Ingeniero Civil / La normativa chilena que regula el diseño sísmico de estructuras industriales de acero es la norma NCh2369.Of2003 Diseño sísmico de estructuras e instalaciones industriales . Esta norma refleja el estado del arte del diseño sísmico en Chile, basada en la experiencia obtenida del comportamiento de estructuras y equipos industriales durante los terremotos de 1960 en Concepción y 1985 en Valparaíso. Tras el terremoto de Maule el año 2010, se han puesto a revisión algunas disposiciones de la normativa. En el caso de estructuras industriales de acero, las disposiciones a modificar se centran en el diseño de arriostramientos y columnas. En el caso de arriostramientos, se evalúa eliminar la limitación del esfuerzo sísmico en diagonales comprimidas al 80% de su capacidad, además de cambios en el cálculo de vigas y riostras en marcos arriostrados de tipo V o V-invertida. En el caso de las columnas, se propone amplificar el esfuerzo sísmico en el factor 0.7R>2.0 con el fin de asegurar la estabilidad del sistema gravitacional posterior al pandeo y fluencia de arriostramientos y la plastificación de los pernos de anclaje. Para evaluar el efecto de estas modificaciones en el diseño y el desempeño, en este trabajo se modelan tres estructuras industriales de acero, basadas en marcos arriostrados concéntricamente, diseñándolas paralelamente con la normativa vigente e incluyendo las modificaciones propuestas. La evaluación del desempeño se lleva a cabo de acuerdo a la metodología indicada en el estándar FEMA P695, incluyendo la no linealidad de arriostramientos, rótulas plásticas y pernos de anclaje. En el caso del diseño, los tamaños relativos de los arriostramientos se ven mínimamente afectados por las modificaciones propuestas, ya que para las estructuras analizadas, el dimensionamiento está controlado por los límites de esbeltez global y local, por sobre los requerimientos de resistencia. En el caso de las columnas, las modificaciones propuestas imponen un aumento de su sección, lo que se traduce en un incremento de la masa sísmica y de las fuerzas de diseño, con variaciones del orden del 3% para ambas variables, además de un aumento de rigidez del sistema. La aplicación de la metodología del estándar FEMA P695 entrega mejoras en el desempeño, dadas principalmente por la ductilidad del sistema, con incrementos del 45%, 7% y 85% para cada una de las estructuras. La sobrerresistencia, por su parte, presenta variaciones del 3%, 5% y 18%, respectivamente. Si bien ninguna de las estructuras fue capaz de alcanzar el margen de seguridad mínimo establecido por la metodología, se aprecia que otorgando una mayor sobrerresistencia o una mayor ductilidad a la estructura y al anclaje estructura - fundación es posible mejorar el desempeño del sistema.

Ingeniero Civil / El presente trabajo de título tiene como objetivo principal determinar analíticamente el mejor valor para el Factor de Sobrerresistencia (Ωo) a partir de 4 valores de prueba (Ωo=2,3,5 y 10.7). Esto se llevó a cabo mediante la evaluación del desempeño sísmico de una serie de modelos analíticos no lineales que representan a nivel macro los fenómenos ocurridos en edificios de acero con marcos arriostrados concéntricamente. Estos macro-modelos consisten en un sistema de estructura de masa y rigidez concentrada con rótulas plásticas, que permiten introducir la no-linealidad al sistema y modelar la resistencia de las estructuras a partir de la utilización de curvas momento-rotación. Para asegurar la correcta utilización de los macro-modelos, éstos debieron ser calibrados a partir de los modelos realizados para los edificios reales. Se desarrollaron 12 arquetipos con distintas alturas, sobrerresistencias y niveles de ductilidad, siguiendo la metodología de FEMA P695 (llámese Metodología). Cada uno de ellos se sometió a un set de 18 registros sísmicos de alta intensidad ocurridos en Chile utilizando el algoritmo de un Análisis Dinámico Incremental (IDA, por sus iniciales en inglés). Finalmente, se evalúo la aceptabilidad de cada uno de los valores estudiados de Ωo de acuerdo a los requerimientos de la Metodología. Como objetivo secundario se estudió una posible relación entre el factor de sobrerresistencia y la ductilidad del sistema (µT), junto con analizar posibles desventajas al implementar altos factores de sobrerresistencia debido a una potencial reducción de la ductilidad total de la estructura. De los resultados, se recomienda la utilización de Ωo=2.0 para los edificios de acero estudiados con R=5. Además, para los niveles de sobrerresistencia analizados se determinó que, para Ωo>5.0, la potencial reducción de ductilidad podría deteriorar el desempeño sísmico del edificio. Estas conclusiones aplican para edificios dentro del rango de características estudiado, con altura de hasta 21[m].

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<p>Composite plate shear walls – concrete-filled (C-PSW/CF) are a new innovative lateral force resisting system intended for high-rise buildings. The walls consist of parallel steel faceplates connected with tie bars and filled with concrete. This dissertation introduces the C-PSW/CF </p> <p>system and coupled C-PSW/CFs consisting of C-PSW/CF walls and composite coupling beams. Three studies are presented herein covering seismic design parameters for C-PSW/CFs, non-linear modeling techniques for composite coupling beams, and the design philosophy for coupled C-PSW/CFs.</p> <p> </p> <p>The first study summarizes the results of a recent FEMA P695 study completed to verify seismic design parameters for uncoupled C-PSW/CFs with rectangular flange plate boundary elements. Seven archetype structures were: (i) designed, (ii) modeled using a benchmarked fiber-based finite element analysis approach, (iii) subjected to nonlinear pushover analysis, (iv) subjected to incremental nonlinear dynamic analysis to failure for 22-sets of scaled ground motions, and (v) the results were statistically analyzed to assess performance. These structures ranged from three (3) to twenty-two (22) stories and included both planar and C-shaped wall configurations. As part of this design process, recommendations for stiffness approximations for linear analysis of C-PSW/CFs</p> <p>were developed. Additionally, these nonlinear incremental dynamic analysis results were post-processed to determine the rotation and strain demands at the base of these structures at the design basis, maximum considered, and failure level earthquakes. These results showed that the rotation and strain demand at failure level earthquakes were comparable regardless of the ground motion. Ultimately, this FEMA P695 approach verified the R factor of 6.5, C_d factor of 5.5, and Ω₀ of 2.5 for C-PSW/CFs with boundary elements. </p> <p><br></p> <p>The second study proposes modeling approaches for composite coupling beams used in combination with C-PSW/CFs. Capturing the behavior of these components is critical to understanding the system behavior of coupled C-PSW/CFs, as the coupling beam components undergo yielding, plastification, and fracture prior to collapse of coupled C-PSW/CF walls. Although steel-concrete composite walls have been a known structural system for decades, only recently have coupled C-PSW/CF systems been investigated and implemented as a seismic force resisting system. As the interest in coupled C-PSW/CF systems increases, the necessity of reliable nonlinear modeling techniques for pushover, cyclic, and seismic analysis has become apparent. This paper presents fiber-based options for modeling composite coupling beam components of coupled C-PSW/CF walls for use in nonlinear and seismic response analyses. Recommendations include effective steel and concrete stress-strain curves, modeling parameters for fiber-based </p> <p>materials, and concentrated plasticity options for additional computational efficiency. These recommendations are then implemented for a full-scale coupling beam section. </p> <p><br></p> <p>In the final study, a capacity design principle is used to establish a basis for the seismic design of coupled composite plate shear walls – concrete filled (CC-PSW/CF) systems. This design philosophy implements a strong wall-weak coupling beam approach, where flexural yielding in coupling beams occurs before flexural yielding at the base of walls. The coupling beams are sized </p> <p>to resist the calculated seismic lateral force level. The walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. Based on this philosophy, recommendations and requirements for appropriate sizing of coupling beams and C-PSW/CFs are presented. These recommendations are used to design four example (8-22 story) structures and evaluate their seismic behavior. The structures were modeled using 2D finite element models and fiber-based models subjected to monotonic and time history analysis. </p> <p>The nonlinear inelastic behavior and seismic responses of the example structures were in accordance with the capacity limited design philosophy (strong wall-weak beam), thus confirming the philosophy’s  efficacy. </p>

