Failure Of Tower Research Articles

18.05: Second‐order effects of cantilever concrete filled double skin tube (CFDST) transmission towers

ABSTRACTConcrete Filled Double Skin Tubes (CFSDT) are an alternative to steel lattice transmission towers for supporting overhead transmission lines due to their many advantages including small footprint, fast construction, easy maintenance and elimination of large number of connections. CFDST transmission towers are tapered cantilever structure consisting of a CFDST pole and steel cross‐arms. Due to high slenderness, one key issue for static design of CFDST poles is the effect of second‐order bending (P‐Delta effect). A parametric study was conducted to investigate the second‐order effects exhibited by the CFDST transmission towers. The main parameters investigated include Horizontal to Vertical Load Ratio (HVLR) which reflects the range of environmental loads such as wind and ice, taper ratio (ratio of the bottom to the top outer diameter of the tower), and Hollow Section Ratio (HSR, ratio of the outer diameter of the inner steel tube to the inner diameter of the outer steel tube). The results of the numerical simulations indicate that the second‐order bending moments at failure of CFDST transmission towers are significant, magnifying the total bending moment by 20% or more of the first‐order bending moments. Based on the results of a parametric numerical investigation of second‐order effects of CFDST transmission tower under different conditions, this paper proposes a simplified analytical equation to estimate the second‐order bending moment.

Stability and Dynamic Analyses of Transmission Tower-Line Systems Subjected to Conductor Breaking

Ice loads exerted on the transmission line can increase the probability of conductor breaking, which will lead to the stability failure of transmission towers. In this paper, a transmission tower-line system is established for two towers and three span lines. Then the nonlinear static stability analysis and nonlinear dynamic stability analysis induced by the conductor breaking are carried out to obtain the load versus displacement curves, while studying the failure modes of the transmission tower-line system. Moreover, the ice load and initial eccentricity are considered in the numerical simulation. In addition, a parametric analysis is performed to investigate the influence of span, insulator length and initial tension force on the stability failure of the system. The results show that the dynamic instability will occur earlier than the static instability due to the dynamic impact effect and conductor breaking with ice loads can lead to the progressive collapse of the transmission tower-line system. Finally, the span length has the greatest effect on the response of transmission tower caused by conductor breaking.

Nonlinear response history analysis and collapse mode study of a wind turbine tower subjected to tropical cyclonic winds

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

The nonlinear analysis of an innovative slit reinforced concrete water tower in seismic regions

Water towers are widely used in our society as one of water distribution facilities within water network systems. In the event of a severe earthquake, however, a single plastic hinge that occurs in a water tower could cause its total collapse before nonlinear resources of the rest of the tower remains fully utilised. This research presents an innovative technique for the assembly of a water tower using the slits in its reinforced concrete shaft for the purpose of mitigating the seismic response. Slit shafts were designed to have four slits at 90° intervals along the full height of the shafts. The shaft parts were connected to each other at the bottom, top and every five meters with coupling beams. The slit width was used as a variable in this study which varied between 50mm and 2000mm. The nonlinear seismic performance of the proposed slit towers was analysed by means of a finite element approach with respect to soil types defined in Eurocode 8 and seismic behaviour were compared to the solid water tower. A detailed observation of the compression and tension stress distributions with respect to the slit width was performed.The obtained analytical results revealed that slit width in the reinforced concrete tower affect the failure mode and stiffness of a water tower significantly. With an appropriate design, the conversion of a solid water tower into a slit tower can significantly increase its ductility under seismic action without significantly compromising its bearing capacity. The results showed that contours of tension and compression stress intensity in shafts, which could lead to a failure of water towers, highly depended on the slit width. In the solid water tower, the stress concentration dominated at the base of the shaft, however in the narrow slit water towers the stresses were equally distributed along the height of the shafts. Also, the stresses were mostly concentrated at the top of the shafts in the wide slit water towers. Conclusively, the results provided useful information regarding the compression stress distribution along the slit shafts in the water towers which can be used in obtaining an optimum slit shaft design for different soil types.

