Comparison of Dynamic Analysis Methods in a Cable-Stayed Tower Under Extreme Wind Loads in Cuba

2019 ◽  
Vol 60 (3) ◽  
pp. 210-220
Author(s):  
Ingrid Fernández Lorenzo ◽  
Bruno Jorge Clavelo Elena ◽  
Olivia Ollet Otero ◽  
Vivian Beatriz Elena Parnás
Keyword(s):  
Dynamic Analysis ◽  
Dynamic Method ◽  
Time History ◽  
Wind Loads ◽  
Wind Loading ◽  
Axial Loads ◽  
Wind Speeds ◽  
Extreme Wind ◽  
Patch Load ◽  
Guyed Mast

Several methods and investigations have been conducted in order to dynamically analyze the behavior of guyed mast telecommunication towers subject to wind loading, due to the importance of such structures in current society. Due to their slenderness, flexibility and lightweight, these structures are particularly susceptible to wind loads, being strong hurricane winds the cause of several tower failures in Cuba. This works conducts the study of a 120 meters tall guyed mast, model MAR 2008, facing extreme wind loads in two different locations. The structure is modeled using the computational assisted software SAP2000 and a dynamic analysis is undertaken using two methods: the equivalent static method "Patch Load" and the full dynamic method "Time History" using Direct Integration. The basic wind speeds are determined according to the Method of Independent Storms (MIS) and standard turbulence intensities for cyclonés regions. Synthetic functions are generated for different heights of the tower in order to apply the "Time History" dynamic method. Finally, a comparison is established between the results in terms of axial loads, joint reactions and displacements. The main conclusion of the study is that as the basic speed decreases, there is a higher resemblance in inner forces and displacements between the results obtained for the two studied methods.

scholarly journals Determining the Magnitude of Wind Loads on Structures in Kenya according to the Eurocodes

2021 ◽  
Author(s):  
Muthomi Munyua
Keyword(s):  
Wind Speed ◽  
Structural Design ◽  
Wind Load ◽  
Wind Data ◽  
Wind Loads ◽  
Wind Loading ◽  
Design Code ◽  
Wind Speeds ◽  
The Uk

This paper provides guidance on the use of existing wind data in Kenya with the Eurocodes despite the absence of the local national annexes. The determination of wind loads in the structural design of buildings according to the Eurocode Standard KS EN 1991-1-4:2005 in Kenya is challenging because of the lack of the Kenya National Annex. The design code commonly used in Kenya is CP3-Chapter V-2:1972 that uses the three-second gust duration. This gust duration results in higher magnitudes of wind loads that end up making the structures unnecessarily robust and uneconomical. Using the Eurocodes has the promise of achieving more economical designs because it uses the 10-minute gust duration. The 10-minute gust duration results in typically lower magnitudes of wind loads than the three-second gust duration for the same wind speed. Kenya adopted the Eurocodes in September 2012 but has not yet developed its national annexes opting instead to use the UK National Annexes. The UK National Annexes are applicable to Kenya in some scenarios but not in others such as wind loading. The lack of the Kenya National Annexes has led to difficulties in the adoption of the Eurocodes. This paper outlines a procedure in which the existing wind data given in three-second gusts could be converted to 10-minute wind speeds. Once converted, the method described in the UK National Annex could then be followed selectively to determine the wind load on a structure. Lastly, the paper recommends that wind data collected from 1977 to 2021 by the Kenya Meteorological Department be incorporated to the development of the wind map for the Kenya National Annex to KS EN 1991-1-4:2005

scholarly journals The mechanical stability of the world’s tallest broadleaf trees

2019 ◽  
Author(s):  
T. Jackson ◽  
A. Shenkin ◽  
N. Majalap ◽  
J. bin Jami ◽  
A. bin Sailim ◽  
...  
Keyword(s):  
Mechanical Stability ◽  
Tree Height ◽  
Wind Loading ◽  
Maximum Height ◽  
Wind Speeds ◽  
Extreme Wind ◽  
North Borneo ◽  
Relative Rarity ◽  
Extreme Wind Speeds ◽  
The Tropics

AbstractThe factors that limit the maximum height of trees, whether ecophysiological or mechanical, are the subject of longstanding debate. Here we examine the role of mechanical stability in limiting tree height and focus on trees from the tallest tropical forests on Earth, in Sabah, Malaysian Borneo, including the recently discovered tallest tropical tree, a 100.8 mShorea faguetiana. We use terrestrial laser scans,in situstrain gauge data and finite-element simulations to map the architecture of tall broadleaf trees and monitor their response to wind loading. We demonstrate that a tree’s risk of breaking due to gravity or self-weight decreases with tree height and is much more strongly affected by tree architecture than by material properties. In contrast, wind damage risk increases with tree height despite the larger diameters of tall trees, resulting in a U-shaped curve of mechanical risk with tree height. The relative rarity of extreme wind speeds in north Borneo may be the reason it is home to the tallest trees in the tropics.

scholarly journals Extreme value analysis of Fiji's wind records

2005 ◽  
Vol 23 (1) ◽  
pp. 1 ◽  
Author(s):  
S P Rattan ◽  
R N Sharma
Keyword(s):  
Tropical Cyclones ◽  
Extreme Value ◽  
Wind Loading ◽  
Extreme Value Analysis ◽  
Value Analysis ◽  
Analysis Techniques ◽  
Wind Speeds ◽  
Extreme Wind ◽  
Modern Methods ◽  
Extreme Wind Speeds

A number of extreme value analysis techniques are utilised to predict basic design gust wind speeds for Fiji, which lies in a tropical cyclone prone region. The study shows that a number of modern methods tend to highly under-predict extreme wind speeds in regions of Fiji severely affected by tropical cyclones, although their skills improve in less severely affected regions. The reference for comparison was Dorman?s method, which has been previously used as a guidance for development of Region D wind speeds in the Australian wind loading code ? the AS1170.2-1989. In the case of Fiji, this study recommends the AS1170.2-1989 Region C provisions for Suva and the eastern coasts of the main island of Viti Levu only, and the AS1170.2-1989 Region D provisions elsewhere. This is significantly different to the provisions of the current National Building Code of Fiji (1990) which allow for the use of AS1170.2-1989 Region C provisions for all of Fiji. This difference is attributed to differences in the frequency and intensity of tropical cyclones visiting Fiji as compared with those for Australian Region C.

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

2012 ◽  
Vol 226-228 ◽  
pp. 1240-1249 ◽  
Author(s):  
Chris Ladubec ◽  
Ashraf A. El Damatty ◽  
Ayman M. El Ansary
Keyword(s):  
Linear Analysis ◽  
Wind Loading ◽  
Nonlinear Behaviour ◽  
Transmission Tower ◽  
Axial Loads ◽  
Frame Element ◽  
Geometric Nonlinear ◽  
Critical Configurations ◽  
Extreme Wind ◽  
Computational Fluid Dynamics Cfd

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.

scholarly journals Determining the Magnitude of Wind Loads on Structures in Kenya according to the Eurocodes

2021 ◽  
Author(s):  
Muthomi Munyua
Keyword(s):  
Wind Speed ◽  
Structural Design ◽  
Wind Load ◽  
Wind Data ◽  
Wind Loads ◽  
Wind Loading ◽  
Code Of Practice ◽  
Wind Speeds ◽  
The Uk

This study provided guidance on the use of existing wind data in Kenya with the Eurocodes despite the absence of the local national annexes. The determination of wind loads in the structural design of buildings according to the Eurocode Standard KS EN 1991-1-4:2005 had several challenges. The code of practice commonly used in Kenya was CP3-Chapter V-2:1972 that used the three-second gust duration. This gust duration resulted in higher magnitudes of wind loads that ended up making the structures unnecessarily robust and uneconomical. Using the Eurocodes had the promise of achieving more economical designs because it used the 10-minute gust duration. The 10-minute gust duration resulted in typically lower magnitudes of wind loads than the three-second gust duration for the same wind speed. Kenya adopted the Eurocodes in September 2012 but had not yet developed its national annexes opting instead to use the UK National Annexes. The UK National Annexes were applicable to Kenya in some scenarios but not in others such as wind loading. The lack of the Kenya National Annexes led to difficulties in the adoption of the Eurocodes. This paper outlined a procedure in which the existing wind data given in three-second gusts could be converted to 10-minute wind speeds. Once converted, the method described in the UK National Annex could then be followed selectively to determine the wind load on a structure. Lastly, the paper recommended that wind data collected from 1977 to 2021 by the Kenya Meteorological Department be incorporated to the development of the wind map for the Kenya National Annex to KS EN 1991-1-4:2005.

A comparison of the gust factor method and the patch load method of analysis of guyed towers

1996 ◽  
Vol 23 (4) ◽  
pp. 862-871 ◽  
Author(s):  
Robert G. Selby ◽  
Robert B. Dryburgh
Keyword(s):  
Dynamic Method ◽  
Wind Loading ◽  
Dynamic Effects ◽  
Gust Factor ◽  
Parametric Studies ◽  
Patch Load ◽  
Load Analysis ◽  
Guyed Towers ◽  
Tower Height ◽  
Supporting Structures

