Lattice Towers Research Articles

A new open‐database benchmark structure for vibration‐based Structural Health Monitoring

Vibration-based Structural Health Monitoring is an ongoing field of research in many engineering disciplines. As for civil engineering, plenty of experimental structures have been erected in the past decades, both under laboratory and real-life conditions. Some of these facilities became a benchmark for different kinds of methods associated with Structural Health Monitoring such as damage analysis and Operational Modal Analysis, which led to fruitful developments in the global research community. When it comes to the continuous monitoring and assessment of the structural integrity of mechanical systems exposed to environmental and operational variability, the robustness and adaptability of the applied methods is of utmost importance. Such properties cannot be fully evaluated under laboratory conditions, which highlights the necessity of outdoor measurement campaigns. To this end, we introduce a test facility for Structural Health Monitoring comprising a lattice tower exposed to realistic conditions and featuring multiple reversible damage mechanisms. The structure located near Hanover in Northern Germany is densely equipped with sensors to capture the structural dynamics. The environmental conditions are monitored in parallel. The obtained continuous measurement data can be accessed online in an open repository. That is the foundation for benchmarks, consisting of a growing data set that enables the development, evaluation, and comparison of Structural Health Monitoring strategies and methods. In this article, we offer a documentation of the test facility and the data acquisition system. Lastly, we characterize the structural dynamics with the help of a finite element model and by analyzing several month of data.

Load-slip behaviour of single-leg bolted angle steel connections at elevated temperatures

Steel lattice transmission towers and communication towers are vital infrastructure components of power grid and telecommunication systems, respectively. They are usually located in rural or urban wildland areas and can be prone to bushfires or wildland fires in the current climate of heatwaves and droughts. However, an understanding of the resilience of steel lattice towers in fire has not received due attention. Such lattice structures are commonly made from steel angle members with bolted connections in which slippage might occur inevitably due to relatively larger size of bolt holes for erection purpose. Therefore, this paper investigates the axial load-slip behaviour of the single-leg bolted angle steel connections at elevated temperatures for the steel lattice structures. A three-dimensional finite element model is developed for the investigation by using ABAQUS software. Temperature-dependent material nonlinearities and the interaction of structural components at elevated temperatures are taken into account in the model. An effective approach of generating bolt pretension and the quasi-static analysis method using the dynamic explicit procedure are adopted for the analysis. The reliability of the developed finite element model is validated by comparing its predictions with available experimental results reported in the open literature. By using the validated finite element model, extensive parametric studies are conducted to elucidate the effects of the change in the angle section dimension, the direction of applied loading, the grade, size and number of the bolts on the load-slip responses of the connections at elevated temperatures. A simplified theoretical model in component formulation form is proposed and verified for predicting the axial load-slip curves of the single-leg bolted angle steel connections at elevated temperatures and would be applicable to advanced analysis of steel lattice structures considering joint slip.

Comparison of the Influence of Double-Limb Double-Plate Joint on the Stability Bearing Capacity of Triangular and Quadrilateral Transmission Tower Structures

The axial stiffness of the connection joints in a transmission tower will affect the stability bearing capacity of the tower. The axial stiffness of different forms of connection joints has different effects on the stability bearing capacities of triangular and quadrilateral lattice towers. This paper takes triangular and quadrilateral lattice towers as the comparative research objects and considers the influence of the stiffness of the single-limb, single-plate joint (SLSPJ) and double-limb, double-plate joint (DLDPJ) of the tower. Under vertical load, the vertical stability bearing capacities of triangular and quadrilateral transmission towers are studied from hte three aspects of theoretical analysis, numerical simulation and test result analysis. The influence rules of the SLSPJ and DLDPJ on the vertical stability bearing capacities of triangular and quadrilateral transmission towers are clarified. Through the energy method, considering the influence of the axial stiffness of connection joints, the calculation expressions of the vertical stability bearing capacities of triangular and quadrilateral lattice towers are derived. Through quantitative analysis, it is found that the axial stiffness of the connection joints has a more significant influence on the vertical stability bearing capacities of triangular lattice towers. The finite element models of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are further established. Through nonlinear finite element analysis, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 22.7% and the quadrilateral lattice tower by 14.9%. Through theoretical calculation, the expressions of the vertical stability bearing capacities of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are obtained. Combined with the test results of the SLSPJ and DLDPJ, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 23.4% and the quadrilateral lattice tower by 15.6%. The research results show that the DLDPJ can improve the vertical stability bearing capacities of triangular and quadrilateral lattice towers. The improvement effect of the vertical stability bearing capacity of the triangular lattice tower is 1.50∼1.52 times that of the quadrilateral lattice tower. The research results can provide a reference for the engineering popularization, application, and design of the DLDPJ in transmission towers.

