Steel Transmission Towers Research Articles

Structural Analysis of Latticed Steel Transmission Towers Subjected to Nondeterministic Wind Loads

Lattice steel towers are commonly used to support overhead power transmission lines. However, the dynamic behavior of these structures is often overlooked in current design practices. Given that many accidents involving these towers occur even at basic wind speeds lower than those specified in the project, it is likely that dynamic actions play a significant role in these failures. This study proposes a method to accurately simulate the interaction between transmission line cables and towers under non-deterministic wind loads to assess displacements and forces in the steel towers. The study examines a transmission line system consisting of towers, conductors, shield wires, and insulators, featuring a central suspension tower of 32.86 m in height, flanked by two end towers with 450 m spans. Finite element modeling was developed to account for the dynamic characteristics of the wind. Wind loads were modeled as a random process based on their statistical properties. The results revealed significant differences in displacement and force values when comparing the results provided by static and dynamic analyses. The structural design of a base leg member indicated potential failure at higher wind velocities, highlighting the importance of considering the wind dynamic effects in the design.

Ultimate bearing capacity of T-shaped retrofitting diagonal members for angle steel transmission towers

Collapse of steel latticed transmission towers under strong winds is a significant safety concern for power systems. Attaching additional members to the tower members can enhance the wind resistance of transmission towers. To establish systematic retrofitting schemes and methods for predicting the ultimate bearing capacity of T-shaped retrofitting diagonal members, static experiments and finite element analysis on various cross-sectional dimensions and member lengths were utilized in this study. The experimental results indicate that retrofitting can effectively increase the bearing capacity of diagonal members. Finite element models are developed and verified based on the discussion of load-displacement curves and failure modes. The finite element analysis reveals that the increase in capacity achieved by reducing connector spacing is relatively small when compared to the ultimate bearing capacity obtained with the spacing of two connectors, and the arrangement of connectors at both ends meets the requirement of connector spacing. The relationship between the retrofitting bearing capacity and the slenderness ratio of diagonal members can be divided into two linear stages, which correspond to different failure modes. Furthermore, a λk coefficient method based on the axial compression equation is proposed to predict the ultimate bearing capacity of T-shaped retrofitting members. The bearing capacity based on the λk method shows agreement with finite element analysis results.

Wind-Induced Response Analysis of the Transmission Tower-Line System Considering the Joint Effect

Wind load is one of the main control loads of transmission tower-line systems. Numerical simulation is the main method for studying the structural wind-induced response. The establishment of a refined transmission tower simulation model is the basis for accurately analyzing the dynamic response of a transmission tower-line system under a wind load. This paper first considered the mechanical properties of bolted joints under cyclic loading and established a transmission tower-line system model considering the joint effects. Then, the wind load was generated by the harmonic superposition method, and the wind dynamic time-history analysis of the tower-line system was conducted. The influence of the joint effect on the wind-induced response of the transmission tower-line system was studied, and the effects of turbulence intensity and wind attack angle on the bolted joint slip effect were discussed. The results showed that the joint effect significantly increased the displacement response of the transmission tower subjected to wind loads and affected the normal service performance of the tower-line system. When the turbulence intensity is 10%, the top displacement of the tower model considering the joint effect is approximately 2 times that of the ideal rigid frame model. After considering the joint effect, the additional [Formula: see text] effect caused by the increased displacement resulted in an increase in the stress of 75.6% members, and the maximum stress of the main member was located near the upper diaphragm of the tower leg. Therefore, considering the joint slip effect in angle steel transmission towers can improve the accuracy of the dynamic response analysis of transmission lines.

Development of Physics-Based Virtual Training Simulator for Inspections of Steel Transmission Towers

Development of Physics-Based Virtual Training Simulator for Inspections of Steel Transmission Towers

Electromagnetic Ultrasonic Shear-Horizontal Wave to Detect Corrosion Defect of Flat Steel for Grounding Device of Transmission Pole Tower

