Results are demonstrated using several traffic poles located around Logan, Utah, which has complex topography that creates drastic changes in wind conditions over short geographical distances. The results illustrate the ability of the remote monitoring application to detect small-scale differences in wind conditions that result in significant differences in the estimated fatigue life of traffic structures within communities. Such results highlight the need for, and feasibility of developing site-specific asset management frameworks at a much finer spatial resolution than previous attempts.

Stochastic Analysis of Fatigue Damage of Transmission Tower-Line System Using Kriging and Bayesian Updated Probability Density Evolution Methods

The wind-induced fatigue damage is an important reason for the structural deterioration of transmission tower-line systems. The study of the fatigue damage of transmission towers is a basic requirement to ensure their normal service. To simulate the fatigue damage evolution occurring in the joints of the tower, a verified hybrid multiscale finite element (FE) model is first developed by concurrent modeling and substructuring techniques. Second, a fatigue damage model based on continuum damage mechanics is calibrated by conducting a fatigue crack initiation experiment and integrated into the FE material model by subroutines technique. Third, an improved Bayesian updated probability density evolution method (BUPDEM) with higher efficiency is proposed based on the Kriging method. Finally, based on the multiscale FE model and the damaged material model, the strategies for stochastic analysis of fatigue damage of transmission tower-line systems are proposed together with a numerical example for illustration. The results of the example show a good accuracy of the proposed BUPDEM.

Wind induced dynamic response and fatigue assessment – Nonlinear time domain versus linear stochastic analysis

By performing the nonlinear dynamic analysis and calculating the wind induced fatigue damage, this paper compares the fatigue calculation results with that obtained from a linear stochastic dynamic analysis in frequency domain. It is noticed that, since linear frequency domain analysis often involves a linearization of relevant non-linear load effects, associated with non-linear drag, coherence of wind loading in space, large deformation and local plasticity development, into the linear solution of dynamic equilibrium equations, and also because the power spectrum of critical stress (quasi-static and dynamic) due to wind loading may not be narrow-banded, initiated by the influence of the background components of incident turbulence, across wind-induced vibrations, wind directional effects and structural damping and so on, the inappropriate use of the linear spectral method developed for Gaussian processes can mis-predict the dynamic response, leading to a significant bias in the fatigue damage assessment. It is found that the disadvantages of the linear method aforementioned have to be compromised by additional assumption of uncertainties implemented in calculating dynamic response, often resulting in an over-conservative evaluation in fatigue damage estimation. The wind induced fatigue calculation procedure using non-linear dynamic analysis can be widely adopted for various types of structures, which can significantly reduce the uncertainties without compromising the safety requirement.

Studying the wind-induced vibrations of a traffic signal structure through long term health monitoring

Recent failures of traffic signal structures have showcased the vulnerability of such structures to wind loading. During the wind-induced vibration of the mast arm, the large mass of the mast arm creates high-level stress at the pole-to-arm connection. Additionally the low mechanical damping results in accumulationof stress cycles ewhich could cause fatigue damage at the pole-to-arm connection. In this study, a traffic signal structure with three vertical traffic lights was selected for long-term health monitoring. The monitored acceleration data at the mast arm tip was used to study the wind-induced behavior and was compared with the theoretical analysis results. The monitored strain data at the pole-to-arm connection was used to evaluate the fatigue damage. Low stress ranges were recorded most of the time, which indicates that the wind-induced fatigue damage might not be a significant concern for the monitored traffic signal structure. However, high stress ranges have been recorded at high wind speeds, indicating fatigue damage can still be an issue at higher wind speed regions. The performance of monitored traffic signal structure was compared with those in the literature. An apparent discrepancy was noticed between their wind-induced behaviors, and the orientation of the attached traffic lights was identified as a key parameter to influence the wind-induced behavior. It was found that at low wind speed, attached vertical traffic lights can reduce the likelihood of vortex-induced vibration and, as a result, lower the stress range at the pole-to-arm connection.

