Self-supporting Towers Research Articles

Dynamic properties of an aeroelastic transmission tower subjected to synoptic and downburst-like outflows

Electrical transmission towers can be vulnerable to high intensity non-synoptic wind events such as downbursts. This paper compares the wind-induced response of a single self-supported transmission tower subjected to experimentally produced downburst outflows and synoptic (i.e., atmospheric boundary layer (ABL)) winds. Wind tunnel tests were carried out on a 1:50 aeroelastic model of the tower. A similar mean wind speed was produced at 1/6th of tower height and tower height in the downburst and synoptic simulations, respectively. Lower drag coefficients were observed under downburst winds in comparison to synoptic winds for the case tested. Lower peak base shear and base moments were subsequently observed in the downburst case. However, the results indicate that the base dynamic response of a self-supported tower can be slightly higher under downburst wind loads in comparison to synoptic winds. Higher dynamic amplification factors (DAF) and deviations from the mean were observed in the base dynamic response to downburst winds in comparison to the synoptic case. This indicates that self-supported towers can be subjected to more wind-induced vibrations under downburst winds with similar peak wind speeds as the synoptic winds.

Seismic analysis of a full scaled self-supported tower using ambient vibration testing

Seismic analysis of a full scaled self-supported tower using ambient vibration testing

Reliability assessment of guyed transmission towers through active learning metamodeling and progressive collapse simulation

This manuscript presents a novel approach to the reliability of guyed transmission line towers (TLTs) considering complete geometric and material non-linear analyses, bolt slippage effects, and progressive collapse simulation, using active learning Kriging to handle the computational burden. In the existing literature, such issues have been considered separately, with the main focus on self-supporting towers. Herein, novelty arises from the combined consideration of the above and the addressing of guyed TLTs. Yet, because the wind speed variability is much higher than those related to the mechanical model, a modified initial sampling plan strategy is successfully proposed to reduce the computational time required. The application case-study addressing long transmission lines in midwest Brazil is also relevant, considering the recent updating of design wind speeds, with increases of up to 25%. Failure probabilities obtained using code resistance models indicate the need for tower retrofitting. However, the more accurate assessment via collapse simulation shows that the support is still safe, even for the updated wind speeds. Results demonstrate the accuracy and efficiency of the proposed analysis framework and show the importance of using accurate numerical models in retrofit evaluations.

Study on Wind-Induced Response of Transmission Tower-Line System under Downburst Wind

Downburst is the main source of extreme wind speed in non-typhoon areas, which has caused a large amount of transmission line damage all over the world. In order to reveal the wind-induced vibration response characteristics of a transmission tower-line system under downburst, the nonlinear dynamic analysis of a single tower and tower-line system is carried out, and the amplification effect of tower-line coupling and fluctuating wind on the dynamic response is studied. Then, the effects of three wind field parameters closely related to the average wind profile on the wind-induced response of the tower-line system are studied. The results show that under the action of the downburst, the tower-line coupling weakens the dynamic response to a certain extent, and the dynamic amplification factor of a single tower and tower-line system is 1.1 ~ 1.3; for the self-supporting tower, when the height of the peak wind speed is close to the height of tower, the responses of the structure are more unfavorable. When the vector superposition method is used, the storm moving speed (Vt) has little effect on the wind-induced response of the tower-line system. For large-span structures such as tower-line systems, to ensure the safety of the structural design, the value of the characteristic radius (Rc) should not be too small.

ANALYTICAL STUDY ON VARIOUS BRACING SYSTEM FOR TRANSMISSION TOWER

Transmission line towers and monopoles. Transmission line towers and monopoles are often used for high steel structures used for electric transmission. The transmission line tower or monopole should be carefully planned so that they won't fail over their whole lifespan and should be followed both nationally and internationally. This paper describes the transmission tower for different spans, such as 3m, 5m, 7m, and 9m, and with 3 types of bracing systems (K, X, and K & X). Comparing each brace with each other and observing the displacement of each tower to bring out the best self-supporting and most economical transmission tower based on the displacement values. The results show that displacement was observed to be high in K-bracing and low in K & X bracing combined. Keywords. Transmission tower, K-bracing, X-bracing, K & X bracing.

Aeroelastic modeling to study the wind-induced response of a self-supported lattice tower

The results from a 1:50 scale aeroelastic model of a self-supported steel lattice tower subjected to simulated hurricane winds are presented. The lattice tower considered is a typical structure that is used as part of a tower-insulator-conductor system for electrical transmission infrastructure. The aeroelastic tests were conducted at the NSF Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). The tower was tested at various wind speeds ranging from 50 m/s to 92 m/s (equivalent full-scale speeds) for varying wind directions. Two system identification (SID) techniques were utilized to evaluate along-wind aerodynamic damping and compare with theoretical estimates. The SID techniques were also utilized to evaluate crosswind aerodynamic damping. A buffeting analysis was conducted to estimate the response of the tower and compare it to measured values at the WOW. Drag and moment coefficients were calculated from the measured responses, and the dynamic amplification factors (DAF) as well as gust effect factors were computed. The analysis required consideration of the variation of the turbulence intensity along the height of the tower in the buffeting analytical equations. The drag coefficients are shown to agree with values proposed in the current standards. However, there might be a need to introduce base moment coefficients in lattice tower design. The resonance contribution is shown to reach a maximum of 18% of the peak response of the tower.

Structural Optimization and Experimental Research of High-rise Guyed Tower

In this paper, the structural optimization of high-rise guyed tower is carried out for the guyed wire and tower column schemes. The schemes are compared from the four guyed wires and eight guyed wires, the width of the tower column, the uniform cross-section tower column and the variable cross-section tower column, etc. And the single-column tower with eight guyed wires and variable cross-section is recommended for the high-rise guyed tower. Through the full-scale test study of the high-rise guyed tower, the safety of the high-rise guyed tower structural optimization and the feasibility of engineering application are verified. According to the technical and economic analysis of traditional self-supporting towers and high-rise guyed towers recommended in this paper, it can be seen that the weight and total cost of the high-rise guyed towers are 75.3% and 88.5% of the traditional self-supporting towers respectively, demonstrating the technical and economic advantages of the high-rise guyed towers. The advantages and disadvantages of high-rise guyed towers and self-supporting towers are summarized for reference in engineering design.

Comparison of the Canadian standard and other standards for wind loading on self-supporting telecommunication towers

Designing telecommunication towers to withstand wind loads requires specific considerations, which has led the international civil engineering community to develop specific standards for these structures. The recent internationalization of the construction business has made it imperative for engineers to acquire knowledge and interpretation of codes from different countries. In light of the 2018 update of Canadian Standard CSA-S37-18 (CSA), evaluating its differences against other international standards for telecommunication towers has become important. This paper presents a comparison of the wind loading specifications for self-supporting telecommunication towers according to CSA; Australian Standard; Eurocode EN-1993-1; and US Standard TIA-222-G. The different standards have also been evaluated with respect to the values of the axial forces and the elements ratio for two self-supporting telecommunication towers. The parameters related to the wind profiles and the gust effect factor presented the highest difference between the standards.

Dynamic analysis of self-supported tower under hurricane wind conditions

Self-supported telecommunication towers are very important structures in the infrastructure of countries. These structures are highly sensitive to the dynamic effects of wind loads. Several self-supported telecommunication towers have collapsed in Cuba during the last decades due to strong hurricane winds, causing important economic and social losses. The aim of this work is to compare the structural response of a self-supported tower in terms of internal forces and displacements by static equivalent and full dynamic time history methods, taking into account hurricane wind conditions. The static equivalent method used in this paper was Gust Response Factor with the formulation proposed in Eurocode EC 3: Part 3-1. Time history analysis was performed using generated simulated wind data obtained through Montecarlo’s technique and the turbulent component of the velocity was obtained by the formula presented by Shinozuka and Jan. Turbulence parameters, such as power spectral density function, integral scale and turbulence variance were assumed in accordance with the international literature on structural monitoring subjected to hurricane action. A 60m high lattice tower having a square in-plane cross-section was studied. Forces on members and displacements on the tower were found to be 20–25% higher when applying the static equivalent method, as compared to time history method.

Behavior of Self-Supporting Communication Tower under Horizontal Loads

Communication towers have been traditionally designed for wind load. The earthquake load has not been observed in the analysis of the communication tower. Recent earthquakes, there have been indications of collapse to the communication tower. Due to the complex nature of the problem, there is a lack of research work in the area of analysis of the communication tower. The purpose of this research is to test the communication tower's response to earthquake ground movement to determine the current design software methodology. The effect of earthquake ground motion spatial variation on multi-support structures dynamic response may be necessary. The aim of this project is to use the traveling wave assumption to investigate the seismic response of high antenna-supporting guyed towers. The horizontal component of the Bhuj earthquake is considered as excitation. Elements of response analyzed are cable tension, base shear, mast axial force and lateral displacement of the tower tip. Parametric analyses show that the structural response tends to increase as the amplitude of the wave decreases and can become much larger than the reaction from synchronous excitation.

