Inestabilidad de tanques de almacenamiento de petróleo con techo cónico durante un incendio

En este trabajo se presenta un análisis del comportamiento estructural de tanques de almacenamiento de petróleo con techo bajo temperaturas procedentes de fuego adya-cente a la estructura. En la simulación numérica se modela la cáscara con elementos finitos de doble curvatura utilizando el código de propósitos generales ABAQUS. Se determinan las configuraciones deformadas y las temperaturas que identifican el es-tado crítico de pandeo y también el comportamiento poscrítico, mediante análisis de bifurcación lineal (conocido como LBA), análisis no lineal geométrico (GNA) y análisis no lineal geométrico con imperfecciones (GNIA). Para el análisis se modelan dos geo-metrías de tanques de almacenamiento de petróleo con techo fijo en su parte superior (representativas de diferentes volúmenes de almacenamiento) expuestos a una dis-tribución de temperatura externa y una carga hidrostática interna, a fin de evaluar la influencia de las diferentes relaciones de esbeltez altura-diámetro del tanque en la respuesta y la posible estabilización producida por el fluido almacenado en el interior. Los resultados muestran que la inestabilidad se produce a temperaturas muy bajas, del orden de 70ºC a 150ºC, con modos de pandeo que afectan la cara directamente ex-puesta al fuego. La inestabilidad se produce en régimen elástico del material.Fil: Calabro, Horacio Daniel. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; Argentin

Reduced stiffness buckling analysis of aboveground storage tanks with thickness changes

The Reduced Stiffness Analysis (RSA) to compute lower bounds to buckling loads of shells has been employed by a number of researchers as a simple way to evaluate the buckling capacity of shells that display unstable behavior and imperfection-sensitivity. It allows the use of simple eigenvalue analysis, without having to perform incremental nonlinear analysis, and is based on the physical behavior of the shell which recognizes that a significant contribution to the stability of a shell under lateral pressure is provided by its membrane stiffness. Unstable post-critical behavior is associated with the loss of this stabilizing membrane contribution. Past use of the approach has been mainly restricted to cases of uniform shell thickness and uniform pressures in the circumferential direction, in which case analytical solutions are possible. Recent applications by the authors and other researchers have shown ways to compute the lower bounds using finite element analysis, for which a modified eigenvalue analysis is constructed by neglecting the membrane contributions to the matrix containing the initial stresses. This paper illustrates the application of the methodology to cases of pressure loaded shells with thickness changes in the meridional direction. A semi-analytical finite element code has been employed for the buckling analysis when uniform pressures act on aboveground steel tanks. The tanks are representative of those constructed for the oil industry, with diameter to thickness ratios of the order of 3000, and height to diameter ratios lower than one.Fil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Croll, James G. A.. University College London; Reino Unid

Failure of steel tanks during their construction: experiments and computational modeling

La construcción de tanques de acero destinados al almacenamiento de petróleo plantea un estado de solicitaciones frente a la acción de viento que no está contemplado en las normativas. En la Patagonia Argentina, como en otros lugares reportados en la bibliografía, se han registrado casos de colapso de este tipo de estructuras durante la etapa constructiva a moderadas velocidades de viento. Estudios numéricos anteriores condujeron a determinar como factor desencadenante del mecanismo de colapso, la falta de integridad estructural por las irregularidades en la continuidad del apoyo en el sentido circunferencial. Un mayor conocimiento del comportamiento fluido-dinámico del viento permite ajustar las acciones actuantes usadas en el abordaje del estudio numérico. Este trabajo completa el análisis de tanques no anclados que colapsaron por acción del viento durante su etapa constructiva evaluando el patrón del flujo interior en los tanques mediante ensayos en túnel de viento, incluyendo estos resultados en el estudio numérico. La estructura se modela por elementos finitos mediante un código de propósitos generales, evaluando la inestabilidad del equilibrio mediante un análisis de bifurcación lineal (LBA) y análisis no lineal geométrico con imperfecciones (GNIA). Los ensayos permitieron determinar la formación de un vórtice interior que produce una depresión mayor que el de la estela a sotavento del tanque.During the construction of steel storage oil tanks, a state of stresses under wind loads is induced which is not covered by the regulations. Cases of collapse of such structures during their construction occurred in Patagonia Argentina and elsewhere under moderate wind speeds, as reported in the literature. Previous numerical studies concentrated on the identification of the collapse mechanism, which was related to the loss of structural integrity due to discontinuity of the support in the circumferential direction. An increased knowledge of the fluid dynamic behavior under wind allows obtaining an improved input used in the subsequent numerical study. This paper provides new insight into the wind behavior of unanchored tanks that collapsed during their construction by wind tunnel tests to evaluate the flow pattern inside the tanks, which is an input for the subsequent numerical study. The structure is modeled using a general purpose finite element code, in which instability is evaluated by Linear Bifurcation Analysis (LBA) and by Geometrically Nonlinear Analysis with Imperfections (GNIA). Tests allowed identifying that an inner vortex is induced which produces a greater depression than the downwind wake in the leeward region of the tank.Fil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Cicerone, Esteban. Universidad Nacional del Comahue; ArgentinaFil: Hernandez, Facundo C.. Universidad Nacional del Comahue; ArgentinaFil: Lassig, Jorge Luis. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentin

Behavior of wall panels in industrial buildings caused by differential settlements

This paper presents the analysis of mechanical behavior of metal wall panels of storehouses and industrial buildings subjected to differential settlements. The storehouses considered are representative of those used in the agricultural activity. A small-scale model was built and tested in order to have evidence of the behavior and to validate computational models. The numerical investigation is carried out through finite element analysis using a general-purpose software, by modeling buildings with different geometries and evaluating different settlements of the ground. To obtain an adequate model, geometric non-linearity has to be taken into account. Models that represent the most usual geometric typologies were investigated under support settlements. The deflected shape of the wall panel and the relationship between the horizontal displacements and the settlement of the foundations are evaluated. The results show that there are large out-of-plane displacements caused by settlements that would be admitted by design recommendations.Fil: Fernández, Suyai. Universidad Nacional del Comahue; Argentina. Intertechne Consultores y Asociados; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentin

Thermal effects of fire on a nearby fuel storage tank

This work presents numerical modeling and quantitative results of the heat transfer process from a burning tank to an adjacent tank. The flame is represented by a solid flame model in which two zones are identified: a lower clear flame layer with high temperatures and a darker upper layer in which the flame carries soot and smoke. Semi-empirical models are used to estimate the geometry of the flame; other models were also adopted to account for wind effects. The emissive power of each layer of the flame was locally evaluated as a function of temperature. A heat transfer process was followed from the flame to the target tank, at which an energy balance is carried out to include radiation from the flame, radiation from target tank surfaces, and convection to air and to fuel stored in the target tank. The results are presented in the form of temperature distributions on the target tank, which are an ingredient to perform structural analysis. Parametric studies are carried out to investigate the influence of the vertical location of the flame, wind speed, level and temperature of the fuel stored in the target tank, size and distance between tanks. Flame location at ground level, wind speed, higher temperatures of stored fluids, and short separation between tanks are identified as crucial elements increasing thermal effects on the target tank, but the results are not so much influenced by tank size.Fil: Espinosa, Susana Noemi. Universidad Nacional del Comahue; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Post-buckling behavior of fluid-storage steel horizontal tanks

This paper focuses on the buckling and post-buckling of horizontal steel tanks with conical end-caps, supported on discrete saddles, under pressure caused by internal vacuum and liquid pressure. Linear bifurcation, as well as geometrically nonlinear analyses with imperfections, was performed on a single geometric configuration in order to highlight modeling differences, imperfection sensitivity, and post-buckling behavior. Results are presented for (a) increasing uniform external pressure; (b) increasing pressure under fixed fluid level; (c) coupled increasing pressure and decreasing fluid. For perfect shells, the lowest maximum loads are reached at the conical end-caps; however, imperfection-sensitivity is more stringent for the cylindrical shell than for the conical caps, with the consequence that the buckling mode has displacements in the cylinder and in the conical caps. The influence of radius to thickness ratio and fluid level are investigated by means of parametric studies.Fil: Burgos Mariguin, Carlos Alberto. Universidad Nacional de Córdoba; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Wind buckling of tanks with conical roof considering shielding by another tank

