Support Tower Research Articles

Centrifuge modelling of the pushover failure of an electricity transmission tower

Centrifuge model tests were conducted to examine foundation failure mechanisms during rapid horizontal pushover of an electricity transmission line support tower, simulating a broken transmission line response or wind gust loading. A model transmission tower supported on four pad foundations in clay and backfilled with sand was loaded horizontally and the loads at each foundation were measured during fast and slow pushover. The tests examined the influence of tensile resistance mobilized at the underside of the footings, which is difficult to reliably incorporate within design practice due to a lack of accepted quantitative design methods. The measured performance of the tower footings was compared with results from a series of tests where a single footing is subjected to purely vertical loading in compression and tension and was found to be in good agreement. The tower response was back-analysed as a simple push–pull model and the calculated uplift capacity of the footing backfill provided a close match to the observed response of the tower footings subjected to slow pushover. During fast pushover, the additional capacity mobilized due to tensile resistance (suction) created by the reverse bearing capacity beneath the base of the footings subjected to uplift was quantified using a suction capacity factor.

Investigation on the Potential Rise and Currents in Insulated Mast Scheme with Single Tower During Stroke Interception

The insulated mast scheme for the lightning protection system can be found in a few practical designs. Many advantages over conventional protection system are some times envisaged. However, the technical literature on the analysis of such schemes and further quantification of their protection efficacy is rather scarce. As a first step to address this problem, the present work is taken up and the potential rise at the top and ground end currents in insulating mast scheme with single tower is investigated for several tower heights and pertinent values of other parameters. The quantities that are investigated are the potential difference across the insulation and ground end currents for both tower and the ground wires. Quantifications are carried out for the relevant range of stroke current front times. The influence of number of ground wires, their earthing location and to a limited extent, the length of the insulating support have been ascertained. Some relevant discussion on insulation strength is made. These findings are quite novel and aid in quantification of the practical efficacy of the insulated mast scheme. The level of induction to the support tower and possible flashover to the same are not in favour of this scheme.

Numerical simulations of the aerodynamic behavior of large horizontal-axis wind turbines

In the present work, the non-linear and unsteady aerodynamic behavior of large horizontal-axis wind turbines is analyzed. The flowfield around the wind turbine is simulated with the general non-linear unsteady vortex-lattice method, widely used in aerodynamics. By using this technique, it is possible to compute the aerodynamic loads and their evolution in the time domain. The results presented in this paper help to understand how the existence of the land–surface boundary layer and the presence of the turbine support tower, affect its aerodynamic efficiency. The capability to capture these phenomena is a novel aspect of the computational tool developed in the present effort.

Simulation of Potential and Electric Field Profiles for Transmission Line Insulators

Since the end of second world war, extra high voltage ac transmission has seen its development. The distances between generating and load centres as well as the amount of power to be handled increased tremendously for last 50 years. The highest commercial voltage has increased to 765kV in India and 1,200kV in many other countries. The bulk power transmission has been mostly performed by overhead transmission lines. The dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower is performed by string insulators. Whether in clean condition or under polluted conditions, the electrical stress distribution along the insulators governs the possible flashover, which is quite detrimental to the system. Hence the present investigation aims to study accurately, the field distribution for various types of porcelain/ceramic insulators (Normal and Antifog discs) used for high-voltage transmission. The surface charge simulation method is employed for the field computation. A comparison on normalised surface resistance, which is an indicator for the stress concentration under polluted condition, is also attempted.

Options for support tower design of a sensitive equipment under ambient vibrations

AbstractThis paper describes the options and methodology adopted for the design of an 18‐m high support tower for a vibration sensitive optical telescope. The telescope was to be housed inside an existing building that provided shielding from atmospheric wind and thermal variations. However, proper functioning of the telescope was dependent on the support tower's structural configuration and stiffness to limit angular distortion of the telescope platform to less than 2 µ radians or 0·4 arc‐sec. This level of sensitivity required investigation of support tower response under ambient vibrations resulting from normal operation of the existing facility. The measured peak ambient vibration acceleration ranged from 0·04 m/s/s to 0·27 m/s/s for various recorded events. Two options for the tower were investigated viz. steel braced frame and concrete shaft. The effect of soil structure interaction (SSI) was also examined. It was concluded that the concrete tower option provided the desired performance for both fixed base and SSI cases. On the other hand, the steel tower performed well for the fixed base case but its performance was close to the threshold when SSI was also considered. Effect of soil properties variation on SSI was also examined for both tower options and was found to be relatively insignificant. Copyright © 2008 John Wiley & Sons, Ltd.

