Dissertations / Theses on the topic 'Eurocode 3'

The twin aims of this research were to improve the presentation of codified design information and to investigate the methods used to calibrate the partial safety factors applied to resistance functions (ΎR-factors) so as to improve both the economy and the reliability of the predictions. A restructured version of EC3 (known as F-EC3) was developed by rearranging the design clauses on the basis of design tasks. This system enables the code to become more user-friendly. Hypertext versions of both EC3 and F-EC3 have been created on PC-based Microsoft Windows compatible software. The implications of hypertext on structural codes are investigated. The procedure used for calibrating the ΥR-factors contained within EC3 - (the Annex Z method) was reviewed and an alternative technique involving less assumption is proposed. A comprehensive set of measurements recording the material strength and the geometric properties of steel were obtained and collated. The large data set (over 7000 tests) was sufficient to evaluate the type of probability distribution characterising the variability of the basic material and geometric properties of structural steel. The resulting data were combined with experimental test results to determine the reliability of plate girder design and restrained beam design. The theoretical shear buckling resistance of plate girders (predicted by the simple post-critical and tension field, methods) was compared with experimental test results to determine reliability. The analysis demonstrated that plate girder design falls well short of the target reliability and an adjustment to the design methods is required in order to ensure safe design. A series of 4-point bending tests on laterally restrained beams were conducted to establish the accuracy of the Mpl.Rd resistance function. This study quantifies the degree of conservatism inherent in the Mpl.Rd design method and provides convincing evidence of the need to reduce the ΥR-factor applied to this resistance function. A modification is proposed to the design formulae which improves accuracy and permits the full moment capacity of restrained beams to be utilised.

The aim of this study is designing steel structures with the same geometry, material and soil conditions but in the different countries, and comparing these designs in terms of material savings. According to three steel building codes, namely TS 648, LRFD, Eurocode 3, same structures with various stories (2, 4, 6, 8, and 10) are analyzed and designed. To calculate the design loads, Turkish Earthquake Code 2007 and Turkish Standard 498 (Design Load for Buildings) are utilized when TS 648 is applied. When LRFD is concerned, ASCE Standard 7-05 (Minimum Design Loads for Buildings and Other Structures) and AISC Standard 341-05 (Seismic Provisions for Structural Steel Buildings) are used for calculation of the design loads and earthquake loads. When Eurocode 3 is applied, Eurocode 8 (Earthquake Resistance Code), Eurocode 1 (Actions of Structures) and Eurocode-EN 1990 (Basis of Structural Design) are used in order to determine the design and earthquake loads. Weight of steel used on 1 m²
is almost the same for procedures of LRFD and EC3. It is important to note that those procedures consider 20 % of material saving compared to TS648.

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.

This work focuses mainly on the resistance of members to flexural buckling according to Eurocode 3. The work provides the mathematical backgrounds to the equations and buckling curves presented in Eurocode 3. The work also, attempts to reveal how different imperfections influence the flexural buckling resistance which is demonstrated through Finite Element (FE) simulations. The work presents modeling and analysis on a steel column in ABAQUS 6.14. Linear and non-linear buckling analyses of the steel column, with the influence of imperfections, are implemented in this work. Specifically, the imperfections considered in this study are material plasticity, initial bow and residual stress. The influence of initial bow imperfection of 0.1% of the length of the column considering flexural buckling was found to be 45.28% of the Euler buckling load. The influence of residual stresses, with a magnitude of maximum about 13% in the flange and 35% in the web, of the yielding strength, on flexural buckling is about 31.9% of the design Euler buckling load. The combined effect of residual stress and initial bow imperfection on flexural buckling is about 45.34% of the design Euler buckling load.

Programa de Pós Graduação em Engenharia Civil. Departamento de Engenharia Civil, Escola de Minas, Universidade Federal de Ouro Preto.
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Este trabalho apresenta o modelo proposto pelo Anexo J do EUROCODE 3, para o dimensionamento de ligações parafusadas com chapa de topo e para a determinação da sua rigidez à rotação. Faz-se a análise do embasamento teórico e das verificações propostas comparando-as às recomendações da NBR 8800 (1986). Compara-se o modelo de dimensionamento em relação à fundamentação teórica do modelo de dimensionamento apresentado pelo Manual Brasileiro de Construção Metálica. Em particular avalia-se a veracidade do modelo de dimensionamento apresentado, utilizando-se resultados experimentais conhecidos. Finalmente apresentam-se as conclusões obtidas bem como tabelas de dimensionamento para vigas e pilares elaboradas a partir de um programa computacional, segundo a metodologia de dimensionamento apresentada. _________________________________________________________________________________
ABSTRACT : This work presents the proposed model of Annex J of EUROCODE 3, to design of bolted connections with extended end plate and to determination of its rotation stiffness. It’s analysed the background theory and the proposed verification. Comparisons are made between design model and the Brazilian Standard (NBR 8800) recommendations. It’s also compared the Annex J model in relation to background theory of Brazilian Manual of Steel Construction model. Special attention is paid to evaluate the behaviour of the presented model using experimental results already knew. Finally, the remarks and conclusion are presented. It’s also presented design tables for beams and columns and a computational program obtained by Annex J model.

Ce sujet est d’actualité suite à une évolution rapide des types de conception de structures élancées utilisées dans les installations provisoires. C’est seulement depuis une vingtaine d’années que ces structures sont préfabriquées en cadres multidirectionnels (de sections tubulaires en acier ou en aluminium). Ces structures sont légères et leur stabilité réside seulement dans les raideurs internes au niveau des files de montants et au niveau horizontal par les planchers ainsi que dans les liaisons avec l’ouvrage. Ce travail concerne l’étude des instabilités (flambement-déversement) en tenant compte de différents types d’imperfections. De nouvelles courbes de flambement ainsi que les facteurs d’imperfection associés sont proposés dans cette thèse. Ces courbes sont obtenues en imposant une déformée initiale représentant les défauts géométriques et mécaniques (contraintes résiduelles). Les résultats expérimentaux confrontés avec les prévisions théoriques de l’Eurocode 3 montrent que les valeurs des imperfections figurant dans la littérature sont extrêmement exagérées. Les valeurs préconisées dans ce travail pourraient présenter un certain intérêt pour une modification éventuelle des courbes européennes de flambement pour ce type de structure. En ce qui concerne l’instabilité latérale, une méthodologie originale d’essais en vraie grandeur de poutres à treillis formés d’éléments tubulaires a été également mise au point. Le système de chargement à « roues libres » développé permet de libérer le point d’application de l’effort dès le début de l’instabilité. Cette technique conduit à des mesures plus précises du moment critique de déversement
This subject becomes topical following a rapid evolution of design procedures for slender structures used widely in the temporary installations. Only through the last twenty years that these structures are prefabricated of multidirectional frames (steel or aluminium tubular sections). These structures are lightweight and their stability lies only in the internal stiffness at rows of posts and horizontally by the planking as well as the links with the building. This work concerns the study of instabilities (buckling - lateral torsional buckling) taking into account different types of imperfections. New buckling curves and the associated imperfection factors are proposed in this thesis. These curves are obtained by imposing an initial deformed representing the geometrical and mechanical defects (residual stress). The experimental results were confronted with theoretical predictions of Eurocode 3 which show that the values of the imperfections in the literature are extremely exaggerated. The values advocated in this work could be of interest for a possible adjustment of the European buckling curves for this type of structure. Regarding the lateral instability, an original methodology in real scale tests of trusses consist of tubular elements was also developed. The developed loading system of "free wheels" allows releasing the point of application of the force from the beginning of instability. This technique leads to more accurate measurements of the critical lateral torsional buckling moment