Detecting defects in grounded flat steel is essential for ensuring the safety and reliability of transmission tower grounding devices. However, traditional inspection methods, such as physical excavation and verification, are costly and time-consuming. This paper proposes a corrosion defect detection method for flat steel transmission tower grounding devices based on electromagnetic ultrasonic SH waves. In addition, using commercial software, a three-dimensional finite element simulation model of grounded flat steel with simulated pitting corrosion defects is constructed. The specified displacements applied to multiple surface sources mimic the horizontal shear vibrations generated by the electromagnetic ultrasonic transducer on the surface of the grounded flat steel during actual inspection. A simulation was used to investigate the propagation and attenuation characteristics of shear-horizontal ultrasonic SH0guided waves for simulated corrosion defects with various geometric configurations in grounded flat steel. The simulation investigated the propagation and attenuation characteristics of the SH0 wave in grounded flat steel and the detection of various defects for linear analysis of the results. The simulation results show that the attenuation of the electromagnetic ultrasonic guided wave is small, at only 0.0016 dB/mm, and the displacement amplitude of the echo signal decreases with the increase of the SH0 wave propagation distance. Increasing the depth and length of corrosion defects increases the echo signal amplitude. At the same time, the width of corrosion defects has little effect on the echo amplitude. Finally, a flat steel defect detection experiment was conducted, and the experimental results fit with the simulation to verify the accuracy of the simulation model. This detection method introduces a new idea for the on-site detection and quantitative identification of corrosion defects in grounded flat steel, which has significant reference value and can provide a more effective and economical method for ensuring the safety and dependability of transmission tower grounding devices.

Modeling and modal analysis of the structure of long-span transmission tower

The structure of the long-span transmission tower is a typical nonlinear structure with the characteristics of great height, large line span, heavy overall weight and flexible tower body. The current design code only analyzes the traditional tower types, but the analysis of the truss structure of transmission tower is limited. Aiming at improving the design defects of the structure of long-span transmission towers, this paper uses the finite element software APDL to build the three-dimensional finite element model of a long-span transmission tower, to carry out the modal finite element analysis as well as to extract the specific parameters of each modal finite element mode: Modality, Natural frequency of vibration, Periodicity. The results show that the natural vibration period of the main machinery of this type of steel transmission tower is about 0.37–1.37 s; The structure of the long-span transmission tower has certain displacements in six degrees of freedom, in which the value of the X-dimensional displacement is the largest. There are some large displacements and local torsion in the high-order mode, combined with the results of modal analysis, so it is suggested to consider the structural improvement or external reinforcement of the weak parts of the long-span transmission tower.

Study on Reradiation Interference Characteristics of Steel Towers in Transmission Lines

With the development of ultrahigh-voltage transmission lines in China, the reradiation interference caused by the steel tower used in ultrahigh-voltage transmission becomes increasingly aggravating for nearby radio stations. In this paper, using the multilevel fast multipole algorithm, the reradiation interference of an ultrahigh-voltage transmission steel tower is investigated. Additionally, the reradiation interference characteristics of a transmission steel tower were investigated with various frequencies and azimuth angles of incidence wave. The results show that the frequency and the azimuth angle of incident wave are the impact factors for the reradiation interference of steel towers. It is better to use a detailed angle steel model for the truss structure of steel towers at high frequency, while a simplified structural model can be used at low frequency. Additionally, the diffraction at the edge of the angle steel has a great influence on the reradiation interference, particularly at high frequencies.

Experimental and numerical study on the ultimate bearing capacity of a K-type tube-gusset plate joint of a steel transmission tower

The ultimate bearing capacity of K-type tube-gusset plate joints was experimentally investigated in the engineering context of ultrahigh voltage (UHV) steel tube transmission towers. Three K-joint specimens were fabricated: ZK30, ZK50 and PK30, where the eccentricity e of the ZK and PK specimens was 0 and D/4, respectively. The branch and main load ratios λ are 29.41% and 50% for ZK30 and ZK50, respectively, and 29.41% for PK30. The experimental results show that increasing λ has a negative effect on the bearing capacity of the main tube. Compared with ZK30, ZK50 has 17% lower main tube axial force and 33% higher branch tube axial force when the specimen was failed. In contrast, the negative eccentricity is beneficial to the bearing capacity of the main tube. Compared with ZK30, PK30 has the same main tube axial force and 6.7% higher branch tube axial force when the specimen was failed. Local buckling occurs in both ZK30 and ZK50, while overall failure occurs in the PK specimen. The finite element model (FEM) in the ABAQUS platform with initial geometric defects was verified by the experimental results. The stress distribution, failure mode and ultimate bearing capacity of the FEM show agreement with the experimental results. The simplified FEM was employed to analyze the bending capacity of K-joints with different diameters of the main tube, different thicknesses of the main tube and different lengths of the gusset plate. The results show that for the K-joints analyzed in this paper, the bending bearing capacity only decreased by 16.41% as the diameter of the main pipe increased by 50.25%, increased by 48.99% as the length of the node plate increased by 37.50%, and increased by 145.33% as the wall of the main pipe increased by 71.43%. The formula for calculating the bending capacity of the K-type tube-gusset plate joint was fitted. Compared with the existing specifications, calculation results with the fitting formula are more similar to those of the FEM.

