Nowadays / design, fabrication and erection of steel structures can be taken place at different locations as a result of rapid globalization / owners may require the use of widely accepted steel design codes. Therefore, engineers are faced with the challenge of being competent with several design specifications for a particular material type. AISC-360 and EC3 are widely accepted steel structure design specifications that utilize limit state principles with some similarities and differences in application. Hereby a study has been undertaken to put together the nominal strength expressions presented in both AISC-360 and EC3 codes in a single document, to identify the similarities and the differences in calculated strengths and to facilitate rapid learning of either of the specifications with prior knowledge of the other. Because of the wide scope of specifications, only fundamental failure modes are considered in this thesis. Resistance equations are directly compared with each other wherever possible. For cases where the treatment of specifications is entirely different, representative members were considered for comparison purposes.

The trend of structural engineering in the recent years is toward the use of lighter and moreeconomical structural elements. In steel construction, peculiarly, thin-walled structural elements arebecoming more popular and have a growing importance. Improved techniques in a manufacturing ofthin-walled elements have led to increased competitiveness of such products in the buildingapplications. Some examples of such structural element can be found in everyday life in form ofcolumns, studs, roofing trusses, and light-weight frames. However, the use of slender profiles and acomplex cross sections shape lead to requirements to study instability phenomenon in a form of local,distortional, flexural, torsional and coupled instability. Such complex structural behavior is inevitablyaccompanied by demand to improve calculation methods and design provisions. In this thesis, aninnovative solution of structural element composed of thin-walled plates is proposed for theapplication on lattice support structure of wind turbine.Thin-walled cold-formed profiles are steel products usually made from cold rolled coils and folded inthe second step. In this way, only open profiles can be produced. The predominant problem of theopen cross-section is the excessive torsional effect caused by the non-coincidence between the shearcenter and mass center, and a poor torsional resistance. A better response is possible with closed crosssections, but such profiles could not be produced by the folding. The solution is to make semi-closedsection by assembling them into polygonal profiles with mechanical fasteners, as presented in thisthesis.Objective of this work is to study the proposed structural sections in design situation and toinvestigate possible design models. The expected structural behavior of the column is a mixturebetween the open and closed cross-section. These cases will be investigated through numerical study.In this thesis presented a comprehensive parametric study on the ultimate strength of proposed coldformedsteel columns using the Finite Element package ABAQUS. FE models were first developedfor columns by using automation that was made through MATLAB and Python script. The bucklingand non-linear FE study was done for the investigation of local (L), distortional (D) and global (G)possible buckling failures and ultimate resistance, respectively. Modelling issues such as boundaryconditions, meshing, initial imperfections, material models, and non-linear solution controls in FEAwere also addressed.The parametric study involved series of profiles of built-up polygonal cross-section types with variedthickness (t), number of corners (n), diameter (d), slenderness (slend), yield strength (fy), number ofpoints along corner radii (np), extension lip length (lext), gusset plate thickness (tg), member length (l),and density of fasteners (s/d ratio), loaded in compression and bending moment. The bending momentoccurs as the effect of forces acting on the connection. The purpose of this analysis is to study thecritical load, cross-sectional behavior, influence of the amplitude of initial imperfections on theultimate load, and influence of each parameter used in the analysis through Full Factorial Design.

