Browsing by Author "Jünemann Ureta, Rosita"

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    Analytical methods to assess the collapse and damage of reinforced concrete walls
    (National Information Centre of Earthquake Engineering, 2017) Jünemann Ureta, Rosita; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés
    During the great 2010, Chile earthquake, reinforced concrete (RC) buildings showed adequate performance. However, in some of them a particular damage pattern involving brittle failure of RC walls was observed in the lower stories, usually associated with high axial loads and vertical irregularities. The brittle nature of the failure led to a sudden degradation of the bending capacity and lateral stiffness of the walls. Significant research including experimental campaigns and numerical models has been conducted in order to describe the observed damage in RC walls and identify the possible causes of this behavior. This research studies the collapse and damage of shear wall buildings during the Maule earthquake using state-of-the-art analytical models. The proposed analytical research lies within the family of micro models, and uses finite element models with 4-node shell elements to represent the physical interactions that occur in the wall section at finite element level. Inelastic finite element models were developed in DIANA, and the concrete was modeled following the total strain rotating crack approach. First, different stress-strain constitutive relationships for concrete in compression were evaluated and validated with experimental data. The stress-strain constitutive laws were regularized by preserving the compressive fracture energy, for both, unconfined and confined concrete. Once the constitutive models were validated, a real RC resisting plane damaged during the 2010, Chile earthquake was studied in detail, and the observed damage pattern reproduced by means of two-dimensional inelastic pushover analysis. It can be shown that the damage geometry of the shear wall cannot be correctly represented by conventional inelastic models that ignore the true deformation kinematics with lateral and axial interaction. Indeed, the failure mechanism of resisting planes shows strong coupling between lateral and vertical deformations in the plane. Finally, results of a threedimensional inelastic dynamic analysis of the entire building are presented, which show to be consistent with the observed damage after the earthquake and with the 2D model results.
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    Experimental assesment of the behavior of expanded glass lightweight reinforced concrete walls and beams
    (2021) Lombardi, Renzo Alessandro; Jünemann Ureta, Rosita; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Esta tesis describe una campaña experimental de especímenes de hormigón armado (RC) fabricados con hormigón liviano (LWC) hecho con agregado de vidrio expandido, mucho más liviano que agregados convencionales, lo que puede afectar el desempeño estructural de los elementos de hormigón armado. Un total de 8 muros RC fueron fabricados y testeados, con dos diseños distintos: esbeltos confinados y no esbeltos sin confinamiento. Para cada diseño de muro, cuatro especímenes fueron considerados: dos con hormigones livianos de resistencia característica f0 c de 30 y 40 MPa (i.e, L30 y L40) y de densidades de 1200 y 1700 kg/m3, respectivamente; y dos hormigones de peso normal (NWC) con la misma resistencia característica como especímenes de control (i.e, N30 y N40), con una densidad cercana a 2400 kg/m3. Estos muros fueron ensayados bajo cargas laterales cíclicas, y se analizan en términos de deriva de fluencia, deriva y resistencia máxima, ductilidad y disipación de energía. Adicionalmente, ocho vigas fueron construidas y testeadas bajo cargas verticales, con dos diseños; baja cuantía de acero y alta cuantía de acero. Para cada tipo de viga, cuatro especímenes fueron considerados, dos con LWC y dos con NWC, con las mismas especificaciones que los muros. Los resultados obtenidos muestran que ambos LWC (L30 y L40) presentan comportamiento estructural prometedor. En particular, L40 presento un comportamiento comparable con los elementos de control de hormigón normal, mientras que L30 presentó una mayor disminución en la resistencia a tracción y cortante comparado con el hormigón L40. Finalmente, modelos de elementos finitos fueron desarrollados para comparar soluciones analíticas con los resultados experimentales en vigas. Los resultados obtenidos para los modelos muestran que herramientas actuales de elementos finitos permiten representar el comportamiento de hormigón liviano, con ciertas complicaciones específicamente en el comportamiento a tracción.
