Gegenstand der hier vorgestellten Arbeit ist die Untersuchung von verschiedenen Nachweismöglichkeiten bei in Stegebene belasteten U-Querschnitten als gabelgelagertem Einfeldträger. Es sollen zum Eurocode 3 konforme Berechnungsmethoden untersucht werden, also müssen die Schnittgrößen nach Theorie II. Ordnung ermittelt werden. Unter Berücksichtigung der Wölbkrafttorsion sowie dem Ansatz geometrischer Ersatzimperfektionen mit anschließendem Querschnittsnachweis, soll ein Vergleich mit Bemessungshilfen nach DIN 18800 geführt werden. Weiterhin werden alternative Nachweismöglichkeiten aus der Literatur für ein modifiziertes Ersatzstabverfahren mit den Ergebnissen nach Eurocode 3 verglichen und auf Anwendbarkeit überprüft. Aus den Erkenntnissen sollen Bemessungshilfen für die Praxis bestätigt bzw. entwickelt werden.:Kurzfassung Abstract Inhaltsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Abkürzungsverzeichnis Vorwort 1 Problemstellung 2 Ziel 3 Stand der Technik 4 Grundlagen 4.1 Wölbkrafttorsion 4.2 Teilschnittgrößenverfahren 5 Forschungsberichte für die Praxis 5.1 P 174 5.2 P 251 5.3 Vergleich der Traglasttabellen 5.3.1 Grundsätzliches 5.3.2 Realisierungsweg 5.3.3 Ergebnisse 5.3.4 Schlussfolgerungen 6 Programmbasierte Nachrechnung 6.1 Auswahl der Eingangslast für die Bemessung 6.2 Dlubal RFEM Berechnungen 6.2.1 Voreinstellungen in RFEM 6.2.2 Zusatzmodule und Erweiterungen 6.2.3 Bauteilimperfektionen 6.2.4 Plastische Tragreserven 6.2.5 Ergebnisse 6.2.6 Bewertung der RFEM Nachweise 6.3 pcae 4H-DULAS Berechnung 6.3.1 Voreinstellungen 6.3.2 Anwendungsüberprüfung 6.3.3 Ergebnisse 6.4 Einordnung der Ergebnisse 7 Berechnung mit dem modifizierten Ersatzstabverfahren 7.1 Ideales Biegedrillknickmoment Mcr 7.1.1 RFEM – Biegedrillknickmoment mittels Eigenwertmethode 7.1.2 Ideales Biegedrillknickmoment nach Baláž und Koleková 7.2 Beispielrechnung 8 Auswertung 8.1 Ergebnisse 8.2 Graphische Darstellung Regelfall 8.3 Graphische Darstellung U 300 8.4 Grenzen des modifizierten Ersatzstabverfahrens 8.5 Schlussfolgerung 9 Zusammenfassung und Ausblick Literaturverzeichnis Erklärung Anhang / A comparison between different calculation methods of single span girders made of channel sections with fork restraints, subject to web loading is being presented. The calculation method according to Eurocode 3, demands the determination of internal forces to comply to the theory of the 2nd order. Minding the effects of warping torsion, whilst taking geometrical substitute imperfections into account, a cross-section analysis is conducted. The results of said calculation are compared to critical load tables, that have been established for the design rules in DIN 18800. Additional to that, a proposed design rule, based on the equivalent member method, will be included into the comparison and consequently the dimensioning aid will be confirmed or revised.:Kurzfassung Abstract Inhaltsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Abkürzungsverzeichnis Vorwort 1 Problemstellung 2 Ziel 3 Stand der Technik 4 Grundlagen 4.1 Wölbkrafttorsion 4.2 Teilschnittgrößenverfahren 5 Forschungsberichte für die Praxis 5.1 P 174 5.2 P 251 5.3 Vergleich der Traglasttabellen 5.3.1 Grundsätzliches 5.3.2 Realisierungsweg 5.3.3 Ergebnisse 5.3.4 Schlussfolgerungen 6 Programmbasierte Nachrechnung 6.1 Auswahl der Eingangslast für die Bemessung 6.2 Dlubal RFEM Berechnungen 6.2.1 Voreinstellungen in RFEM 6.2.2 Zusatzmodule und Erweiterungen 6.2.3 Bauteilimperfektionen 6.2.4 Plastische Tragreserven 6.2.5 Ergebnisse 6.2.6 Bewertung der RFEM Nachweise 6.3 pcae 4H-DULAS Berechnung 6.3.1 Voreinstellungen 6.3.2 Anwendungsüberprüfung 6.3.3 Ergebnisse 6.4 Einordnung der Ergebnisse 7 Berechnung mit dem modifizierten Ersatzstabverfahren 7.1 Ideales Biegedrillknickmoment Mcr 7.1.1 RFEM – Biegedrillknickmoment mittels Eigenwertmethode 7.1.2 Ideales Biegedrillknickmoment nach Baláž und Koleková 7.2 Beispielrechnung 8 Auswertung 8.1 Ergebnisse 8.2 Graphische Darstellung Regelfall 8.3 Graphische Darstellung U 300 8.4 Grenzen des modifizierten Ersatzstabverfahrens 8.5 Schlussfolgerung 9 Zusammenfassung und Ausblick Literaturverzeichnis Erklärung Anhang