[pt] Um dos métodos adotados para a caracterização das ligações mistas semirrígidas é o método das componentes descrito no Eurocode 3 e no Eurocode 4. O modelo de componentes desenvolvido nesse método considera para a contribuição mista à incorporação da componente da barra de armadura, aspectos relativos ao concreto e a resistência do conector. Porém, o modelo é baseado em suposições ainda não totalmente estudadas quanto à resposta estrutural da parcela mista da ligação, principalmente em regiões de momento negativo. Todo esse aspecto tem limitado o uso do método para o projeto de estruturas mistas. Esse fato motivou a concepção e o desenvolvimento de um programa experimental para investigar as ligações em estruturas mistas, por meio de testes de pull out, considerados os modos de falha devido a ruptura da barra, da ancoragem da barra e da solda dos conectores. Adicionalmente, foi realizada uma investigação da influência da solda dos conectores devido a falha desse elemento no decorrer de alguns ensaios. Os resultados dos ensaios desenvolvidos permitiram que conclusões gerais pudessem ser determinadas e possibilitaram um maior conhecimento sobre a solda e seus impactos ao sistema. A correta utilização de soluções de ligações mistas pode aumentar a competitividade do sistema estrutural, propiciando construções mais econômicas e eficientes. / [en] One of the methods adopted for the characterization of the composite semirigid joints is the method of the components described in Eurocode 3 and Eurocode 4. The model developed in the method considered for the composite contribution the incorporation of reinforcement bar components, aspects related to the concrete and the connector strength. However, the model is based on not fully validated assumptions as to structural response of the composite portion of the joint, mainly negative moment areas. All this aspect has limited the use of the method for the design of composite structures. This fact encouraged to the conception and development of an experimental program to investigate joints in composite structures, by means of pull out tests, considering the failure modes due to rupture of the reinforcement bar, of the anchorage of the bar, and of the weld connectors. Additionally was made a research of the weld connectors influence due to failure of this element in the course of a few pull out tests. The results of the tests developed have allowed general conclusions could be determined and made possible a better understanding of the weld and its impacts to the system. The correct use of composite joints solutions can increase the competitiveness of the structural system, providing more economical and efficient buildings

This thesis work is carried out in Cargotec Sweden AB, Bromma Conquip to study the behavior of load carrying welded joints in different weld metal strength mismatch conditions and various penetration ratios. Static and fatigue strength calculations have been made using FEA and experimentation. The joint in the Telescopic beam of the spreader STS45 has been analyzed. Telescopic beam is one of the critical and main parts in the spreader, which is directly subjected to the load of containers at various ports. Previous studies show that this joint limits the strength of the spreader, it has thus been analyzed. To check the effect of different strength mismatch conditions in the weld metal, static strength calculations have been carried out. The effect of different penetration ratios on static and fatigue strength has also been studied. A cruciform test specimen is designed according to the joint configuration and the capacity of testing machine. Criteria for the selection of consumables has also been developed and following standards: Eurocode 3, AWS D1.1 and BSK07, have been compared for static joint design. Sub modelling, effective notch stress and beam theory techniques have been used to study the effect of weld metal penetration and size of weld throat on the fatigue strength of the welded joint in the Telescopic beam. The study show that matching or slight under matching in the filler material along with full penetration increases the ultimate strength capacity as well as the ductility in the joint. Results of Eurocode 3, AWS D1.1 and BSK 07 are close to each other. Apart from strength mismatch and penetration ratios, it is observed that the weld geometry and joint preparation has also effect on the strength of the joint. Fatigue analysis of the weld in the Telescopic beam using 3D Finite element analysis show that effective notch concept is not applicable to this part of the spreader.