Typhoon-Induced Fragility Analysis of Transmission Tower in Ningbo Area Considering the Effect of Long-Term Corrosion

The purpose of this paper was to investigate the influence of long-term corrosion on the deterioration of wind resistance of a steel transmission tower during its service life. An analytical model for predicting the long-term corrosion depth of carbon steel was established, and the corrosion depth of carbon steel in the Ningbo area was predicted based on the local atmospheric environment data. With the help of typhoon full-track simulation and wind field simulation technology, a joint probability distribution model of multidirectional extreme wind speeds was constructed using the t-Copula function to determine the typhoon climate of the transmission tower site. Finite element models of the ZM4 cathead transmission tower under 30/60/90 corrosion years were then established, respectively, according to the predicted corrosion depth of carbon steel in Ningbo. Three damage modes, i.e., minor damage, moderate damage and severe damage, corresponding to the transmission tower under wind loads, were defined, and pushover analyses were used to determine the limit values of each damage mode so as to obtain the typhoon-induced fragility curves of the transmission tower within 30/60/90 corrosion years. The results show that the increase in corrosion age leads to a deterioration in the nominal mechanical properties of the transmission tower components, making the damage probability to the transmission tower increase. Under the typhoon wind loads of a 50-year return period in the most unfavorable wind direction in Ningbo, the probability of moderate damage of the tower is within 10% and the probability of minor damage is controlled between 10% and 40%.

Mechanical behavior of steel transmission tower legs reinforced with innovative clamp under eccentric compression

Most steel lattice towers have been in service for over 20 years in China. Many existing towers are now required to carry higher loads than those for which they were originally designed because of new heavier devices and revised wind design codes. An effective way of increasing the carrying capacity of a tower is to reinforce its core leg members by attaching additional elements with bolted connections. However, the reinforcing methods proposed in previous studies require drilling into the core leg members, which results in considerable construction inconvenience. Therefore, an innovative clamp-type (IC) method is proposed herein. To evaluate the effectiveness of the proposed IC method, this paper presents results from 90 new cases comprising 10 eccentric compression tests and 80 finite element (FE) analyses of the load capacity of starred compound members, by varying the interconnector arrangement, form, spacing and bolt row, and slenderness ratio of the compound members. The experimental results show that the compound members with the IC interconnector mainly exhibit buckling failure in the core member. However, in the case of instability about the imaginary axis, the bearing capacity of the compound members with the IC interconnector is approximately 41%–62% higher than that of the single angle member. A nonlinear FE model is developed, which considers the material, contact non-linearity, and geometric imperfections. The FE model is validated against the experimental test results, which show good agreement, both in terms of failure mode and load–displacement curve. The validated FE model is used to conduct a parametric analysis to investigate the effect of slenderness ratio on the bearing capacity of the compound member. Four width–thickness ratios of connected angles and five IC interconnector spacings are considered in the parametric study. The bearing capacity values obtained from the experimental tests and FE analyses are used to assess the performance of current design guidelines. The results show that the current DL/T 5154-2012 code is too conservative by an average value of 30%. Therefore, a kd coefficient method is proposed to improve the prediction accuracy of the bearing capacity, and the method is verified against the FE and test results of the compound member with the IC interconnector under eccentric compression tests.

Quantification of the Seismic Behavior of a Steel Transmission Tower Subjected to Single and Repeated Seismic Excitations Using Vulnerability Function and Collapse Margin Ratio

Transmission towers are a vital lifeline for modern living and are crucial structures that must remain operational even after a seismic event. However, the towers are largely designed to withstand the effects of wind alone and not earthquakes, and the seismic influences on tower design and construction have hitherto been ignored. The purpose of this study was to evaluate the seismic performance of a latticed steel transmission tower-line system that is subjected to a variety of seismic situations (Far-Field, Near-Field and Repeated Earthquakes) using probabilistic vulnerability functions and Collapse Margin Ratios in accordance with FEMA-P695. Nonlinear Time History Analyses were performed by incorporating an array of 36 strong ground motions to develop the Incremental Dynamic Analysis and to generate the fragility functions for three performance limit states as referenced in FEMA 356. The results showed that the single event seismic performance of the tower is better than its performance after multiple ground motions owing to aftershock impact, while near-field excitations led to greater susceptibility and fragility than far-field scenarios. Thus, near-field ground motion is more harmful to the tower and could result in its failure or collapse with only a small reduction in damage relative to the impact of the aftershock.