Des barres en acier à section ouverte sont, dans la majorité des cas, soumises à une combinaison d’effort normal et de flexion bi-axiale. Cependant, en raison de leur utilisation elles peuvent également être soumises à un moment de torsion. Même si les barres à section ouverte peuvent être soumises à des charges de torsion en pratique, l’Eurocode 3, ne définit pas comment la résistance de la barre peut être déterminée dans ces conditions. Ce pourquoi, l’objectif principal de cette thèse est de remplir cette lacune. Pour atteindre cet objectif, le comportement des barres métalliques soumises à une combinaison complexe de charges est étudié par voie théorique, expérimentale et numérique. Tout d’abord, la résistance plastique des barres est étudiée. En cas de torsion, il a été montré que les barres à section ouverte possèdent une réserve plastique importante qui ne peut pas être mise en évidence à l’aide d’une simple analyse élastique. Afin de tenir compte de l’effet bénéfique de la réserve plastique en torsion, une méthode d’analyse simplifiée est développée et validée par des analyses numériques. Ensuite, l’interaction plastique entre les efforts internes est étudiée. Des essais en laboratoire ont été réalisés afin de caractériser l’interaction entre l’effort tranchant et le moment de flexion. L’étude est ensuite étendue à l’aide de simulations numériques sur des cas d’interaction plus complexes incluant notamment des moments de torsion. Les essais accompagnés par l’étude numérique ont permis de mettre au point un modèle de résistance basé sur la méthode « Partial Internal Force Method » développée dans le passé. La dernière partie de la thèse concerne la résistance des barres à l’instabilité. Un modèle de résistance incluant l’effet de l’instabilité élasto-plastique est développé pour les barres métalliques en présence de torsion. Cette méthode est basée sur une extension des formules d’interaction proposées dans l’Eurocode. Afin de franchir certaines limitations liées à cette méthode, un deuxième modèle de résistance est développé pour les barres en I dans le format du « Overall Interaction Concept »
Structural steel members with open cross-section are, in the majority of cases, subject to a combination of axial forces and mono- or bi-axial bending. Nonetheless, owing to specific use they may be subject to torsion as well. Even if torsional loads are of practical interest for steel members of open section, the European standard for the design of steel structures, Eurocode 3, does not contain a generally accepted design method addressing the resistance of these members. Consequently, the main objective of this thesis is to close the lack in the current standard. So as to attain this objective the behaviour of members of open section subject to a complex load combination has been studied theoretically, experimentally and numerically. First, the plastic resistance of steel members has been analysed. It has been shown that members subject to torsion may possess a high plastic system reserve that cannot be predicted by simple elastic analysis. So as to account for the beneficial effect of the plastic reserve, a simplified analysis method has been developed and validated with numerical simulations. After this, the plastic interaction between all internal forces and moments has been studied. Several laboratory tests have been performed to characterise the interaction between bending moments and the shear force. The study is then extended to more complex interaction cases including torsion by means of numerical simulations. The laboratory test and the numerical simulations allowed the development of a precise resistance model based on the “Partial Internal Force Method” developed in the past. The last part of this thesis was dedicated to the member resistance including instability. A resistance model has been developed based on the Eurocode 3 interaction equations. So as to overcome some of the limitations linked to this method, a second design approach is developed based on the “Overall Interaction Concept”

I den mest grundläggande delen av Eurocode 3, SS-EN 1993-1-1, finns olika sätt att kontrollera bärförmågan för en balkpelare som utsätts för böjknäckning, d.v.s. en kombination av transversell och axiell last. Genom att använda formler där det dimensionerande värdet på andra ordningens moment ingår kan man kontrollera om balkpelaren håller för den aktuella belastningen.   Beräkningar av andra ordningens moment ger differentialekvationer som kan vara besvärliga och tidskrävande att lösa, men beräkningarna kan förenklas om man känner till den momentfaktor, kallad Cm-faktor, som tar hänsyn till momentfördelningens form i det aktuella lastfallet.   Denna rapport visar hur man kan härleda både exakta och approximativa värden på Cm-faktorer genom att studera två lastfall som skulle kunna vara av intresse för praktiskt bruk då konsolbalkar utsätts för böjknäckning. Resultaten visar att den approximativa metoden, som innebär avsevärt förenklade beräkningar, ger fullgoda resultat för de två fall som behandlas i rapporten.   Cm-faktorerna presenteras som grafer för att kunna läsas av då normalkraften som angriper i konsolbalkens fria ände varierar. I rapporten ges även bakgrunden till begreppet momentfaktor genom förklaring och beräkning av förstoringsfaktorn, ofta kallad f.

Os pilares mistos de aço e concreto consistem em um ou mais perfis de aço ligados entre si, trabalhando em conjunto com o concreto, simples ou armado, solicitados à compressão ou à flexocompressão. Os pilares mistos são, basicamente, de dois tipos: revestidos ou preenchidos. O sistema misto apresenta grandes vantagens estruturais, uma vez que herda a capacidade resistente dos pilares de aço e, dos pilares de concreto, sua robustez. Este trabalho estuda o emprego dessa solução de acordo com as principais normas internacionais de dimensionamento à temperatura ambiente, comparando-as entre si e às normas brasileiras. A ABNT NBR 8800:2008, apresenta dois modelos de cálculo simplificados para o dimensionamento de pilares mistos com seções transversais simétricas, com base em duas normas internacionais. O primeiro, o Modelo I, com base no ANSI/AISC 360 (2005) e o segundo, o Modelo II, no Eurocode 4 Part 1-1 (2004). Fica a critério do engenheiro estruturista a escolha do método a ser utilizado. Apresenta-se uma comparação gráfica e tabular da capacidade resistente à temperatura ambiente entre os dois modelos de cálculo da norma brasileira e as normas internacionais. No caso de seções transversais não simétricas, são propostos dois roteiros de dimensionamento inéditos em aplicações de pilares mistos: um com base no Fiber Elemento Method e nas recomendações do Eurocode 4 Part 1-1 (2004), e outro adaptando o primeiro às normas brasileiras. Ambos são avaliados graficamente e por meio de tabelas. Para o auxílio de todos esses estudos, foi utilizado o código CalcPM v1.0, desenvolvido especialmente para esse estudo.
The composite columns have the concrete and the steel profile working together to support loads. The composite columns are basically of two types: encased and filled. The composite system has the advantage to unite the inherent robustness of the concrete columns and high resistance of the steel columns. This work studies the use of this solution according to the main international standards, comparing them with each other and with the Brazilian norms. The Brazilian standard ABNT NBR 8800:2008, presents two simplified models of the composite columns design with symmetrical cross sections, based on two international standards. Model I, based on American standard ANSI/AISC 360 (2005) and Model II, with reference to the European standard Eurocode 4 Part 1-1 (2004). Is up to the engineer to choose the method to be used. It presents a tabular and graphical comparison of the strength between the two calculation models of the Brazilian and international standards. In the case of non-symmetrical cross sections there are two proposed routes unprecedented scale applications of composite columns: one based on \"Fiber Element Method\" and the recommendations of Eurocode 4 Part 1-1 (2004) and another one to adapt the first one to the Brazilian standards. Both are evaluated graphically and by the use of tables. To support all these studies the software CalcPM v1.0 was used and specially developed for this study.