[EN] Concrete filled steel tubular columns have many advantages in terms of bearing capacity, aesthetics, execution and fire resistance, thanks to the collaborative work of both materials steel and concrete. The effort made in the last decades to rise a high understanding of their behaviour subjected to different loads and assuming multiple variations has resulted in the wide spread of its use between the designers. Nonetheless, how to solve the connection with I-beams is still a handicap and requires a specific study. One of the most common and popular solution to connect open section steel beams (I-beams) to open section steel columns are endplate connections. In the cases of columns with hollow section, special fastenings are needed, which are able to be tightened from one external side and are denominated blind-bolts. Nowadays, there are several fastener systems that allow these types of connections. The characterization of their response and their capacity to support different loads is the objective of several investigations, where the geometrical definition and the material properties are crucial parameters. Despite the promising results of these connections at room temperature regarding their capability to resist bending moments, their performance is un-known at high temperatures. Therefore, the aim of this thesis is the study of the tensile behaviour of blind-bolts in endplate connections to concrete filled tubular columns at elevated temperatures and subjected to bending moment. Primarily, the research comprises the understanding of the pure thermal transfer problem. The temperature distribution through the connection section is obtained experimental and numerically. The thermal parameters that characterize the connections response are determined through the calibration of the numerical models with the experiments. Secondly, the blind-bolt capacity under pull out and at high temperatures is under analysis. During the fire the temperature increases while connection transmits loads from the beam to the column, the objective of this dissertation is to know how the mechanical response of the pulled blind-bolts changes under these conditions. Thus, the study of the material properties dependent on the temperature and their effect on the connection response is covered by the investigation. Furthermore, the influence of the concrete and the type of fastener is a highlighted aspect through the thermal and the fire analysis. Finally, the reliability of these connections to comply with requirements of 30 minutes fire exposure before the collapse is evaluated. As a result, valuable Finite Element models able to simulate the thermal and thermo-mechanical behaviour of the connection are developed, providing useful behavioural patterns of the blind-bolts. Among the main conclusions, it is noted the temperature reduction due to concrete core in concrete filled columns compared to hollow sections, in the exposed bolt surface means 100ºC less. Conversely, a longer bolt shank of the fastener system embedded in concrete has a negligible effect on the temperature of the resistant part of the bolt. Regarding the fire capacity, the concrete core in the steel tube columns presents significant benefits in terms of fire resistance time and connection stiffness. Besides, the bolt anchorage enhances the stiffness at elevated temperatures, however, the failure of the shank next to the bolt head causes that the anchorage does not mean an improvement on the fire time resistance. / [ES] Las columnas tubulares de acero rellenas de hormigón presentan múltiples ventajas en términos de capacidad de carga, estética, ejecución y resistencia al fuego, gracias a la acción combinada de acero y hormigón. El esfuerzo realizado en las últimas décadas por conocer su comportamiento frente a diferentes cargas y bajo distintos parámetros ha dado lugar a una amplia difusión de su uso entre los diseñadores. No obstante, la forma de resolver la conexión con vigas de sección en I sigue siendo un hándicap y requiere un estudio específico. Una de las soluciones más comunes y populares para conectar las vigas de acero de sección abierta (vigas I) a columnas de acero de sección abierta es la conexión con chapa de testa, que en el caso de sección hueca requiere de tornillos especiales denominados tornillos ciegos, puesto que reciben el par de apriete desde una cara de la sección. En la actualidad existen diversos sistemas de fijación que permiten este tipo de conexiones y cuya respuesta y caracterización es objeto de numerosas investigaciones. En este sentido, la definición geométrica de la unión y las propiedades de los materiales son parámetros cruciales en el rendimiento de la conexión. La presente tesis analiza el comportamiento de los tornillos ciegos en el área traccionada de conexiones de placa de testa a columnas tubulares de acero rellenas de hormigón sometidas a momentos de flexión y a elevadas temperaturas. Las prestaciones de esta solución constructiva