Publication: Desarrollo y caracterización del comportamiento cíclico de un sistema de disipación de energía multidireccional en base a elementos u- shaped
Loading...
Date
2022-12
Authors
González Galleguillos, Jorge Ignacio
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Posterior al mega terremoto de Maule 2010 (8.8 Mw), se evidenciaron graves deficiencias en algunos puentes viales chilenos, especialmente en aquellos que presentan un ángulo de esviaje. Debido a esto, y con el fin de disminuir la vulnerabilidad símica de dichas estructuras, nuevos criterios de diseño sísmico fueron plasmados en el Manual de Carreteras. A pesar de lo anterior, estudios recientes han planteado que estos criterios no apuntan a que los puentes permanezcan operacionales luego de un evento sísmico severo, lo cual podría afectar la resiliencia de la red vial nacional.
Este trabajo se enmarca en un proyecto FONDECYT que tiene por objetivo mejorar la resiliencia de los puentes esviados chilenos mediante la incorporación de sistemas de disipación de energía. En particular, en esta tesis se presenta el desarrollo y evaluación de un sistema de disipación de energía multidireccional en base a elementos con forma de U (U-Shaped) que pueda ser implementado en puentes viales.
Con tal objetivo, en este trabajo se llevó a cabo una campaña experimental donde se ensayaron probetas de acero tipo U-Shaped, las cuales fueron sometidas a varios protocolos de carga cíclicos de amplitud constante y de amplitud creciente. El fin de estos ensayos es poder caracterizar el comportamiento de un elemento U-Shaped cuando es solicitado en dos direcciones de carga. Lo anterior, se llevó a cabo mediante registros visuales de los daños experimentados por los especímenes, identificando los patrones para las grietas observadas, y más importante aún, registrando las fuerzas y desplazamientos de cada espécimen. Los resultados de la campaña experimental evidenciaron que las curvas de histéresis de los elementos U-Shaped presentan un comportamiento estable a medida que los ciclos de desplazamiento transcurrieron, sin que existiera una notoria degradación de la resistencia. De las curvas fuerza-desplazamiento se pudo observar su propiedad de simetría con respecto al sentido de la carga. Adicionalmente, los resultados experimentales se contrastaron con fórmulas analíticas encontradas en la literatura, de la cual se pudieron obtener factores para poder estimar de mejor manera los valores importantes para el diseño.
De manera paralela al trabajo de laboratorio, se realizaron estudios numéricos mediante el desarrollo de modelos de elementos finitos para su posterior calibración y comparación con los resultados experimentales. En este contexto, en primer lugar, se realizó una cantidad importante de modelos para poder calibrar los parámetros del material utilizado. A partir de esta calibración, se pudo evidenciar que el software es capaz de representar de manera adecuada el comportamiento cíclico que experimentan los elementos U-Shaped. Posterior a esto, se realizaron más simulaciones que permitieron establecer relaciones entre las propiedades de estos elementos cuando son cargados en 0° y cuando son cargados en 90°. Estas relaciones permitieron establecer un factor CK, el cual permite calcular la rigidez de un elemento U-Shaped cargado en 90° a partir de su rigidez cuando es cargado en 0°. De la misma forma se estableció un factor CFy que permite relacionar la fuerza de fluencia del elemento cargado en 90° y 0°.
A partir de las simulaciones de los elementos U-Shaped, se realizaron modelos a nivel de sistema, es decir, del sistema multidireccional. Para ello, se definieron cuatro configuraciones distintas, donde se contrastaron las curvas de histéresis entre los resultados obtenidos. De estos análisis se determinó que el comportamiento de un sistema multidireccional de elementos U-Shaped queda completamente determinado si es que se conoce el comportamiento de un solo elemento cargado en 0° y 90°. Además, gracias a esto y los coeficientes anteriores se pudo establecer una ecuación que permite calcular la rigidez y fuerza de fluencia de un sistema de disipación de energía en base a elementos U-Shaped, lo cual se prevé será de mucha utilidad para el diseño e implementación de este sistema.