Joint Slip Formulation for Members with Double Angle Section Based on Experimental Results in Wind Turbine Lattice Towers

Joint Slip Formulation for Members with Double Angle Section Based on Experimental Results in Wind Turbine Lattice Towers

Corrosion Damage to Joints of Lattice Towers Designed from Weathering Steels

The article dealt with the load-bearing capacity and durability of power line lattice towers designed from weathering steel. Attention was paid in particular to the bolted lap joints. The article evaluates the static and corrosion performance of bolted lap joints in long-term operating towers, and also presents and evaluates design measures that can be applied in the design of new lattice towers, or in the reconstruction of already operating structures. Power line lattice towers are the most extensive realization of weathering steel in the Czech Republic. On the basis of the inspections carried out to evaluate the working life of the transmission towers in operation, it can be stated that a sufficiently protective layer of corrosion products generally developed on the bearing elements of the transmission towers. However, the development of crevice corrosion at the bolted joints of the leg members is a significant problem. In this paper, the corrosion damage of bolted joints was evaluated considering two basic aspects: (1) the influence of crevice corrosion on the bearing capacity of the bolted joint was evaluated, using experimental testing and based on analytical and numerical calculations; (2) appropriate design measures applicable to the rehabilitation of developed crevice corrosion of in-service structures, or the elimination of crevice corrosion in newly designed lattice towers, was evaluated. Calculation analyses and destructive tests of bolted joints show that the development of corrosion products in the crevice does not have a significant effect on the bearing capacity of the joint, provided that there is no significant corrosion weakening of the structural elements, and bolts of class 8.8 or 10.9 are used. The results of the long-term experimental programme, and the experience from the rehabilitations carried out, show that, thanks to appropriate structural measures, specified in detail in the paper, the long-term reliable behaviour of the lattice towers structures is ensured.

Structural design of a lattice pykrete tower

Pykrete is a material used for temporary structures in cold environments. In the last decade, this material has generally been used in shell structures that were constructed using inflatable fabric formwork and ropes. Recently, research has been carried out to use pykrete in structures made of linear elements and some structures of low heights have been able to be built.A pykrete tower-like structure was built in 2019 for the International Ice and Snow Innovation Design and Construction competition, based on a proposal made by the Eindhoven University of Technology. This structure raised to 11 m, making it the tallest pykrete structure with linear elements built so far. This paper describes the base concepts, design process, testing methodology and building methods of this tower.

Numerical and full-scale test case studies on post-elastic performance of transmission towers

Post-elastic capacity of transmission tower is critical for the realistic assessment of tower vulnerability under the extreme loading conditions. This paper first presented a series of numerical simulations of a lattice transmission tower section under torsional (longitudinal) or bending (transverse) loading in both static and dynamic scenarios. From the results of the numerical simulations, four prototypes of lattice transmission towers were constructed and tested for the investigation of the post-elastic performances of the towers under different loading conditions. The tests results showed that there existed significant post-elastic strength reserve of the tower under investigation. For the towers tested in this research, the post-elastic strength reserve was 1.22 for flexure-torsion (i.e. tower under longitudinal loading) governed by diagonals, and 1.37 for bending (i.e. tower in transverse loading) governed by inelastic buckling of the main legs. Diagonal members affected the failure modes of transmission towers and their connection design may be a weak link in the development of their post-elastic capacity.

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.

Static and dynamic analysis of telecommunication towers subjected to wind

The expansion of the telecommunications sector in Brazil in recent years and the consequent increase in demand for telecommunication towers open space for a discussion about the guidelines to be taken during the execution of projects of this type of structure. Because they are light and slender structures, wind loads become preponderant for the design of these towers and wind analysis is an important topic to be discussed. Thus, this work analyzes design aspects employing numerical modeling and parametric studies. The Brazilian standard NBR 6123:1988 was used to obtain the wind speed and its static and dynamic loads, to compare the responses generated by each of the methods. Then, this process was repeated following the European standard IEC 60826:2017, to compare the results between the two standards methods. A parametric study was also performed with towers of different heights to better understand the structure behavior. The tower responses were obtained using the finite element software SAP2000, in which a lattice tower model with a constant square section was developed, to which the wind loads calculated according to the aforementioned standards were applied. The results showed that each analysis method generates considerably different results, revealing that this is a point that should be very well studied during the design of telecommunication towers.

