A numerical model capable of predicting the dynamic response of pre-stressed concrete transmissio... more A numerical model capable of predicting the dynamic response of pre-stressed concrete transmission poles under both the mean and fluctuating components of synoptic wind loads is developed in this study. A full non-linear dynamic analysis is conducted under a time history variation of wind velocity. The peak total responses, such as conductors’ reactions and poles’ base moments, are determined from this analysis. The same analysis is repeated in a quasi-static manner. Dynamic amplification factors (DAF), defined as the ratio between the maximum response based on a non-linear dynamic analysis and the corresponding value based on a quasi-static analysis, are calculated for the poles and the conductors to quantify the dynamic impact of synoptic wind loads. This factor is used to assess the importance of including the resonant component while estimating the response of the transmission poles. In addition, gust response factors (GRF) defined as the ratio between the peak and mean response...
This study aims at modeling boundary layers (BLs) encountered in sparse and built environments (i... more This study aims at modeling boundary layers (BLs) encountered in sparse and built environments (i.e., open, suburban and urban) at the subsonic Wind Tunnel (WT) at Ryerson University (RU). This WT has an insignificant turbulence intensity and requires a flow-conditioning system consisting of turbulence generating elements (i.e spires, roughness blocks, barriers) to achieve proper turbulent characteristics. This system was developed and validated in the current study in three phases. In phase I, several Computational Fluid Dynamic (CFD) simulations of the tunnel with generating elements were conducted to understand the effect of each element on the flow. This led to a preliminary design of the system, in which horizontal barriers (slats) are added to the spires to introduce turbulence at higher levels of the tunnel. This design was revisited in phase II, to specify slat dimensions leading to target BLs encountered by tall buildings. It was found that rougher BLs require deeper slats ...
Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas o... more Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas of USA, such as Florida and Louisiana. Available design codes provide information about the design of regular roof geometries (e.g. hip/gable roofs), but refer to wind tunnel modelling for complex roof geometries. Due to time and financial constraints physical modelling may not always be possible to carry out. Computational modelling through Large Eddy Simulation (LES) has been used successfully for several wind engineering applications. This paper presents comparisons between LES and previously obtained wind tunnel data of mean and peak pressure coefficients on a low rise building with complex roof geometry. Two different cases, namely: isolated building and the effect of neighbouring buildings have been considered for the most critical wind direction of 135 degrees. Results show that the mean pressure coefficients on the low rise building roof for the case with adjacent buildings were s...
Steel liquid storage tanks in the form of truncated cones are commonly used as containment vessel... more Steel liquid storage tanks in the form of truncated cones are commonly used as containment vessels for water supply or storing chemicals. A number of failures have been recorded in the past few decades for steel liquid tanks and silos under wind loading. A steel conical tank vessel will have a relatively small thickness making it susceptible to buckling under wind loads especially when they are not fully-filled. In this study, a wind tunnel pressure test is performed on an elevated conical tank in order to estimate the external wind pressures when immersed into a boundary layer. The tested tank configuration represents combined conical tanks where the cone is capped with a cylinder. In addition, the effect of terrain exposure and wind speed on the pressure values and wind forces is assessed. The mean and rms pressure coefficients are presented for different test cases in addition to the mean and rms total drag forces that are obtained by integrating the pressure coefficient over the...
This paper studies the dynamic behavior of a multi-span transmission line system under synoptic w... more This paper studies the dynamic behavior of a multi-span transmission line system under synoptic wind considering various speeds to determine the range of wind speeds in which the system experiences resonance. A finite element numerical model was developed for the purpose of this study. This model is employed to assess the dynamic behavior of a self-supported lattice tower line under various wind speeds. Dynamic Amplification Factor (DAF), defined as the ratio between the peak total response to the peak quasi-static response, is evaluated. It is found that conductors’ responses exhibit large DAF compared to the towers especially at low wind speeds (v ≤ 25 m/s). This results from the low natural frequency of the conductors (0.19 Hz) which is close to the wind load frequency while the natural frequency of the tower is equal to 2.36 Hz. In addition, the conductors’ aerodynamic damping decreases with the decrease of wind speed which leads to higher dynamic effect while the tower’s aerody...