Towers for Antarctic Telescopes

To take advantage of the exceptional seeing above the boundary layer on Antarctic sites, a high-resolution telescope must be mounted on a support tower. An open transparent tower of framework minimizes the upward temperature-disturbed airflow. A typical minimum height is 30 m. The tower platform has to be extremely stable against wind-induced rotational motions, which have to be less than fractions of an arc second, unusually small from a mechanical engineering viewpoint. In a traditional structure, structural deflections result in angular deflections of the telescope platform, which introduce tip and tilt motions in the telescope. However, a structure that is designed to deflect with parallel motion relative to the horizontal plane will undergo solely translation deflections in the telescope platform and thus will not degrade the image. The use of a parallel motion structure has been effectively demonstrated in the design of the 15-m tower for the Dutch Open Telescope (DOT) on La Palma. Special framework geometries are developed, which make it possible to construct high towers in stories having platforms with extreme stability against wind-induced tilt. These geometric solutions lead to constructions, being no more massive than a normal steel framework carrying the same load. Consequently, these lightweight towers are well suited to difficult sites as on Antarctica. A geometry with 4 stories has been worked out.

Development of a Robot for Inspecting Electricity Transmission Support Towers

The paper describes the first phase of development of a robot for inspecting the steel towers that support overhead electrical transmission lines. A summary of the robot's mechanical design is presented. Details are given of the software architecture used to control the robot including perception, planning, task execution and motor control. The construction and performance of a small-scale laboratory model are discussed.

The Dutch Open Telescope on La Palma

The Dutch Open Telescope (DOT) on La Palma is an innovative solar telescope combining open telescope structure and an open support tower with a multi-wavelength imaging assembly and with synchronous speckle cameras to generate high-resolution movies which sample different layers of the solar atmosphere simultaneously and co-spatially at high resolution over long durations. The DOT test and development phase is nearly concluded. The installation of an advanced speckle processor enables full science utilization including “Open-DOT” time allocation to the international community. Co-pointing with spectropolarimeters at other Canary Island telescopes and with TRACE furnishes valuable Solar-B precursor capabilities.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

On Eagle's Wings: The Parkes Observatory's Support of the Apollo 11 Mission

AbstractAt 12:56 p.m., on Monday 21 July 1969 (AEST), six hundred million people witnessed Neil Armstrong's historic first steps on the Moon through television pictures transmitted to Earth from the lunar module, Eagle. Three tracking stations were receiving the signals simultaneously. They were the CSIRO's Parkes Radio Telescope, the Honeysuckle Creek tracking station near Canberra, and NASA's Goldstone station in California. During the first nine minutes of the broadcast, NASA alternated between the signals being received by the three stations. When they switched to the Parkes pictures, they were of such superior quality that NASA remained with them for the rest of the 2-hour moonwalk. The television pictures from Parkes were received under extremely trying and dangerous conditions. A violent squall struck the telescope on the day of the historic moonwalk. The telescope was buffeted by strong winds that swayed the support tower and threatened the integrity of the telescope structure. Fortunately, cool heads prevailed and as Aldrin activated the TV camera, the Moon rose into the field-of-view of the Parkes telescope. This report endeavours to explain the circumstances of the Parkes Observatory's support of the Apollo 11 mission, and how it came to be involved in the historic enterprise.

Finite element modelling of transmission line galloping

A computationally efficient, finite element idealization is presented to analyse galloping, which is characterized by large amplitude vibrations of iced, multi-span, electrical transmission lines. A three-node, isoparametric cable element having three translational and a torsional degree-of-freedom at each node is developed to model a conductor. Support insulator strings and remote conductor spans are represented by linear static springs. A transmission line's interactions with a support tower are modelled through the tower's equivalent stiffness at the conductor's suspension point. An expedient time marching scheme is developed to obtain the envelope of galloping. The scheme can be utilized to integrate dynamic equilibrium equations involving not only geometric and material nonlinearities but also nonlinear damping. Time integration is performed in the sub-space to minimize computational effort. The finite element model has been employed to successfully simulate field galloping records. It is shown that it is necessary to consider a multi rather than a single span for a conservative estimate of the galloping amplitudes to enable sufficient clearances to be designed between adjacent conductors.

The vibration modes of a wind turbine support structure

SYNOPSIS Lightweight wind turbines offer a considerable reduction in capital and operating costs for electricity generation from the wind. Environmental impact of installation works can be reduced. Lightweight machines are likely to be structurally flexible. It is essential for the designer to study their dynamic characteristics in order to reduce: 1. The magnitude of the stresses in the structure particularly in components loaded cyclically; 2. The electrical noise and power fluctuation experienced by electricity consumers; 3. The acoustic noise emitted. Using Rayleigh analysis, the vibration frequencies of a mathematical model of the wind turbine support tower can be estimated. Additional structural components can easily be added and components can be modelled more accurately as the process is refined. Available experimental measurements compare favourably with corresponding predictions.