Finite element analysis of edge gripper processing of carbon fiber composite cables

Light-weighted and high-strength CFRP cables are increasingly being used to increase the transmission capacity and improve the sag of suspended transmission line. CFRP cables are covered with aluminum and steel layers in sequence and compressed with a dies when the conductor is connected to the lattice tower. In the process, a mechanism that transmits a tensile load from the metal part to CFRP was implemented by utilizing the plastic deformation of aluminum and steel and the elastic deformation of CFRP. In this study, damage to CFRP cables that occurs during the processing of an edge gripper was simulated by a finite element analysis (FEA). A three-dimensional (3D) matrix of Hashin’s theory was coded, and a 3D damage analysis using Abaqus, a generic FEA software suite, was conducted. The analysis was carried out with a model that uses the dimensions of each material as parameters to discuss the relationship between the damage on the CFRP cable that may occur during the edge gripper processing and the gripping force generated.

Determining the Optimal Scalar Intensity Measure of Floor Communication Towers

Various structural types and ground motion characteristics lead to distinct intensity measures of structural seismic performance. For the lattice high-rise steel structure of communication towers, determining the intensity measures to adjust ground motion is critical. Additionally, a crucial problem is whether the ground motion intensity parameters of pulse-like ground motion and ordinary ground motion are consistent. In this study, a standard floor four-leg angle steeled communication tower was considered the study object, and 50 pulse-like ground motions and 50 ordinary ground motions were identified to form a pulse-like ground motion set and ordinary ground motion set, respectively. For comparative analyses, 15 ground motion parameters, including amplitude, spectrum, duration, and energy parameters, were selected. The results revealed that for the lattice towers, such as communication tower, under the action of pulse-like ground motion or ordinary ground motion, efficiency, practicability, and sufficiency should be considered. Furthermore, the most suitable intensity measure was the spectral acceleration corresponding to the natural period of the tower. This study provides a basis for selecting the ground motion for dynamic time history analysis of the lattice steel tower.

Optimization of Antenna Lattice Towers using Genetic Algorithm

Optimization of Antenna Lattice Towers using Genetic Algorithm

Load-Sway Control for Rotary Crane Considering Torsional Deformations of Vertical Jib

Large rotary cranes have a lattice structure tower boom which causes torsional deformation when transporting heavy loads. Therefore, it is necessary to design a controller that takes into account the torsion of the tower boom to control the load-sway and position of the jib. This study proposes a linear state-space model of rotary cranes that takes into account the torsion of the tower boom which stands vertically, and designs a controller using this model. Both simulation and experimental results are investigated to illustrate the superior performance of the controller designed in this study.

Weight optimization of steel lattice transmission towers based on Differential Evolution and machine learning classification technique

Transmission towers are tall structures used to support overhead power lines. They play an important role in the electrical grids. There are several types of transmission towers in which lattice towers are the most common type. Designing steel lattice transmission towers is a challenging task for structural engineers due to a large number of members. Therefore, discovering effective ways to design lattice towers has attracted the interest of researchers. This paper presents a method that integrates Differential Evolution (DE), a powerful optimization algorithm, and a machine learning classification model to minimize the weight of steel lattice towers. A classification model based on the Adaptive Boosting algorithm is developed in order to eliminate unpromising candidates during the optimization process. A feature handling technique is also introduced to improve the model quality. An illustrated example of a 160-bar tower is conducted to demonstrate the efficiency of the proposed method. The results show that the application of the Adaptive Boosting model saves about 38% of the structural analyses. As a result, the proposed method is 1.5 times faster than the original DE algorithm. In comparison with other algorithms, the proposed method obtains the same optimal weight with the least number of structural analyses.

Wind load investigation of self-supported lattice transmission tower based on wind tunnel tests

Through a series of wind tunnel tests on a self-supported lattice transmission tower model, the wind loads on the tower were investigated in this paper. According to similarity laws, the scaled tower model was designed and fabricated, and the atmospheric boundary layer wind field of Category-B specified in Chinese load code was simulated in the wind tunnel laboratory. Based on the aeroelastic wind tunnel tests and the high frequency force balance tests, the dynamic vibrations, the nondimensional wind force coefficients and the generalized power spectral densities (PSDs) of dynamic wind forces were analyzed and discussed. For the convenient application, the empirical formulas of the generalized PSDs of dynamic wind forces were established and the nonlinear mode shape correction was introduced, which were verified via comparison between the aeroelastic tests and the calculated dynamic responses of tower top. It is indicated that the unfavorable wind attack angles may happen around θ = [15° 30°] and θ = [60° 75°] for this type of tower; the generalized PSDs of wind forces are unimodal in shape, and the corresponding effective bandwidths and the nondimensional frequencies of peaks vary with the wind attack angle θ, especially those of the cross-wind forces are larger than those of the along-wind forces obviously; the established empirical formulas of the generalized PSDs of dynamic wind forces and the derived nonlinear mode shape correction factor are applicable.