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    Experimental assessment of the behavior of expanded glass lightweight reinforced concrete walls
    (Elsevier Ltd, 2022) Lombardi, Renzo Alessandro; Jünemann Ureta, Rosita; López Casanova, Mauricio Alejandro
    Structural lightweight concrete (LWC) can significantly reduce the dead loads of reinforced concrete (RC) structures and therefore the associated seismic forces. A new LWC was made using expanded glass as lightweight aggregate (LWA), which is comparatively much lighter than conventional LWAs, and might lead to different performance in lightweight RC elements. An experimental study was conducted to evaluate the structural behavior of expanded glass LWC RC walls. Two types of RC walls were built and tested under cyclic displacement protocol: slender confined and squat unconfined walls. For each type of wall, four specimens were considered: two with LWCs with fc′ of 30 and 40 MPa (i.e., L30 and L40) and densities of 1200 and 1700 kg/m3, respectively; and two with normal weight concretes (NWC) with the same specified strengths acting as control specimens (i.e., N30 and N40) and a density of about 2400 kg/m3. These walls were analyzed in terms of yield drifts and strengths, maximum drifts and strengths, ductility and energy dissipation. Results show that slender confined walls made with L30 mixture showed reductions in ductility and energy dissipation of about 56 and 34%, respectively when compared to N30 specimens. Meanwhile, L40 specimens showed the same tendency, but with smaller reductions compared to N40 of about 36% of ductility and 10% of energy dissipation. In squat unconfined walls, a significant reduction of strength was observed for both types of LWCs, although a bigger difference was observed in L30 concrete. Overall, expanded glass LWC showed promising structural behavior, especially L40 mixture, which presented relatively small differences compared to its NWC counterpart and had only 70% of its unit weight.
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    Experimental behavior and design of a new kinematic isolator
    (Elsevier Sci Ltd, 2010) Besa Bandeira, Jaime; Llera Martin, Juan Carlos de la; Jünemann Ureta, Rosita
    This paper reports on the experimental behavior and design of a rolling self-centering precast prestressed pile (PPP) isolator. This isolation device was developed as an alternative for use in light-weight and low-cost housing located in sites with poor soils. The specimens tested had a spherical and flat-spherical top and bottom end rolling surfaces, respectively, and they generate the self-centering action by a prestressed central cable. Eight full-scale PPP specimens were tested, including two with yielding reinforcement bars at the rolling interface. The axial load on the tested specimens was constant and equal to 147.2 kN, which corresponds to a typical vertical load on a PPP for the types of building considered in this research. The experimental results validate in general the predictions of the analytical model presented; however, the theoretical model is not able to predict the energy dissipation observed in specimens without passive reinforcement, and the apparent larger initial flexibility in the element force-displacement relationship. Additionally, a procedure is developed for simplified isolation design of light-weight structures, which combines the use of flat-spherical PPPs and steel-Teflon sliders in parallel. As an example, the procedure was tested on a design alternative for a low cost housing complex built under conventional fixed-to-base foundations. (C) 2009 Elsevier Ltd. All rights reserved.