Oil storage tanks are usually arranged in groups in tank farms, and this configuration may affect their buckling and postbuckling strength under wind loads. The assessment of wind action on tank structures is performed in this work by means of wind tunnel experiments to evaluate the pattern of pressure distribution for a tank which is shielded by another tank under various configurations and separation between them. The experimental results show significant changes in pressures due to shielding effects. In a second stage the structural response under the pressures previously evaluated is performed by finite element analysis using both linear bifurcation and geometrically nonlinear analysis. Results of two-tank interaction are compared with those of an isolated tank. Based on the results, it is concluded that the changes in wind pressures due to group effects induce changes in buckling loads and in the associated deflected patterns.Fil: Burgos, Carlos. Universidad Nacional del Comahue; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Lassig, Jorge Luis. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentin

Thermal post-buckling behavior of oil storage tanks under a nearby fire

This paper reports research on the thermal buckling and post-buckling of vertical steel tanks under heat induced by a nearby burning tank. A two-layer solid flame model is adopted and a heat transfer analysis is carried out to compute temperatures in the target tank. The temperatures are used as input in the structural analysis based on a geometrically nonlinear analysis and temperature-dependent properties of steel. The structural problem is solved by a finite element analysis to trace the pre- and post-critical equilibrium path. The lower critical temperature is detected and subsequent instabilities are identified until the temperature reaches the maximum value that can be transferred for the specific fuel burning. The post-buckling response is investigated to account for wind effects, separation between tanks, and fluid stored in the target tank. The ratio between first critical temperature and the final temperature at which the process reaches a thermal steady state, is computed in each case.Fil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Calabró, Horacio D.. Universidad Nacional del Comahue; ArgentinaFil: Espinosa, Susana Noemi. Universidad Nacional del Comahue; Argentin

A penalty approach to obtain lower bound buckling loads for imperfection-sensitive shells

The strategy of Reduced Stiffness (or Reduced Energy) Analysis, in which selected energy components are eliminated to account for mode interaction and imperfection-sensitivity in a simplified way, was developed by Croll and co-workers since the early 1980s. This physical interpretation allows the formulation as an eigenvalue problem, in which the eigenvalue (critical load) is a lower bound to experiments and to nonlinear incremental analysis. This paper considers the computational implementation of both reduced stiffness and reduced energy approaches to the buckling of shell structures by means of perturbation techniques and penalty parameter methods. The structural configurations of interest in this work are cylindrical shells with or without a roof. The reduced stiffness approach has been implemented in a special purpose finite element code for shells of revolution, whereas the reduced energy methodology was implemented in a general purpose finite element code. The present results are compared with geometrically nonlinear analysis including geometric imperfections. Achievements and difficulties in extending the methodologies to complex problems in engineering practice are highlighted.Fil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Estructuras; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Sosa, Milton Eduardo. West Virginia University; Estados UnidosFil: Flores, Fernando Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Estructuras; Argentin

Displacements of side walls with wall- girts in industrial building under vertical settlements

The localized settlement of columns in large metal industrial buildings induces out-of-plane displacements of side walls of the same order as the settlement, which may affect service conditions in the building. For a structural configuration formed by frames, side-walls and wall-girts, this work reports results from testing a small-scale model together with computational modeling of the full-scale structure. Dimensional analysis was used to scale the geometry and properties from full-scale to small-scale, leading to an overall scale factor of 1:15. Differential settlements having a controlled amplitude were imposed at the central column, and displacements were monitored using mechanical devices. The computational model employed shell elements for side-walls and wall-girts. Good agreement was found between tests and computer modeling. The results at the full-scale level, indicate that, for settlements likely to occur in granular soils, the associated lateral displacements exceed those allowed by current US regulations. Stiffening the structure was investigated by use of stiffer girts, as well as by reducing their spacing. The influence of frame height was also investigated. The overall conclusion is that out-of-plane displacements of side-walls may easily exceed allowable values unless they are specifically considered at a design stage.Fil: Subelza, Noemí Marta. Universidad Nacional del Comahue; ArgentinaFil: Verónica A. Pedrozo. Universidad Nacional del Comahue; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin