Steel Tower Research Articles

Structural effects of unequal leg lengths in lattice steel towers with the D-type bracing system

This paper presents a structural modeling analysis of transmission towers with varied leg length combinations to examine the structural effects of unequal leg lengths. Power transmission towers in mountainous areas often use unequal leg lengths to accommodate the changing slope of the terrain. In this study, three types of 345 kV steel transmission towers with the D-type bracing system were considered as analytical examples to discuss the internal force distribution of the tower structure subjected to a load under a fully wired condition. Different tower structural types exhibit similar structural characteristics. The upper part of the force distribution of a tower structure is less affected by varied leg length configurations. The central parts affected by unequal leg lengths are the extension part and the tower leg component. Analytical results indicate the critical elements of tower structures with unequal leg lengths, which can serve as a valuable reference for disaster prevention and reduction. In this study, the primary elements of the towers were all under the permissible strength even with the leg length differences exceeding the current specifications. This implies that adjusting the regulation of leg length differences of a transmission tower with unequal leg lengths can serve as the basis for future research, highlighting the advantages of unequal leg length tower applications.

Hybrid Wind Turbine Towers Optimization with a Parallel Updated Particle Swarm Algorithm

The prestressed concrete–steel hybrid (PCSH) wind turbine tower, characterized by replacing the lower part of the traditional full-height steel tube wind turbine tower with a prestressed concrete (PC) segment, provides a potential alterative solution to transport difficulties and risks associated with traditional steel towers in mountainous areas. This paper proposes an optimization approach with a parallel updated particle swarm optimization (PUPSO) algorithm which aims at minimizing the objective function of the levelized cost of energy (LCOE) of the PCSH wind turbine towers in a life cycle perspective which represents the direct investments, labor costs, machinery costs, and the maintenance costs. Based on the constraints required by relevant specifications and industry standards, the geometry of a PCSH wind turbine tower for a 2 MW wind turbine is optimized using the proposed approach. The dimensions of the PCSH wind turbine tower are treated as optimization variables in the PUPSO algorithm. Results show that the optimized PCSH wind turbine tower can be an economic alternative for wind farms with lower LCOE requirements. In addition, compared with the traditional particle swarm optimization (PSO) algorithm and UPSO algorithm, the proposed PUPSO algorithm can enhance the optimization computation efficiency by about 60–110%.

Development of a transition piece for a self‐erecting wind energy plant

AbstractFor the construction of wind towers with large hub heights up to 200m, the FOSTA research project P1392 HYTOWER [1] investigated a concept for a self‐erecting wind energy plant with steel‐steel hybrid tower. A tubular steel tower is lifted inside a lattice tower using a strand lifting system. During this process the tubular steel tower is stabilized by hydraulic cylinders. A specially developed transition piece is used to accommodate the lifting system during the lifting process and to finally connect the two tower parts. In this paper, the erection process as well as the development of the transition piece is presented.

Buckling analysis of tower shells under patch loading for self‐erecting wind energy plants

AbstractTo achieve a higher performance level and lower erection costs for wind turbines in the future, a concept for the automatic erection of a wind turbine with a hybrid tower was investigated in the FOSTA research project P1392. The tubular steel tower is lifted through the lattice tower using a strand lifting system and stabilized during this lifting process with the help of hydraulic cylinders arranged in two levels in the transition piece. This stabilization results in a transverse pressure acting on the tower shell, which does not occur in the load cases during operation, but only in the construction state. In this paper, the transverse forces (patch load) acting on the tower are investigated, whereby different system states are considered.

Buckling Verification of Manhole Area of Tubular Steel Wind Turbine Towers via Non‐linear Finite Element Analysis

AbstractAs wind turbine towers grow in height and their blades become longer, actions on the towers are also increased and their safe and cost‐effective design becomes critical for the further development of the wind energy sector. One potential failure mechanism of tubular steel towers is shell local buckling between ring flanges. In the present paper, the buckling behavior of a 120m tall wind turbine tower under realistic wind loads is investigated numerically, focusing on the buckling response near the man‐hole opening. To that effect, nonlinear finite element analyses accounting for geometrical and material nonlinearity and imperfections (GMNIA) is employed. GMNIA is performed taking into account initial geometric imperfections with the most unfavorable shapes resulting from the three primary buckling modes, determining the imperfection size according to EN1993‐1‐6 depending on the assumed fabrication quality class A, B or C. Numerical results are compared to analytical verification according to EN1993‐1‐6. Different wind directions are considered. Moreover, to investigate the influence of the stiffening of the manhole to the tower buckling strength, a comparison between three alternatives of stiffened and an unstiffened manhole is performed.