Low-aspect-ratio reinforced concrete (RC) shear walls, characterized by height-to-length ratios of less than two, have been widely used as a seismic force-resisting system (SFRS) in a wide array of structures, ranging from conventional buildings to critical infrastructure systems such as nuclear facilities. Despite their extensive applications, recent research has brought to light the inadequate understanding of their seismic performance, primarily attributed to the intricate nonlinear flexure-shear interaction behaviour unique to these walls. In this respect, the current research dissertation aims to bridge this knowledge gap by conducting a comprehensive evaluation to quantify the seismic performance of low-aspect-ratio RC shear walls when used in different applications. Chapter 2 focuses on low-aspect-ratio RC shear walls that are employed in residential and industrial structures. Considering their significance, the seismic response modification factors of such walls, as defined in various standards, are thoroughly examined and evaluated utilizing the FEMA P695 methodology. The analysis revealed potential deficiencies in the current code-based recommendations for response modification factors. Consequently, a novel set of response modification factors, capable of mitigating the seismic risk of collapse under the maximum considered earthquake, is proposed. Such proposed values can be integrated into the forthcoming revisions of relevant building codes and design standards. While the FEMA P695 methodology offers a comprehensive approach to assessing building seismic performance factors, its practical implementation is associated with many challenges for practicing engineers. Specifically, the methodology heavily relies on resource-intensive and time-consuming incremental dynamic analyses, making it less feasible for routine engineering practices. To enhance its practicality, a data-driven framework is developed in Chapter 3, circumventing the need for such demanding analyses. This framework provides genetic programming-based expressions capable of producing accurate predictions of the median collapse intensities—a key metric in the acceptance criteria of the FEMA P695 methodology, for different structural systems. To demonstrate its use, the developed framework is operationalized to low-aspect-ratio RC shear walls and the predictive expression is evaluated considering several statistical and structural parameters, which showed its adequacy in predicting the median collapse intensities of such walls. Furthermore, the adaptability of this framework is showcased, highlighting its applicability across various SFRSs. Chapters 4 and 5 tackle the scarcity of experimental assessments pertaining to the seismic performance of low-aspect-ratio RC walls in nuclear facilities. The seismic hybrid simulation testing technique is employed herein to merge the simplicity of numerical simulations with the efficiency of experimental tests. Hybrid simulation can overcome obstacles related to physical specimen sizes, limited actuator capacities, and space constraints in most laboratories. In these two chapters, the experimental program delves into evaluating the seismic performance of three two-storey low-aspect-ratio nuclear RC walls under different earthquake levels, including operational, design, and beyond-design-level scenarios. Diverse design configurations, including the use of increased thickness boundary elements and different materials (i.e., normal- and high-strength reinforcement), are considered in such walls to provide a comprehensive understanding of several structural parameters and economic metrics. Key structural parameters, such as the force-displacement responses, multi-storey effects, lateral and rotational stiffnesses, ductility capacities, displacement components, rebar strains, crack patterns and damage sequences, are all investigated to provide direct comparisons between the walls in terms of their seismic performances. Additionally, economic metrics, including the total rebar weights, overall construction costs and the expected seismic repair costs, are considered in order to evaluate the seismic performance of the walls considering an economic perspective. The findings of this experimental investigation are expected to inform future nuclear design standards by enhancing the resilience and safety of their structures incorporating low-aspect-ratio RC shear walls. / Thesis / Doctor of Philosophy (PhD)