Behaviour of transmission line conductors under tornado wind

Hamada, Ahmed,El Damatty, Ashraf A. Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.22 No.3

Electricity is transmitted by transmission lines from the source of production to the distribution system and then to the end users. Failure of a transmission line can lead to devastating economic losses and to negative social consequences resulting from the interruption of electricity. A comprehensive in-house numerical model that combines the data of computational fluid dynamic simulations of tornado wind fields with three dimensional nonlinear structural analysis modelling of the transmission lines (conductors and ground-wire) is used in the current study. Many codes of practice recommend neglecting the tornado forces acting on the conductors and ground-wires because of the complexity in predicting the conductors' response to such loads. As such, real transmission line systems are numerically simulated and then analyzed with and without the inclusion of the lines to assess the effect of tornado loads acting on conductors on the overall response of transmission towers. In addition, the behaviour of the conductors under the most critical tornado configuration is described. The sensitivity of the lines' behaviour to the magnitude of tornado loading, the level of initial sag, the insulator's length, and lines self-weight is investigated. Based on the current study results, a recommendation is made to consider conductors and ground-wires in the analysis and design of transmission towers under the effect of tornado wind loads.

Behaviour of transmission line conductors under tornado wind

Ahmed Hamada,Ashraf A. El Damatty 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.22 No.3

Electricity is transmitted by transmission lines from the source of production to the distribution system and then to the end users. Failure of a transmission line can lead to devastating economic losses and to negative social consequences resulting from the interruption of electricity. A comprehensive in-house numerical model that combines the data of computational fluid dynamic simulations of tornado wind fields with three dimensional nonlinear structural analysis modelling of the transmission lines (conductors and ground-wire) is used in the current study. Many codes of practice recommend neglecting the tornado forces acting on the conductors and ground-wires because of the complexity in predicting the conductors` response to such loads. As such, real transmission line systems are numerically simulated and then analyzed with and without the inclusion of the lines to assess the effect of tornado loads acting on conductors on the overall response of transmission towers. In addition, the behaviour of the conductors under the most critical tornado configuration is described. The sensitivity of the lines` behaviour to the magnitude of tornado loading, the level of initial sag, the insulator`s length, and lines self-weight is investigated. Based on the current study results, a recommendation is made to consider conductors and ground-wires in the analysis and design of transmission towers under the effect of tornado wind loads.

Behavior of self supported transmission line towers under stationary downburst loading

Mohamed M. Darwish,Ashraf A. El Damatty 한국풍공학회 2011 Wind and Structures, An International Journal (WAS Vol.14 No.5

During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on assessing the behaviour of self supported transmission line towers under downburst loading. A parametric study is performed to determine the critical downburst configurations causing maximum axial forces for various members of a tower. The sensitivity of the internal forces developing in the tower’s members to changes in the downburst size and location was studied. The structural behaviour associated with the critical downburst configurations is described and compared to the behaviour under ‘normal’ wind loads.

Application of tuned liquid dampers in controlling the torsional vibration of high rise buildings

Andrew S. Ross,Ashraf A. El Damatty,Ayman M. El Ansary 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5

Excessive motions in buildings cause occupants to become uncomfortable and nervous. This is particularly detrimental to the tenants and ultimately the owner of the building, with respect to financial considerations. Serviceability issues, such as excessive accelerations and inter-story drifts, are more prevalent today due to advancements in the structural systems, strength of materials, and design practices. These factors allow buildings to be taller, lighter, and more flexible, thereby exacerbating the impact of dynamic responses. There is a growing need for innovative and effective techniques to reduce the serviceability responses of these tall buildings. The current study considers a case study of a real building to show the effectiveness and robustness of the TLD in reducing the coupled lateral-torsional motion of this high-rise building under wind loading. Three unique multi-modal TLD systems are designed specifically to mitigate the torsional response of the building. A procedure is developed to analyze a structure-TLD system using High Frequency Force Balance (HFFB) test data from the Boundary Layer Wind Tunnel Laboratory (BLWTL) at the University of Western Ontario. The effectiveness of the unique TLD systems is investigated. In addition, a parametric study is conducted to determine the robustness of the systems in reducing the serviceability responses. Three practical parameters are varied to investigate the robustness of the TLD system: the height of water inside the tanks, the amplitude modification factor, and the structural modal frequencies.

Finite-element modeling of a light-framed wood roof structure

Ryan B Jacklin,Ashraf A. El Damatty,Ahmed A. Dessouki 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.6

Past high speed wind events have exposed the vulnerability of the roof systems of existing light-framed wood structures to uplift loading, contributing greatly to economic and human loss. This paper further investigates the behaviour of light-framed wood structures under the uplift loading of a realistic pressure distribution. A three-dimensional finite-element model is first developed to capture the behaviour of a recently completed full-scale experiment. After describing the components used to develop the numerical model, a comparison between the numerical prediction and experimental results in terms of the deflected shape at the roof-to-wall connections is presented to gain confidence in the numerical model. The model is then used to analyze the behaviour of the truss system under realistic and equivalent uniform pressure distributions and to perform an assessment of the use of the tributary area method to calculate the withdrawal force acting on the roof-to-wall connections.

