Browsing by Author "Milani, Gabriele"

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    Detailed micro-modeling of partially grouted reinforced masonry shear walls: extended validation and parametric study
    (2021) Calderón Díaz, Sebastián Andrés; Sandoval Mandujano, Cristián; Milani, Gabriele; Arnau, Oriol
    Partially grouted reinforced masonry (PG-RM) shear walls have been widely used as structural elements in low- and medium-rise earthquake-resistant buildings. Nonetheless, assessing its shear strength represents a complex task mainly because the partial grouting provides a non-constant cross section, which results in heterogeneous stress–strain patterns. Consequently, refined modeling techniques are needed to reproduce local failure mechanisms taking place in these walls, which significantly influence the global response. In response to this issue, a detailed micro-modeling approach based on the finite element method was proposed in previous studies by the authors. Although the numerical strategy provided accurate results, further validation is required. Therefore, in this study, the experimental results of seven PG-RM shear walls of multi-perforated clay bricks with bed-joint reinforcement are employed as validation cases. These seven walls presented variations in five design parameters. The validated numerical model was then employed to perform a parametric study to assess the influence of the wall aspect ratio, axial pre-compression stress, and horizontal reinforcement ratio on the in-plane lateral behavior of PG-RM shear walls. The obtained results show that the three studied design parameters modified the crack patterns of the walls. Besides, increasing the axial pre-compression stress or reducing the aspect ratio resulted in higher walls’ shear strength. Additionally, decreasing the horizontal reinforcement ratio or increasing the aspect ratio generated a higher story-drift ratio at maximum lateral force. Finally, it was corroborated that the positive effect of the axial pre-compression stress on the walls’ shear strength decreases inversely proportional to the aspect ratio.
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    Experimental and numerical study of partially grouted reinforced masonry shear walls subjected to in-plane loading
    (2021) Calderón Díaz, Sebastián Andrés; Sandoval Mandujano, Cristián; Milani, Gabriele; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Los muros de corte de mampostería armada parcialmente rellena (PG-RM, por sus siglas en inglés) tienen una gran presencia en muchos países, incluso en regiones sísmicas. Estos muros han tenido un desempeño sísmico aceptable en terremotos fuertes, aunque se han reportado fallas por corte dentro del plano. Aunque estudios anteriores han abordado algunos de los problemas detectados, la información experimental aún es limitada, una situación aún más notoria cuando se enfoca en muros de corte de PG-RM con refuerzo embebido en la juntas de mortero horizontal (BJR, por sus siglas en inglés). Además, la mayoría de los enfoques numéricos propuestos para analizar elementos de mampostería tienen como objetivo reproducir elementos de mampostería no reforzados. Adicionalmente, estudios recientes han demostrado la inexactitud de algunos códigos de diseño y algunas expresiones existentes al estimar la resistencia lateral de muros de corte de PG-RM. Por lo tanto, es necesario recopilar más datos experimentales sobre muros de corte de PG-RM, mejorar o adaptar enfoques numéricos para estudiarlos, y también proponer fórmulas adecuadas para estimar su resistencia al corte dentro del plano. En respuesta a las necesidades identificadas, se ensayaron 18 muros de corte de PG-RM de escala real bajo carga axial constante y carga cíclica lateral incremental dentro del plano. Se construyeron nueve muros con ladrillos de arcilla multiperforados (MPCBL, por sus siglas en inglés) y nueve con bloques huecos de hormigón (HCB, por sus siglas en inglés). Se variaron diferentes propiedades de diseño, tales como las propiedades geométricas de los muros, las cuantías de refuerzo, la disposición del refuerzo y las propiedades de los materiales. Todos los muros ensayados fallaron en un modo de falla de tensión diagonal. En general, las variables estudiadas afectaron la respuesta de los muros. Por ejemplo, utilizando una relación de aspecto o un espesor de junta menores; y una mayor relación de carga axial, una relación de refuerzo horizontal o vertical o la resistencia a la compresión del mortero se midió una mayor resistencia al corte en los muros de MPCLB con BJR. En los muros de HCB con BJR, el uso de una relación de refuerzo vertical u horizontal más