The design of back-anchored retaining walls in Sweden has traditionally not included global elastic instability of the retaining wall as a possible failure mode. Eurocode 3 part 5 (SS-EN 1993-5) requires design of steel structural members for retaining walls to assess the risk of buckling if the normal force exceeds 4 % of the critical buckling load of the retaining wall. The geological conditions in Eastern Sweden are characterized by the intersection of very hard Precambrian rock and very soft Holocene clays. Thus often ground anchors anchored in rock at a 30-50 degree angle to the vertical plane are used to support retaining walls, resulting in a very high utilization of the ground anchor and a significant normal force in the retaining wall. The threshold value for buckling risk is consequently frequently exceeded and the specific failure mode, of global buckling, is often limiting the use of the structural members in practical design. The buckling load can either be calculated using Euler’s second or third buckling mode, or by modelling the soil-structure interaction by a suitable model. Since no such model is specified in the code, the aim of this thesis was to develop a model which takes into account the stabilizing effect of the soil for the calculation of the buckling force and to model the soil-structure interaction with a beam-spring model connected to Winkler springs. The model simulations show that the soil has a significant influence on the critical load, especially when the retaining wall base is driven to depths greater than 2 meters below excavation depth. The model simulations suggest that higher utilization, with up to 4 times greater critical load, of the steel members is possible for some specific cases and an idealized design factor is also elaborated.
Dimensioneringen av bakåtförankrade spontväggar har traditionellt sett i Sverige inte tagit hänsyn till risken för global knäckning. I och med införandet av Eurokod 3 kapitel 5 (SS-EN 1993-5) som styrande dokument vid dimensionering av sponter måste risken för knäckning nu mera beaktas när normalkraften överstiger 4 % av den kritiska knäckningslasten. De geologiska förhållandena i de östra delarna av Sverige, med lösa leror som täcker hårt berg, leder till att bakåtförankrade sponter med brant lutande stag ofta används. Detta leder till en hög utnyttjandegrad av ankaret och också stora normalkrafter i sponten, vilket leder till att knäckning ofta blir dimensionerande brottmod för sponten. Metoden för att beräkna knäckningslasten kan enligt SS-EN 1993-5 göras med Eulers andra eller tredje knäckningsfall eller med en modell som tar hänsyn till jordens stabiliserande effekt. Idag finns ingen sådan numerisk modell att hitta i litteraturen, varför målet med detta arbete har varit att finna en lämplig modell för att ta hänsyn till jordens inverkan vid bestämning av knäckningslasten. För att modellera samverkan mellan jorden och sponten användes en balkmodell med Winkler fjädrar. Simuleringarna visar att jorden har en signifikant inverkan på den kritiska knäckningslasten, särskilt när nedslagsdjupet är större än 2 meter. Flera simulerade geometrier har gett drygt fyra gånger högre knäcklast jämfört med den knäcklast som erhålls om SS-EN 1993-5 följs. Om jorden tas hänsyn till i dimensioneringen av en spont skulle således slankare konstruktioner kunna användas.

Welding is a widely used method of connecting components because of its efficiency, great value and almost endless possibilities of join types. A great variability of geometrical configurations of welds is problematic due to the assessment of the weld joint. Depending on this topic this thesis was focused on the assessment of weld joints statically and cyclically. Work in the first part deals with the search of methods for evaluation of welds and depending on identified options is subsequently selected American standard AISC assessment of welded joints. The method is applied into FEA analysis and simple welded joints are evaluated. Using FEM are computed three examples on which a comparative analysis was performed. Comparisons were made with the analytical solution based on changes in the parameters of the computational model. The change is primarily related to material properties, mesh size and division of the weld on segments. On the basis of knowledge from analysis of simple joints, method was extended to more general welded joints with the possibility of determining the maximum loading force.

In order to predict the behaviour of bolted steel connections, different methods can be applied to calculate the design tension resistance. In this thesis, the tension resistance is evaluated in the context of the so called Component Method according to Eurocode 3 part 1-8. The design approach establishes a unified procedure of modelling steel joints. Each joint configuration is decomposed into its basic components depending on loading type. In order to design the resistance of components subjected to tensile forces, a simple substitute model, the so-called Tstub flange is adopted. The Component Method is rather complicated to apply for all joint configurations. Therefore, the aim of this thesis is to create a brief and facilitated handbook covering the most common types of connections Kadesjös’ engineers deal with. The topic to be studied is rather comprehensive. Thus, this work is only focusing on the resistance calculation of components located in tension zone of HEA-sections in order to go deeper into the equivalent T-stub approach. To get a complete view about the designing procedure, general information about the Component Method are gathered by a literature study. Thereafter, the technical rules for calculation introduced in codes and standards were used to generate a general solution algorithm for two different connection configurations. The calculations have been performed using Mathcad, and the obtained results from a parametric analysis for particular profiles in each example are then summarised in tables and diagrams using Microsoft Excel.
Att förutse skruvförbands beteende kan kräva tillämpning av diverse metoder. Metoderna används för att kalkylera den dimensionerande lastkapaciteten. I denna avhandling värderas lastkapaciteten i enlighet med den så kallade Komponentmetoden från del 1-8 i Eurokod 3. Denna dimensioneringsmetod fastslår en enhetlig procedur när det gäller modelleringen av stålförband. Varje förbandstyp bryts ner till sina baskomponenter med avseende på belastningstypen. För att beräkna den dimensionerande lastkapaciteten för dragbelastade komponenter används en förenklad substitutionsmodell en så kallad T-knut. Komponentmetoden är något komplicerad att tillämpa för alla former av skruvförband. Därmed är den huvudsakliga ambitionen med arbetet att skapa en kortfattad handbok vars syfte är att täcka de vanligaste typerna av skruvförband som Kadesjös konstruktörer använder sig av. Ämnet som kommer att studeras är relativt omfattande, således bestämdes det att i huvudsak sätta fokus på bärförmågan hos komponenter i dragzonen för HEA-profiler och därav dyka djupare i den ekvivalenta T-knutmetodiken. För att få en helhetsbild av dimensioneringsprocessen samlades allmän information om komponentmetoden genom litteraturstudier. Därefter användes dimensioneringsreglerna, presenterade i koder och standarder, för beräkning av lastkapacitet. Dessa utnyttjades för att generera en lösningsalgoritm för två skilda förband. Beräkningen genomfördes med hjälp av beräkningsprogrammet Mathcad. De erhållna resultaten, från en parametrisk analys för särskilda profiler i varje exempel, sammanfattades i form av tabeller och diagram med hjälp av Microsoft Excel.