Transparent and subtle structures are features of modern architecture. Structural glass is constructional material that provides to realize architect's visions and ideas. Glass as a constructional material is more often used as a material for primary load-bearing structures. Realization of safe, reliable and economic glass structure is real challenge for structural engineers because of absence of standards for designing of glass members and elements. Compressed members (columns), bended members (beams) and members loaded by compression and bending (beam-columns) were analysed in the frame of the doctoral thesis whereby the emphasis is being placed on the lack of stability – flexural buckling, lateral-torsional buckling and flexural-lateral-torsional buckling. Measuring of shape and amplitude of initial geometrical imperfections is a part of doctoral thesis. The theoretical analysis describes the behaviour of the member by means of solving the differential equations. The solution according to the second order theory developed for metal members is applied on structural laminated glass members with use of effective cross-sectional characteristics. Numerical analysis is focused on the use of commonly available software based on finite element method in order to predict the load-bearing resistance of laminated glass members. Actual behaviour of laminated and monolithic structural glass members was found within experimental program. The correctness of FEM model and analytical solutions were evaluated by comparing with test results. The goal of the doctoral thesis was determine of buckling curves for calculation of flexural buckling and lateral-torsional buckling resistances by the same calculation procedure as for metal members. Because of small number of experimentally tested specimens the Monte Carlo simulation was performed.

The aging infrastructure worldwide and the typical increase in service loads relative to original design loads make it essential to develop effective techniques for strengthening and rehabilitating existing structures, to enhance their resistance. An effective method for strengthening existing steel I-beams is to weld either one or two cover plates to the flange(s). In many cases, it is not feasible to completely unload the beam before carrying out the strengthening procedure. In these conditions, operators resort to strengthen beams while under loading. In such scenarios, it becomes a challenging task to assess the lateral torsional buckling (LTB) capacity of the member under present steel design standards (e.g., CAN/CSA-S16 2019 and ANSI/AISC360 2022) which do not consider the effect of pre-strengthening loads on LTB resistance. Within this context, the present study investigates the effects of pre-strengthening loads on the critical moment capacity by developing a series of solutions, ranging from elaborate and accurate to simplified but approximate, to predict the elastic LTB capacity of beams strengthened with cover plate(s) while under load. In this respect, the study contributes to the existing body of knowledge through four aspects: In the first contribution, a shell-based finite element (FE) study is developed to analyze the effect of various geometric and loading parameters on the LTB capacity of doubly symmetric beams strengthened symmetrically with two cover plates. The study carefully simulates the entire history, including the application of pre-existing loads, clamping forces to align the initially straight steel cover plates with the bent beam configuration, the rebound effect arising after clamping force removal, the contact at the interfaces between cover plates and flanges induced by welding, and the application of post-strengthening loads up to the point of elastic LTB initiation for the strengthened system, as determined by eigenvalue analysis. A simplified design equation is then proposed to quantify the post-strengthening critical moment capacity. The validity of the equation is assessed against FE results and its merits and limitations are discussed. The study shows that web distortional effects play a crucial role in reducing the elastic critical moment capacity. Practical recommendations are provided to mitigate such distortional effects and hence maximize the elastic critical moment capacity of the strengthened beams. The second contribution formulates a variational principle for the LTB analysis of doubly symmetric beams strengthened symmetrically with identical steel cover plates. The formulation considers the full sequence of loading and strengthening and captures the effects of pre-strengthening loads and the beneficial effects of pre-buckling deformation (PBD). The study examines the effect of geometry, partial strengthening schemes, presence of different pre- and post-strengthening load patterns, and load height effects. The variational principle is subsequently used to develop a FE formulation, culminating in a quadratic eigenvalue problem. The validity of the FE formulation is assessed through comparisons with other numerical techniques predictions as well as experimental results by others, and subsequently used to conduct a parametric study to characterize the gain in elastic critical moment capacity attained by cover plate strengthening. For beams partly strengthened with cover plates along their spans, the study identifies the optimum locations for cover plates that maximize the critical moments. The third contribution builds upon the variational principle developed by formulating a simple and approximate energy-based design-oriented solution to quantify the LTB resistance of simply supported I-beams strengthened with cover plates. The solution captures the detrimental effect of loads acting on the beam before strengthening and the beneficial effects resulting from PBD, pre- and post-strengthening load heights, as well as moment gradient effects. The potential use of the equations developed in practical applications involving beam strengthening is illustrated through design examples. The fourth contribution expands the variational formulation to include beams with monosymmetric cross-sections and/or symmetric beams with unsymmetric cover plate geometries. The modified variational principle is used to develop a thin-walled beam FE formulation, which is subsequently employed to predict the non-distortional LTB capacity of monosymmetric strengthened beams. Comparative analyses with shell models confirm the validity of the proposed solutions, and practical design recommendations for suppressing web distortion are provided. The effects of various design parameters on the total elastic critical moment capacity are evaluated in a systematic parametric study. The study identifies the loading conditions under which the magnitude of pre-strengthening loads significantly influences the predicted total critical moments. The solutions developed in the present study equip structural designers and analysts with novel techniques that reliably quantify the LTB strength of steel beams strengthened with cover plates, thus enabling them to optimize strengthening strategies for beams whose strengths are governed by LTB modes of failure.

The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

The doctoral thesis is focused on evaluation of global sensitivity analysis of load-carrying capacity of steel hot-rolled beams. These beams are subjected to lateral-torsional buckling, weak axis buckling and strong axis buckling. Very comprehensive computational models which were both geometrically and materially nonlinear were created in Ansys software using solid finite elements to calculate the load-carrying capacity. The computational models allowed modelling of random initial imperfections such as initial curvature, deviations of cross-section dimensions and steel properties. Sensitivity analysis quantified their influence on the load-carrying capacity. Simulation runs of random imperfections were generated using the Latin Hypercube Sampling method. Since the evaluation of sensitivity analysis of load-carrying capacity of all finite element models would cost an extreme amount of computer time, the thesis aimed at developing a meta-model (also known as surrogate model) based on approximation of FEM model. The approximation polynomial then facilitated the evaluation of sensitivity indices using a high number of simulation runs. At the end, the relationships between the slenderness and the first and second-order sensitivity indices are plotted in graphs. Those random input imperfections that influence the variability of load-carrying capacity the most are pointed out.

The doctoral thesis focuses on problem of stability of steel thin-walled beams with lateral and torsional restraints along the spans. Theoretical background of lateral-torsional buckling of an ideal beam with and without restraints preventing out-of-plane buckling is briefly described. In the following chapters the problem of stabilization of steel thin-walled beams by planar members is dealt with. The state of the art in this field is summarized and some open questions are identified. The research in this field could bring new findings about actual behavior of these structural systems. The rate of stabilization can be quantified using values of shear and rotational stiffness provided to a thin-walled member by a planar member. In the frame of the thesis the problem of torsional restraint given to steel cold-formed members by sandwich panels under load is discussed. In case of the uplift load applied on the sandwich panels the torsional restraint should be verified by experimental analysis. To contribute to this field, experimental verification of rotational stiffness provided to steel cold-formed beams by sandwich panels was proposed and performed. Torsional restraint under no external load as well as under uplift load applied on the panels was investigated. The purpose was to obtain the values of the rotational stiffness provided by planar members. The performed tests indicate significant and practically applicable rate of the torsional restraint even in case of the uplift load on the surfaces of the panels. Utilization of the values of the rotational stiffness might result in more economical, effective and reliable structural design. Selected problems were investigated using numerical modeling in a finite element method based software.

For the stability assessment of members and structures according to EN 1993-1-1 the equivalent member method, the geometrical nonlinear calculation with equivalent geometrical imperfections or the GMNIA analysis with geometrical imperfections and residual stresses can be used alternatively. The second possibility requires a corresponding model for the cross-section resistance. For the verification of lateral torsional buckling, bow imperfections e0 out of plane are defined, which lead in combination with the given loading in plane and the geometrical non-linear analysis to bending Mz and torsion of the members. The amplitudes of the imperfections are highly dependent on the nature of the approach (e.g., scaling of the buckling shape, assumption of bow imperfections) and the resistance model for the members. Within the framework of the scientific work supervised by the TU Dresden and the TU Darmstadt [1], extensive parameter studies were carried out to calibrate imperfections for lateral torsional buckling based on the GMNIA. After determining the nature of imperfections and the design models for section resistance, this paper presents results of these parameter studies and shows the calibration of imperfections for a standardisation proposal based on EN1993-1-1. The evaluation of the data in combination with the necessary simplifications for the design practice leads to appropriate definitions of imperfection values e0,LT and the necessary differentiations.

For the stability assessment of members and structures according to EN 1993-1-1, the equivalent member method, the geometrical non-linear calculation with equivalent geometrical imperfections or the GMNIA analysis with geometrical imperfections and residual stresses can be used alternatively. The second possibility requires a corresponding model for the cross-section resistance. For the verification of lateral torsional buckling, bow imperfections e0 out-of-plane are defined, which lead in combination with the given loading in-plane and the geometrical non-linear analysis to bending moments Mz and torsion of the members. The amplitudes of the imperfections are highly dependent on the nature of the approach (e.g., scaling of the buckling shape, assumption of bow imperfections) and the verification method for the members. Within the framework of the scientific work supervised by the TU Dresden and TU Darmstadt, extensive parametric studies were conducted to calibrate imperfections for lateral torsional buckling based on the GMNIA. After determining the nature of imperfections and the design models for section resistance, this article presents results of these parametric studies and shows the calibration of imperfections for a standardisation proposal based on EN1993-1-1. The evaluation of the data in combination with the necessary simplifications for the design practice leads to appropriate definitions of imperfection values e0,LT and the necessary differentiations.

Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.

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 / TESIS / Compendio