Reckitt's Colours re-named

Many thin-walled cylindrical shells are used in structural applications in which the dominant loading condition is global bending. Key examples include chimneys, wind turbine support towers, pipelines, horizontal tanks, tubular piles and silos. The buckling behaviour of these structures in bending is complex due to the coupling between cross-section ovalisation and local bifurcation buckling. Analytical treatments of this problem have a history going back almost a century and still constitute an active and challenging research area.This paper investigates in detail the effect of cylinder length on the nonlinear elastic buckling behaviour of clamped cylindrical tubes under global bending, covering a very wide range of lengths. It is found that the behaviour may be classified into four distinct length-dependent domains with clearly-defined boundaries which have here been assigned the names ‘short’, ‘medium’, ‘transitional’ and ‘long’. Algebraic characterisations of the computed nonlinear moment–length relationships are proposed for design purposes.

Dynamic Responses of Pipeline Suspension Bridges

The objective of this engineering study is to determine the dynamic responses of pipeline suspension bridges. To this end, four existing pipeline suspension bridges are analyzed: the 259.2‐m Patterson Loop Aerial Crossing (PLAC) and the 307.2‐m Avalon Extension Aerial Crossing (AEAC), both of which span the Wax Lake Outlet near Patterson, Louisiana, the 457.2‐m Missouri River Pipeline Bridge (MORB) in Plattsmouth, Nebraska, and the 655.3‐m Mississippi River Pipeline Bridge (MIRB) in Grand Tower, Illinois. Modal and response spectrum seismic analyses are performed on finite element models of these bridges. The results indicate that the MORB and the MIRB could experience high levels of stress approaching the yield stress at the end connections of the suspended pipes under earthquake excitations with maximum ground accelerations of 0.50g. These high levels of seismic intensity could also cause distress in the support towers of the PLAC and the AEAC.

Multiple source DF signal processing: An experimental system

The multiple signal characterization (MUSIC) algorithm is an implementation of the signal subspace approach to compute parameter estimates of multiple point-source signals from the observed voltages received on an array of M antennas. In it, the solution to the multiple source direction finding (DF) problem is provided by the intersection of the signal subspace (obtained from the received data) and the array manifold (obtained via array calibration or prior knowledge of array directional characteristics). The MUSIC algorithm was implemented to experimentally verify the performance of the signal subspace approach to DF under very general scenarios and conditions which are regarded as difficult to impossible in traditional systems. The results of those experiments are described herein. The experimental system consisted of an eight-element antenna array 13 wavelengths in diameter, an eight-channel receiver and digitizer, and a minicomputer with disk storage to process the digitized data. With ideal instrumentation, the MUSIC algorithm provides performance that, as the amount of data collected increases without limit, is asymptotically ideal. However, with finite precision and finite data collection, the performance of even an ideal system can be a sensitive function of source and scenario parameters. Tests demonstrated the resolution of three sources all within one beamwidth (5 \deg ), even when the closer two were spaced less than 0.2 beamwidths. Sources that were polarized differently could be resolved at closer spacings. Experimental DF accuracy was limited by the oncalibrated scattering of source energy from the test range support tower and from the ground. The measured direction of arrival of one source changed by less than 0.01 beamwidths as the other two sources were switched on and off in all combinations. In general, results indicated that all parameters of a source can be measured and the signal waveform can be recovered as well in the presence of other sources less than a beamwidth away.

A note on tower wake/blade interaction noise of a wind turbine

Experimental observations on wind turbine tower wake/blade interaction noise are presented. Results for circular, elliptical and square sections of the support tower legs are compared and quantified with respect to the acoustic frequency spectra produced. The results are preliminary ones obtained in a continuing study aimed at constructing a shape that may yield a lower interaction noise.

Combined Shear and Tension on Grouted Base Details

Braced structures with large height-to-width ratios, i.e., transmission towers, water towers or industrial equipment support towers, when subjected to lateral loads, often have resultant uplift and shear forces transmitted to their foundations. The base details must transmit combined tension and shear from the column to the foundation. For ease of construction, the columns are often set with base plates shimmed 1 to 2 in, above the top of the foundation; the shimmed volume is later grouted to complete the base detail. The two major codes governing steel and reinforced concrete construction do not specify design formulas for grouted anchor bolt-base plate connection details. The Uniform Building Code, representative of general building codes, states bolts shall be solidly embedded in plain or reinforced concrete, and the connection shall be designed so that the tension or shear on every bolt is not greater than a value defined in their tables. Previous investigators have studied anchor bolts embedded in concrete subjected to combined shear and tension, but have not included the effects of the grout.

