Browsing by Author "Chacón, Matías F."

Now showing 1 - 9 of 9
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    A Human Prion Protein Peptide (Prp(59-91)) Protects Against Copper Neurotoxicity
    (2003) Chacón, Matías F.; García-Huidobro Toro, Juan Pablo; Inestrosa Cantín, Nibaldo
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    Comparison of 3D stress-strain concrete models
    (2021) Llera Martin, Juan Carlos de la; Chacón, Matías F.; Hube, M. A.; Celentano, Diego J.
    The inelastic response of reinforced concrete buildings is strongly sensitive to the material stress-strain constitutive model adopted for concrete. This paper is a first step on an ongoing work to do a complete benchmark analysis of available concrete models. Consequently, this article quantifies the differences in the response of three well-known 3D stress-strain continuum concrete models: (i) the Hyperbolic Drucker-Prager (DPH) plastic model; (ii) the UNIlateral (UNI) damage model; and (iii) the Faría-Oliver-Cervera (FOC) plastic-damage model. Consistent algorithms in terms of the updated stresses and the tangent stiffness tensor for all these models were implemented in the ANSYS software using user-material FORTRAN routines adapted to solid-type finite elements. Models results were validated using a set of experimental benchmark tests subjected to uniaxial and biaxial stress states under monotonic and cyclic loading. Moreover, the unilateral (crack opening-and-closure) effect was compared among these models. A set of ten response parameters were compared relative to the experimental tests, e.g., the peak stress, the unloading stiffness at each loading cycle, and the total dissipated energy. Results show that the dissipated energy and the unloading stiffness in the last loading cycle, for all tests, leads to the largest errors.
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    D-serine regulation of the timing and architecture of the inspiratory burst in neonatal mice
    (2020) Beltrán Castillo, S.; Olivares, M. J.; Ochoa, M.; Barria, J.; Chacón, Matías F.; Bernhardi Montgomery, Rommy von; Eugenin, J.
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    Epistemic uncertainty in the seismic response of RC free-plan buildings
    (2017) Chacón, Matías F.; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés; Marques, J.; Lemnitzer, A.
    Complex building models consider multiple degrees of freedom and modeling assumptions that influence the accuracy of the predicted seismic response. This study evaluates the epistemic uncertainty inherent to modeling assumptions by evaluating the seismic response behavior of six instrumented reinforced concrete free-plan structures in Santiago, Chile. The free-plan structural concept is frequently used in office buildings and consists of a core of shear walls, a perimeter frame, and a flat slab connecting both lateral force resisting systems. Epistemic uncertainties studied in this paper are inherent to the following modeling assumptions: (1) the type of finite elements used in the building models; (2) the in-plane and out-of-plane stiffness of the diaphragms; (3) the interaction between the basement and the surrounding soil; and (4) the decision where to apply base fixity. The response uncertainty was first evaluated by comparing predicted and measured vibration periods using ambient vibrations and aftershock records of the 2010 Maule, Chile earthquake. Additionally predicted global and local seismic response parameters such as story shears, torques, and drifts were compared between a predefined reference model typically used in design and a set of variant models. A statistical evaluation of the modeling uncertainty showed a strong dependency on the response parameter considered. Larger uncertainties were observed for shear force related response parameters, including the influence of soil-structure interaction on base and story shears, while uncertainties for predicting fundamental periods or the depth at which building fixity was assumed had moderate impact on the overall building response. In general, uncertainties identified in core forces were larger than uncertainties in story forces and also larger at the underground stories than in comparison to upper levels.
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    Study of the damage of reinforced concrete shear walls during the 2010 Chile earthquake
    (2016) Jünemann Ureta, Rosita; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés; Vásquez P., Jorge; Chacón, Matías F.
    Reinforced concrete shear wall buildings have shown, in statistical terms, an adequate performance in past seismic events. However, a specific damage pattern was observed in 2010 Chile earthquake in some shear walls located in the lower building stories, usually associated with high axial stresses, lack of transverse reinforcement, and vertical irregularity. Results show that the nature of this failure led to a sudden degradation in strength and stiffness of walls and resulted in very limited ductility. This research aims to study analytically this damage pattern of shear wall buildings during the 2010 earthquake. By starting with two-dimensional inelastic pushover finite element models using diana, two walls that were severely damaged during the earthquake were studied in detail using different load patterns and stress–strain constitutive relationships for concrete in compression. These models were validated with experimental data of four reinforced concrete walls available in the literature. It can be shown that the geometry of the damage in the building walls cannot be correctly represented by conventional pushover load patterns that ignore the lateral and axial interaction. Indeed, the failure mechanism of walls shows strong coupling between lateral and vertical deformations within the plane of the wall. Results shown for a three-dimensional inelastic analysis of the building are consistent with these two-dimensional results, and predict a brittle failure of the structure. However, these models predict a large increase in axial load in the walls, which needs to be validated further with more experimental and analytical studies. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
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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.
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    Uncertainty in the inelastic behavior of reinforced concrete walls due to material properties
    (2020) Llera Martin, Juan Carlos de la; Gallardo, J. A.; Santa María, H.; Chacón, Matías F.
    Reinforced concrete (RC) walls are structural elements widely used to resist lateral forces in highly seismic countries. Design codes provide minimum requirements to ensure an adequate performance of shear walls during ground motions; however, during recent earthquakes such as the 2010 Maule earthquake in Chile, or the Canterbury, Christchurch 2010 and 2011 earthquakes in New Zealand, some shear walls underwent an unprecedented and somewhat unexpected brittle failure. This fact evidenced that current analysis and design procedures for shear wall buildings do not provide a close representation of the true seismic response of these walls under severe cyclic earthquake loading, which is an imperative in performance-based design. Keeping that in mind, the present research implemented a Nonlinear Finite Element Wall (NLFEW) model, which was validated using parametric analyses. A micro-model using layered-shell elements was selected that uses an effective material model for concrete based on theory of plasticity and continuum damage mechanics. The wall model was validated simulating the behavior of four experimental RC benchmark wall test specimens subjected to quasi-static cyclic loads. Five response parameters were considered to evaluate the accuracy of the model: the initial stiffness, peak base-shear force, peak displacement at the top, ultimate base-shear force, and energy dissipated throughout the cyclic loading. The same parameters were used to quantify the uncertainty generated by the material properties in the global response of each wall. Results show that the model fits very well the experimental tests, and localization of damage is correctly predicted. Moreover, results from sensitivity analyses suggest that the initial stiffness is mainly influenced by variables of concrete in tension; the maximum top displacement (ductility of the element) depends largely on the parameters of concrete in compression; and base-shear forces and dissipated energy are sensitive to the post-yield stiffness of steel reinforcement.
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