Structural performance of a steel tower model under seismic loading

This research represents the dynamic behavior of the steel tower structural model due to applying seismic load. The 3D finite element model is created using ANSYS-software to simulate the real structure used in experiment. The dynamic properties, natural frequencies and mode shapes, are extracted and compared with the experimental model values. The comparison is implemented to verify the FE analysis procedure of the tower model with experimental model results and they are accepted by 83% tuning ratio. The nonlinear seismic analysis is applied to the structural model using observed ground motion in 1999 Turkey Earthquake. The seismic load is applied in two cases; the first is in the x-direction of the structural tower model and the other in the y-direction of the model in a horizontal plane. The maximum response displacements in x and y-axis and load displacement hysteresis for both loading cases are exhibited. The results display that the tower structural model failed with large response displacement in the first few time of ground motion according to IBC-2018 and NBCC-2005. The collapse of the tower structural model occurred after time 18 sec and the applied seismic loading in x-axis has significant effect.

Iron-rich microstructure records of high temperature multi-component silicate melt behavior in nuclear fallout

Above-ground nuclear explosions that interact with the surface of the earth entrain materials from the surrounding environment, influencing the resulting physical and chemical evolution of the fireball, which can affect the final chemical phase and mobility of hazardous radionuclides that are dispersed in the environment as fallout particles. The interaction of iron with a nuclear explosion is of specific interest due to the potential for iron to act as a redox buffer and because of the likelihood of significant masses of metals to be present in urban environments. We investigated fallout from a historic surface interacting nuclear explosion conducted on a steel tower and report the discovery of widespread and diverse iron-rich micro-structures preserved within the samples, including crystalline dendrites and micron-scale iron-rich spheres with liquid immiscibility textures. We assert these micro-structures reflect local redox conditions and cooling rates and can inform interpretation of high temperature events, enabling new insights into fireball condensation physics and chemistry when metals from the local environment (i.e. structural steel) are vaporized or entrained. These observations also significantly expand the availability of silicate immiscibility datasets applicable to rapidly quenched systems such as meteorite impact melt glass.

Experimental and numerical investigation of steel-grout-steel sandwich shells for wind turbine towers

Aiming at enhancing a wind turbine tower's performance while keeping its external diameter below transportability-imposed limits, a steel-grout-steel sandwich base segment comprising a high diameter-to-thickness ratio is investigated herein, as an alternative to plain steel towers. An experimental campaign was firstly carried out, involving downscaled tower specimens which comprise the above said cross-section under bending loads, followed by the development of an elaborate finite-element (FE) model which can accurately capture the experimental behavior in terms of strength, stiffness and failure mechanism. A full-scale version of the validated model, representing the bottom segment of a wind turbine tower under design loads, was finally employed for the conduction of a parametric analysis, as regards the structure's geometry and material properties, and the investigation of the sandwich concept's possible advantages over a conventional steel structure. Owing to the synergy between the steel tubes and the grout core, the composite specimens almost reached their plastic moment capacity, premature buckling was prevented, and ductility was preserved, despite the significantly high diameter-to-thickness ratio of the steel tubes and the thin grout core. Although performance deteriorates as the diameter-to-thickness ratio of the two steel tubes increases, the relative advantage of the sandwich tower over a plain steel one becomes more prominent, especially when high-strength grout is used. It is thus demonstrated that a sandwich-type shell comprising a thin layer of grout may improve a wind turbine tower's load capacity, stiffness and stability without increasing the total amount of steel, nor extending its base diameter beyond transportability-related restrictions.