Structural integrity of wind turbines impacted by tropical cyclones: A case study from China

This study presents a case study on wind turbines impacted by tropical cyclones in China. A quantitative investigation is conducted by integrating aerodynamic, aero-elastic and structural analysis to provide insights into structural integrity of wind turbines under extreme wind conditions. Local mean wind profiles at each turbine site are reconstructed using threedimensional CFD calculation considering terrain topography of the wind farm. Failure modes and failure locations of rotor blades and tubular towers are predicted using finite element analysis. “The lesser of two evils” principle in the turbine design is addressed regarding the criticality of blade fracture and tower collapse. Referring to the current IEC standard for wind turbine design, it is suggested that the partial safety factor associated with failure of turbine tower should be larger than, instead of equal to, the one for the rotor blade to reduce the risk of the total loss of wind turbines in extreme wind conditions.

Fatigue Testing and Retrofit Details of High-Mast Lighting Towers

Fatigue cracking has been the cause of a number of high-mast lighting tower (HMLT) failures throughout the United States. In almost every case, forensic evaluations have shown cracking initiates and propagates due to wind-induced fatigue at mainly the base plate–to–tube wall connection detail or the hand-hole weld detail. Simply replacing the towers is not an economically feasible alternative because thousands of HMLTs are in use along major highways across the United States. As a result, strategies to retrofit existing HMLTs are needed. Results from laboratory testing performed on two HMLT retrofit configurations are presented. The retrofit strategies are employed without removing the pole from the foundation using simple bolting techniques and moderately skilled labor, providing cost savings for owners and increasing safety for the motoring public.

An adaptive support vector regression method for structural system reliability assessment and its application to a cable-stayed bridge

Engineering structures are most statically indeterminate structures consisting of various types of components and their failure modes exhibit randomness under random loads. A new adaptive support vector regression method is proposed for structural system reliability assessment. Compared with traditional support vector regression, the proposed adaptive support vector regression method involves two updating procedures to estimate structural limit state functions. Three verification examples involving a nonlinear limit state function, a truss bridge structure, and a geometrically nonlinear suspended structure are provided to illustrate the accuracy and the efficiency of the adaptive support vector regression method. A pre-stressed concrete cable-stayed bridge is utilized to demonstrate the applicability of the proposed method. The verification studies show that the proposed adaptive support vector regression method is an efficient method with reasonable accuracy for problems where closed-form failure functions are not available and the failure sequences exist in the structural system. The main failure sequences of the cable-stayed bridge are identified. The application studies of the cable-stayed bridge indicate that (a) the foremost failure sequence is the strength failure of side-span cables followed by the bending failure of towers and (b) the secondary failure sequence is the strength failure of mid-span cables followed by bending failure of mid-span girders.

A theoretical model of rain–wind–induced in-plane galloping on overhead transmission tower-lines system

Rain–wind–induced galloping phenomenon often occurs on overhead transmission tower-lines system, just as icing galloping and vortex-excited vibration; this kind of instability oscillation can cause power-line breakage or tower failure. However, the existing theoretical models of rain–wind–induced galloping are mainly based on the hypothesis of the overhead power-lines with fixed ends, which is inconsistent with the actual operation situation. Therefore, this article thus presents a preliminary theoretical study and proposes a new theoretical model taking into account the effect of tower excitations on the in-plane galloping of the overhead power-line and on the motion of the upper rain-line. The theoretical model is solved by Galerkin method and verified by the comparison with the test data obtained in the available literature involved with the overhead power-lines with fixed towers or moving towers. It turns out that the tower excitations may intensify the in-plane galloping amplitude of the overhead power-line within a certain range of frequency ratio and enable better comprehension of rain–wind–induced galloping mechanism.