para la unión viga-columna tubular, junto con la ausencia de datos relacionados con su comportamiento en situación de incendio la convirtió en el objetivo del trabajo. En primer lugar, la investigación aborda el problema de transferencia de calor, analizando experimental y numéricamente la distribución de temperaturas en la sección de la conexión. En esta parte del estudio se obtienen los parámetros térmicos que caracterizan la respuesta térmica de la conexión a través de la calibración de los modelos numéricos con los datos experimentales. En segundo lugar, se realiza el estudio de la capacidad de los tornillos ciegos para soportar cargas de tracción en situación de incendio, es decir, se analiza cómo cambia el comportamiento de la conexión con sus características alteradas debido a las altas temperaturas. El estudio de las propiedades del material en función de la temperatura y su efecto sobre la respuesta de la conexión constituyen una parte importante de la investigación. Además, se evalúa la influencia del hormigón y el tipo de elemento de sujeción tanto en el comportamiento mecánico como termo-mecánico de la conexión. Por último, se estudia la capacidad de las uniones para cumplir con requerimientos de exposición al fuego de 30 minutos previamente al colapso. Como resultado de este trabajo se obtuvieron modelos de elementos finitos capaces de simular la conexión térmica y termo-mecánicamente, proporcionando patrones de comportamiento de gran utilidad en el diseño de las mismas. Entre las principales conclusiones, se observó la reducción de la temperatura en los tornillos gracias al núcleo de hormigón en columnas de hormigón lleno en comparación con secciones huecas, que ya en la superficie expuesta del tornillo se cuantificaba en 100ºC menos. Por el contrario, los elementos de fijación que presentaban mayor longitud de vástago de tornillo embebida en el hormigón, no generaban un efecto significativo sobre la temperatura de la parte resistente del perno. En cuanto a la capacidad resistente frente a fuego, el núcleo de hormigón supuso una mejora en términos de rigidez y de tiempo de resistencia al fuego. Sin embargo, el fallo de los pernos en una sección próxima a la superficie expuesta redujo el efecto esperado del anclaje del tornillo, que si bien implicaba una mayor rigidez de la conexión, no parecía mejorar el tiempo de resistencia a fuego. Finalmente se planteó la necesidad de / [CA] Els pilars tubulars d'acer omplerts de formigó (CFT) presenten molts avantatges en termes de capacitat de carrega, estètica, execució i resistència al foc, gràcies a l'acció combinada de l'acer i el formigó. L'esforç realitzat en les darreres dècades per conèixer el seu comportament enfront a diferents càrregues i sota distints paràmetres ha donat lloc a una amplia difusió del seu ús entre el dissenyadors. No obstant això, la manera de resoldre la connexió amb bigues de secció en I, continua sent un handicap i requereix d'un estudi específic. Una de les solucions més comuns i populars per a connectar les bigues d'acer de secció oberta (bigues I) a columnes d'acer de secció oberta és la connexió amb 'chapa de testa', que en el cas de la secció buida requereix de perns especials denominats perns cecs perquè es rosquen des d'una cara de la secció. En l'actualitat existeixen diversos sistemes de fixació que permeten aquest tipus de connexions, la resposta i caracterització dels quals es l'objectiu de nombroses recerques. En aquest sentit, la definició geomètrica de la unió i les propietats dels materials son paràmetres crucials en el rendiment de la connexió. Aquesta tesi analitza el comportament dels perns cecs en l'àrea traccionada de connexions de 'chapa de testa', a pilars tubulars d'acer omplerts de formigó, sotmeses a moments de flexió i a elevades temperatures. Les prestacions d'aquesta solució constructiva per a la unió biga-pilar tubular junt amb l'absència de dades relacionades amb el comportament en situació d'incendi, la van convertir en l'objectiu d'aquest treball. En primer lloc, la recerca aborda el problema de transferència de calor, analitzant tant experimental com numèricament la distribució de temperatures en la secció de la connexió. En aquesta part de l'estudi, s'obtenen el paràmetres tèrmics que caracteritzen la resposta tèrmica de la connexió mitjançant el calibratge del models numèrics amb les dades experimentals. En segon lloc, es realitza l'estudi de la capacitat dels perns cecs per a suportar càrregues de tracció en situació d'incendi, es a dir, s'analitza com canvia el comportament de la connexió amb les seues característiques alterades degut a les altes temperatures. L'estudi de les propietats del material en funció de la temperatura i el seu efecte en la resposta de la connexió formen també part de la recerca. Un contingut important d'aquest treball consisteix en determinar l'influencia del formigó i el tipus d'element de fixació tant en el comportament mecànic com termo-mecànic de la connexió. Per