Parametric Study of the Dynamic Along-Wind Response of a Guyed Tower

As wireless communications spread, there is an increasing demand for antenna supportingstructures. Lattice towers are commonly used systems, either self-supported or guyed. The latter arechosen for economical reasons when there is enough space for their location. Radio and television em-ploy structures that range between 100 and 600 m and communication towers for mobile phones arearound 60 m though higher structures are also constructed. For large heights, guyed masts are indi-cated. However, it depends on the customer preferences, suppliers, budget and location. Generally,self-supported structures are preferred in urban areas and guyed masts in the countryside. Nowadays thedemand for more accurate and reliable communication systems poses higher structural demands sincethe signal technology sometimes requires of very small motions of the supporting structures to achieve ahigh quality transmission. The design of these structures is, in general, carried out following the standardcodes and simplified models. The dynamic actions, as wind and earthquakes, are not addressed in detailwith exception of special cases, despite the large potential of adverse impact. Guyed structures stiffnessare highly dependent on the guys tension. The influence of this parameter is relevant to the dynamicresponse. Also, the mast stiffness and damping are variables of interest. In this work, the dynamic re-sponse of a communication lattice guyed tower is analyzed under wind loads and the degree of influenceof the mentioned parameters is assessedLaboratorio de Capa Límite y Fluidodinámica AmbientalGrupo Fluidodinámica Computaciona

Parametric Study of the Dynamic Along-Wind Response of a Guyed Tower

As wireless communications spread, there is an increasing demand for antenna supportingstructures. Lattice towers are commonly used systems, either self-supported or guyed. The latter arechosen for economical reasons when there is enough space for their location. Radio and television em-ploy structures that range between 100 and 600 m and communication towers for mobile phones arearound 60 m though higher structures are also constructed. For large heights, guyed masts are indi-cated. However, it depends on the customer preferences, suppliers, budget and location. Generally,self-supported structures are preferred in urban areas and guyed masts in the countryside. Nowadays thedemand for more accurate and reliable communication systems poses higher structural demands sincethe signal technology sometimes requires of very small motions of the supporting structures to achieve ahigh quality transmission. The design of these structures is, in general, carried out following the standardcodes and simplified models. The dynamic actions, as wind and earthquakes, are not addressed in detailwith exception of special cases, despite the large potential of adverse impact. Guyed structures stiffnessare highly dependent on the guys tension. The influence of this parameter is relevant to the dynamicresponse. Also, the mast stiffness and damping are variables of interest. In this work, the dynamic re-sponse of a communication lattice guyed tower is analyzed under wind loads and the degree of influenceof the mentioned parameters is assessedLaboratorio de Capa Límite y Fluidodinámica AmbientalGrupo Fluidodinámica Computaciona

Modal Features and Dynamic Behavior of a Nonlinear 3D Guyed Mast with Uncertain Guys Pretension

The study of the nonlinear dynamic characteristics and response of a guyed mast, considering the uncertainty of the guys pretension is reported in this work. A computational model is constructed with the mast represented by an equivalent beam-column and the three guys at one level by cables with an initial pretension and only having tensile capacity. Starting from the energy formulation of beams and nonlinear cables, the continuous equations are discretized using finite element techniques, considering Hermite elements for the mast (Bernoulli beam theory) and quadratic elements for the nonlinear guys. Also, the second order effect due to the axial loads on the mast is taken into account. An ad hoc software, developed by the first author, is employed here to explore natural frequencies and modes of the structure considering the uncertainty propagation of the stochastic guys pretension. Since the guys design value can be modified at the construction stage and more, during the service life, the pretension force is modeled as a random variable with a probability density function (PDF) derived from the Principle of Maximum Entropy (PME). The model herein presented contributes to attain a more realistic description of the structure, mainly regarding the three-dimensional representation and the sensibility to the variability of the guys pretensions. The results here presented (natural frequencies and modes) obtained through an uncertainty quantification analysis, improve the understanding of the real dynamic properties and behavior of slender and flexible guyed structures.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Modal Features and Dynamic Behavior of a Nonlinear 3D Guyed Mast with Uncertain Guys Pretension