Design recommendations for the stability of transmission steel lattice towers

Lattice towers are extensively built in Europe and worldwide to serve telecommunication or power transmission purposes. Their members are usually made of equal leg angle profiles that are bolted at their extremities. Such types of towers are mainly designed to EN 1993-3-1 and EN 50341-1, based on a first-order linear elastic structural analysis of a truss structure. In this paper, an assessment of the current design approach is performed, where the tower has been simulated with a full non-linear finite element software, considering relevant imperfections as well as geometrical and material non-linearities. The importance of the second order effects in the analysis is underlined while the existence of an instability mode not properly covered directly by the norms, and usually therefore not checked, is highlighted. Two analytical models for the prediction of the critical load of this buckling mode are proposed and validated numerically. Both proposed models are rather easy to apply and may fill the gap in the existing design recommendations for lattice towers.

Design Study of Multi-Rotor and Multi-Generator Wind Turbine with Lattice Tower—A Mechatronic Approach

New locations for onshore technology, which have not been considered so far, must be developed to increase the total installed capacity of renewable energies, especially wind energy. For this purpose, cost-effective wind turbines, even in difficult-to-access locations, such as mountainous and high-mountainous areas, must be designed. This paper presents a novel wind turbine with a related control system that meets these requirements. The proposed turbine uses a multi-rotor configuration with five rotors arranged in a star shape configuration. Each rotor drive train combines up to 12 generators in a maintenance-friendly multi-generator concept. A suitable observer-based control for load mitigation in the full-load region is proposed for the multi-rotor and multi-generator design. Simulations are used to demonstrate the applicability and practical benefits of this concept.

Reliability-Based Approach for Fragility Analysis of Lattice Transmission Tower in the Type Test

Precise prediction of the structural capacity of lattice transmission towers under various loads is essential to assess the reliability of the transmission network accurately. In doing so, the uncertainties inherent in the modeling parameters of the towers need to be taken into account. In this paper, a probabilistic framework is developed to analyze the failure of a 230 kV double-circuit tower in full-scale type test accounting for the uncertainties including eccentricity at the connections, joint slippage, and initial imperfection in the members. Three loading patterns are applied to the manufactured full-scale tension tower. A finite element model of the tower with consideration of mentioned uncertainties is built and verified by the test results. The importance vectors derived from reliability analysis clarifiy the effect of each of these parameters on the target points' displacement, as well as the maximum load carrying capacity in towers' members for these load patterns. Besides, the additional moments due to eccentricity at the connections are considered by a proposed regression-based equation. The failure probability of the tested tower is determined for various load factors, and the results are presented in terms of fragility curves. Besides, the effect of eccentricity on the tower’s failure is quantified.

Performance based assessment of transmission lines to seismic events

Typical transmission line steel lattice towers are not designed for seismic excitations, based on the assumption that their ultimate limit state is governed by climatic actions (wind and ice). However, it is not unusual for line inspection reports to indicate the observation of moderate to severe structural damages after intense ground motions, which can ultimately reduce the capacity of tower elements. Performance-Based Earthquake Engineering (PBEE) assessment is a modern technique to earthquake resistant design frequently adopted for building frame structures, but not yet employed in the design of transmission line supports, to the best of the authors’ knowledge. The present article evaluates the seismic performance of two typical 230kV transmission towers in a PBEE framework, considering artificial and actual ground motions based on Chilean seismicity. Time-domain nonlinear dynamic analysis is employed to numerically obtain tower responses considering distinct earthquake loading scenarios according to two model configurations: stand-alone and tower-line section. Significant structural damage was detected even for moderate ground motions, which might reduce the tower capacity to future climatic events. The estimated failure probability for the ultimate limit state was found greater than the recommended values in the standard IEC 60826 (2017).

A member-based porous method for predicting flow distortions around a lattice tower

In the wind field measurement, the readings of an anemometer mounted on a lattice tower will be influenced by the tower. Therefore, evaluation of the flow distortions generated by a lattice tower is essential for correcting the wind speed data or guiding the arrangement of anemometers. Wall-refined CFD is a powerful tool to simulate the flow field but is quite time consuming for lattice structures. As an alternative approach for improving the computational efficiency of CFD, a member-based porous method was proposed by this article. It employs porous zones to substitute the real members of a lattice tower, so that the computational resources can be considerably saved. Wind tunnel test of two lattice tower segments were conducted to validate the member-based porous method. Models of wall-refined CFD were also established. Results of the member-based porous method are in acceptable agreement with those of test and wall-refined CFD. The method is proved to be an effective way to predict flow distortions of a lattice tower. Both the test and numerical simulations (wall-refined CFD and member-based porous) reveal that disparities exist between the flow field of different measurement planes. The results highlight the need to consider the impacts of member arrangement in predictions of the flow distortion. At last, some crucial issues on the flow distortion effects of a lattice tower were also discussed, results of the classic theoretical methods were compared with those of the member-based porous method.