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    Implicancias del código sísmico chileno en el diseño y desempeño de edificios con muros acoplados
    (2025) Arriagada Molina, Maycol David; Hube Ginestar, Matías Andrés; Jünemann Ureta, Rosita; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Los edificios de muros de hormigon armado son ampliamente utilizados tanto en Chile como en otros paises, ya que proporcionan gran rigidez lateral y han mostrado un buen desempeno siısmico. Investigaciones previas han evaluado el diseno y desempeño s ismico de edificios de hormigon armado diseñados segun las disposiciones actuales de diseño sismico. Sin embargo, debido a la complejidad de los edificios y modelos, se han analizado un numero limitado de casos. El objetivo de esta tesis es evaluar el diseño y deesempeño sısmico de un numero significativo de edificios chilenos de muros acoplados de hormigon armado, variando la configuracion en planta, numero de pisos y tipos de suelo. Para lograr este objetivo, se implementa una plataforma computacional en Python para automatizar el analisis lineal, diseño y analisis no lineal de edificios 2D mediante modelos de OpenSeesPy. A partir de las caracteristicas de los edificios residenciales chilenos, se consideraron ocho plantas estructurales de muros acoplados, de 5 a 30 pisos, sobre suelos densos (tipo C) y muy densos (tipo B), resultando en 416 casos de estudio. Para cada edificio, se creo un modelo lineal utilizando elementos elasticBeamColumn y un modelo no lineal utilizando elementos MVLEM. Primero, se analizan las implicancias del actual codigo chileno en el diseño sismico. Segundo, se evalua el desempeño sismico de los edificios a traves de analisis estaticos y dinamicos no lineales. Finalmente, se estudia la demanda de curvatura en la base de los muros. Esta investigacion presenta conclusiones relevantes sobre parametros como el corte basal y el drift maximo de entrepiso. Se discuten diferentes limitaciones del drift de entrepiso para el codigo chileno, considerando desplazamientos tanto elasticos como reducidos. Adicionalmente, se estiman las cuantias de refuerzo longitudinal y transversal requeridas en los edificios y la necesidad de elementos especiales de borde. Se estiman tambien factores de sobreresistencia y desplazamiento mediante analisis pushover, asi como factores de corte y desplazamiento maximo a traves de analisis tiempo-historia. Finalmente, se proponen ecuaciones simplificadas para estimar la demanda de curvatura en la base de los muros, en funcion del desplazamiento de techo.
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    Performance of a RC wall building subjected to earthquake and tsunami loads in sequence
    (2019) Tagle Lizana, Santiago José; Jünemann Ureta, Rosita; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    El presente estudio investiga el comportamiento de un edificio típico chileno de hormigón armado, bajo la acción secuencial de un sismo y tsunami utilizando un doble análisis de pushover. Un edificio real dañado luego del terremoto del Maule en 2010 (MW = 8:8) es considerado como edificio de estudio. Un modelo simplificado del edificio es propuesto y validado con un modelo 3D no lineal del edificio. Los resultados muestran que el modelo simplificado replica satisfactoriamente el comportamiento para sismo y tsunami. El modelo validado es sujeto a una carga en cascada de sismo y tsunami. Diferentes casos de tsunami son aplicados a diferentes estados de daño en la estructura producto de un sismo. El análisis de la carga de tsunami mostró que la capacidad y comportamiento de la estructura depende del número de Froude en el flujo. Además, la respuesta del edificio ante un tsunami no se ve afectado por el sismo previo, excepto si el sismo es severo. En este último caso, la capacidad del edificio frente a un tsunami se reduce considerablemente si este actúa en la misma dirección del sismo.
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    Performance of a reinforced concrete wall building subjected to sequential earthquake and tsunami loading
    (2021) Tagle Lizana, Santiago José; Jünemann Ureta, Rosita; Vásquez González, Jorge Andrés; Llera Martin, Juan Carlos de la; Baiguera, Marco
    This paper investigates the behavior of a typical Chilean reinforced concrete wall building under sequential earthquake and tsunami actions using a double pushover analysis approach. A real concrete wall structure that was damaged after the Mw = 8.8 2010 Maule earthquake is considered as a case study building and a simplified nonlinear finite element model of a fictitious slice of the building is subjected to earthquake and tsunami loading in sequence. The analysis of the building under these loadings consists of three stages: the structure is first subjected to seismic loading by means of a pushover analysis until a specific damage state is reached; then a pushover with the same load pattern but in the opposite direction is applied until the shear at the base is zero; and finally, the building is subjected to tsunami loading by means of a variable depth pushover analysis until the maximum capacity is reached. Different tsunami load cases are considered in this study, varying the Froude number and the direction of the tsunami loading. The results show that the tsunami response of the building is mainly dependent on the Froude number of the tsunami flow; however, when the seismic damage is severe, the tsunami capacity of the building is found to be reduced. This is more likely to occur when the effect of the tsunami increases the damage previously induced by the earthquake in the same direction.