The Canadian standard CAN/CSA-S37-94 "Antennas, towers and antenna supporting structures" (S37) has introduced as an appendix a quasi-dynamic method of analysis. This patch load method yields a more realistic pattern of forces in a guyed tower, but S37 contains no firm guidelines as to when this new method is required over the conventional static gust factor approach. This paper describes various comparative studies that were made to determine the conditions under which the normally used gust factor approach does not give sufficiently acceptable results so that patch load analyses are required. Results of the parametric studies and the analyses of a large number of actual towers showed that leg loads in the upper few spans tended to be about 15% larger on average in a patch load analysis. Face shears at the guy supports were also about 15% higher on average in the patch load method. The studies revealed no strong trends between the patch load and gust factor correlation and the tower parameters, although there were slight trends suggesting that a patch load analysis was warranted if the tower height was greater than 250 m, the aspect ratio was greater than 120, or the drag area exceeded 2.0 m2/m. The presence of a cantilever accentuated the margin between the results of the two methods. Key words: guyed towers, analysis, wind loading, dynamic effects, patch load, gust factor.

Forecasting of Tornadoes and Downbursts

2020 ◽  
Author(s):  
Djordje Romanic
Keyword(s):  
Chaos Theory ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Weather Forecasts ◽  
Wind Speeds ◽  
The Past ◽  
Extreme Wind ◽  
Extreme Wind Speeds ◽  
Numerical Weather Prediction Models

Tornadoes and downbursts cause extreme wind speeds that often present a threat to human safety, structures, and the environment. While the accuracy of weather forecasts has increased manifold over the past several decades, the current numerical weather prediction models are still not capable of explicitly resolving tornadoes and small-scale downbursts in their operational applications. This chapter describes some of the physical (e.g., tornadogenesis and downburst formation), mathematical (e.g., chaos theory), and computational (e.g., grid resolution) challenges that meteorologists currently face in tornado and downburst forecasting.

scholarly journals A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam

2021 ◽  
Vol 9 (3) ◽  
pp. 246
Author(s):  
Difu Sun ◽  
Junqiang Song ◽  
Xiaoyong Li ◽  
Kaijun Ren ◽  
Hongze Leng
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Sea Surface ◽  
High Wind Speed ◽  
Wave State ◽  
Wind Speeds ◽  
Sea Surface Roughness ◽  
Extreme Wind ◽  
The Impact

A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.

Safety Analysis of Static & Dynamic Method in Foundation Pit Considering Unsaturated Seepage

2013 ◽  
Vol 444-445 ◽  
pp. 946-950
Author(s):  
Yi Hong Zhou ◽  
Xiu Wen Li ◽  
Yun Feng Peng ◽  
Ting Zhang
Keyword(s):  
Slope Stability ◽  
Dynamic Analysis ◽  
Unsaturated Zone ◽  
Dynamic Method ◽  
Soil Consolidation ◽  
Main Study ◽  
Dynamic Boundary Conditions ◽  
Foundation Pit ◽  
Consolidation Settlement ◽  
Unsaturated Seepage

In order to study whether foundation pit is stable or not after excavation, the article adopted the Duncan E-B model to make static analysis for the excavation scheme which considering the soil consolidation settlement and to make dynamic analysis under the action of earthquake wave of EL Centro. To make a slope stability of foundation pit analysis by calculating static and dynamic boundary conditions which further coupled with the Newmark method. The main study is the foundation settlement and earth-rock dams, slope stability of foundation pit conditions that considering unsaturated zone seepage conditions of earth-rock dams after the excavation. The results indicated that: in the static & dynamic analysis, the distribution about settlement is reasonable, earth-rock dam and foundation pit slope is in the steady state, the excavation scheme is reasonable and feasible.

Seismic Ratchetting of Single-Degree-of-Freedom Steel Bridge Columns

2018 ◽  
Vol 763 ◽  
pp. 295-300 ◽  
Author(s):  
Khaled Saif ◽  
Chin Long Lee ◽  
Trevor Yeow ◽  
Gregory A. MacRae
Keyword(s):  
Time History ◽  
Steel Structures ◽  
Bridge Columns ◽  
Steel Bridge ◽  
Axial Loads ◽  
Maximum Displacement ◽  
Residual Displacements ◽  
Average Maximum ◽  
Force Reduction ◽  
Nonlinear Time History

Nonlinear time history analyses of SDOF bridge columns with elasto-plastic flexural behaviour which are subject to eccentric gravity loading are conducted to quantify the effect of ratchetting. Peak and residual displacements were used as indicators of the degree of ratchetting. The effects of member axial loads and design force reduction factors were also investigated. It was shown that displacement demands increased with increasing eccentric moment. For eccentric moment of 30% of the yield moment, the average maximum and residual displacements increase by 4.2 and 3.8 times the maximum displacement, respectively, which the engineers calculate using static methods without considering ratchetting effect. Design curves for estimating the displacement demands for different eccentric moments are also developed. The current NZ1170.5 (2016) provisions were found to be inadequate in estimating the maximum displacement for steel structures, and hence, new provisions for steel structures should be presented.

Sign in / Sign up

Export Citation Format

Share Document