Ghyslaine McClure

Modeling the structural dynamic response of overhead transmission lines

Static analysis forms the basis of calculations in structural design of overhead power lines. The environmental loads considered in design can be assumed static (icing) or quasi-static (idealized steady wind). However, dynamic analysis is necessary to predict line transient response to shock loads such as those induced by the sudden failure of components or sudden ice-shedding effects on the conductors. This paper summarizes a macroscopic modeling approach to line dynamic analysis where emphasis is put on capturing the salient features of the propagation of such shock loads in a line section. The approach is illustrated with a case study of a line section having suffered two tower failures due to conductor breakages during an ice storm. The cable dynamics model proposed has been applied successfully to several examples, using the commercial software ADINA.

Elasto-plastic modeling of wood bolted connections

A plasticity based constitutive compressive material model is proposed to model wood as elasto-plastic orthotropic according to the Hill yield criterion in regions of bi-axial compression. Linear elastic orthotropic material response is applied otherwise with maximum stresses taken as failure criteria. The model is implemented in the finite element code to carry out the analysis of bolted connections using ADINA software. Reasonable agreement is found between numerical simulations and experimental measurements of local and global deformation of one-bolt connection. The predicted failure modes are consistent with experimental observations.

Simulation of ice-shedding on electrical transmission lines using adina

Abstract Overhead power transmission lines are subject to various static and dynamic loads. Among the dynamic loads treated quasi-statically in the line design process are imbalances due to the sudden fall of ice accreted on conductors and ground wires, a phenomenon known as ice-shedding. In order to study the static and dynamic effects of this physical phenomenon on towers as well as on phase-to-phase and phase-to-tower spacing, a series of laboratory tests were conducted on a two-span reduced-scale setup representing two level, equal conductor spans anchored at the end points and suspended in the middle by an insulator string. In these experiments, ice-shedding loads were simulated by suddenly dropping dead-weights from the conductors. Concurrently, a nonlinear finite-element model using ADINA was developed to simulate the static and transient dynamic responses of the physical model. This paper describes the essential characteristics of the numerical model and compares its predictions with the experimental results from a typical case. The comparison shows the good performance of ADINA in modelling the static and transient dynamic responses of this highly nonlinear engineering phenomenon.

Nonlinear seismic response of antenna-supporting structures

Abstract In the event of a severe seismic excitation, preservation of essential infrastructures, such as telecommunication facilities, is of high priority. The objective of this paper is to investigate the geometrically nonlinear response of antenna-supporting guyed towers under earthquake loading. Two guyed towers are analysed: a 350 ft (107 m) tower with six stay levels and an 80 ft (24m) mast with only two stay levels. Two horizontal accelerograms are used, El Centro and Parkfield, with each record being scaled to match the elastic design spectra of the 1990 National Building Code of Canada. Elements of response analysed are: guy tensions, horizontal shears, and displacements and rotations at the tip of the mast. Results indicate that although the absolute values of the dynamic amplifications are well below the limit strength and serviceability criteria for such towers, dynamic interactions between the guywires and the mast are important, especially in the vertical direction. Multiple support excitation of the tallest tower also causes additional dynamic effects that are not present when only synchronous ground motion is studied.

Application of ADINA to stress analysis of an optical ground wire

Abstract Ground wires are metallic wires used in overhead power lines to protect the line conductors against lightning. An optical ground wire (OPGW) is composed of an envelope of one or two layers of metallic helical strands wound around a core containing optical fibers. In most OPGW constructions, the fibers are designed to be stress free or to experience only low stresses under normal operation loads. A three-dimensional finite element model of a cable was constructed to predict the stress distribution in each component when the cable is subjected to a given elongation. Modeling considerations are discussed, which pertain to geometric modeling and meshing, boundary conditions, contact and numerical methods. Results of stress analysis are presented in some detail for two examples; six wires and ten wires wound around a central tube. The results are compared with analytical approximate solutions available in the literature dating from 1973.