ABSTRACT An effective numerical technique to calculate the reactions of a multi-spanned transmiss... more ABSTRACT An effective numerical technique to calculate the reactions of a multi-spanned transmission line conductor system, under arbitrary loads varying along the spans, is developed. Such variable loads are generated by High Intensity Wind (HIW) events in the form of tornadoes and downburst. First, a semi-closed form solution is derived to obtain the displacements and the reactions at the ends of each conductor span. The solution accounts for the nonlinearity of the system and the flexibility of the insulators. Second, a numerical scheme to solve the derived closed-form solution is proposed. Two conductor systems are analyzed under loads resulting from HIW events for validation of the proposed technique. Non-linear Finite Element Analyses (FEA) are also conducted for the same two systems. The responses resulting from the technique are shown to be in a very good agreement with those resulting from the FEA, which confirms the technique accuracy. Meanwhile, the semi-closed form technique shows superior efficiency in terms of the required computational time. The saving in computational time has a great advantage in predicting the response of the conductors under HIW events, since this requires a large number of analyses to cover different potential locations and sizes of those localized events.
In the current study, dynamic and quasi-static analyses were performed to investigate the respons... more In the current study, dynamic and quasi-static analyses were performed to investigate the response of multiple-spanned and single-spanned transmission line conductors under both downburst and synoptic winds considering different wind velocities and different length spans. Two critical downburst configurations, recommended in the literature and expected to cause maximum conductor reactions, were considered in the analyses. The objective of the study was to assess the importance of including the dynamic effect when predicting the conductor`s reactions on the towers. This was achieved by calculating the mean, the background and the resonant reaction components, and evaluating the contribution of the resonant component to the peak reaction. The results show that the maximum contribution of the resonant component is generally low (in the order of 6%) for the multiple-spanned system at different wind velocities for both downburst and synoptic winds. For the single-spanned system, the result show a relatively high maximum contribution (in the order of 16%) at low wind velocity and a low maximum contribution (in the order of 6%) at high wind velocity for both downburst and synoptic winds. Such contributions may justify the usage of the quasi-static approach for analyzing transmission line conductors subjected to the high wind velocities typically used for the line design.
Aerodynamic response of a standard tall building (commonly known as the CAARC model) is investiga... more Aerodynamic response of a standard tall building (commonly known as the CAARC model) is investigated using LES. The LES employs the Consistent Discrete Random Flow Generation (CDRFG) technique to generate the inflow boundary condition allowing accurate depiction of the turbulence spectra and coherency. The building aerodynamic behavior is investigated for two configurations (an isolated building and a building with complex surrounding buildings) and the results are compared with a previous wind tunnel test. It is found that pressure and other wind-induced responses, such as top displacement, top acceleration and base moments, obtained from the LES are in a good agreement with those in the wind tunnel. The average difference between LES and wind tunnel results is found to be 4% for the pressures and 6% for the dynamic responses for the simulated wind directions, which emphasizes the accuracy of the employed model. As expected, comparison between the results for the isolated and the complex surrounding configuration showed 50% and 40% difference for mean and rms pressure coefficients, respectively. The employed LES model leads to an acceptable estimation for the wind pressure distribution and responses of the study building in a time-efficient manner. Therefore, it is expected to encourage the use of CFD in similar wind engineering applications in the future.
Abstract This study reviews the literature on the dynamic response of a Transmission Line (TL) sy... more Abstract This study reviews the literature on the dynamic response of a Transmission Line (TL) system under synoptic wind (conventional atmospheric boundary layer) as well as non-synoptic wind loading (downbursts). Gust-induced response for the conductors and the towers are covered and the limitations in the current structural design codes for wind loading are identified. Three main sections are considered in this study covering synoptic wind loading, downburst, and main conclusions and recommendations. For the case of synoptic wind events, four design codes (ASCE 74 2010, AS/NZS 2010, BS 2001, IEC 2003) specialized in TLs are considered for comparison. Using the ASCE 74 as a datum for normalization, a code ratio (CR) is evaluated for various parameters to assess the discrepancy between the codes. The code ratio for conductor forces CRFc is found to be ranging between 0.81 and 1.44. For tower forces code ratio CRFt, a discrepancy range of 0.68 and 1.85 is noticed. The study highlights the main reasons behind these discrepancies. For the case of downbursts, the study reveals that the event’s size and its relative location to the tower lead to a number of critical load cases that need to be considered. The study provides important design considerations for both synoptic and non-synoptic winds. At the end of the study, a list of the main gaps existing in current design codes and recommendations to fill out these gaps is provided.
A numerical model capable of predicting the dynamic response of pre-stressed concrete transmissio... more A numerical model capable of predicting the dynamic response of pre-stressed concrete transmission poles under both the mean and fluctuating components of synoptic wind loads is developed in this study. A full non-linear dynamic analysis is conducted under a time history variation of wind velocity. The peak total responses, such as conductors’ reactions and poles’ base moments, are determined from this analysis. The same analysis is repeated in a quasi-static manner. Dynamic amplification factors (DAF), defined as the ratio between the maximum response based on a non-linear dynamic analysis and the corresponding value based on a quasi-static analysis, are calculated for the poles and the conductors to quantify the dynamic impact of synoptic wind loads. This factor is used to assess the importance of including the resonant component while estimating the response of the transmission poles. In addition, gust response factors (GRF) defined as the ratio between the peak and mean response...
This study aims at modeling boundary layers (BLs) encountered in sparse and built environments (i... more This study aims at modeling boundary layers (BLs) encountered in sparse and built environments (i.e., open, suburban and urban) at the subsonic Wind Tunnel (WT) at Ryerson University (RU). This WT has an insignificant turbulence intensity and requires a flow-conditioning system consisting of turbulence generating elements (i.e spires, roughness blocks, barriers) to achieve proper turbulent characteristics. This system was developed and validated in the current study in three phases. In phase I, several Computational Fluid Dynamic (CFD) simulations of the tunnel with generating elements were conducted to understand the effect of each element on the flow. This led to a preliminary design of the system, in which horizontal barriers (slats) are added to the spires to introduce turbulence at higher levels of the tunnel. This design was revisited in phase II, to specify slat dimensions leading to target BLs encountered by tall buildings. It was found that rougher BLs require deeper slats ...
Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas o... more Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas of USA, such as Florida and Louisiana. Available design codes provide information about the design of regular roof geometries (e.g. hip/gable roofs), but refer to wind tunnel modelling for complex roof geometries. Due to time and financial constraints physical modelling may not always be possible to carry out. Computational modelling through Large Eddy Simulation (LES) has been used successfully for several wind engineering applications. This paper presents comparisons between LES and previously obtained wind tunnel data of mean and peak pressure coefficients on a low rise building with complex roof geometry. Two different cases, namely: isolated building and the effect of neighbouring buildings have been considered for the most critical wind direction of 135 degrees. Results show that the mean pressure coefficients on the low rise building roof for the case with adjacent buildings were s...
Steel liquid storage tanks in the form of truncated cones are commonly used as containment vessel... more Steel liquid storage tanks in the form of truncated cones are commonly used as containment vessels for water supply or storing chemicals. A number of failures have been recorded in the past few decades for steel liquid tanks and silos under wind loading. A steel conical tank vessel will have a relatively small thickness making it susceptible to buckling under wind loads especially when they are not fully-filled. In this study, a wind tunnel pressure test is performed on an elevated conical tank in order to estimate the external wind pressures when immersed into a boundary layer. The tested tank configuration represents combined conical tanks where the cone is capped with a cylinder. In addition, the effect of terrain exposure and wind speed on the pressure values and wind forces is assessed. The mean and rms pressure coefficients are presented for different test cases in addition to the mean and rms total drag forces that are obtained by integrating the pressure coefficient over the...
This paper studies the dynamic behavior of a multi-span transmission line system under synoptic w... more This paper studies the dynamic behavior of a multi-span transmission line system under synoptic wind considering various speeds to determine the range of wind speeds in which the system experiences resonance. A finite element numerical model was developed for the purpose of this study. This model is employed to assess the dynamic behavior of a self-supported lattice tower line under various wind speeds. Dynamic Amplification Factor (DAF), defined as the ratio between the peak total response to the peak quasi-static response, is evaluated. It is found that conductors’ responses exhibit large DAF compared to the towers especially at low wind speeds (v ≤ 25 m/s). This results from the low natural frequency of the conductors (0.19 Hz) which is close to the wind load frequency while the natural frequency of the tower is equal to 2.36 Hz. In addition, the conductors’ aerodynamic damping decreases with the decrease of wind speed which leads to higher dynamic effect while the tower’s aerody...