últim, s'estudia la capacitat de les unions per a complir amb els requeriments d'exposició al foc de 30 minuts prèviament al col·lapse. Com a resultat d'aquest treball s'obtingueren models d'elements finits amb capacitat per a simular el comportament tèrmic i termo-mecànic de la connexió, proporcionant patrons de comportament de gran utilitat en el disseny. Entre les principals conclusions, es va observar la reducció de la temperatura en els perns gràcies al nucli de formigó en pilars omplerts de formigó en comparació amb el pilars buits, on ja en la superfície esposada del cargol es quantificava en 100 ºC menys. Pel contrari, els elements de fixació que presentaven major longitud de embeguda en el formigó, no generaven un efecte significatiu en la temperatura de la part resistent del pern. En quant a la capacitat resistent davant del foc, el nucli de formigó va suposar una millora en termes de rigidesa i de temps de resistència al foc. Tanmateix, la fallada dels perns en una secció pròxima a la superfície esposada va reduir l'efecte esperat de la fixació del pern, que si be implicava una major rigidesa de la connexió, no semblava millorar el temps de resistència al foc. Finalment, es va plantejar la necessitat de aprofundir en l'anàlisi incorporant un major rang de paràmetres. / Pascual Pastor, AM. (2015). Fire behaviour of blind-bolted connections to concrete filled tubular columns under tension [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53240

<p>У овом раду спроведене су опсежна експериментална и нумеричка<br />испитивања понашања веза са чеоном плочом и четири завртња у реду,<br />као и карактеристичне компоненте ових веза - Т-елемента.<br />Експериментална испитивања укључују тестирања 36 узорака<br />Т-елемената у природној величини, као и четири везе греда-стуб са<br />чеоном плочом и четири завртња у реду, такође у природној величини.<br />Нумеричке анализе, спроведене у софтверском пакету ABAQUS, су<br />обухватале све типове нелинеарности, али и отказ материјала, те се као<br />такве сврставају међу ретке којима су слични проблеми нумерички<br />испитивани. Параметарска студија обухвата 33 различите конфигурације<br />Т-елемената са четири завртња и представља највећу такву студију<br />изведену за ову компоненту. Као основни још увек нерешен проблем,<br />круцијалан за понашање Т-елемената, препознати су положај сила услед<br />ефеката полуге, али и савијање завтњева. Приказан је и предложен нови<br />аналитички модел прорачуна носивости Т-елемената са четири завртња,<br />и квантификована његова предност над до сада постојећим моделима.</p> / <p>U ovom radu sprovedene su opsežna eksperimentalna i numerička<br />ispitivanja ponašanja veza sa čeonom pločom i četiri zavrtnja u redu,<br />kao i karakteristične komponente ovih veza - T-elementa.<br />Eksperimentalna ispitivanja uključuju testiranja 36 uzoraka<br />T-elemenata u prirodnoj veličini, kao i četiri veze greda-stub sa<br />čeonom pločom i četiri zavrtnja u redu, takođe u prirodnoj veličini.<br />Numeričke analize, sprovedene u softverskom paketu ABAQUS, su<br />obuhvatale sve tipove nelinearnosti, ali i otkaz materijala, te se kao<br />takve svrstavaju među retke kojima su slični problemi numerički<br />ispitivani. Parametarska studija obuhvata 33 različite konfiguracije<br />T-elemenata sa četiri zavrtnja i predstavlja najveću takvu studiju<br />izvedenu za ovu komponentu. Kao osnovni još uvek nerešen problem,<br />krucijalan za ponašanje T-elemenata, prepoznati su položaj sila usled<br />efekata poluge, ali i savijanje zavtnjeva. Prikazan je i predložen novi<br />analitički model proračuna nosivosti T-elemenata sa četiri zavrtnja,<br />i kvantifikovana njegova prednost nad do sada postojećim modelima.</p> / <p>In this research, extensive experimental and numerical investigations of<br />behaviour of end-plate moment connection with four bolts per row are<br />performed, as well as specific component of the connection &ndash; T-stub element.<br />Experimental research comprises tests on 36 unscaled specimens of T-stub<br />elements and 4 specimens of beam-to-column joints with end-plate connection<br />and four bolts per row, also in full-size. Numerical analyses, performed with<br />software ABAQUS, included all types of nonlinearities, and material<br />deterioration, hence they can be considered as one of the few most<br />sophisticated analyses used for investigation of the considered problem. The<br />parametric study comprises 33 different configurations of the T-stub element<br />with four bolts per row and it presents the biggest study of this kind for this type<br />of component. Bending of the bolts and position of the prying forces are<br />recognized as the largest, still unsolved problem, crucial for the behavior of the<br />T-stub elements. A new theoretical model for the resistance of the T-stub<br />element with four bolts per row is proposed and its advantage over the existing<br />models is presented and quantified.</p>