The study of the nonlinear dynamic characteristics and response of a guyed mast, considering the uncertainty of the guys pretension is reported in this work. A computational model is constructed with the mast represented by an equivalent beam-column and the three guys at one level by cables with an initial pretension and only having tensile capacity. Starting from the energy formulation of beams and nonlinear cables, the continuous equations are discretized using finite element techniques, considering Hermite elements for the mast (Bernoulli beam theory) and quadratic elements for the nonlinear guys. Also, the second order effect due to the axial loads on the mast is taken into account. An ad hoc software, developed by the first author, is employed here to explore natural frequencies and modes of the structure considering the uncertainty propagation of the stochastic guys pretension. Since the guys design value can be modified at the construction stage and more, during the service life, the pretension force is modeled as a random variable with a probability density function (PDF) derived from the Principle of Maximum Entropy (PME). The model herein presented contributes to attain a more realistic description of the structure, mainly regarding the three-dimensional representation and the sensibility to the variability of the guys pretensions. The results here presented (natural frequencies and modes) obtained through an uncertainty quantification analysis, improve the understanding of the real dynamic properties and behavior of slender and flexible guyed structures.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Modal Features and Dynamic Behavior of a Nonlinear 3D Guyed Mast with Uncertain Guys Pretension

The study of the nonlinear dynamic characteristics and response of a guyed mast, considering the uncertainty of the guys pretension is reported in this work. A computational model is constructed with the mast represented by an equivalent beam-column and the three guys at one level by cables with an initial pretension and only having tensile capacity. Starting from the energy formulation of beams and nonlinear cables, the continuous equations are discretized using finite element techniques, considering Hermite elements for the mast (Bernoulli beam theory) and quadratic elements for the nonlinear guys. Also, the second order effect due to the axial loads on the mast is taken into account. An ad hoc software, developed by the first author, is employed here to explore natural frequencies and modes of the structure considering the uncertainty propagation of the stochastic guys pretension. Since the guys design value can be modified at the construction stage and more, during the service life, the pretension force is modeled as a random variable with a probability density function (PDF) derived from the Principle of Maximum Entropy (PME). The model herein presented contributes to attain a more realistic description of the structure, mainly regarding the three-dimensional representation and the sensibility to the variability of the guys pretensions. The results here presented (natural frequencies and modes) obtained through an uncertainty quantification analysis, improve the understanding of the real dynamic properties and behavior of slender and flexible guyed structures.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Reliability ofwood utility poles under stochastic wind load and material considering knots

Wood utility poles are simple structures used in power networks and their failure may produce a significant impact on their reliability as well as economic consequences. Wind loads are one of the main causes of damage in wood utility poles. The present study addresses the dynamic behavior of Argentinean Eucalyptus grandis wood poles with uncertain material properties under stochastic wind load. Regarding the material, the lengthwise variability of the Modulus of Elasticity (MOE) and the second moment of area are simulated through the Weak Zone (WZ) model taking into account the knots presence. The stochastic wind velocity field is derived using the Spectral Representation Method (SRM) considering temporal and spatial correlation. Then, the wind load is obtained under the considerations of the Argentinean standard CIRSOC 102. The governing equations are discretized through the Finite Element Method (FEM). The stochastic analysis is performed by means of Monte Carlo Simulations (MCS). In this study, displacements are evaluated such that a percentage of damage is found for each wind velocity. Fragility curves are a useful means to evaluate the failure probability of the poles for a defined failure mode, under a given range of demand, here the wind load. The WZ model results are compared with other MOE models previously developed (as a random variable and as a random field through the Non Gaussian Karhunen-Loève Expansion). Also, confidence bands of the fragility curves are obtained for 95% of confidence.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Reliability ofwood utility poles under stochastic wind load and material considering knots