This master theses depicts FEM analysis of bolt joints where the focus is on investigating the stressrelationship between plate and bolt. Two bolts, M8 and M16, have been analyzed where they havebeen prestressed to 70 % of the ultimate tensile strength for steel type 8.8. A surface load has beenapplied in tension along the lateral surface of a cylindrical plate. The load distribution between plateand bolt of the external load varies between 2-28 % and 1-99 % for M8 and M16 in comparison to 20% stated in equation 2.7 in SS-EN 1993-1-8.The conclusion of studies shows that the behavior between the bolt and plate is not as previouslythought in SS-EN 1993-1-8. The bolt deforms negatively first when the system is subjected to externalload. This causes the resulting force to decrease. This behavior means that the bolt is designed towithstand larger loads than necessary. The factor 0.2 should be redefined. The authors recommendthat methods proposed by Pedersen and Pedersen [2008] or Haidar et al. [2011] should be used.

At the turn of 2010/2011, Sweden went from designing structures according to nationaldesign codes to the new European standards Eurocode. For bridge engineers, this implieda change from a combination of BRO 2004 and BSK 07 to the Eurocode as the maindocuments, complemented by national documents such as TRVK Bro 11. The normtransition did not only change the calculation methods, but also turned a phenomenonthat never was of great importance for road bridges before into something that could limitthe carrying capacity of the structure. This phenomenon is called fatigue, i.e. repeatedload cycles, where each load is much lower than the ultimate limit state capacity, thatfinally results in collapse. This master thesis investigates why fatigue is significant in the design today. This is donethrough a comparison of how the new and old regulations assesses fatigue. A bridge builtin 2011, designed by ELU Konsult AB according to the old regulations, was modelledin the finite element program LUSAS. Several lorry crossings from different fatigue loadmodels were then simulated. The output from LUSAS was then used to calculate theutilization ratios for three critical points along the bridge. The result indicates that both regulations give rise to similar stress ranges, i.e. thedifference between the maximum and minimum stress obtained during a crossing. Thedifferences between the regulations are instead within the fatigue calculations, where themajor difference is the number of lorries crossing the bridge during its lifetime. Theutilization ratio according to the old regulations for the worst exposed point is 27.0 %,corresponding to 9.13 daily crossings by heavy lorries, which is the maximum numberof daily crossings provided by BRO 2004. The lowest utilization ratio according tothe Eurocode is 70.0 %, calculated for 137 daily crossings which is the lowest amountof crossings allowed. An interpretation of the Eurocode, which allows usage of fatigue loadmodel 5 even for smaller bridges, results in a utilization ratio of 56.0% which correspondsto 90.0 daily crossings, i.e. lower than the other fatigue load models provided by theEurocode but clearly above the old regulations. The conclusion is that an alternative way of deciding the number of crossings shouldbe provided by the Eurocode. Today, the classification consists of four steps, which arevery rough. Instead, a proposal is given in this thesis which advocates usage of a linearfunction for deciding the number of design crossings based on the number of daily crossingsby lorries. The proposed alternative design method is between the two regulations withrespect to daily crossings and utilization ratio.
Vid årsskiftet 2010/2011 övergick Sverige från att dimensionera byggnadsverk enligt nationellastandarder till den nya europastandarden Eurokod. För brokonstruktörer innebar dettaen övergång från en kombination av BRO 2004 och BSK 07, till att Eurokod blev dethuvudsakligt styrande dokumentet, med bland annat TRVK Bro 11 som ett dokumentmed tillhörande nationella val. Övergången medförde inte bara att verksamma konstruktörertvingades lära sig förändrade beräkningsmetoder, utan också att ett fenomen som tidigaresällan var dimensionerande för vägbroar nu kunde vara det som ställde högst krav påbärförmågan. Detta fenomen kallas utmattning, dvs. upprepade av- och pålastningar, varoch en betydligt lägre än brons maximala bärförmåga, som i slutändan resulterar i brott. I detta examensarbete utreds det varför utmattning numera är en betydande del avdimensioneringen. Detta sker genom en jämförelse av hur de gamla och nya normernautvärderar utmattning. Som modell har en befintlig bro invigd 2011, dimensioneradav ELU Konsult AB enligt de gamla normerna, använts. Denna bro har modellerats ifinita element programmet LUSAS, varpå en mängd olika lastbilsöverfarter simulerats ochutmattningsutnyttjandet för tre utvalda kritska punkter beräknats. Resultatet indikerar att båda normerna har liknande storlekar på spänningsvidderna,dvs. skillnaden på största och minsta spänningen som uppstår vid en överfart. Däremotråder det skillnader vid utmattningsberäkningarna, där den stora skillnaden är antalettunga fordon som passerar bron under dess livslängd. Enligt de gamla normerna ärutnyttjandegraden för den värst utsatta studerade punkten 27.0 %, vilket är beräknatpå det högsta antalet dagliga passager från tunga fordon som BRO 2004 tillåter, d.v.s.9.13 dagliga passager. Enligt Eurokod uppgår den lägsta utnyttjandegraden till 70.0 %,vilket motsvarar 137 dagliga överfarter vilket är det lägsta Eurokod tillåter. Vid ettalternativt sätt att tolka Eurokod, som tillåter användandet av utmattningslastmodell5 även för mindre broar, fås en utnyttjandegrad på 56.0% vilket motsvarar 90.0 dagligaöverfarter. Detta är något lägre än de andra utmattningslastmodellerna enligt Eurokodmen fortfarande högre än det gamla regelverket. Slutsatsen av uppsatsen är att ett alternativt sätt att bestämma antalet överfarter bordeerbjudas i Eurokod, då indelningen idag består av fyra stora trappsteg vilket ger en väldigtsnäv indelning. I detta examensarbete presenteras ett förslag som innebär att antaletdimensionerande överfarter istället bör bestämmas som en rätlinjig funktion av antaletdagliga överfarter från tung trafik. Det föreslagna sättet ligger mellan de båda normernamed hänsyn till passager och utnyttjandegrad.