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    Self-Centering Frictional Damper (SCFD)
    (2019) Westenenk Orrego, Benjamín; Edwards, J. J.; Llera Martin, Juan Carlos de la; Jünemann Ureta, Rosita
    This paper describes the behavior and design of a new self-centering frictional damper. This device is based on conic friction surfaces that lead to a flag-shaped hysteretic behavior. Its self-centering property and different possible configurations make it a very versatile device to be used in seismic applications of high-rise buildings subject to earthquakes. A simple mathematical model is presented first to describe the cyclic behavior of the device. Then, important variables related with the geometry and materials used in the device are analyzed to better understand their influence on the hysteretic behavior of the damper and optimize its design. Different friction materials, rubber samples, and coil springs are tested in the laboratory for the design of a proof-of-concept prototype. To test the theoretical model, the 115 kN large-scale damper was manufactured and dynamically tested in the laboratory obtaining excellent agreement between the theoretical and experimental results. Finally, a detailed finite element model was generated to study the local stress concentrations of the different components of the device as well as compare the hysteretic behavior for different possible configurations using metallic and rubber springs.
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    The 2010 Chile Earthquake: a five-year reflection
    (Australian Earthquake Engineering Society, 2015) Llera Martin, Juan Carlos de la; Mitrani-Reiser, Judith; Rivera Jofré, Felipe Andrés; Fortuño, C.; Jünemann Ureta, Rosita; Poulos Campbell, Alan John; Vásquez P., Jorge
    At 3:34AM local time, on February 27th, 2010, a moment magnitude Mw 8.8 megathrust earthquake struck offshore the coast of Chile. The earthquake ruptured a 540 by 200 km mature seismic gap of the underlying subduction pacific plate interlocking mechanism. More than 75% of the 16 million Chileans spread over several large urban areas in the center-south of the country were affected by the earthquake, which caused 521 fatalities with 124 of them due to the tsunami, and an overall damage estimate of USD 30 billion. Because the earthquake struck the most densely populated area of the country, it represents a very unique opportunity to reflect on its ubiquitous impact over many different physical and social systems. The reflection contained in this article occurs five years later, once reconstruction and recovery are complete from this longitudinal wound of the country. Seismic codes have changed, research on the supposedly indestructible reinforced concrete shear walls has been done, new seismic protection technologies have been incorporated, and whole new seismic standards have been adopted by communities and people. The price it took was quite high, but we can confidently say that Chile is better prepared today for the next large earthquake.
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    Three-dimensional nonlinear response history analyses for earthquake damage assessment : A reinforced concrete wall building case study
    (2020) Vásquez P., Jorge; Jünemann Ureta, Rosita; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés; Chacón, Matías F.
    Nonlinear dynamic analysis techniques have made significant progress in the last 20 years, providing powerful tools for assessing structural damage and potential building collapse mechanisms. The fact that several reinforced concrete shear wall residential buildings underwent severe structural damage in walls at the lower building levels during the 2010 Maule earthquake (Chile) presents a scientific opportunity to assess the predictive quality of these techniques. The objective of this research is to compare building responses using two completely different three-dimensional nonlinear dynamic models and study in detail the observed damage pattern and wall collapse of one reinforced concrete shear wall building in Santiago, Chile. The first model is a mixed fiber-shell model developed in MATLAB, and the second is a shell finite element model developed in the software DIANA. Results of both models are consistent with the hypothesis that high axial loads trigger a limited ductility failure in critical walls at roof-to-base drift ratios less than 0.34% with little capacity of hysteretic energy dissipation, which contradicts the ductile design philosophy of current code provisions.