Wood utility poles are simple structures used in power networks and their failure may produce a significant impact on their reliability as well as economic consequences. Wind loads are one of the main causes of damage in wood utility poles. The present study addresses the dynamic behavior of Argentinean Eucalyptus grandis wood poles with uncertain material properties under stochastic wind load. Regarding the material, the lengthwise variability of the Modulus of Elasticity (MOE) and the second moment of area are simulated through the Weak Zone (WZ) model taking into account the knots presence. The stochastic wind velocity field is derived using the Spectral Representation Method (SRM) considering temporal and spatial correlation. Then, the wind load is obtained under the considerations of the Argentinean standard CIRSOC 102. The governing equations are discretized through the Finite Element Method (FEM). The stochastic analysis is performed by means of Monte Carlo Simulations (MCS). In this study, displacements are evaluated such that a percentage of damage is found for each wind velocity. Fragility curves are a useful means to evaluate the failure probability of the poles for a defined failure mode, under a given range of demand, here the wind load. The WZ model results are compared with other MOE models previously developed (as a random variable and as a random field through the Non Gaussian Karhunen-Loève Expansion). Also, confidence bands of the fragility curves are obtained for 95% of confidence.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Reliability ofwood utility poles under stochastic wind load and material considering knots

Wood utility poles are simple structures used in power networks and their failure may produce a significant impact on their reliability as well as economic consequences. Wind loads are one of the main causes of damage in wood utility poles. The present study addresses the dynamic behavior of Argentinean Eucalyptus grandis wood poles with uncertain material properties under stochastic wind load. Regarding the material, the lengthwise variability of the Modulus of Elasticity (MOE) and the second moment of area are simulated through the Weak Zone (WZ) model taking into account the knots presence. The stochastic wind velocity field is derived using the Spectral Representation Method (SRM) considering temporal and spatial correlation. Then, the wind load is obtained under the considerations of the Argentinean standard CIRSOC 102. The governing equations are discretized through the Finite Element Method (FEM). The stochastic analysis is performed by means of Monte Carlo Simulations (MCS). In this study, displacements are evaluated such that a percentage of damage is found for each wind velocity. Fragility curves are a useful means to evaluate the failure probability of the poles for a defined failure mode, under a given range of demand, here the wind load. The WZ model results are compared with other MOE models previously developed (as a random variable and as a random field through the Non Gaussian Karhunen-Loève Expansion). Also, confidence bands of the fragility curves are obtained for 95% of confidence.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí

Interacción en las aulas de matemáticas de primaria de Reino Unido y España

La investigación en Educación Matemática se ha interesado por el análisis de la interacción entre un maestro de Primaria y sus alumnos cuando resuelven conjuntamente problemas en el aula (e.g., Sánchez et al., 2014). Los resultados obtenidos en estudios en España mostraron que el maestro promueve escasamente el razonamiento cuando resuelve problemas con sus estudiantes (Rosales et al., 2012). Por eso es de interés conocer qué sucede en otros países. En este trabajo se pretenden comparar los procesos que se explicitan durante la interacción de maestros de Primaria de Reino Unido y España cuando resuelven problemas similares con sus estudiantes

Cuantificación de incertidumbre en una columna de iluminación con cargas axiales y laterales

En este trabajo, se estudia el problema estructural estático de una columna de iluminación de tres tramos sujeto a cargas gravitatorias y la acción lateral del viento. La torre que soporta una luminaria es modelada como una viga-columna bajo la acción de fuerzas y momentos concentrados, cargas axiales y laterales distribuidas representando las acciones del viento y el peso propio tanto respecto de la columna como de la luminaria. En una primera etapa, se deducen las ecuaciones diferenciales de coeficientes variables que, junto a las condiciones de borde, gobiernan el problema. Se incluye el efecto de segundo orden debido a las cargas axiales. La solución analítica expresada en series de potencia es verificada con un modelo de una torre similar resuelto con un software comercial de elementos finitos dando lugar a excelentes resultados. Una vez resuelto el problema determinístico, se utiliza la solución analítica para abordar la cuantificación de incertidumbre ante la hipótesis de que la velocidad de referencia del viento pueda ser una variable estocástica suponiendo que la torre pueda instalarse en una región dentro de la cual varía dicha velocidad. Se propone una función exponencial truncada para la distribución de probabilidad que surge de aplicar el Principio de Máxima Entropía con la información disponible de la variable aleatoria, i.e. un valor medio y un rango de valores. Las simulaciones se realizan utilizando el método de Monte Carlo. Se analizan desplazamientos en la cima de la columna y momentos en la base a través de herramientas estadísticas para valorar la sensibilidad estructural a las variaciones de la velocidad de referencia del viento.Publicado en: Mecánica Computacional vol. XXXV, no. 21Facultad de Ingenierí