alta produjo un aumento en la resistencia al corte y proporcionar elementos de borde generó un comportamiento post-pico más estable. Además, en los muros de HCB, proporcionar una combinación de refuerzo horizontal embebido en juntas de lecho de mortero y en bond-beams resultó en un mejor comportamiento histerético, capacidad de disipación de energía y ductilidad en comparación con los muros provistos de un solo tipo de refuerzo horizontal. Asimismo, se realizó un estudio numérico sobre la implementación de micromodelos detallados (DMM, por sus siglas en inglés) de muros de corte de PG-RM. Se obtuvo una buena precisión al reproducir el comportamiento experimental de los muros MPCLB probados en este estudio, siendo más preciso que las expresiones de corte seleccionadas. Se destaca la importancia de elegir una estrategia de resolución numérica adecuada para evitar resultados erróneos, considerando la fuerte respuesta no lineal de este tipo de modelos. Además, se utilizaron DMM para realizar un estudio paramétrico sobre la influencia de las variables de diseño seleccionadas en la respuesta al corte de muros de PG-RM de MPCLB. Los resultados también se emplearon para corroborar el efecto combinado de la tensión axial y la relación de aspecto en la resistencia al corte de las paredes. Además, se dan detalles de la implementación de micromodelos simplificados (SMM, por sus siglas en inglés) de muros de corte de PG-RM de HCB. Con este enfoque se reprodujeron dos muros de corte de PG-RM de HCBs con BJR, obteniendo una precisión adecuada. Finalmente, se ajustaron expresiones de diseño para estimar la resistencia de muros de corte de PG-RM de MPCLB y HCB con BJR. En este proceso se utilizaron bases de datos compuestas de resultados experimentales y numéricos. Las expresiones obtenidas son más precisas que las expresiones de código estudiadas en términos del promedio y rango de error.
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    Quasi-static testing of concrete masonry shear walls with different horizontal reinforcement schemes
    (2021) Calderón Díaz, Sebastián Andrés; Sandoval Mandujano, Cristián; Araya Letelier, Gerardo Andrés; Inzunza, Ernesto; Milani, Gabriele
    Constructions built with partially grouted reinforced masonry (PG-RM) shear walls are common in several countries, and consequently, different construction solutions can be expected. In this context, one of the main differences detected is the type of horizontal steel reinforcement used. The most traditional options consist of bed-joint reinforcement and bond-beam reinforcement. Despite the advances in this research area, there is little experimental evidence to determine which of these horizontal reinforcement schemes exhibits a superior performance under seismic loads. Thus, the research described in this paper focused on assessing and comparing the seismic performance of PG-RM shear walls with different horizontal reinforcement options. For this purpose, four concrete masonry walls with an aspect ratio of 0.86 were tested undergoing constant axial pre-compression and quasi-static cyclic incremental lateral displacements. The tested walls had the same horizontal reinforcement ratio but different layouts (only bed joint reinforcement, only bond beam reinforcement, and a combination of them). The other design characteristics remained constant. The obtained results were analyzed in terms of the force-displacement curves and seismic performance parameters such as the maximum resistance, stiffness decay, energy dissipation, and equivalent viscous damping ratio. In addition, a comparative analysis of damage progression of the tested walls was carried out using the digital image correlation (DIC) technique. The tested walls experienced progressive deterioration of the lateral stiffness in proportion to drift increments regardless of the reinforcement scheme. Once achieved the lateral resistance, the degradation of the behavior accelerated, turning into a rather unpredictable response. Employing different horizontal reinforcement layout showed no influence on the lateral capacity of the walls when the same horizontal reinforcement ratio and material qualities are used. It was also observed that the distributed bed-joint reinforcement was better than the bond-beam reinforcement layout in controlling crack widths. Additionally, a combination of bond-beams and bed-joint reinforcement seems to be the most suitable reinforcement strategy based on hysteretic behavior, energy dissipation capacity, and ductility. The presented experimental evidence is promising, although further studies are required in order to promote its use in design codes and construction projects.
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    Shear design equation and updated fragility functions for partially grouted reinforced masonry shear walls
    (2022) Calderón Díaz, Sebastián Andrés; Vargas Carvajal, Laura Andrea; Sandoval Mandujano, Cristián; Araya Letelier, Gerardo Andrés; Milani, Gabriele
    This paper proposes specific ultimate shear strength expressions for partially-grouted reinforced masonry (PG-RM) shear walls that are bed-joint reinforced (BJR) and made with either multi-perforated clay bricks (MPCLBs) or hollow concrete blocks (HCBs). For each unit type, a set of constant coefficients of an arbitrary mathematical expression is optimized to minimize the error against experimental databases of walls made with the same unit types. Additionally, the assembled databases are employed to calculate lognormal empirical fragility functions, following performance-based earthquake engineering (PBEE) methodologies. For this, two different engineering demand parameters (EDPs) (story drift ratio, SDR, and normalized diagonal shear demand, NDSD) are proposed, and two damage states (DS) (named DS4 for moderate damage and DS5 for severe damage) are investigated. The proposed shear formulae are used in the normalization of calculated NDSD values. Moreover, databases are sorted by a selected design parameter (aspect ratio) to calculate design parameter-sensitive fragility functions. Overall, the results indicate that the proposed expressions are more accurate than the corresponding expressions proposed by the American and Canadian codes when assessing BJR-PG-RM shear walls in terms of the average error and dispersion of relative prediction error. All the fragility curves adjusted to the whole database pass the Lilliefors goodness of fit test (). Comparing SDR-based curves of walls of a different unit type, DS4 curves present a smaller difference in the median value () than DS5 curves. Additionally, the variations in the of NDSD-based curves of walls of different units are smaller than those observed in SDR-based fragility functions, indicating that NDSD represents a less variant EDP to describe the probability of shear damage at DS5 when a proper expression is employed for the normalization. Regarding design parameter-sensitive fragility functions, sorting databases reduces the number of data points used to calculate the functions, which produced two SDR-based and one NDSD-based function to fail the Lilliefors test (). In general, the value of SDR-based curves increases in proportion to the aspect ratio. Additionally, classifying the databases by a design parameter (aspect ratio) corroborated that the proposed expression has acceptable accuracy based on the adjusted NDSD-based DS5 fragility functions. It is highlighted that calculating design parameter-sensitive functions might increase the accuracy of PBEE assessments (e.g., loss estimations) when an EDP insensitive to design parameters normalization (e.g., SDR) is employed.
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    Simplified micro-modeling of partially-grouted reinforced masonry shear walls with bed-joint reinforcement: Implementation and validation
    (2021) Calderón Díaz, Sebastián Andrés; Milani, Gabriele; Sandoval Mandujano, Cristián
    Partially grouted reinforced masonry (PG-RM) shear walls of hollow concrete blocks (HCB) have been an object of study during the last years. The non-constant cross-section of this type of structural element and the presence of reinforcement set a challenging scenario when assessing their lateral resistance. This scenario makes simple approaches (e.g., design expressions) lacking accuracy. Besides, the most accurate existent analysis methodologies rely on user-defined sub-routines that are not available for commercial use. Therefore, proper analysis methodologies are still a need. In this regard, this research aims at reproducing the behavior of PG-RM shear walls with bed-joint reinforcement with a simple but also accurate approach. In this line, the in-plane behavior of PG-RM shear walls was reproduced by implementing 2D micro-models in a multi-purpose commercial FE code without requiring excessive work, advanced programming skills, and unaffordable hardware. The model approach was validated by reproducing two identical full-scale PG-RM shear walls. Although the model was not able to reproduce cyclic loading as in the tests, the model captured the experimental failure mode and lateral resistance with an acceptable degree of accuracy. Moreover, the distribution of cracks and deformations in horizontal reinforcement elements were appropriately reproduced at the lateral resistance, indicating the most demanded reinforcement portions. Additionally, the proposed modeling approach was compared with two alternative approaches: a 2D model that reproduced tensile failure employing interfaces and a smeared crack model and a 3D model that reproduced tensile failure utilizing a smeared crack model. The benchmark results pointed out the advantages of the reference model over the alternative modeling approaches. The first alternative model reproduced an excessive displacement capacity, and the second alternative model simulated an inaccurate crack pattern and was associated with a heavy computational burden.