Application of tuned liquid dampers in controlling the torsional vibration of high rise buildings

Ross, Andrew S.,El Damatty, Ashraf A.,El Ansary, Ayman M. Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5

Excessive motions in buildings cause occupants to become uncomfortable and nervous. This is particularly detrimental to the tenants and ultimately the owner of the building, with respect to financial considerations. Serviceability issues, such as excessive accelerations and inter-story drifts, are more prevalent today due to advancements in the structural systems, strength of materials, and design practices. These factors allow buildings to be taller, lighter, and more flexible, thereby exacerbating the impact of dynamic responses. There is a growing need for innovative and effective techniques to reduce the serviceability responses of these tall buildings. The current study considers a case study of a real building to show the effectiveness and robustness of the TLD in reducing the coupled lateral-torsional motion of this high-rise building under wind loading. Three unique multi-modal TLD systems are designed specifically to mitigate the torsional response of the building. A procedure is developed to analyze a structure-TLD system using High Frequency Force Balance (HFFB) test data from the Boundary Layer Wind Tunnel Laboratory (BLWTL) at the University of Western Ontario. The effectiveness of the unique TLD systems is investigated. In addition, a parametric study is conducted to determine the robustness of the systems in reducing the serviceability responses. Three practical parameters are varied to investigate the robustness of the TLD system: the height of water inside the tanks, the amplitude modification factor, and the structural modal frequencies.

Finite-element modeling of a light-framed wood roof structure

Jacklin, Ryan B.,El Damatty, Ashraf A.,Dessouki, Ahmed A. Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.6

Past high speed wind events have exposed the vulnerability of the roof systems of existing light-framed wood structures to uplift loading, contributing greatly to economic and human loss. This paper further investigates the behaviour of light-framed wood structures under the uplift loading of a realistic pressure distribution. A three-dimensional finite-element model is first developed to capture the behaviour of a recently completed full-scale experiment. After describing the components used to develop the numerical model, a comparison between the numerical prediction and experimental results in terms of the deflected shape at the roof-to-wall connections is presented to gain confidence in the numerical model. The model is then used to analyze the behaviour of the truss system under realistic and equivalent uniform pressure distributions and to perform an assessment of the use of the tributary area method to calculate the withdrawal force acting on the roof-to-wall connections.

Behavior of self supported transmission line towers under stationary downburst loading

Darwish, Mohamed M.,El Damatty, Ashraf A. Techno-Press 2011 Wind and Structures, An International Journal (WAS Vol.14 No.5

During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on assessing the behaviour of self supported transmission line towers under downburst loading. A parametric study is performed to determine the critical downburst configurations causing maximum axial forces for various members of a tower. The sensitivity of the internal forces developing in the tower's members to changes in the downburst size and location was studied. The structural behaviour associated with the critical downburst configurations is described and compared to the behaviour under 'normal' wind loads.

Behaviour and design of guyed pre-stressed concrete poles under downbursts

Ahmed M. Ibrahim,Ashraf A. El Damatty 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.5

Pre-stressed concrete poles are among the supporting systems used to support transmission lines. It is essential to protect transmission line systems from harsh environmental attacks such as downburst wind events. Typically, these poles are designed to resist synoptic wind loading as current codes do not address high wind events in the form of downbursts. In the current study, the behavior of guyed pre-stressed concrete Transmission lines is studied under downburst loads. To the best of the authors’ knowledge, this study is the first investigation to assess the behaviour of guyed pre-stressed concrete poles under downburst events. Due to the localized nature of those events, identifying the critical locations and parameters leading to peak forces on the poles is a challenging task. To overcome this challenge, an in-house built numerical model is developed incorporating the following: (1) a three-dimensional downburst wind field previously developed and validated using computational fluid dynamics simulations; (2) a computationally efficient analytical technique previously developed and validated to predict the non-linear behaviour of the conductors including the effects of the pretension force, sagging, insulator’s stiffness and the non-uniform distribution of wind loads, and (3) a non-linear finite element model utilized to simulate the structural behaviour of the guyed pre-stressed concrete pole considering material nonlinearity. A parametric study is conducted by varying the downbursts locations relative to the guyed pole while considering three different span values. The results of this parametric study are utilized to identify critical downburst configurations leading to peak straining actions on the pole and the guys. This is followed by comparing the obtained critical load cases to new load cases proposed to ASCE-74 loading committee. A non-linear failure analysis is then conducted for the three considered guyed pre-stressed concrete transmission line systems to determine the downburst jet velocity at which the pole systems fail.

Dynamic characteristics of transmission line conductors and behaviour under turbulent downburst loading

Mohamed M. Darwish,Ashraf A. El Damatty,Horia Hangan 한국풍공학회 2010 Wind and Structures, An International Journal (WAS Vol.13 No.4

During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on the assessment of the dynamic behaviour of the line conductors under downburst loading. A non-linear numerical model, accounting for large deformations and the effect of pretension loading, is developed and used to predict the natural frequencies and mode shapes of conductors at various loading stages. A turbulence signal is extracted from a set of full-scale data. It is added to the mean component of the downburst wind field previously evaluated from a CFD analysis. Dynamic analysis is performed using various downburst configurations. The study reveals that the response is affected by the background component, while the resonant component turns to be negligible due large aerodynamic damping of the conductors.