Fundamental aspects on the seismic vulnerability of ancient masonry towers and retrofitting techniques

Ancient masonry towers constitute a relevant part of the cultural heritage of humanity. Their earthquake protection is a topic of great concern among researchers due to the strong damage suffered by these brittle and massive structures through the history. The identification of the seismic behavior and failure of towers under seismic loading is complex. This strongly depends on many factors such as soil characteristics, geometry, mechanical properties of masonry and heavy mass, as well as the earthquake frequency content. A deep understanding of these aspects is the key for the correct seismic vulnerability evaluation of towers and to design the most suitable retrofitting measure. Recent tendencies on the seismic retrofitting of historical structures by means of prestressing are related to the use of smart materials. The most famous cases of application of prestressing in towers were discussed. Compared to horizontal prestressing, vertical post-tensioning is aimed at improving the seismic behavior of towers by reducing damage with the application of an overall distribution of compressive stresses at key locations.

The Weighted Support Vector Machine Based on Hybrid Swarm Intelligence Optimization for Icing Prediction of Transmission Line

Not only can the icing coat on transmission line cause the electrical fault of gap discharge and icing flashover but also it will lead to the mechanical failure of tower, conductor, insulators, and others. It will bring great harm to the people’s daily life and work. Thus, accurate prediction of ice thickness has important significance for power department to control the ice disaster effectively. Based on the analysis of standard support vector machine, this paper presents a weighted support vector machine regression model based on the similarity (WSVR). According to the different importance of samples, this paper introduces the weighted support vector machine and optimizes its parameters by hybrid swarm intelligence optimization algorithm with the particle swarm and ant colony (PSO-ACO), which improves the generalization ability of the model. In the case study, the actual data of ice thickness and climate in a certain area of Hunan province have been used to predict the icing thickness of the area, which verifies the validity and applicability of this proposed method. The predicted results show that the intelligent model proposed in this paper has higher precision and stronger generalization ability.

Numerical Simulation on the Mechanical Performance of the Wind Generator Latticed Concrete-Filled Steel Tubular Tower

Nonlinear finite element parameters analysis on the lattice type steel pipe concrete wind turbine tower, it shows the entire process of load bearing, failure mode and ultimate bearing capacity, researches on the influence law of aspect ratio, form of tower webs, tower diameter to thickness ratio and web member stiffness to tower column stiffness ratio on the ultimate bearing capacity and tower failure mode. The finite element analysis results shows that the tower aspect ratio λ, the diameter-thickness ratio γ of tower columns and the increase of stiffness ratio β between web members and tower columns has great influence on ultimate bearing capacity and failure mode, while the form of webs has small influence on that. with the increase of tower aspect ratio λ, the decrease of diameter-thickness ratio γ of tower columns and the increase of stiffness ratio β between web members and tower columns, the ultimate bearing capacity of this kind of latticed towers increase, the failure mode changed from Web local buckling to The combined damage of Web local buckling and the tension tower yield. This paper suggests that in the design of wind turbulent generator tower, the tower aspect ratio λ should be best controlled at 1/9, the bottom layers of this kind of tower should best use the re-divided web members, and other web member forms used on above layers, the diameter-thickness ratio γ of tower column should be taken less than 30, and the stiffness ratio β between webs and columns should be controlled less than 0.05 in order to avoid damage occurring on the tower columns earlier than the webs. The results can provide evidence for the engineering design.

FE Simulation of Transmission Tower

The vital components of the transmission line are the electrical transmission towers. They are commonly used to support the phase conductors and shield wires of a transmission line. Also the accurate prediction of tower failure is very important for the reliability and safety of the transmission system. The current research describes nonlinear FE models of predicting the transmission tower failure. In the current FE simulations, the eccentricity and the joint effect of the tower were considered. The current models have been calibrated with results from previous full-scale tower tests and numerical models with good accuracy in terms of both the failure load and the failure mode.