Fire Protection on the Beryl A Platform

This paper describes the fire protection systems of a large offshore platform in the North Sea. The Beryl A platform had several unique risk platform in the North Sea. The Beryl A platform had several unique risk factors, including size, high production rates, and platform construction, that required careful analysis. Fire protection solutions and safe operation of the facility also are discussed. Introduction With more exploration and production in the North Sea, new engineering techniques are required to provide protection from fire and explosion. The severe risk of protection from fire and explosion. The severe risk of fire associated with North Sea platforms is illustrated by the Beryl A platform, compared in Fig. I with some well known landmarks. Located more than 200 miles offshore in 392 ft of water, the platform has a concrete base support topped with a steel deck structure and quarters. Sixteen of the 19 base cylinders are used for crude oil storage and have a capacity of 950,000 bbl. These cylinders extend 150 ft above the sea floor. The remaining three cylinders are used as main support towers and extend an additional 300 ft to support the steel deck structure. The steel deck rises 100 ft above low average tide. The steel deck structure is 197 x 230 ft with two levels, each about 1 acre in area and spaced 33 ft apart. The enclosed compartmental steel structure houses equipment and facilities for production, drilling, recompression, utilities, and life support systems.Over-all weight of the structure is 350,000 tons, which keeps the structure in place, anchored by steel dowels more than 6 ft across and projecting into the sea bed 16 ft below the bottom of the structure. The platform eventually will produce up to 100,000 B/D. Crude oil will be pumped from the platform to a single-point mooring pumped from the platform to a single-point mooring structure and then to specially designed bow-loading tankers. Fig. 2 shows the platform in its towing position and illustrates the size of the structure. Design Objective Fire protection and safety provisions incorporated in the platform provide maximum protection against risks of platform provide maximum protection against risks of fire and limit the exposure of employees to fire and explosion.Fire safety design includes several interrelated fire safety systems, including detection systems for hazardous accumulations of flammable gases, fire detection, smoke detection in areas with potential for smoldering fires (such as quarters and electrical equipment areas), fire extinguishing systems, fireproofing of structural elements, and fire walls between compartments. A major element of the fire system design is the combustible gas detection system. These devices provide warning of hazardous conditions well ahead of a potential fire. Combustible Gas Detection The combustible gas detection system has a network of sensors located strategically throughout each compartment, signaling in the control room. The sensors are sensitive to hydrocarbon vapors and will be calibrated to signal an alarm when vapor concentration reaches 20% of the lower explosive limit (LEL). The LEL is that point where flammable vapors mixed with air can be ignited. At 60% of the LEL, the detection systems will signal an alarm and also begin interlocking with other fire safety systems. The function of the interlock varies, depending on occupancy of the compartment where flammable vapors are detected, and may include fire extinguishing or deactivating systems, and/or process shutdown. JPT P. 1377

The Aerodynamic Efficiency of Windmills

SummaryThe paper reproduces the results of an earlier report on the vortex theory of windmills and follows that theory through to establish the aerodynamic design procedure for a horizontal axis windmill. The results are shown to differ considerably from those given in a recent paper by Griffith and the differences are explained. The main conclusion is that, when full allowance is made for the drag of the blades, hub and tip losses, and losses due to interference with the support tower, the power output coefficient or efficiency of a horizontal axis windmill cannot exceed 30 to 35 per cent, as compared to an ideal efficiency of 59 per cent.

Tracking the Wandering Waters

In 1972 the International Field Year for the Great Lakes finally took to the field as a multidisciplinary study of Lake Ontario. Various physical, biological, and human use factors affecting the entire water mass are being investigated. Measurement of the circulation patterns within the water mass relates to all aspects of the lake and is vital for a true cross‐discipline study.As a brief, concise layman's catalogue of the instruments and techniques presently being used to obtain measurements of currents in the Great Lakes, Measurement of Currents in the Great Lakes is an excellent job. The differences between the fixed meter, or Eulerian technique, and the free‐drifter, or Lagrangian technique, and the advantages of each are clearly stated, as are the discussions of the various support buoys and towers. The technical descriptions and diagrams are explicit and uncluttered with technical details needed only when actually working with the equipment. Appendix 2 provides the concerned reader with the names and addresses of the current meter manufacturers who can supply all the technical information concerning specific meters mentioned in the manual.

TREATING A SUPPORT TOWER

A lattice‐work structure made of galvanized steel angles bolted together has been in use for some time as a support tower for an overhead conveyor system, it has been noticed that the steelwork is now badly discoloured by corrosion product and it has been decided to take steps to give the structure further anti‐corrosion treatment. The tower cannot be dismantled.