After the 2010 Maule mega-earthquake (8.8 Mw), serious deficiencies were found in some Chilean highway bridges, especially those with a skew angle. Due to this, and to reduce the seismic vulnerability of these structures, new seismic design criteria were included in the Bridge Design Manual (Manual de Carreteras). Despite the above, recent studies have stated that these criteria do not indicate that the bridges remain operational after a severe seismic event, which could affect the resilience of the national road network. This work is part of a FONDECYT project that aims to improve the resilience of Chilean skewed bridges by incorporating energy dissipation systems. This thesis presents the development and evaluation of a multidirectional energy dissipation system based on U-shaped elements that can be implemented on highway bridges. With this objective, in this work an experimental campaign was carried out where U-Shaped steel specimens were tested, which were subjected to various cyclical load protocols of constant amplitude and increasing amplitude. The purpose of these tests is to be able to characterize the behavior of a U-Shaped element when it is requested in two load directions. This was done by visually recording the damage experienced by the specimens, identifying the patterns for the observed cracks, and more importantly, recording the forces and displacements of each specimen. The results of the experimental campaign showed that the hysteresis curves of the U-Shaped elements present a stable behavior as the displacement cycles elapsed, without there being a noticeable degradation of resistance. From the force-displacement curves it was possible to observe its property of symmetry with respect to the direction of the load. Additionally, the experimental results were contrasted with analytical formulas found in the literature, from which factors could be obtained to better estimate the important values for the design. Parallel to the laboratory work, numerical studies were carried out through the development of finite element models for their subsequent calibration and comparison with the experimental results. In this context, first of all, a significant number of models were made in order to calibrate the parameters of the material used. From this calibration, it was possible to show that the software is capable of adequately represent the cyclical behavior experienced by the U-Shaped elements. After this, more simulations were carried out that allowed establishing relationships between the properties of these elements when they are loaded at 0° and when they are loaded at 90°. These relations allowed establishing a CK factor, which allows to calculate the stiffness of a U-Shaped element loaded at 90° from its stiffness when loaded at 0°. In the same way, a CFy factor was established that allows the yield force of the loaded element at 90° and 0° to be related. From the simulations of the U-Shaped elements, models were made at a system level, that is, in the multidirectional system. For this, four different configurations were defined, where the hysteresis curves between the results obtained were contrasted. From these analyzes it was determined that the behavior of a multidirectional system of U-Shaped elements is completely determined if the behavior of a single element loaded at 0° and 90° is known. In addition, thanks to this and the previous coefficients, it was possible to establish an equation that allows calculating the stiffness and yield strength of an energy dissipation system based on U-Shaped elements, which is expected to be very useful for the design and implementation of this system.
After the 2010 Maule mega-earthquake (8.8 Mw), serious deficiencies were found in some Chilean highway bridges, especially those with a skew angle. Due to this, and to reduce the seismic vulnerability of these structures, new seismic design criteria were included in the Bridge Design Manual (Manual de Carreteras). Despite the above, recent studies have stated that these criteria do not indicate that the bridges remain operational after a severe seismic event, which could affect the resilience of the national road network. This work is part of a FONDECYT project that aims to improve the resilience of Chilean skewed bridges by incorporating energy dissipation systems. This thesis presents the development and evaluation of a multidirectional energy dissipation system based on U-shaped elements that can be implemented on highway bridges. With this objective, in this work an experimental campaign was carried out where U-Shaped steel specimens were tested, which were subjected to various cyclical load protocols of constant amplitude and increasing amplitude. The purpose of these tests is to be able to characterize the behavior of a U-Shaped element when it is requested in two load directions. This was done by visually recording the damage experienced by the specimens, identifying the patterns for the observed cracks, and more importantly, recording the forces and displacements of each specimen. The results of the experimental campaign showed that the hysteresis curves of the U-Shaped elements present a stable behavior as the displacement cycles elapsed, without there being a noticeable degradation of resistance. From the force-displacement curves it was possible to observe its property of symmetry with respect to the direction of the load. Additionally, the experimental results were contrasted with analytical formulas found in the literature, from which factors could be obtained to better estimate the important values for the design. Parallel to the laboratory work, numerical studies were carried out through the development of finite element models for their subsequent calibration and comparison with the experimental results. In this context, first of all, a significant number of models were made in order to calibrate the parameters of the material used. From this calibration, it was possible to show that the software is capable of adequately represent the cyclical behavior experienced by the U-Shaped elements. After this, more simulations were carried out that allowed establishing relationships between the properties of these elements when they are loaded at 0° and when they are loaded at 90°. These relations allowed establishing a CK factor, which allows to calculate the stiffness of a U-Shaped element loaded at 90° from its stiffness when loaded at 0°. In the same way, a CFy factor was established that allows the yield force of the loaded element at 90° and 0° to be related. From the simulations of the U-Shaped elements, models were made at a system level, that is, in the multidirectional system. For this, four different configurations were defined, where the hysteresis curves between the results obtained were contrasted. From these analyzes it was determined that the behavior of a multidirectional system of U-Shaped elements is completely determined if the behavior of a single element loaded at 0° and 90° is known. In addition, thanks to this and the previous coefficients, it was possible to establish an equation that allows calculating the stiffness and yield strength of an energy dissipation system based on U-Shaped elements, which is expected to be very useful for the design and implementation of this system.
Description
Keywords
Disipador de energía , u-shaped , puentes