Reliability Analysis of Wind Turbine Towers

To increase energy density in order to meet increasing electricity demands, increasingly large-scale designs for wind turbines have been developed. Wind turbine towers of larger sizes can generate more electricity, but such large sizes also create higher costs in terms of development and maintenance. The present research sets up a wind turbine tower model, wherein the loads of towers are calculated by their relation to wind speed. The finite element method is used to analyze the stress distribution of towers under these loads. Impacts from different loads are compared as well. The wind speed distribution is derived from data collected in Penghu, Taiwan using statistical methods. Fatigue analysis of towers is then conducted using fatigue loads and wind speed distribution, and the mean time to failure (MTTF) of towers is calculated with quantitative reliability theory. The results show that the main loads of towers are the wind force acting on the rotation area of wind turbine blades and the moment caused by non-uniform wind speed. After comparing this research finding with loads calculated by a wind turbine design software, it is concluded that it is a feasible and conservative method to analyze a wind turbine tower structure with the loads calculated by its relation to wind speed. In addition, it is shown that both the average and maximum hourly wind speeds in Penghu can be fitted into Weibull distribution. In conclusion, the fatigue analysis shows that the probability is greater than 99.8% for the tower model's failure time to be above 331,416 cycles, and it further shows that the tower model in this research possesses appropriate fatigue durability and is considered a safe tower design for Penghu.

New Methodology of On-Line Monitoring for High Voltage Overhead Transmission Line Icing

In recent years,transmission lines icing leads to failure and accidents,such as large area ice flashover, fittings damaged, line dancing, pole (tower) failure, lines breakage even large-scale power outage, causing serious threat to grid. Nowadays, icing monitoring system mainly relies on detecting the meteorological parameters and the changes of dynamic characteristics for early warning, but the methodologies need additional equipment for data collection. In order to ensure the security and reliability of the grid, a safe, effective and economical methodology of monitoring transmission lines icing has great significance. The project proposed a Transmission Line Icing monitoring principle and algorithm, the method based only on the voltage and current from both ends of transmission lines can be generated dynamically monitoring criterion line icing. According to the criterion maximum, line icing center area, extent and severity can be recognized. The criterion of the method is used as a mathematical scanner, swept from one end of the line to the other end, comprehensive judgments are made on the basis of comprehensive criteria for integrated maximum value, thus the method has a high diagnostic accuracy and reliability. The methodology proposed in this paper is different from the current monitoring methodology; additional hardware devices are not required, and the methodology is simple and practical, has strong operability and enormous economic benefits, adapting to the requirements of the development of the smart grid.

Reliability analysis of the Sutong Bridge Tower under ship impact loading

This study discusses the development of a procedure that can be used to assess the reliability of cable-stayed bridge towers under ship impact loading. Consideration is given to maintain reasonable computational effort for both the structural analysis and reliability models. Cable-stayed bridge towers including soil–pile interaction were modelled using the finite element method and ship impact loading, and were described in terms of the equivalent static loads. Reliability indices are estimated for three load combinations and two limit state functions. Results of the study show that the type of load combinations has a significant effect on the probability of failure of cable-stayed bridge towers under ship impact loading. Furthermore, a detailed sensitivity study shows that the reliability of cable-stayed bridge towers under ship impact loading is highly influenced by the design wind speed, the equivalent ship impact load, the nominal bending moment capacity about the element y-axis at the bottom section of the pylon and the allowable maximum lateral deflection.

LOW FREQUENCY IDENTIFICATION OF CRITICAL STATES OF TRANSMISSION TOWER STRUCTURES

Transmission towers are vital parts of the overhead power line infrastructures. Any damage to these supporting structures may result in decreased load-bearing capacity and, in consequence, their collapse. Failures of transmission towers are much more severe than power failures, as they not only cause interruption to the energy supply but can also result in considerable costs of infrastructure repairs and damage. Therefore, supporting structures of overhead power lines should be subjected to structural health monitoring. This paper presents a comprehensive database containing natural frequencies and strain energies of all elements for various (simulated) damage states. On the basis of structure modal parameters, by finding the correlation between natural frequencies of damaged structure stored in the created database and natural frequencies of the structure of interest, state of the test structure can be identified. In order to verify this method, a numerical experiment was carried out. Observing the strain energy variation as compared to the undamaged state makes it possible to localize the damage and assess its importance for the further structure exploitation.

Reliability of Cooling Tower Drives: Improving Efficiency with New Motor Technology

Cooling towers are used in many process applications in the petrochemical industry, so reliability of these towers is crucial. In many cases, redundant towers need to be installed to ensure that a process will not have to be stopped due to a cooling tower failure. The most prevalent cause of cooling tower downtime is failure of the right-angle gearbox or associated mechanical components, such as the driveshaft or disc couplings. The elimination of these components can reduce the losses in the drive system and offer the possibility for improved overall system efficiency. This article describes new developments in motor technology that allow for the replacement of high-speed motors, driveshafts, couplings, and gearboxes with a slow-speed permanent magnet (PM) motor. A case study is presented with provisions of maintenance and efficiency improvement data.

Effect of Geometric Nonlinear Behaviour of a Guyed Transmission Tower under Downburst Loading

Downburst winds, which are a source of extreme wind loading and are referred to as high intensity wind (HIW) loads, have caused numerous transmission tower failures around the world. A previous investigation was conducted to study the performance of a transmission tower under downburst wind loading, where the behaviour of the tower was limited to a linear response. In the current study, a nonlinear frame element is used to assess the performance of the tower under downburst wind loading. The behaviour is studied using downburst wind field data obtained from a computational fluid dynamics (CFD) model. In order to assess the geometric nonlinear behaviour of the tower, the results are compared to a previous linear analysis for a number of critical configurations of a downburst. The nonlinear analysis predicted that peak axial loads in certain members can be up to 34% larger than those predicted by the linear analysis.

Wind Speed Profiles of an Actual Downburst Based on CFD Numerical Simulation

Downbursts have led to large number of transmission tower failures in the world, so more and more wind engineers are very interested in such strong wind load. Currently the main numerical simulation method of downburst wind load for structural analysis is based on the horizontal divergent wind speed profile of downburst. There have been several available types of empirical wind speed profiles in which some parameters still need to be artificially determined. So, this is a semi-empirical-analytical method which can not be linked with actual downbursts. Some academics have also used CFD numerical method to simulate downburst wind speed profile of high precision grid. But the initial conditions of these CFD simulations were all assumed ideally. In this paper, the wind speed profiles of an actual downburst are simulated by CFD method based on the initial speed of downdraft entrance provided by cloud model. The simulated wind speed profile decays more slowly than an empirical wind speed profile. This conclusion could be of significance for structural engineers to consider downburst wind load reasonably in the structural wind resistant design.

Studies on failure of transmission line towers in testing

The towers are vital components of the transmission lines and hence, accurate prediction of their failure is very important for the reliability and safety of the transmission system. When failure occurs, direct and indirect losses are high, leaving aside other costs associated with power disruption and litigation. Different types of premature failures observed during full scale testing of transmission line towers at Tower Testing and Research Station, Structural Engineering Research Centre, Chennai are presented. Failures that have been observed during testing are studied and the reasons discussed in detail. The effect of non-triangulated hip bracing pattern and isolated hip bracings connected to elevation redundant in ‘K’ and ‘X’ braced panels on tower behaviour are studied. The tower members are modeled as beam column and plate elements. Different types of failures are modeled using finite element software and the analytical and the test results are compared with various codal provisions. The general purpose finite element analysis program NE-NASTRAN is used to model the elasto-plastic behaviour of towers. Importance of redundant member design and connection details in over all performance of the tower is discussed.