Study on Improved CG Algorithm for Reradiation Interference Calculation of Transmission Steel Tower

With the development of extra-high voltage and ultra-high voltage transmission line in China, the reradiation interference generated by induced current on the surface of transmission steel tower becomes more serious to the radio station in the vicinity. In this paper, the calculation method for reradiation interference of transmission steel tower based on method of moment is analyzed. And in order to reduce the impedance matrix storage data in the memory space and the number of iterations in the calculation, the preprocessing of matrix sparse and diagonal norm precondition is presented to improve the performance of the conjugate gradient algorithm for the reradiation interference calculation. The reradiation interference of a standard 500 kV transmission steel tower is calculated using the improved conjugate gradient algorithm. And the results show that the algorithm enhances the convergence and stability after preprocessing and is suitable to calculate the reradiation interference of super-large metal truss structure target.

Calculation method of stability bearing capacity of transmission tower angle steel considering semi-rigid constraint

Abstract The angle steel member is the most commonly used component form of the transmission tower structure. Considering its connection characteristics, we must deal with its stability analysis under semi-rigid constraint conditions for the proper study of the overall structure’s mechanical performance. Therefore, in order to establish a simple and high-precision method suitable for the ultimate bearing capacity analysis of the transmission tower, we build the refined finite element models of typical steel tower joints, analyze its moment-rotation curve and utilize simulation technique of spring elements to acquire the calculation method of its single angle stability bearing capacity, which is considering initial imperfection and residual stress. Furthermore, we analyze its bearing capacity under different constraint conditions such as rigid, semi-rigid and articulated connection. The results show that it is necessary to consider joint stiffness in the bearing capacity analyses. Finally, it’s confirmed that the calculation results of this method agree well with the experimental data, which validates its high accuracy. Therefore, the method provides technical support for high efficient component stability simulation in overall stability analyses of the transmission steel tower.

Experimental testing and evaluation of real-scale lap-splice bolted connections used in typical lattice steel transmission towers

Typically, lattice steel transmission towers (LSTTs) are built using bolted connections, although the performances of these connections are complicated. Generally, lap-splice bolted connections are used for long primary (leg) members to ensure their continuity. Herein, 17 lap-splice bolted joints, with real-scale dimensions as used in three LSTTs, are experimentally tested under compression, with the bolts being under shear. The considered three LSTTs carry 33 kV double-circuits overhead transmission lines, where the loading conditions and design are complied with the relevant requirements of the technical specification of ASCE-10/97 (2000). The main objective of this paper is to study the behaviour and failure mode of the lap-splice bolted joints of such three LSTTs, which are often considered either pinned or fully-rigid in practice. The joints relationships by means of the axial load versus joint deformation under shear forces on bolts are measured and evaluated, where the lap-splice bolted joints are found to show pre-slippage, slippage, bearing and plastic stages. The joints are found to fail due to bearing of either inner angle members or the splice plates. The axial stiffness of the lap-splice bolted joints is then obtained from these load–displacement curves. Moreover, stiffness and shear strength of the current joints are compared with the component based method (CBM), as presented in EN 1993−1−8 (2005). In this method, the structural steel joint under shear loading is treated as a multi-spring model composed of in-series springs, which enables obtaining its force–displacement relationship. The initial stiffness and strength comparison based on this simple method shows a good agreement with the experimental results. Additionally, the strength obtained by CBM is shown to conform to the experimental failure modes. Based on the results, the laboratory experimental compression tests as well as CBM estimations of bolted lap-splice joints connections are useful tools to evaluate the behaviour of these joints. Hence, they are suggested to be taken into consideration during the overall elastic design of the towers by using well calibrated finite element modelling instead of using expensive full-scale loading prototype testing method in accordance to IEC 60652 (2002).

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.