Doutoramento em Engenharia Civil
This thesis is a research work aiming the increasing of knowledge of the behaviour of steel plate girders subjected to shear buckling in fire situation. The main objective of this thesis is to overcome the lack of rules for the design of steel structural elements subjected to shear buckling at high temperatures. For this purpose, a numerical model was developed in the finite element software SAFIR to simulate the behaviour of steel plate girders under shear loading at elevated temperatures. These numerical analyses fall into the methodology commonly referred as GMNIA – geometrically non-linear materially imperfect analysis. After validation of the numerical model with experimental tests from the literature, the influence of the geometric imperfections and residual stresses on the bearing capacity of the girders, at both normal and elevated temperatures, was evaluated. Eurocode 3 states that the shear buckling resistance of steel I girders is given by the sum of two components, the web resistance and the contribution from the flanges. Firstly it was assessed the contribution from flanges and it was found that the results obtained with the Eurocode 3 expressions could be improved. Thus, it was proposed the application of a corrective factor in order to improve the predictions of Eurocode 3 for the contribution from the flanges to the shear buckling resistance. The main part of the shear buckling resistance comes from the web. The expressions of Eurocode 3 for determining the web resistance to shear buckling were evaluated. This analysis demonstrated that some of the results are not on the safe side and the accuracy of these expressions could be improved. So, changes to the expressions applied for the design at normal temperature were proposed. Furthermore, new expressions for fire design of such structural elements were also proposed. The expression of Eurocode 3 used for the safety calculation of steel structural elements under interaction between shear and bending was also evaluated. It was verified that the application of the proposals for modification of the expressions used to determine the shear buckling resistance introduces improvements on the results provided by this expression, mainly at elevated temperatures. Finally, an analysis of the influence of different parameters on the ultimate shear strength of steel plate girders subjected to shear buckling, such as the web thickness, the web depth, the flange thickness and the steel yield strength, is presented.
A presente tese resulta de um trabalho de investigação, cujo propósito se centrou no aumento de conhecimento do comportamento de vigas metálicas compostas de alma cheia sujeitas a encurvadura por esforço transverso em situação de incêndio. O principal objetivo desta tese consiste em suprir a ausência de regras para o dimensionamento de elementos estruturais metálicos sujeitos a encurvadura por esforço transverso a temperaturas elevadas. Com essa finalidade, foi desenvolvido um modelo numérico no programa de elementos finitos SAFIR para a simulação do comportamento deste tipo de vigas quando sujeitas a temperaturas elevadas. Estas análises numéricas enquadram-se na metodologia habitualmente designada por GMNIA – geometrically and materially non-linear imperfect analysis. Após a validação do modelo numérico com ensaios experimentais da literatura, foi também avaliada a influência das imperfeições geométricas e das tensões residuais na capacidade resistente das vigas, tanto à temperatura normal como a temperaturas elevadas. O Eurocódigo 3 estabelece que a resistência à encurvadura por esforço transverso de vigas em I resulta da soma de duas componentes, a resistência da alma e a contribuição dos banzos. Começou-se por avaliar a contribuição dos banzos e verificou-se que os resultados obtidos com as expressões do Eurocódigo 3 poderiam ser melhorados. Assim, foi proposta a aplicação de um fator corretivo de forma a melhorar as previsões do Eurocódigo 3 para a contribuição dos banzos para a resistência à encurvadura por esforço transverso. A principal parcela da resistência à encurvadura por esforço transverso é dada pela alma. As expressões do Eurocódigo 3 para a determinação da resistência da alma à encurvadura por esforço transverso foram avaliadas. Esta análise demonstrou que a alguns dos resultados não estão do lado da segurança e que a precisão das expressões de dimensionamento do Eurocódigo 3 poderia ser melhorada. Portanto, foram propostas alterações a estas expressões usadas para o dimensionamento à temperatura normal. Para além disso, foram propostas novas expressões para o dimensionamento deste tipo de elementos em caso de exposição ao fogo. A expressão do Eurocódigo 3 usada para a verificação da segurança de elementos estruturais metálicos sujeitos à interação entre esforço transverso e momento fletor foi também avaliada, verificando-se que a aplicação das propostas para modificação das expressões usadas para a determinação da resistência à encurvadura por esforço transverso origina melhorias nos resultados desta expressão, principalmente a temperaturas elevadas. Por fim, apresenta-se uma análise da influência de diferentes parâmetros na capacidade resistente de vigas compostas de alma cheia sujeitas a encurvadura por esforço transverso, tais como a espessura da alma, a altura da alma, a espessura dos banzos e a tensão de cedência do aço.

L’intégrité structurelle des composants mécaniques et de leurs assemblages est un objectif majeur de conception. Les applications peuvent concerner l’aéronautique, l’automobile, le ferroviaire ainsi que les ouvrages tels que les ponts ou encore des mâts soumis à des sollicitations cycliques ou à amplitude variable. Cela amène l’ingénieur de conception à prendre en compte différents phénomènes dont celui de la fatigue, facteur dominant pouvant conduire, sous sollicitation dynamique, à la défaillance des structures ou de certaines pièces les constituant. Un outil de post-traitement a, d’une part, été développé et implémenté sous Matlab pour évaluer le niveau d’endommagement à la limite d’endurance fixée du matériau (2.106 cycles) et, d’autre part, une démarche itérative a été proposée pour le calcul de durée de vie en fatigue. Les deux critères multiaxiaux de fatigue utilisés sont le critère de Dang Van (approche de type plan critique) et celui de Zenner (approche intégrale). L’outil de post-traitement est validé par des résultats d’essais de fatigue issus de la bibliographie. Ces essais de fatigue sont réalisés sur des boulons M10 de classe de qualité 8.8. Les résultats établis sont comparés avec ceux obtenus à partir des normes existantes (Eurocode 3 et VDI 2230 notamment). Les deux critères multiaxiaux de fatigue retenus dans le cadre de ce travail sont confrontés à la banque de données des essais multiaxiaux qu’on trouve dans lalittérature. Les assemblages, boulonnés ou soudés, constituent des zones singulières dans les structures. Dans le butde mieux comprendre le comportement en fatigue du boulon dans un assemblage, un tronçon en té boulonné dans lequel le boulon peut être précontraint par serrage est modélisé par éléments finis sous le logiciel Salomé-méca. La précharge est modélisée numériquement en imposant un déplacement axial relatif entre les noeuds de l’écrou et ceux de la tige de la vis. L’effort axial FB et le moment fléchissant MB obtenus dans la vis avec le modèle numérique du tronçon en té sont validés par des solutions analytiques et des analyses expérimentales (essais de traction statique sur tronçon en té). Une étude paramétrique est menée pour analyser les influences en fatigue de la précharge dans le boulon, du diamètre de celui-ci, de son excentration par rapport à l’âme du tronçon en té et de l’épaisseur de la semelle. L’analyse s’est intéressée d’abord au niveau d’endommagement du boulon, puis à sa durée de vie en fatigue multiaxiale en utilisant l’outil de post-traitement construit dans le cadre du présent travail. Les simulations numériques de l’endommagement et de la durée de vie en fatigue montrent un comportement différent des deux approches utilisées de la fatigue multiaxiale pour la prise en compte de l’effet d’un pré-serrage important. Enfin, une campagne d’essais expérimentaux sur des tronçons en té a également été menée pour la validation du modèle numérique par rapport à l’effort axialFB et au moment de flexion MB dans le boulon
The structural integrity of mechanical components and their assemblies is a major design purpose. The applications may concern the aeronautics, the automobile, the railway as well as structures such as bridges or masts subjected to cyclic loads or to variable amplitude stress states. This leads the design engineer to take into account various phenomena, including fatigue, a dominant factor that may lead, under dynamic stress, to the failure of structures or parts of them. The mechanical components are generally subjected in service to multiaxial stress states. Taking into account the triaxiality of stress states requires the use of multiaxial fatigue criteria. They are suitable tools for assessing the material fatigue resistance against periodical stress states, especially when they are multiaxial. A fatigue post-processing tool is developed and implemented under Matlab software to assess on the one hand, the damage level at the fixed endurance limit of the material (2.106 cycles) and, on the other hand, the fatigue life up to crack initiation from an iterative fatigue calculation process. The two multiaxial fatiguecriteria used are Dang Van criterion (critical plane approach) and Zenner criterion (integral approach). Then, the fatigue post-processing tool is validated by fatigue test results from the bibliography. These fatigue tests are performed on M10 bolts of 8.8 quality class. The results are compared with those obtained from existing standards (Eurocode 3 and VDI 2230). The two multiaxial fatigue criteria used inthis work are compared and validated from the database of multiaxial tests found in the literature. Bolted or welded assemblies are singular areas in the structures. In order to better understand the fatiguebehavior of the bolt in an assembly, a tee-stub in which the bolt can be pre-stressed by clamping is modeled by finite elements under Salome-meca software. The preload is modeled numerically by imposing a relative axial displacement between the nodes of the nut and those of the rod of the screw. The FB axial force and the MB bending moment obtained in the screw with the numerical model of the tee-stub is validated by analytical solutions on the one hand and by experimental results (static tension tests on a tee-stub) on the other hand. A parametric study is conducted to analyze the fatigue influences of the bolt preload, its diameter, its location with respect to the tee-stub soul and the flange thickness. The analysis first focused on the bolt damage level, then on its fatigue life using the multiaxial fatigue post-processing tool built as part of this work. Numerical simulations of damage and fatigue life show a different behavior of the two multiaxial fatigue approaches to take into account the effect of a significanttightening. Experimental tests run on a tee-stub were also conducted to validate the numerical model with respect to the FB axial force and the MB bending moment