Modelling the Dynamic Response of Iced Transmission Lines Subjected to Cable Rupture and Ice Shedding

This study is concerned with accurate numerical modelling of the propagation or progression of ice-shedding phenomena and resulting forces in overhead lines following an initial trigger, such as a controlled shock load applied locally with a cable de-icing device, or uncontrolled shocks due to cable rupture. The ice failure criterion used for the ice deposits in the simulations is based on a maximum effective plastic strain limit. This criterion has been verified in models of reduced- and real-scale single spans subjected to shock loads. After showing the improved performance of this ice failure model, it is applied to the case study of a 120 kV two-circuit line section that failed during a localized ice storm event in 1997. A nonlinear dynamic analysis of the line section is performed which considers ice-shedding effects following the conductor ruptures. The results confirm that considering ice-shedding effects in the iced spans subjected to cable rupture is essential to predict the general dynamic response of the line as the cable ruptures may induce ice shedding. The improved performance of the modelling procedure described in this paper can have practical use in the design of transmission lines in industry.

Experimental Evaluation of Load Paths in Light-Frame Wood Structure

Despite much experience that low-rise wood buildings are vulnerable to damage by extreme wind events, few such structures have been tested in fullsize to understand how they respond to wind loads as a whole system. This paper presents a study that measured internal force flows throughout the framing of a typical North American single-story structure with platform construction. Applied forces were concentrated horizontal loads normal to walls and patches of gravity loads on the sloped roof. Two series of load cells were embedded into the system, between the roof trusses and supporting walls and between the floor platform and the foundation. It was observed that even localized external forces have effects that propagate through the entire system. For instance, horizontal loads applied near eave level or to the roof were reacted at the top of the foundation around the entire wall perimeter of the building footprint, both parallel and transverse to the applied loading. For vertical loads, measurements showed ...

New Robust Linearized Seismic Analysis Method For Tall Guyed Telecommunication Masts

AbstractDesign of tall telecommunication masts is usually governed by serviceability criteria under high wind conditions, typically combined with icing in cold climates. However, there is a need for seismic design checks for guyed masts constructed in zones with moderate to high seismicity, as is routinely prescribed for buildings in modern codes. There have been few efforts towards proposing a robust simplified method of general applicability for the seismic analysis of tall masts. These structures can be represented by the simple concept of a continuous beam-column (the lattice mast) on nonlinear elastic supports (the guy cable clusters at various stay levels). In this study, the guy cables are replaced by equivalent linear lumped parameters (stiffness, mass, and viscous damping) and the effects of their interaction with the mast stiffness and inertia on the structural characteristics are discussed. The approach was tested with nine case studies of real telecommunication masts subjected to five differen...

Notice of Retraction Failure analysis of lattice transmission tower considering joint effects

Lattice transmission towers are widely used in overhead transmission lines. Accurate prediction of the load bearing capacity of lattice towers under different failure modes is very important for the accurate assessment of the reliability of transmission lines. Traditionally, lattice towers are analyzed as ideal trusses or frame-truss systems without explicitly considering loading eccentricity and slippage effects in bolted joints. Such effects are always observed in full-scale tower tests and introduce great differences in ultimate bearing capacity and failure modes obtained from linear analysis models. In this paper several numerical models of a 110 kV height-adjustable transmission tower are studied to investigate the influence of joint eccentricity and slippage on the bearing capacity of the tower, and the numerical results are compared with some experimental results available from prototype tests. The numerical simulation results confirm that joint slippage has dramatic influence on the deformation of the lattice tower, while only slightly reducing its load bearing capacity. Joint eccentricity is shown to greatly decrease bearing capacity and even to change its failure mode and sequence. Tower failure (pushover static) analysis considering both joint slippage and eccentricity is found in good agreement with the experimental results.

Dynamic analysis of cable roofs under transient wind: A comparison between time domain and frequency domain approaches

At present, high-speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures. Although deterministic approaches require considerable analysis time and effort in relation to modeling, running, and data processing, they seem to be the only alternative to obtain high accuracy. Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise. This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs. The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase, or can be used to validate results obtained from more elaborated numerical models. The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain.