Browsing by Author "Chacon, Matias F."

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    Damage and sensitivity analysis of a reinforced concrete wall building during the 2010, Chile earthquake
    (2021) Gallardo, Jose A.; Llera Martin, Juan Carlos de la; Santa María Oyanedel, Hernán; Chacon, Matias F.
    Buildings with Reinforced Concrete (RC) walls are commonly used to resist lateral forces in seismic countries because they provide high lateral stiffness and strength. In recent earthquakes, shear wall buildings have shown good behavior in general; however, a small percentage underwent severe damage localized typically in lower stories. Several numerical models have been developed and proposed to simulate the failure mechanism and behavior of RC walls. From the existing models, only those denoted as micro-models can accurately simulate the stress and strain distributions. The aim of this research is double: (i) to validate a nonlinear finite element wall model and the associated material stress-strain constitutive relationship using the behavior of a real building during the 2010 Chile earthquake; and (ii) to analyze the uncertainty of the response of the building due to changes in model parameters. To validate the response of the wall model, four experimental benchmark RC wall specimens were studied, and model accuracy was evaluated using five parameters: initial stiffness, peak baseshear, ultimate base-shear, maximum displacement, and dissipated energy. A sensitivity analysis was carried out to study the influence of material parameters in the wall response and its damage. The case-study is a 18story building with 1 basement, which suffered severe damage during the 2010 Chile earthquake, which has been studied by non-linear response-history analysis. Uncertainty in the building response due to three important modeling assumptions was considered: Rayleigh's damping model parameters; effective elastic bending stiffness of the structural elements; and effect of the vertical ground motion component. Results showed that the proposed model can predict the seismic response of the building with reasonable accuracy by identifying correctly the damage location. This case-study enabled us to assess also the effect of damping in non-ductile structures, the important influence of the slab stiffness in the response, and the effect of the vertical ground motion component in the sequence of damaged walls.
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    Empirical fragility curves for houses in Chile using damage data from two earthquakes
    (2024) Cabrera, Tamara; Hube, Matias A.; Maria, Hernan Santa; Silva, Vitor; Martins, Luis; Yepes-Estrada, Catalina; Chacon, Matias F.
    Strong seismic events frequently strike Chile. The last three significant events that caused considerable damage and losses are the 2010 (Mw\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M}_{w}$$\end{document} 8.8, Maule), 2014 (Mw\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M}_{w}$$\end{document} 8.2, Iquique), and 2015 (Mw\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M}_{w}$$\end{document} 8.3, Illapel) earthquakes. Therefore, reliable fragility curves are necessary to evaluate the threat of earthquakes to the built environment. This study aims to develop empirical fragility curves of Chilean houses using damage from the 2014 and 2015 earthquakes. The data from 9085 and 7431 damaged houses from the 2014 and 2015 earthquakes, respectively, was obtained by the government. The fragility curves were estimated for reinforced concrete, reinforced masonry, timber, and adobe houses. Additionally, the fragility curves were constructed using three different Peak Ground Acceleration (PGA) maps to quantify the variation of the fragility parameters based on the selected PGA map and to identify which PGA map generates the highest correlation with observed damage. Additionally, fragility curves obtained in this study are compared with curves from other studies. The median theta\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta$$\end{document} values of the fragility curves obtained in this study are larger than those from other reported studies.
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    Flexural performance of full-scale two-span Nail-Laminated Timber Concrete composite slabs
    (2024) Adema, Andres; Chacon, Matias F.; Santa Maria, Hernan; Opazo-Vega, Alexander; Casanova, Euro; Guindos, Pablo
    This study examines the flexural performance of six 9-m full-scale two-span Nail-Laminated Timber Concrete (NLTC) composite slabs. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. The multi-span configuration of slabs reduces their deflections simply and effectively. Fivepoint monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pullout tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests of shear connections were also included to emulate the negative bending moments that occur in the middle of the slabs. Failure modes, load-mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab at the serviceability range. Moreover, an analytical elastic TCC beam with the Girhammar method was assessed and demonstrated as more precise than the traditional gamma-method. Finally, an accurate prediction of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity is observed, with errors in a range of 2-23% and 9-74%, respectively.
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    In-plane testing and hysteretic modeling of steel-spline cross-laminated timber diaphragm connection with self-tapping screws
    (2024) Chacon, Matias F.; Jara-Cisterna, Alan; Benedetti, Franco; Veliz, Fernando; Guindos, Pablo
    This study examines experimentally and numerically the in-plane behavior of a steel-spline Cross-Laminated Timber (CLT) connection with self-tapping screws. Although this connection is a strong, rapid, and cost-effective alternative suitable for CLT diaphragms of tall timber-concrete buildings, no previous cyclic/monotonic testing has been documented. Two specimens were tested under axial and in-plane shear loads, where a ductile failure mode was observed due to bending and withdrawal of screws, and deformation and buckling of the strap. Mechanic properties, such as strength capacity, stiffness, ductility, energy dissipation, equivalent viscous damping, stiffness/strength degradation, and damage index characterize the joint. Furthermore, the yield point and ductility were calculated with the EEEP, CEN, and Yasumura-Kawai methods, the last approach most accurate, with a mean ductility of 7.25 and 5.50 for the axial and in-plane shear tests, respectively. Overstrength factors of about 2.6 and 1.9 were also estimated for respective tests by comparing analytical expressions from timber codes and literature. Finally, three numerical models (SAWS, DowelType, and ASPID) were assessed to measure their epistemic uncertainty, showing an adequate force and dissipated energy history simulation, with a normalized root mean square less than 8.8% and 4.5%, and R(2 )over 87% and 97%, respectively. {GRAPHICAL ABSTRACT}
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    Structural performance of strong timber diaphragms: High-capacity light-timber frames and cross-laminated timber
    (2024) Veliz, Fernando; Chacon, Matias F.; Lagos, Jorge; Berwart, Sebastian; Lopez, Nicol; Guindos, Pablo
    The construction of tall timber buildings is not only challenging because it requires stronger vertical lateral systems but also because it demands much Stronger Timber (ST) diaphragms in comparison to the ones required by low-rise timber construction. Two main ST alternatives exist: High -capacity Light -Timber Frame (HLTF) and Cross -Laminated Timber (CLT) diaphragms. Both approaches provide more strength, stiffness, and still have the potential to provide ductile failure than traditional timber diaphragms. However, it is unclear the structural performance differences between these two ST alternatives, which is the aim of this research. In this study, an experimental program comprising the monotonic and cyclic testing of several representative sheathing -toframing connections, plus the full-scale monotonic bending testing of six HLTF and CLT diaphragms was accomplished to characterize and compare the performance of both ST diaphragm configurations. Failure modes and mechanical properties such as stiffness, load -bearing capacity, and ductility were evaluated for all specimens. Results show that HLTF diaphragms have larger load -bearing capacity than CLT ones. Conversely, CLT diaphragms perform more ductile than HLTF ones, with a mean of /4 = 1.87 and /4 = 3.5, respectively, where the first was due mainly to high plastification of fasteners and the second to premature brittle failure of some components. Furthermore, the experimental findings were utilized to evaluate the precision of prevailing analytical and numerical models, thereby illustrating their capability to adequately represent the elastic and nonlinear responses of both ST alternatives. Finally, a sensitivity analysis of a two - story wall building with varying diaphragm (LTF, HLTF and CLT) and different light -frame shear walls (rigid and flexible) was studied. Both the diaphragms and shear walls were modeled under two different equivalent diagonal link models. The sensitivity analysis concluded that both flexible diaphragm assumption and envelope approach might not be an efficient solution, while semi -rigid approach with flexibility index eta ranging 0 - 0.5 may be expected when using ST with LTF shear walls. Finally, the diaphragm model employed enabled the validation of its elastic behavior under lateral loads, with use factors under 30% for typical setups.