Mestrado em Engenharia Civil
A presente dissertação tem como propósito aumentar o conhecimento sobre vigas híbridas metálicas compostas por aço carbono e aço inoxidável, analisar o comportamento à flexão em situação de incêndio e analisar a possível suscetibilidade à ocorrência de fenómenos de instabilidade, em particular a encurvadura lateral. São referidas as vantagens de cada material em termos de comportamento ao fogo e apresentadas propostas de constituições de secções possíveis de modo a explorar mecanicamente a potencialidade dos materiais a atuarem em conjunto. As metodologias de cálculo são preconizadas pelas partes 1-1, 1-2 e 1-4 do Eurocódigo 3 e comparadas com valores obtidos por simulação numérica através do programa de elementos finitos SAFIR. Paralelamente é analisada a resistência à encurvadura lateral obtida e comparada pelos mesmos métodos de cálculo, analítico (Eurocódigo 3) e simulação numérica (SAFIR).
This thesis aims to increase knowledge of híbrid metalic beams, composed of stainless steel and carbon steel, analyze the flexural behavior in fire situation and analyze the possible susceptibility to the occurrence of instability phenomena, in particular the lateral buckling. The advantages of each material are referred in terms of fire behavior and proposals of constitutions sections so as to mechanically exploit the potential of the materials to act together. The calculation methodologies are recommended for parts 1-1, 1-2 and 1-4 of Eurocode 3 and compared with values obtained by numerical simulation using the finite element program SAFIR. The lateral torsional buckling resistance is determined and compared by the surface calculation method and by numerical simulation (SAFIR).

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.

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.

Mestrado em Engenharia Civil
A presente dissertação tem como propósito aumentar o conhecimento do comportamento ao fogo de vigas-coluna metálicas de secção transversal esbelta, isto é, suscetíveis à ocorrência de fenómenos de instabilidade, tais como a encurvadura local, lateral e por flexão. Sabe-se que os elementos metálicos com secção transversal esbelta possuem vantagens em termos de eficiência e economia de material. Esta atratividade faz com que sejam amplamente utilizados na construção. Contudo, a verificação da resistência ao fogo destes elementos carece de fórmulas simplificadas que se adequem a esta solução. O principal objetivo desta dissertação direciona-se na elaboração de um estudo numérico do comportamento ao fogo de vigas-coluna em aço com secção transversal esbelta. Seguidamente, efetuar-se-á uma comparação entre os resultados obtidos numericamente através do método de elementos finitos e as metodologias presentes no Eurocódigo 3, no que se refere especificamente às fórmulas a frio, contidas nas Parte 1-1 e às fórmulas para situação de incêndio na Parte 1-2. No que diz respeito ao estudo numérico, este foi efetuado com elementos finitos de casca recorrendo ao programa SAFIR. É demonstrado que a metodologia presente no Eurocódigo 3 para a verificação da resistência em situação de incêndio pode ser melhorada. Sendo assim, são propostas alterações a nível do cálculo dos fatores de interação. Finalmente, concluiu-se que as fórmulas de interação do Eurocódigo 3 conduzem a resultados fora da segurança ou muito conservativos e que necessitam de ser melhoradas para que seja possível calcular estruturas mais seguras e económicas.
The present thesis aims to increase the knowledge of the fire behaviour of steel beam-columns with slender cross-section, that is, susceptible to the occurrence of instability phenomena, such as local, lateral-torsional and bending buckling. It is known that steel members with slender cross-section have advantages in terms of efficiency and economic material. This attraction makes them widely used in construction. However, the verification of the fire resistance of these members need simplified formulas that are appropriate to this solution. The main objective of this thesis consist in the elaboration of a numerical study of the fire behaviour of steel beam-columns with slender cross-section. Posteriorly, shall be make a comparison between the results obtained numerically with the finite element method and the methodologies in Eurocode 3, which specifically refers to cold formulas, contained in Part 1-1, and fire situation formulas, contained in Part 1-2. Regarding the numerical study, this was made with finite shell elements using the program SAFIR. It is shown that the present methodology in Eurocode 3 for the verification of the resistance in fire situation can be improved. Therefore, some changes are proposed in the calculation of the interaction factors. Finally, it was concluded that the interaction formulas of Eurocode 3 lead to results that may be outside the safety or be very conservative and need to be improved so that becomes possible to calculate safer and more economical structures.

[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
[CAT] 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 no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53240
TESIS

