Thesis ESTUDIO DEL COMPORTAMIENTO DE PUENTES CHILENOS CON AISLACIÓN SÍSMICA UTILIZANDO ANÁLISIS NO-LINEALES
Date
2019
Authors
ZLATAR REYES, BLAS IGNACIO
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Abstract
Al ocurrir un terremoto de gran magnitud en un país, los gobiernos establecen un estado de emergencia con el propósito de entregar ayuda y protección a las personas afectadas. Para que esto ocurra, es de vital importancia que el país posea una red de conectividad vial en servicio permanente. En otras palabras, los elementos de una red vial deben estar diseñados de tal manera de poder resistir las demandas que genera un evento sísmico.Uno de los elementos más importantes dentro de una red vial son los puentes, ya que éstos permiten una fácil y rápida conexión a través de zonas de terreno complejo, como ríos o valles. Existen variadas técnicas para proteger los puentes de un terremoto como el uso de disipadores de energía, fusibles estructurales o un sistema de aislación sisma.La aislación sísmica corresponde a un método de protección que se basa en la disminución de las demandas sísmicas en una estructura, a través del desacople de ésta con el movimiento horizontal del suelo durante un terremoto. Este desacople se logra colocando aisladores sísmicos entre la estructura principal y el movimiento horizontal del terremoto. Al permitir que la estructura se mueva durante el terremoto se logra que exista un menor traspaso de fuerzas desde el suelo a la estructura, lo cual se traduce en una disminución de la demanda sísmica en los elementos.La presente memoria analiza el uso de aisladores sísmicos como método de protección sísmica en puentes. Para esto se realizan modelos computacionales de tres puentes chilenos aislados, ocupando el software SAP2000, a los cuales se les procede a realizar análisis no-lineal estático (pushover), y análisis no-lineal tiempo-historia, de manera de estudiar su comportamiento sísmico. Los puentes estudiados corresponden al puente Juan Soldado, el viaducto las Cruces y el puente Fiscal. Los dos primeros tienen un sistema de aislación conformado por aisladores de goma con núcleo de plomo (LRB), mientras que el sistema de aislación del puente Fiscal está compuesto de aisladores de alto amortiguamiento (HDRB).Durante el proceso de diseño de un puente, al realizar el modelo computacional se omite la rigidez que entregan las barras sísmicas a la interfaz entre la superestructura y la subestructura. Las barras sísmicas son barras de acero que se encuentran ancladas en el hormigón de la superestructura y la infraestructura, con el propósito de evitar el levantamiento de la superestructura debido a una demanda sísmica vertical. Sin embargo, durante el estudio se encontró que omitir la rigidez de las barras sísmicas podría ser un error, ya que las barras sísmicas proveen cierta rigidez a la unión entre la superestructura y subestructura del puente, disminuyendo el desplazamiento de la superestructura, lo cual a su vez genera un aumento en la demanda sísmica en las columnas.Por otra parte, se encuentran limitaciones para el modelo no-lineal en el software SAP2000, tanto en la dificultad de modelar correctamente elementos importantes, como el comportamiento cíclico de barras y topes.
When there is a large magnitude earthquake in a country, the governments usually declare a state of emergency, with the goal of delivering help to those who are affected. For this to happen properly, it is of vital importance that the country has a connectivity network in service. In other words, the elements of the network must be designed to withstand the demands generated by a seismic event.Bridges are one of the most important elements in a connectivity network. They allow easy and fast passage through areas of difficult terrain, such as rivers or valleys. There are several techniques to protect the bridges from seismic forces such as the use of energy dissipaters, structural fuses or seismic isolation.Seismic isolation is a methodology based on decreasing the seismic demands in a structure through decoupling the structural vibration from the horizontal movement of the ground during an earthquake, while also adding energy dissipation capabilities. This decoupling is achieved through the use of seismic isolators between the main structure and the ground. By allowing the structure to move along with the earthquake, there is a lower transmission of forces from the ground to the structure, which translates into a decrease in the seismic demand in the elements.The present thesis analyzes the use of seismic isolators as a seismic protection method for bridges. For this, three computational models of isolated bridges from Chile are made using SAP2000. Then, a static nonlinear pushover analysis and a dynamic nonlinear time history analysis are performed in the bridges, in order to study their seismic behavior. The studied bridges correspond to the Juan Soldado bridge, the Las Cruces viaduct and the Fiscal bridge. The first two have isolation systems consisting of lead rubber bearings (LRB), while the Fiscal bridge isolation system is composed of high damping rubber bearings (HDRB).During the bridge design process, the numerical model usually does not consider the extra stiffness given by the seismic bars to the interface between superstructure and substructure. The seismic bars correspond to steel bars that are anchored in the concrete of the superstructure and the infrastructure, with the purpose of avoiding the lifting of the superstructure due to a vertical seismic demand However, during the study it was observed that the omission of this stiffness can lead to major differences in response. The seismic bars stiffen the interface between the bridge superstructure and substructure, decreasing the displacement of the superstructure, which in turn generates an increase in seismic demand in the columns.On the other hand, limitations were found for the non-linear model in SAP2000. In particular, in the difficulty of modeling important elements, such as the cyclic behavior of seismic bars and stoppers.
When there is a large magnitude earthquake in a country, the governments usually declare a state of emergency, with the goal of delivering help to those who are affected. For this to happen properly, it is of vital importance that the country has a connectivity network in service. In other words, the elements of the network must be designed to withstand the demands generated by a seismic event.Bridges are one of the most important elements in a connectivity network. They allow easy and fast passage through areas of difficult terrain, such as rivers or valleys. There are several techniques to protect the bridges from seismic forces such as the use of energy dissipaters, structural fuses or seismic isolation.Seismic isolation is a methodology based on decreasing the seismic demands in a structure through decoupling the structural vibration from the horizontal movement of the ground during an earthquake, while also adding energy dissipation capabilities. This decoupling is achieved through the use of seismic isolators between the main structure and the ground. By allowing the structure to move along with the earthquake, there is a lower transmission of forces from the ground to the structure, which translates into a decrease in the seismic demand in the elements.The present thesis analyzes the use of seismic isolators as a seismic protection method for bridges. For this, three computational models of isolated bridges from Chile are made using SAP2000. Then, a static nonlinear pushover analysis and a dynamic nonlinear time history analysis are performed in the bridges, in order to study their seismic behavior. The studied bridges correspond to the Juan Soldado bridge, the Las Cruces viaduct and the Fiscal bridge. The first two have isolation systems consisting of lead rubber bearings (LRB), while the Fiscal bridge isolation system is composed of high damping rubber bearings (HDRB).During the bridge design process, the numerical model usually does not consider the extra stiffness given by the seismic bars to the interface between superstructure and substructure. The seismic bars correspond to steel bars that are anchored in the concrete of the superstructure and the infrastructure, with the purpose of avoiding the lifting of the superstructure due to a vertical seismic demand However, during the study it was observed that the omission of this stiffness can lead to major differences in response. The seismic bars stiffen the interface between the bridge superstructure and substructure, decreasing the displacement of the superstructure, which in turn generates an increase in seismic demand in the columns.On the other hand, limitations were found for the non-linear model in SAP2000. In particular, in the difficulty of modeling important elements, such as the cyclic behavior of seismic bars and stoppers.
Description
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Keywords
AISLADOR HDRB , AISLADOR LRB , AISLADORES SISMICOS , ANALISIS NO-LINEAL , BARRAS SISMICAS , PROTECCION SISMICA