Tension and compression stiffness of ring stiffener in tube–gusset plate connections

Tube–gusset plate joints with multiple ring stiffeners are commonly used in steel tube towers. The load on the gusset plate can be distributed to each stiffener according to its Tension and Compression (T&C) stiffness. The ultimate state of joints with multi-stiffener plates can be equivalent to that of the stiffener plate. In this study, an experimental investigation and theoretical analysis of the failure mode and T&C stiffness of ring stiffener under symmetrical loading were performed. The experimental programme included material tests and 10 groups of static loading tests of the ring stiffener plates. Then, finite-element models were developed and validated against the test results. The validated numerical models were utilised to perform numerical investigations of 280 different single-ring stiffener plate specimens with D/t=32.3–55.9 and R/tr = 6–33.3. Using the experimental and numerical results, the parameters affecting the T&C stiffness of the ring stiffener plates were identified. According to the deformation characteristics of the ring stiffener plates, a T-shaped ring beam calculation model was established, along with the corresponding calculation formula. Calculation results based on the formula were compared with the numerical analysis results, and the results indicated that the theoretical model can accurately calculate the T&C stiffness of the ring stiffener plate. Thus, the proposed calculation method for the T&C stiffness of a ring stiffener can be used to guide the design of joints in actual engineering projects.

Structural calculation analysis and design of a Towering concrete building

This Towering building is a concrete tower with a height of 199. 10m and an octagonal plane, with a complex structure. The structure is calculated as a whole through the programs of two different mechanical models, the calculation results are relatively close, and the control indicators meet the requirements of relevant specifications and regulations. This article introduces and analyzes the structural system, structural calculation and analysis methods, seismic performance objectives, and overall calculation results of the project, and details the design of the steel tower.

관주형 철탑 상태 감시를 위한 음향 방출 신호처리에 따른 특징 분석

In this study, we propose and analyze a machine learning method based on the genetic algorithm (GA) and supporting vector machine (SVM) for the effective classification of faults detected by an acoustic emission test on the welding parts of tubular steel towers. A band-pass filter, an envelope analysis (EA), and an intensified EA (IEA) are employed to generate feature vectors for the machine learning method based on the GA. After signal processing, the signals are applied to GA-based machine learning to derive the representative features of the received signal, and the SVM classifies the fault signals and normal signals from the detected signals. Consequently, it is confirmed that the received signal processed by EA and IEA can classify faults with an accuracy of 93 % or more. Hence, the proposed fault test and classification method is expected to be useful in the development of a system for constant monitoring and early detection of welding faults inside a tubular steel tower.

Reliability assessment of existing transmission line towers considering mechanical model uncertainties

Reliability assessment of transmission line towers (TLTs) becomes particularly important in the context of the growing demand for increasing the energy transport capacity of existing lines. However, a comprehensive literature survey in this field reveals that important discrepancies may exist between the original design model analysis results and the actual lattice steel tower behavior. For instance, it has been demonstrated (Kaminski-Jr, 2007; CIGRE, 2009; Souza et al., 2019, 2020) that bolt slippage effects, which are disregarded in the current industrial practice, is importantly impacted by the tower topology that is defined by the tower engineer based on experience. Therefore, because several existing structures have topologies prone to connections’ slippage, they may be operating with a lower reliability when compared to modern recommended values. Within this context, the main goal of this paper is to assess the structural reliability of existing TLTs considering mechanical model uncertainties induced by connection details. For this purpose, the failure probability of two real TLTs built in Brazil are investigated employing different levels of structural modeling complexity. The first tower was designed 40 years ago and, several TLs operating in Brazil have adopted a similar design. The second is a newer structure, designed 15 years ago. In addition, to better understand the impact on the results when following the classical design procedure, the progressive collapse of both TLTs is modelled through a full material and geometric nonlinear analysis with and without the consideration of bolt-slippage effects. The results show that the older tower design, which presents a topology highly impacted by bolt slippage, is associated with a lower reliability than the current target values.

Rectifier Circuit using High-Impedance Feedback Line for Microwave Wireless Power Transfer Systems

Research on wireless power transmission technology is being actively conducted, and studies on spatial transmission methods such as SSPS are currently underway for applications such as power transfer to the upper part of steel towers and power transfer to flying objects such as drones. To enable such applications, it is necessary to examine the configuration of the power-transfer and power-receiving antennas and to improve the RF-DC conversion efficiency (hereinafter referred to as conversion efficiency) of the rectifier circuit on the power-receiving antenna. To improve the conversion efficiency, various methods that utilize full-wave rectification rather than half-wave rectification have been proposed. However, these come with problems such as a complicated circuit structure, the need for additional capacitors, the selection of components at high frequencies, and a reduction in mounting yield. In this paper, we propose a method to improve the conversion efficiency by loading a high-impedance microstrip line as a feedback line in part of the rectifier circuit. We analyzed a class-F rectifier circuit using circuit analysis software and found that the conversion efficiency of the conventional configuration was 54.2%, but the proposed configuration was 69.3%. We also analyzed a measuring circuit made with a discrete configuration in the 5.8-GHz band and found that the conversion efficiency was 74.7% at 24dBm input.

Numerical modal analysis of a 850 KW wind turbine steel tower

AbstractThe study deals with the numerical analysis aspects that are necessary for identifying of modal parameters of the tower structure as the most important part of the horizontal axis wind turbine, which are basic for the dynamic response analysis. In the present study, the modal behavior of an actual 55-m-high steel tower of 850 KW wind turbine (GAMESA G52/850 model) is investigated by using three-dimensional (3D) Finite Element (FE) method. The model was used to identify natural frequencies, their corresponding mode shapes and mass participation ratios, and the suggestions to avoid resonance for tower structure under the action wind. The results indicate that there is a very good agreement with the fundamental vibration theory of Euler-Bernoulli beam with lamped masse in bending vibration modes. When the rotor of the wind turbine runs at the speed of less than or equal to 25.9 rpm it will not have resonant problems (stiff–stiff tower design). Furthermore, in case the rotor runs at the speed of between 25.9 and 30.8 rpm, the adequate controller is necessary in order to avoid the corresponding resonant susceptible area of the tower structure (soft–stiff tower design).

State-of-the-art investigation of wind turbine structures founded on soft clay by considering the soil-foundation-structure interaction phenomenon – Optimization of battered RC piles

Nonlinear dynamic modelling of full-scale wind turbine structures and soil-structure interaction considerations using the 3D detailed approach is the most accurate method of investigating the mechanical response of these structures, but not yet feasible due to numerous reasons. The two main numerical problems that do not allow for this type of analysis to be performed, are the numerical instabilities that immerse during the dynamic analysis and the excessive computational demand. This work will present the computational response of a newly developed algorithm that is used herein to perform modal analysis of wind turbine structures for the investigation of soil-foundation-structure interaction phenomenon. An extensive numerical investigation is presented that foresees the performance of modal and pushover analysis on a wind turbine structure that has an 80 m steel tower and is founded on different soil profiles. The 3D detailed models constructed herein consider the effect of soil-foundation-structure interaction by discretizing for the first time the superstructure, pile foundation and soil domains through 8-noded hexahedral elements, achieving maximum modelling accuracy. The soil material properties used in this research work derived from an onsite geotechnical investigation performed for the needs of the WindAfrica project. After validating the ability of the proposed modelling approach to capture the mechanical behaviour of reinforced concrete foundations through the use of experimental data found in the international literature, the optimum inclination of battered piles was studied through an excessive numerical parametric investigation. Based on the numerical findings, the optimum inclination of the battered piles was that of 10 degrees, where the failure of the wind turbine structure was found to be located at the base of the steel tower due to local buckling.

Influence of diameter thickness ratio of main tube on bearing capacity of steel tube tower joints

In order to study the influence of steel tube diameter thickness ratio on the bearing capacity of steel tube angle steel tower joint, the finite element model of tube plate joint was established, and the failure mode and bearing capacity of the joint under different steel tube diameter thickness ratios were studied, and the influence law of steel tube diameter thickness ratio on the bearing capacity of steel tube tower joint was obtained, and the relationship between steel tube diameter thickness ratio and steel tube tower joint bearing capacity was established through regression analysis in this paper. The results show that angel steel tube plate K-type joint has two kinds of failure mode, and in a certain range, the bearing capacity of the joints increases with the increase of the steel tube diameter thickness ratio, and decreases after reaching the maximum bearing capacity.