ABSTRACT An effective numerical technique to calculate the reactions of a multi-spanned transmiss... more ABSTRACT An effective numerical technique to calculate the reactions of a multi-spanned transmission line conductor system, under arbitrary loads varying along the spans, is developed. Such variable loads are generated by High Intensity Wind (HIW) events in the form of tornadoes and downburst. First, a semi-closed form solution is derived to obtain the displacements and the reactions at the ends of each conductor span. The solution accounts for the nonlinearity of the system and the flexibility of the insulators. Second, a numerical scheme to solve the derived closed-form solution is proposed. Two conductor systems are analyzed under loads resulting from HIW events for validation of the proposed technique. Non-linear Finite Element Analyses (FEA) are also conducted for the same two systems. The responses resulting from the technique are shown to be in a very good agreement with those resulting from the FEA, which confirms the technique accuracy. Meanwhile, the semi-closed form technique shows superior efficiency in terms of the required computational time. The saving in computational time has a great advantage in predicting the response of the conductors under HIW events, since this requires a large number of analyses to cover different potential locations and sizes of those localized events.
In the current study, dynamic and quasi-static analyses were performed to investigate the respons... more In the current study, dynamic and quasi-static analyses were performed to investigate the response of multiple-spanned and single-spanned transmission line conductors under both downburst and synoptic winds considering different wind velocities and different length spans. Two critical downburst configurations, recommended in the literature and expected to cause maximum conductor reactions, were considered in the analyses. The objective of the study was to assess the importance of including the dynamic effect when predicting the conductor`s reactions on the towers. This was achieved by calculating the mean, the background and the resonant reaction components, and evaluating the contribution of the resonant component to the peak reaction. The results show that the maximum contribution of the resonant component is generally low (in the order of 6%) for the multiple-spanned system at different wind velocities for both downburst and synoptic winds. For the single-spanned system, the result show a relatively high maximum contribution (in the order of 16%) at low wind velocity and a low maximum contribution (in the order of 6%) at high wind velocity for both downburst and synoptic winds. Such contributions may justify the usage of the quasi-static approach for analyzing transmission line conductors subjected to the high wind velocities typically used for the line design.
Aerodynamic response of a standard tall building (commonly known as the CAARC model) is investiga... more Aerodynamic response of a standard tall building (commonly known as the CAARC model) is investigated using LES. The LES employs the Consistent Discrete Random Flow Generation (CDRFG) technique to generate the inflow boundary condition allowing accurate depiction of the turbulence spectra and coherency. The building aerodynamic behavior is investigated for two configurations (an isolated building and a building with complex surrounding buildings) and the results are compared with a previous wind tunnel test. It is found that pressure and other wind-induced responses, such as top displacement, top acceleration and base moments, obtained from the LES are in a good agreement with those in the wind tunnel. The average difference between LES and wind tunnel results is found to be 4% for the pressures and 6% for the dynamic responses for the simulated wind directions, which emphasizes the accuracy of the employed model. As expected, comparison between the results for the isolated and the complex surrounding configuration showed 50% and 40% difference for mean and rms pressure coefficients, respectively. The employed LES model leads to an acceptable estimation for the wind pressure distribution and responses of the study building in a time-efficient manner. Therefore, it is expected to encourage the use of CFD in similar wind engineering applications in the future.
Abstract This study reviews the literature on the dynamic response of a Transmission Line (TL) sy... more Abstract This study reviews the literature on the dynamic response of a Transmission Line (TL) system under synoptic wind (conventional atmospheric boundary layer) as well as non-synoptic wind loading (downbursts). Gust-induced response for the conductors and the towers are covered and the limitations in the current structural design codes for wind loading are identified. Three main sections are considered in this study covering synoptic wind loading, downburst, and main conclusions and recommendations. For the case of synoptic wind events, four design codes (ASCE 74 2010, AS/NZS 2010, BS 2001, IEC 2003) specialized in TLs are considered for comparison. Using the ASCE 74 as a datum for normalization, a code ratio (CR) is evaluated for various parameters to assess the discrepancy between the codes. The code ratio for conductor forces CRFc is found to be ranging between 0.81 and 1.44. For tower forces code ratio CRFt, a discrepancy range of 0.68 and 1.85 is noticed. The study highlights the main reasons behind these discrepancies. For the case of downbursts, the study reveals that the event’s size and its relative location to the tower lead to a number of critical load cases that need to be considered. The study provides important design considerations for both synoptic and non-synoptic winds. At the end of the study, a list of the main gaps existing in current design codes and recommendations to fill out these gaps is provided.
Uploads
Papers by Haitham Aboshosha