Lightning Strikes Mitigation Plan on Transmission Line Tower at Kedah Paddy Field

This paper presents a mitigation plan for lightning strikes towards the transmission line tower at Kedah paddy field area. The ATP Draw software produces a schematic diagram of an incoming main intake sub-station and a transmission tower struck by lightning. Simulation on multiple soil resistance values and multiple soil conditions are then plot into graphs. A static eliminator reduces the electrostatic force between negatively charged thunder clouds with a positively charged steel transmission tower. It shows that a static eliminator makes the transmission line act invisibly in the lightning pathway. This protection level avoids surge current from transmitting in the transmission line reduces the possibility to damage surge arrestor.

Simplified joint-slippage model of bolted joint in lattice transmission tower

Joint-slippage models are key parameters in structural deflection prediction of angle steel transmission towers. Depended by number of bolts, bolt diameter, bolt arrangement, cross section dimensions of angle steel and so on, there are so many different bolted joints with various joint-slippage characteristics in which only a few angle steel bolted joints were experimental tested. To determine the load-deformation relationship of bolted joints, a simplified joint-slippage model was proposed based on the component method. Then, the load-deformation relationship of two specimens of single-leg bolted joints and two specimens of lap-splice bolted joints were predicted by the proposed model and the finite element method in ABAQUS. Compared with the corresponding experimental results of other researchers, the validation of the proposed model and the finite element method were all verified. Furthermore, the load-deformation relationship of a single-leg bolted joint and a lap-splice bolted joint of a full-scale test tower were also predicted by the proposed model to further verify the validation of the model. Finally, structural deflection prediction of the test tower was conducted in ANSYS based on the proposed joint-slippage model. The predicted tower deflections were in good agreement with the test results.

The Effect of Nonlinear Behavior of Bolted Connections on Dynamic Analysis of Steel Transmission Towers

Transmission towers are kinds of complex lattice structures which affects their accurate modeling and analysis and brings about some problems in the prediction of their actual behavior. For this reason, full-scale experiments are usually applied for transmission towers to examine their resistance and control their behavior. In this paper, the displacements of a transmission tower in the full-scale test, including effective parameters such as geometric and material nonlinearity and joint slip effect are attained applying the developed nonlinear analysis software. These displacements for four cases of analysis: linear, geometric nonlinear, geometric and material nonlinear and lastly, geometric and material nonlinear along with joint slip effect are obtained and compared with the results of the full-scale test. In this comparison, the results of geometric and material nonlinear analysis along with joint slip effect coincide well with the results of the full-scale experiment which demonstrates the joint slip effect importance and the capability of developed software. Finally, the tower natural frequencies are obtained and it is obvious that taking the joint slip effect into account of the analysis reduces the natural frequencies of the tower as a significant parameter in the dynamic analysis of these kind of structures either individually or as coupled system along with conductors.

Predicting remaining life of lattice steel transmission tower based on condition assessment and corrosion hazard data

This paper presents a novel approach for predicting the remaining life of lattice steel transmission towers in Malaysia. The transmission tower components assessment grouped into ground corrosive condition, foundation condition, lattice steel body of the tower, and conductor. Significant and scientific field investigation and visual assessment evaluate the state of the tower. The corrosion hazard, which is a product of climate and air pollution data, is used. Three separated lines and 84 towers were selected with different ages of the tower in service. The Weighing Scoring Method with Analytical Hierarchy Process to impose the weighed factor was used. The survival function analysis is used to predict service life, and the tower remaining life was determined. The paper shows how to use the model to predict the remaining life of a transmission tower and how this can be used to advise maintenance planning.

Structural Analysis of Steel Transmission Towers for Large River Crossing of Overhead Transmission Lines

This study aims to investigate the structural behavior of steel transmission towers used for large river crossings. Design standards usually applied to analyze these structures don’t consider situations in which the transmission towers are used in river crossings. In Brazil, due to the fact that it is necessary to cross large areas owing to the rivers’ size, these towers assume great heights. It should be noted that the towers can weigh up to 24,500kN and exceed 300m in height. The current study develops an analysis that surpasses the existing standard methodologies, aiming for a structural optimization compatible with vast crossings and new materials, aiming to resolve this design challenge regarding power transmission lines. To do this, a river crossing spanning 2,300m, situated in the northern region of Brazil, was studied based on the use of three different conductor configurations, electrically equivalent, commonly used wind design standards, and structural solutions utilizing tubular and angle profiles.