송전선로 드론점검을 위한 딥러닝 기반 자동촬영 카메라짐벌 시스템 개발

In this paper, a new automatic camera gimbal system was developed to efficiently inspect transmission lines using a drone. As drone technology has advanced tremendously over the past few years, drones are being used to replace dangerous tasks in the electric power industry. Especially, Korea Electric Power Corporation has used the automatic drone inspection system developed for power transmission lines, but while this drone system flies on autopilot, its camera gimbal is still controlled manually. Moreover, the camera gimbal control in the field was often interrupted by electromagnetic interference from ultra-high voltage power lines. To overcome this problem, we developed the new camera gimbal system that can automatically shoot power facilities on the basis of Deep Learning. Its control algorithms mainly consists of a photographing algorithm for a steel tower, a photographing algorithm for power conductors, and an automatic drone landing algorithm. This fully automated system is expected to greatly increase the task efficiency and accuracy for transmission line inspection without any kinds control efforts.

Predicting single freestanding transmission tower time history response during complex wind input through a convolutional neural network based surrogate model

As the steel towers in the power system are vulnerable to intensive wind loads, it is essential to understand their dynamics response to estimate its potential failure. Conventional structural analysis methods like the finite element analysis or the field test are either computational heavy or cost expensive. Thus, this paper proposes a machine learning approach based on convolutional neural network (CNN) to predict the time history response of the transmission tower during the complex wind input. By preprocessing the time history of wind load and the tower’s dynamic response, a well-developed CNN can capture the time and spatial correlation of the wind load successfully and provide high accuracy results. CNN configuration, window size selection, and training data scale are carefully discussed to optimize the CNN design to maximize the prediction accuracy as well as minimize its computational time. Finally, to evaluate the performance of the surrogate model, the accuracy of the optimal CNN is tested in predicting the time history response of the transmission tower under 15 m/s to 70 m/s wind speed. The effectiveness of the CNN surrogate model is validated through a fragility model development, and its robustness is investigated using two wind inputs generated from a random wind profile and a random wind spectrum.

Dynamic Characteristics Evaluation on Portable Steel Frame due to Mass Irregularities

Application of irregular mass configuration in modern design era of buildings is unavoidable in order to serve various building functionality. The effect of mass irregularities was investigated on 5-storey portable moment resisting steel tower (PostFrame), against its dynamic behaviour. PostFrame was designed at five meter height and assembled on the strong floor in Jamilus Research Centre laboratory, UTHM. The predominant frequencies and mode shapes were determined on bare frame, uniform mass frame and mass irregularities’ frames. A total of four steel blocks at 800 kg were placed in uniform, ascending and alternating orientations on the first to fourth level of the PostFrame. Ambient vibration testing (AVT) was conducted using uni-axial accelerometer sensors. The sensors were aligned in bi-axial horizontal directions with respect to the North-South (NS) and East-West (EW) directions. ARTeMIS processing tool and Frequency Domain Decomposition (FDD) methods were used in the analysis of dynamic behaviour. Comparative findings were made between bare frame and mass action frame. Two translation mode shapes and torsional mode were illustrated by respective three predominant frequencies. Significant reduction of predominant frequency showed up to 37.79% between bare frame and frame with ascending mass orientation.Uniform mass orientation shows at the lowest percentage discrepancy percentage compared to others. Even though some changes have be found in predominant frequencies, but comparable mode shapes illustration were observed from all three predominant frequencies from all frame configurations.

Buckling strength of steel tube for lifting telescopic wind steel tower

A telescopic pole for wind energy production with low environmental impact and its lifting system for a 60–250 kW turbine and a height of 30 m have been designed and manufactured. The tower, was raised and lowered by automation or by remote control, that allows one to differentiate the presence of the generator within the landscape over time. The jacking systems acting on the legs had a combination of holes (on the legs) and pegs actuated by hydraulic pistons. The aim of the paper was the experimental and the analytical verification of the stability condition of the steel piston as a lifting system of the prototype. An experimental investigation was carried out on small-scale specimens to examine the influence of lateral restraints constituted by external steel tubes and transverse devices to increase the buckling load and to ensure a stability condition during the elevation operation of the telescopic steel pole. Finally, the experimental results were numerically validated. The original contribution of the paper to research was the design of lifting system of telescopic wind tower though a steel piston with transverse stiffeners.