Browsing by Author "Wilches, Jose"

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    Buckling of steel tanks under earthquake loading: Code provisions vs FEM comparison
    (2023) Moreno, Matias; Colombo, Jose; Wilches, Jose; Reyes, Sergio; Almazan, Jose
    A poor seismic design of liquid storage tanks may result in large economic losses or environmental impacts due to the spillage of their contents; therefore, an effective seismic design of these tanks is of vital importance. Moreover, many liquid storage tanks have suffered severe damage during recent earthquakes worldwide due to the buckling of their wall, which is one of the most common failures. In continuously supported tanks, anchors are an essential part of the seismic design; however, the effectiveness of incorporating them and the predictive ability of design codes on the behavior of these structures has not been extensively studied. This research evaluates the design recommendations (API-650 and NZSEE) through a comparison with nonlinear 3D finite element models. In particular, the compressive stress and the buckling capacity of the tank wall are evaluated. Three anchorage conditions are analyzed: (i) tank with a fully anchored base, (ii) tank with flexible anchors at the periphery of the base (bolted anchorage), and (iii) unanchored. Four tank geometries, two materialities (stainless steel and carbon steel), and different amounts of anchors for each geometry were analyzed. In total, 24 nonlinear 3D finite element models were developed and analyzed. The presented results provide a better un-derstanding of the effectiveness of including anchors depending on the tank slenderness and the predictability capacity of design codes for these structures. Finally, some code guidelines for flat tanks are validated, and the need for additional detailed guidelines for slender tanks is highlighted.
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    CFT Connections: State-of-the-art Report and Numerical Validation by 3D FEM
    (2024) Wilches, Jose; Leon, Roberto; Maria, Hernan Santa; Graterol, Anibal
    Connections between concrete filled members are common in tall buildings, bridges, and offshore structures because of their robust structural performance. While extensive research has been done on isolated concrete-filled structural members, relatively little research has been conducted on composite connection regions. This article first describes a database on experimental/analytical investigations on concrete-filled connections comprising 135 tests. It then develops a generic numerical model capable of capturing the entire range of behavior of these connections, including local buckling of the steel tubes and friction/contact resistance between steel and concrete. The model was calibrated against a single test and its performance was verified against three other very different tests. The results indicate that the four models can track well the strength and stiffness of the specimens up to ultimate and predict well different failure patterns. Comparisons of the experimental and numerical load-deformation curves show very good agreement in predicting the strength and deformations at which different behaviors arise, and that performance is controlled primarily by both the strength of the concrete and the confinement effect of the steel tube in the connection area.
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    Influence of soil- foundation- tank interaction on buckling strength of liquid storage tanks
    (2024) Ulloa-Rojas, Juan; Colombo, Jose; Wilches, Jose; Leon, Roberto; Almazan, Jose
    Large earthquakes in the last 25 years have caused significant damage to buildings and infrastructure, including the partial or total collapse of storage tanks in various industries. Elephant foot buckling, or local buckling at the base, is one of the main failure modes observed in these structures, and this failure mode can lead to their collapse and/or complete loss of contents. Although hydrostatic and hydrodynamic loads typically affect the seismic response of tanks, the effect of soil type on tank buckling behavior has not been widely studied or recognized. This research aims to evaluate the effect of soil type on seismic fragility of tanks by analyzing typical storage tanks used in the wine industry. The work focuses on elephant foot buckling for tanks with both unanchored and anchored bases and compares the influence of three different types of soil and two different tank geometries. The approach uses the capacity spectrum method, as opposed to the more commonly used incremental dynamic analysis, to determine a critical peak ground acceleration to cause buckling at the tank. The tanks were subjected to 21 Chilean seismic records with three different soil types and a no-soil condition. From the results a lognormal fragility curve, and its median and standard deviation, are calculated. The results indicate that unanchored tanks built softer soils exhibit poorer performance, while tanks in competent soils and rock exhibit good performance. Anchored tanks show less sensitivity to soil types than unanchored tanks. The study demonstrates the importance of considering soil-foundation-structure interaction for wine storage tanks, but the results indicate that many comparable storage structures will be similarly affected.