Behaviour of Self-Supporting Communication Tower Subjected to Wind Load

The main objective of the Project is the “Behaviour Of Self-Supporting Communication Tower Subjected To Wind Load” The thesis deals with the study of the behaviours of self supporting tower under static and dynamic loading cases. The study is extended for the behaviour of tower in both face and corner wind0cases. As wind force plays a major role as far as loading is considered in tall structures. For the details study of this project a case study is done0considering a 100m high self supporting tower. In addition to the wind loading the loads of the communication antennas that will come on the tower are also considered. It describes the wind load calculations, analysis procedure and design of tower members. The tower is analyzed for both corner wind and face wind directions. Analysis if performed using SAP 80/90. The basic activity starts with modelling of the tower. Modelling of tower is an assembly structure with different configuration parts stands one above the other, each we call it as BAY. For this come typical bay types are formatted which could be used as data for generation of tower configuration. These typical configurations shall help in generation0of easy model with different options in achieving the required parameters of optimum design results of0minimum tonnage of the total structure with allowable deflections at maximum wind in both static and dynamic cases. Wind load and antenna load calculations0are carried out by using ‘C’ program. Tower configuration, wind load calculations on tower, dimensions and properties of the tower (input to ‘C’) are explained by taking typical Bay-1. For analysis of tower, the required formatted input for Structural0Analysis Program (SAP) is obtained by ‘C’) program output. Member forces are obtained by genol 1.f3f file (SAP output file). All tower members are designed as axially0loaded compression members as per standard specifications. Design of members are carried out for maximum0member forces obtained by both corner and face wind analysis. If capacity of member is less than member force higher sections0are selected and analysis & design is carried out until member capacity is more than member force. Output (analysis & design data for all members is obtained using member0forces file and “Design” C program file. This output is shown in Tables. Foundation forces and joint displacements are obtained by SAP output file (genol.sol) and the maximum deflection is checked as per specifications. In the tower structures, the leg members are governed0when the wind acts in corner direction. Similarly the horizontal and diagonal members are governed when wind acts in face direction. The results tabulated shows0the forces that are changing in static and dynamic loading.

Optimization Design of Transmission Tower Based on Intelligent Selection

In this work, the optimal design method for self-supporting transmission tower is put forward, whose procedure is that the tower body form is selected intelligently firstly and then the members types of tower are chosen. The case base of towers is established with application of object-oriented technology. Then, the knowledge of tower body is mined out with case based reasoning and data mining technology. At the same time, the structural regulations of tower in the standard are merged into the knowledge base. So, the intelligent selection system of tower structural scheme based on case reasoning and data mining is explored. A 500kV self-supporting tower is optimized according to above method and a real model test is conducted. Comparison between optimal tower and original tower indicates that weight of optimal tower is decreased by 3% and its ultimate bearing capacity is increased by 19%. Statistical analysis results of 20 optimal towers indicates that the weight is average reduced by 4.7%, the components of the optimal tower are stressed more uniformly and bearing capacity of the tower is enhanced 12% at least.

Buckling Analysis of Transmission Tower Considering Ice Load

Transmission lines are important lifeline projects. The stable operation of transmission lines is closely related to economic and social security and stability. Ice storm seriously affects the safety of transmission lines. The simulation analysis of ice damage of transmission tower structure has important theoretical significance and engineering value. In this paper, the finite element software ANSYS is used to analyze the buckling of the self-supporting tower based on eigenvalue buckling analysis and nonlinear buckling analysis. The effects of vertical span, uniform ice coating, uneven ice coating, and wind load were considered. The ice thickness of the tower buckling is reduced with the vertical span decreasing under uniform ice coating the transmission line. As the coefficient of unevenness increases, the thickness of the unstable ice coating of the tower drops sharply. The unstable wind speed decreases with the increase of ice thickness.

Estudio comparativo de normas para el análisis dinámico de una torre autosoportada bajo carga de viento

El estudio de los métodos de análisis dinámicos para la consideración de la carga de viento es de gran importancia en las torres autosoportadas de telecomunicaciones debido a que son estructuras altamente vulnerables a los vientos extremos. En Cuba el análisis de las torres autosoportadas se realiza según lo establecido en la norma cubana de viento NC-285:2003 (NC). Esta norma es de carácter general para todas las edificaciones y no presenta las particularidades del análisis de las torres reticuladas bajo carga de viento por esta razón es necesario evaluar sus diferencias con respecto a otras normas internacionales. El presente trabajo tiene como objetivo comparar los valores de fuerzas en los elementos y desplazamientos en una torre autosoportada obtenidos de la aplicación de los métodos de análisis propuestos en las normas NC, ISO 4354- 2009 (ISO), AS/NZS1170.2-2011 (AS/NZ) y EC3: 2007 (EC3). La comparación entre las normas arrojó como resultado que las fuerzas axiales y desplazamientos obtenidos por la norma NC son menores que las obtenidos por las normas ISO, AS/NZ, EC3.

Dynamic Response of Self-Supported Power Transmission Tower Subjected to Wind Action

A power transmission tower carries electrical transmission conductor at adequate distance from the ground. It must withstand all nature’s forces besides its self-weight. In structural analysis, natural frequency, mode shape and damping ratio are used to define the structural dynamic properties which relate to the basic structural features. This paper described the dynamic analysis including the modal and the time history analysis on each segment of the self-supported transmission tower to understand its dynamic responses subjected to wind action. The factors such as different height above ground, a different value of wind speed and different wind angle of attack were included in this study to see the influence of those factors towards dynamic response of the structure. The contribution of the wind towards the displacement of the structure is determined in this study by comparing the result obtained in a linear static analysis which considered the load combination without and with the presence of wind action. It was found that displacement using dynamic analysis is bigger than static linear analysis. The result illustrates that the studied factors gave a significant effect on the dynamic response of the structure and the findings indicate that dynamic analysis is vital in structural design.

Effects of Subsoil Characteristics on the Earthquake Loading of Steel Lattice Telecommunication Towers in the South Asia

Self-supporting lattice towers, which are having quite a few unique structural features, play a vital role in communication networks. Ensuring structural stability of these giant structures under all possible natural and human threats are vital as failures of such structures may cause a catastrophic human & property damages. Further, possible communication outages caused by failure of tower/towers in disaster situation are a critical as it may hamper rescue and other emergency operations. This was experienced by South and South East Asian countries during 2004 Tsunami. Hence, need of mitigating these situations have been highlighted by various reports. Therefore, ensuring structural integrity of self-supporting lattice towers under seismic forces is an essential and timely need. This paper discusses a seismic performance of four leg and three leg lattice towers under Response Spectrum analysis under different sub soil conditions. Results of seismic analyseshas also been compared with wind analyses results.

A Study on Wind and Non-Linear Dynamic Analysis of Self-Supporting Telecommunication Tower

A Study on Wind and Non-Linear Dynamic Analysis of Self-Supporting Telecommunication Tower

A model for the determination of the critical buckling load of self-supporting lattice towers

Most tall columns under axial load fail by buckling. Considering the widespread use of this type of structure and the critical role it plays in service delivery, its failure will result in possible loss of lives and property and disruption of services. It is therefore necessary to evolve alternative methods of determination of the buckling load of self-supporting lattice towers. This paper therefore proposes a simple model for the determination of the critical buckling load of self- supporting lattice towers. The proposed model idealizes the lattice tower as an equivalent solid beam-column whose cross-sectional-dimensions are the unknowns to be determined. The expression is proposed by the model for the critical buckling load of self- supporting lattice tower, whose equivalent solid beam-column has a dimension b at its free end. The results obtained using the proposed model are shown to be acceptable, with a percentage difference of about0.036% when compared with results obtained using conventional methods. http://dx.doi.org/10.4314/njt.v37i1.8

Comparison of Various Bracing System for Self-Supporting Steel Lattice Structure Towers

This paper deals with the effectiveness of various bracing systems used in lattice towers. Seven types of bracings used in 4-legged square based self-supporting power transmission and telecommunication towers and four types of bracings used in 3-leg triangular based self-supporting telecommunication towers are analyzed. The investigated bracing systems are K, KD, Y, YD, D, XB and X. This study has focused on identifying the economical bracing system for a given range of tower heights. Towers of height 40 to 60 m for telecommunication and 35 m for transmission towers have been analyzed under critical loads such as wind and earthquake loads. The load cases include diagonal wind has been found to be most critical cases for towers. The performance of various bracing system has been identified and reported.

Analysis and strengthening of caisson foundations for uplift loads

Many existing self-supporting towers are built with constant-width caisson foundations. Due to the increased demand to add more antennas to the towers, and more stringent strength requirements in recently revised design standards, many existing caisson foundations require significant strengthening for additional uplift resistance. Although a number of retrofit design solutions are frequently used in practice, there is a lack of literature providing guidelines for the proper analysis of retrofitted foundations. This study proposes a detailed analysis and design methodology to significantly increase the uplift capacity of existing caissons through the use of helical micro piles and reinforced concrete cap beams. Strut-and-tie models are developed and nonlinear finite element analyses are undertaken to verify the behaviour of the proposed design. The overall design methodology is presented in a case study involving an existing tower. The proposed design has a general applicability and is suitable for applications where there is limited space around the existing foundations.