Above ground steel storage tanks are used worldwide for the storage of various liquids. EN 14015:2005, which has traditionally been used to design the tanks, does not necessarily fulfil the requirements of the Swedish Building Code. This has been underlined by hand calculation models in EN 1993-1-6:2007, EN 1993-4-2:2007 and numerical analysis using Finite Element Method (FEM). Therefore, this thesis investigates the differences between these design models and, preliminarily, the use of high-strength steel in tank shells. A 10600 m3 cylindrical steel tank of diameter 26 m and height of 21 m located in Gothenburg, Sweden is studied. The study is limited to the assessment of the stress in the shell courses due to the hydrostatic pressure from the fluid action of a filled tank, and the buckling behaviour of the shell courses of an empty tank subjected to self-weight, snow and wind loads. Particularly, models of the tank shell with a yield strength of 355 MPa are investigated in detail, while the results of the 700 MPa model are considered as preliminary study, since the material is currently not used for tank shells. An analysis of the fluid action on the tank shell courses in each of the three hand calculation models, showed that the EN 14015 model utilizes thicker courses than both Eurocodes. One benefit of the Eurocode models is that they do not limit the thickness of the shell courses, but it is still necessary to have thicker courses in the upper part of the tank in order to achieve sufficient resistance against buckling. EN 14015:2005, on the other hand, limits the minimum thickness to 6 mm for the investigated tank. Furthermore, only EN 1993-1-6 is applicable to the models with a yield strength of 700 MPa as per EN 1993-1-12 and this resulted in a uniform shell thickness of 6 mm. However, an increase in yield strength has no buckling benefits whatsoever.  Buckling is the most critical aspect as observed in this study. EN 14015 has no specific buckling calculations but uses the approach of determining the number of stiffening rings which are deemed adequate against buckling. In this study, 3 secondary stiffening rings were found to be adequate. In comparison, the results of EN 1993-4-2 are very conservative and lead to a very high and uneconomical number of stiffening rings, ranging from 30 to 52 stiffening rings depending on the reliability class. EN 1993-1-6 resulted in 6-17 stiffening rings, for reliability classes 1-3 and fabrication classes A-C. Therefore, the so-called analytical models in the Eurocodes result in a much denser spacing of stiffening rings than 14015:2005.  The buckling stresses due to the design loads were found to be lower than the yield strength of the tank shells for both hand calculation and FEM models. This means that the tank shells failed in buckling before the yield strength of the material was reached. Based on the parametric study of the EN 1993-1-6 (355 MPa) model regarding reliability class 1 and fabrication class A using FEM, the spacing of the stiffening rings can be increased up to 60 % (from 3825 mm to 6120 mm) with the variable loads also increased simultaneously up to 3.8 times before the shell buckles. Therefore, the design of future tanks using numerical analysis guarantee’s more reliability than all the aforementioned standards.  The design for buckling according to EN 14015 is only valid for a design snow load and under-pressure ≤ 1.2 KN/m2. However, according to the standard itis possible to agree to use it for larger actions or use another design model for buckling.