Toward Development of Design and Maintenance Approach for Buildings Subjected to Wind-induced Fatigue Damage

Toward Development of Design and Maintenance Approach for Buildings Subjected to Wind-induced Fatigue Damage

Spectral Fatigue Analysis for Topside Structure of Offshore Floating Vessel

In this study, a spectral fatigue analysis was performed for the topside structure of an offshore floating vessel. The topside structure was idealized using beam elements in the SACS program. The fatigue analysis was carried out considering the wave and wind loads separately. For the wave-induced fatigue damage calculation, motion RAOs calculated from a direct wave load analysis and regular waves with different periods and unit wave heights were utilized. Then, the member end force transfer functions were generated covering all the loading conditions. Stress response transfer functions at each joint were produced using the specified SCFs and member end force transfer functions. fatigue damages were calculated using the obtained stress ranges, S-N curve, wave spectrum, heading probability of each loading condition, and their corresponding occurrences in the wave scatter diagrams. For the wind induced fatigue damage calculation, a dynamic wind spectral fatigue analysis was performed. First, a dynamic natural frequency analysis was performed to generate the structural dynamic characteristics, including the eigenvalues (natural frequencies), eigenvectors (mode shapes), and mass matrix. To adequately represent the dynamic characteristic of the structure, the number of modes was appropriately determined in the lateral direction. Second, a wind spectral fatigue analysis was performed using the mode shapes and mass data obtained from the previous results. In this analysis, the Weibull distribution of the wind speed occurrence, occurrence probability in each direction, damping coefficient, S-N curves, and SCF of each joint were defined and used. In particular, the wind fatigue damages were calculated under the assumption that the stress ranges followed a Rayleigh distribution. The total fatigue damages were calculated from the combination with wind and wave fatigue damages according to the DNV rule.

Effect of uncertainties in wind speed and direction on the fatigue damage of long-span bridges

In order to estimate wind-induced fatigue damage, most methods use the probability density functions of wind speed and direction. Conventional approaches assume that these functions are error-free and provide a single estimated damage value. However, the estimated damage may contain significant errors because the probability density functions are generally inexact, and the parameters for the functions rely on limited measured data. We propose a Bayesian approach to determine the fatigue damage while considering the uncertainties in the probability model and the parameter. The proposed approach provides a distribution of damage values, which enables more comprehensive analysis of fatigue damage using bounds and exceedance probability. The approach is applied to the estimation of fatigue damage of long-span bridges. We also illustrate an additional feature of the Bayesian approach, which is to systematically update the damage index as more measurements become available over time. Effect of data size is investigated to quantify the error due to the limited measured data. The influence of uncertainties in other parameters and effects of long term wind speed variability is also included in this study.

Probabilistic Fatigue Assessment Based on Bayesian Learning for Wind-Excited Long-Span Bridges Installed with WASHMS

For long-span bridges located in wind-prone regions, it is a trend to install in situ Wind and Structural Health Monitoring System (WASHMS) for long-term real-time performance assessment. One of the functions of the WASHMS is to provide information for the assessment of wind-induced fatigue damage. Considering the randomness of wind, it is more reasonable to describe wind-induced fatigue damage of bridge in a probabilistic way. This paper aims to establish a probabilistic fatigue model of fatigue damage based on Bayesian learning, and it is applied to a wind-excited long-span bridge installed with a WASHMS. Wind information recorded by the WASHMS is utilized to come up with the joint probability density function of wind speed and direction. A stochastic wind field and subsequently wind-induced forces are introduced into the health monitoring oriented finite element model (FEM) of the bridge to predict the statistics of stress responses in local bridge components. Bayesian learning approach is then applied to determine the probabilistic fatigue damage model. The Tsing Ma suspension bridge in Hong Kong and its WASHMS are finally utilized as a case study. It shows that the proposed approach is applicable for the probabilistic fatigue assessment of long-span bridges under random wind loadings.

Bi-modal spectral method for evaluation of along-wind induced fatigue damage

Several analytical procedures available in literature, for the evaluation of wind induced fatigue damage of structures, either assume the wide band random stress variations as narrow band random process or use correction factors along with narrow band assumption. This paper compares the correction factors obtained using the Rainflow Cycle (RFC) counting of the measured stress time histories on a lamp mast and a lattice tower, with those evaluated using different frequency domain methods available in literature. A Bi-modal spectral method has been formulated by idealising the single spectral moment method into two modes of background and resonant components, as considered in the gust response factor, for the evaluation of fatigue of slender structures subjected to along-wind vibrations. A closed form approximation for the effective frequency of the background component has been developed. The simplicity and the accuracy of the new method have been illustrated through a case study by simulating stress time histories at the base of an urban light pole for different mean wind speeds. The correction factors obtained by the Bi-modal spectral method have been compared with those obtained from the simulated stress time histories using RFC counting method. The developed Bi-modal method is observed to be a simple and easy to use alternative to detailed time and frequency domain fatigue analyses without considerable computational and experimental efforts.

Prediction of wind-induced fatigue on claddings of low buildings

This paper presents an analytical approach for the prediction of wind-induced fatigue on claddings of low buildings. The method uses digitally simulated wind pressure data, long-term wind climate of the region and experimental fatigue characteristics data of claddings. The wind pressure data is analyzed using rainflow technique to establish the fatigue characteristics of pressure data. For low buildings located in temperate regions, the accumulation of wind load cycles during the design life of cladding is estimated using a probabilistic approach by integrating the long-term wind climate of the region with the fatigue characteristics of pressures. Finally, the wind-induced fatigue damage is calculated utilizing Miner’s rule and Goodman’s method. Analytical predictions for the case of roof claddings are validated by experimental measurements in a boundary layer wind tunnel. This approach seems promising for a parametric investigation of wind-induced fatigue.

Elastoplastic response of steel damper subjected to wind by the typhoon model

The object of this study is to evaluate the wind-induced fatigue damage of a steel damper installed at an H-type steel beam for earthquakes. A typhoon model is proposed to evaluate the extreme wind speed and the duration time of a strong wind. The applicability of the two methods, Methods 1 and 2, approximating the elastoplastic response is examined, by comparing the approximated response with that calculated by an exact analysis. The typhoon model simulates the observed typhoon conditions well. The wind speeds and accumulated duration times by typhoons are obtained. The difference between approximated and exact responses is small by about 20% even when the deformation of damper becomes nine times of that at the yield point. Overall, it became evident that the across wind response affects the fatigue damage more than the along-wind.

Fatigue damage estimation of metal roof cladding subject to wind loading

This paper introduces a procedure for estimating wind-induced fatigue damage to metal roof cladding. Fatigue loading on roof cladding is determined using a rainflow count method and considering long-term wind climate. Linear or bilinear S-N curves on a log-log plot are derived based on fatigue tests of three types of commonly used light gauge steel roofing sheets. Fatigue damage indexes are calculated by a modified Miner's rule. Roof pressures measured on a low-rise building at Wind Engineering Research Field Laboratory of Texas Tech University (TTU Building) are used to carry out a comparison of fatigue damage caused by the new fatigue loading found in this study with that caused by the fatigue loading currently used in Australia and Europe with respect to design life of roofing sheets, wind return period, annual occurrence of cyclone, and others. The limit fatigue load-bearing capacity of roofing sheets is also obtained.

A simplified method for assessing wind-induced fatigue damage

This work, initiated and funded by BP International, considered a method of simplifying the procedure for the analysis of wind-induced fatigue damage. Common practice currently is to employ a time consuming deterministic stress-cycle counting algorithm to a synthesized time history. It has been shown that by normalizing the damage in a certain way the value of normalized damage becomes completely independent of the wind spectrum and even the structure. It is thus only necessary to compute denormalizing factors which are readily found from wind data and structural analyses. The proposed method is believed to be suitable for a first assessment of fatigue performance and, because of its simplicity and its ability to be presented in calculation sheet format, should be easily used by design engineers.