Tesis por compendio / [ES] El fuego es uno de los principales riesgos que pueden afectar a las estructuras de acero. El impacto del fuego en estas estructuras es muy adverso y complejo de simular, principalmente en escenarios de fuego realistas, donde el calentamiento en los miembros de acero no es uniforme y en miembros de acero esbeltos porque fallan prematuramente por la aparición de abolladuras locales. Para predecir con exactitud la respuesta de las estructuras de acero al fuego, se han desarrollado modelos avanzados y complejos de EF con elementos de cáscara y sólidos. Sin embargo, estos modelos son costosos desde el punto de vista computacional, lo que complica la realización de análisis más complejos que requieren muchas simulaciones en poco tiempo y con bajos costes computacionales. Por lo tanto, es necesario desarrollar modelos computacionales sencillos, precisos y de bajo coste, tan fiables como los modelos de cáscara, que abran el camino más fácilmente hacia la modelización de problemas estructurales de acero más complejos en situación de incendio. En esta tesis se presentan propuestas sencillas y de bajo coste computacional para simular la respuesta mecánica de estructuras de acero en condición de incendio utilizando un elemento finito de viga de Timoshenko de Ansys. Una de las propuestas consiste en una nueva metodología para el análisis en 3D de estructuras de acero sometidas a temperaturas no uniformes por el fuego. Las otras consisten en dos estrategias de modelización para analizar el pandeo lateral torsional en miembros de acero de clase 4 a temperaturas elevadas. Las propuestas simplifican significativamente la modelización estructural y se validan satisfactoriamente con resultados numéricos y experimentales. Esto significa que problemas complejos de ingeniería de incendio, como los análisis probabilísticos y de optimización, pueden tratarse con mucha más facilidad, lo que representa un paso importante hacia la aplicación generalizada de enfoques basados en el desempeño para tratar los efectos del fuego en las estructuras de acero. / [CA] El foc és un dels principals riscos que poden afectar les estructures d'acer. L'impacte del foc en estes estructures és molt advers i complex de simular, principalment en escenaris de foc realistes, on el calfament en els membres d'acer no és uniforme i en membres d'acer esvelts perquè fallen prematurament per l'aparició d'abonyegadures locals. Per a predir amb exactitud la resposta de les estructures d'acer al foc, s'han desenvolupat models avançats i complexos d'elements finits de corfa i sòlids. No obstant això, estos models són computacionalment costosos, la qual cosa complica la realització d'anàlisi més complexos que requerixen moltes simulacions en poc de temps i amb baixos costos computacionals. Per tant, és necessari desenvolupar models computacionals senzills, precisos i de baix cost, tan fiables com els models de corfa, que òbriguen el camí més fàcilment cap a la modelització de problemes estructurals d'acer més complexos en situació d'incendi. En esta tesi es presenten propostes senzilles i de baix cost per a simular la resposta mecànica d'estructures d'acer en condició d'incendi utilitzant un element finit de biga de Timoshenko d'Ansys. Una de les propostes consistix en una nova metodologia per a l'anàlisi en 3D d'estructures d'acer sotmeses a temperatures no uniformes pel foc. Les altres consistixen en dos estratègies de modelització per a analitzar el bombament lateral torsional en membres d'acer de classe 4 a temperatures elevades. Les propostes simplifiquen significativament la modelització estructural i es validen satisfactòriament amb resultats numèrics i experimentals. Açò significa que problemes complexos d'enginyeria d'incendi, com les anàlisis probabilístiques i d'optimització, poden tractar-se amb molta més facilitat, la qual cosa representa un pas important cap a l'aplicació generalitzada d'enfocaments basats en l'exercici per a tractar els efectes del foc en les estructures d'acer. / [EN] Fire is one of the main hazards that can affect steel structures. The impact of fire on these structures is highly adverse and complex to simulate, mainly in realistic fire scenarios, where heating in steel members is non-uniform and in slender steel members because they fail prematurely by local buckling. In order to accurately predict the response of steel structures to fire, advanced and complex FE models with shell and solid elements have been developed. However, these shell models are computationally expensive, complicating the carrying out of more complex analyses that require many simulations in a short time and at low computational costs. Therefore, there is a need to develop simple, accurate, and low-cost computational models as reliable as shell-type models that open the path more easily towards modeling more complex steel structural problems in fire conditions. This thesis presents simple and low-cost proposals to simulate the mechanical response of steel structures under fire using Timoshenko's beam-type finite element available in Ansys. One of the proposals consists of a new methodology for the 3D-analysis of steel frames subjected to non-uniform temperatures by fire. The others consist of two modeling strategies for analyzing the lateral-torsional buckling in class-4 steel structural members at elevated temperatures. The proposals significantly simplify the structural modeling and satisfactorily validate numerical and experimental results. That means that complex fire engineering problems, such as probabilistic and optimization analyses, can be handled much more easily, representing a significant step toward the generalized application of performance-based approaches to deal with fire effects on steel structures. / Pallares Muñoz, MR. (2022). New Proposals for Modeling the Thermo-Mechanical Response of Steel Structures Under Fire Using Beam-Type Finite Elements [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/182768 / Compendio