Connections between different structural elements, despite the fact that very often have been despised as structural components and have been considered as simple constructive details ,are key elements to guarantee a corree! force distribution and also to ensure a complete fitting between the model used in the design phase and the final built reality. Traditionally they have been design according only to the resistance criterion but, since the introduction of new standards as Eurocode, nowadays their calculation and design can be complemented with stiffness considerations and,still in an early development stage, with their rotation capacity or their ductility. This paper focuses on a particular type of connection: column bases. Besides to summarize all the theoretical approach of the componen! method,the Eurocode predictive method, it has been practically implemented to a specific column base example untilits predictive M-0 behaviour graphs have been obtained. The predicted behaviour of this worked example has been compared with the real ones, extracted from a finite element model appropriately tes ted and calibrated, with the main goal of determining the prediction precision of the method offered by the European standard. Accordi ng to this comparison, this doctoral thesis studies the relations hip between the precision of the M-0 behaviour obtained for the worked example and the stiffness ratio (µ) used.This paper develops new formulation for the stiffnes s ratio that brings it closer to its real val ue. Slight improvements of the predicted rotational behaviour are obtained for the example column base when these new expressions are implemented on the componen! method framework. Finally, and judging by the modest improvement got by affecting exclusively the stiffness ratio value ,this thesis develops mathematical expressions for the unitary stiffness variation (y) that modify the predicted graph plotting and unfailingly brings it closer to the real M-0 representation.In the case studied the precision obtained is nearly absolute. The main future research line proposed by the author is faced to keep on using the working method devised for this docto ral thesis on different geometrical and materialcolumn base configurations. The main objective to be achieved by working the results obtained is to gel a general form ulation, valid for any colum n base configuration, which allows improving its rotational behaviour prediction. Once more reliable approaches can be achieved, the last step of this future research line,and the most importan! for the practica! and professional approach, is jusi the opposite approximation, that is starting off a specific rotationalbehaviour desired by the designer, provide him with severa! possible column bases configurations that satisfy this requirement.
Les unions entre els diversos elements estructurals, malgrat que sovint han estat menystingudes a nivell estructural i s'han considerat com a simples detalls constructius, són claus per garantir la correcta distribució d'esforços i assegurar una avinença entre model utilitzat pel càlcul i realitat construïda. Al llarg dels anys s'han dissenyat exclusivament sota el criteri de resistència aspecte que, arrel de la introducció de les noves normatives tals com l'Eurocodi, actualment es pot complementar amb el de rigidesa i, encara en una fase inicial de desenvolupament, amb el de capacitat de rotació o ductilitat. El present treball aprofundeix en un tipus d'unió determinat: les bases de pilars. A part de resumir tot el marc teòric del mètode dels components, que és el mètode predictiu de l'Eurocodi, aquest és aplicat també a nivell practic en un exemple concret de basa de pilar, arribant a obtenir els grafics que la norma preveu pel seu comportament M-0. Aquests es comparen amb els reals, extrets d'una modelització informàtica amb elements finits convenientment calibrada i testejada, per tal de coneixer la precisió que la predicció del metode ofert per la normativa posseeix. En base a aquesta comparació s'estudia la relació existent entre la precisió del comportament M-0 de la unió obtinguda per l'exemple treballat i el valor del ratio de rigidesa (µ) utilitzat. La tesi desenvolupa una nova formulació pel valor del rati de rigidesa que l'acosta més al real, expressions que quan s'incorporen a les del mètode dels components tan augmentar lleument, amb caracter general, la precisió de la predicció del comportament rotacional obtingut per la basa del pilar. Finalment, i a tenor de la millora modesta que provoca incidir únicament en el valor del rati de rigidesa, la tesi desenvolupa una formulació per la variació unitaria de la rigidesa (y) que modifica el traçat del gràfic M-0 de la predicció i l'acosta indefectiblement al real, aconseguint una precisió gairebé absoluta en el cas d'estudi. La principal línia futura d'investigació que es proposa és seguir amb el mètode de treball ideal en aquesta tesi, amb diferents configuracions geomètriques i materials de bases de pilars.Treballant els resultats extrets l'objectiu és aconseguir una formulació de caràcter general, vàlida per qualsevol configuració de basa de pilar que es tingui, que permeti millorar la predicció del seu comportament rotacional. Un cop aconseguides aproximacions més fiables, l'últim pas a per aquesta línia de treball, i el més important a nivell pràctic i professional, és l'invers, és a dir, a partir d'un determinat comportament rotacional desitjat pel dissenyador, oferir diverses configuracions de bases de pilars possibles.

У овом раду спроведене су опсежна експериментална и нумеричкаиспитивања понашања веза са чеоном плочом и четири завртња у реду,као и карактеристичне компоненте ових веза - Т-елемента.Експериментална испитивања укључују тестирања 36 узоракаТ-елемената у природној величини, као и четири везе греда-стуб сачеоном плочом и четири завртња у реду, такође у природној величини.Нумеричке анализе, спроведене у софтверском пакету ABAQUS, суобухватале све типове нелинеарности, али и отказ материјала, те се каотакве сврставају међу ретке којима су слични проблеми нумеричкииспитивани. Параметарска студија обухвата 33 различите конфигурацијеТ-елемената са четири завртња и представља највећу такву студијуизведену за ову компоненту. Као основни још увек нерешен проблем,круцијалан за понашање Т-елемената, препознати су положај сила уследефеката полуге, али и савијање завтњева. Приказан је и предложен новианалитички модел прорачуна носивости Т-елемената са четири завртња,и квантификована његова предност над до сада постојећим моделима.
U ovom radu sprovedene su opsežna eksperimentalna i numeričkaispitivanja ponašanja veza sa čeonom pločom i četiri zavrtnja u redu,kao i karakteristične komponente ovih veza - T-elementa.Eksperimentalna ispitivanja uključuju testiranja 36 uzorakaT-elemenata u prirodnoj veličini, kao i četiri veze greda-stub sačeonom pločom i četiri zavrtnja u redu, takođe u prirodnoj veličini.Numeričke analize, sprovedene u softverskom paketu ABAQUS, suobuhvatale sve tipove nelinearnosti, ali i otkaz materijala, te se kaotakve svrstavaju među retke kojima su slični problemi numeričkiispitivani. Parametarska studija obuhvata 33 različite konfiguracijeT-elemenata sa četiri zavrtnja i predstavlja najveću takvu studijuizvedenu za ovu komponentu. Kao osnovni još uvek nerešen problem,krucijalan za ponašanje T-elemenata, prepoznati su položaj sila usledefekata poluge, ali i savijanje zavtnjeva. Prikazan je i predložen novianalitički model proračuna nosivosti T-elemenata sa četiri zavrtnja,i kvantifikovana njegova prednost nad do sada postojećim modelima.
In this research, extensive experimental and numerical investigations ofbehaviour of end-plate moment connection with four bolts per row areperformed, as well as specific component of the connection – T-stub element.Experimental research comprises tests on 36 unscaled specimens of T-stubelements and 4 specimens of beam-to-column joints with end-plate connectionand four bolts per row, also in full-size. Numerical analyses, performed withsoftware ABAQUS, included all types of nonlinearities, and materialdeterioration, hence they can be considered as one of the few mostsophisticated analyses used for investigation of the considered problem. Theparametric study comprises 33 different configurations of the T-stub elementwith four bolts per row and it presents the biggest study of this kind for this typeof component. Bending of the bolts and position of the prying forces arerecognized as the largest, still unsolved problem, crucial for the behavior of theT-stub elements. A new theoretical model for the resistance of the T-stubelement with four bolts per row is proposed and its advantage over the existingmodels is presented and quantified.

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
During its lifetime a structure can be exposed to several actions, in which the seismic action plays an important role. When subjected to an earthquake, the performance of a structure is evaluated by the level of damage that it presents, as well as the damage caused to the non-structural elements, having always to be guaranteed the protection of human lives, as well as the functioning of important structures for civil protection. Due to the unpredictability associated with this type of action and the consequences that it can bring, during the development of a project, it can be difficult to find a balance between the minimum desired performance for the structure and the most economical solution.The present dissertation, inserted in a study prepared by the University of Coimbra for the world steel manufacturer ArcelorMittal, Collective Housing - benchmark study on different structural systems for the residential market, fits the theme mentioned above. In its elaboration, three solutions usually adopted for the construction of a building in metallic and composite steel-concrete structure were designed, with and without considering the seismic action. Subsequently, an assessment of competitiveness was carried out in relation to the quantities of materials required for the construction of the solutions mentioned, and of two other structural alternatives included in the same study: a structure composed essentially of prefabricated reinforced concrete elements, and a structure mainly formed by cross-laminated timber panels (CLT). Finally, the execution programmes for all solutions were compared.All structural analyzes, both for the current and seismic design, were performed using the finite element calculation software ETABS®. The seismic effects and the effects of the other actions included in the seismic project were taken into account with an analysis by response spectrum. The design of all alternatives was carried out based on Eurocodes.This dissertation intends to evaluate the competitiveness of the different structural solutions considered in this work, in relation to the quantities of materials and execution times associated with their constructions.
Durante o período de vida útil de uma estrutura, esta encontra-se sujeita a diversas ações entre as quais se poderá destacar a ação sísmica. Quando sujeita a um sismo, o desempenho de uma estrutura é avaliado conforme o nível de danos que esta apresente, assim como os danos provocados nos elementos não estruturais, devendo ser sempre garantida a proteção das vidas humanas, assim como a operacionalidade das estruturas importantes para a proteção civil. Devido à imprevisibilidade associada a este tipo de ação e às consequências que a mesma poderá trazer, em situação de projeto pode tornar-se difícil encontrar um equilíbrio entre o desempenho mínimo pretendido para a estrutura, e a solução mais económica.A presente dissertação, inserida num estudo elaborado pela Universidade de Coimbra para a fabricante mundial de aço ArcelorMittal, Collective Housing - benchmark study on different structural systems for the residential market, enquadra-se no tema supramencionado. Na sua elaboração, foram dimensionadas três soluções habitualmente adotadas para a construção de um edifício em estrutura metálica e mista aço-betão, com e sem consideração da ação sísmica. Posteriormente foi realizada uma avaliação da competitividade em relação às quantidades de materiais necessárias para a construção das soluções mencionadas, e de outras duas alternativas estruturais inseridas no mesmo estudo: uma estrutura composta essencialmente por elementos pré-fabricados de betão armado, e uma estrutura maioritariamente formada por painéis de madeira lamelada-colada cruzada (CLT). Por fim, foram comparados os planeamentos da execução de todas as estruturas.Todas as análises estruturais, quer para a situação de projeto corrente, quer para a situação de projeto sísmica, foram realizadas com recurso ao software de cálculo por elementos finitos ETABS. Na determinação dos efeitos sísmicos e dos efeitos das outras ações incluídas no projeto sísmico, foi adotado o método de análise modal por espectro de resposta. Os dimensionamentos de todas as alternativas foram realizados com base nos Eurocódigos.Com a realização desta dissertação pretende-se avaliar a competitividade das diferentes soluções estruturais consideradas neste trabalho, relativamente às quantidades de materiais e tempos de execução associados às suas construções.

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
A construção de edifícios com estrutura em aço teve início no final do século XIX, tendo o uso desta solução construtiva aumentado até aos nossos dias. No que refere às estruturas em pórticos simples de aço, apresentam várias vantagens em relação a outros materiais, quer em relação ao betão armado, por permitir estruturas mais leves, versáteis e recicláveis, quer em relação a estruturas em aço com pórticos contraventados, por permitir vãos abertos, sem impedimentos arquitetónicos.A introdução de irregularidades em planta e em altura em edifícios com estrutura de pórticos simples implica o aumento da quantidade de aço por unidade de área de construção, quando verificados pela Norma EN 1993-1-1, sem ação sísmica, quer pela Norma EN 1998-1, considerando a ação sísmica.A presente dissertação abordou a introdução de irregularidades em planta, na forma de “U” e de irregularidades simétricas e assimétricas em altura, para edifícios de vários pisos em aço com estrutura resistente em pórticos simples.O dimensionamento foi realizado com base nas normas Europeias em vigor, a Norma EN 1990, a Norma EN 1991, a Norma EN 1993-1 e a Norma EN 1998-1. Os modelos estruturais espaciais foram definidos com o programa Autodesk Robot Structural Analysis Profissional 2019. A verificação pela Norma EN 1993-1-1 da resistência e estabilidade dos elementos estruturais que constituem as estruturas estudadas foram verificadas utilizando o programa SemiComp Member Design e o programa LTBeam. Para a verificação pela Norma EN 1998-1 foi preparada uma folha de cálculo em Microsoft Excel com as condições definidas na referida norma.No presente trabalho pretende-se estudar a influência da ação sísmica na quantidade de aço por unidade de área de construção para edifícios com irregularidades em planta e em altura.
Construction of steel-framed buildings began in the late 19th century, and the use of this building solution has increased to the present day. In what it refers, to Moment Resisting Frames, they have several advantages over other materials, whether compared to reinforced concrete, because they allow lighter, more versatile and recyclable structures, or braced steel frames, because they allow open, without architectural impediments.The introduction of irregularities in plan and height in buildings with Moment Resisting Frames structure implies an increase in the amount of steel per unit of construction area when verified by Standard EN 1993-1-1, without seismic action, or by Standard EN 1998. -1, considering the seismic action.The present dissertation dealt with the introduction of U-shaped plan irregularities and symmetrical and asymmetrical irregularities in height for multi-storey steel buildings with resisting structure in Moment Resisting Frames.The “design” was based on the European standards, EN 1990, EN 1991, EN 1993-1 and EN 1998-1. The spatial structural models were defined with the Autodesk Robot Structural Analysis Professional 2019 program. The verification by EN 1993-1-1 of the strength and stability of the structural elements that constitute the studied structures were verified using the SemiComp Member “design” program and the LTBeam program. For verification by Standard EN 1998-1 an Excel spreadsheet has been prepared with the conditions defined in that standard.The present work intends to study the necessity of the quantity of steel per unit of construction area for buildings with irregularities in plan and in height.

This thesis has the objective to contribute to increase the knowledge on the structural behaviour of cold-formed steel profiles in case of fire. These elements application, with thin-walled sections, is increasingly while maintaining a significant load bearing capacity. These slender cross-sections provide greater susceptibility to the occurrence of local instability phenomena in the respective cold-formed profiles. Additionally, the global instability of the elements and the distortional buckling related to the existing of reinforcements in the section are also very common collapse modes in these profiles. These instability phenomena are intensified when the profiles are subjected to high temperatures, such as the ones in case of fire. The present study, which focuses on the determination of the ultimate strength of coldformed steel columns, beams and beam-columns at high temperatures, is based on non-linear numerical analyses with imperfections, using the finite element software SAFIR. In order to validate the different numerical models applied, numerical analysis of different cold-formed profiles experimental tests at normal and high temperatures was performed. Subsequently, a parametric study was carried out to understand the influence of different parameters for numerical modelling (such as initial imperfections, residual stresses and the corner enhancements) and to stablish case studies to be considered in the validation of cold-formed steel columns, beams and beam-columns design proposals. Through the parametric studies performed varying the cross-sections slendernesses, temperatures, steel grades and loading types, the ultimate loads numerically obtained are compared with the resistances provided by Eurocode 3 prescriptions, for these profiles. And finally, following the observations obtained with such comparisons, new design formulations are proposed that improve the analytical predictions of the different structural elements at high temperatures
A presente dissertação tem como objetivo contribuir para o aumento do conhecimento do comportamento estrutural de perfis em aço enformados a frio em situação de incêndio. A aplicação destes elementos, com secções transversais de paredes finas, é cada vez mais comum mantendo uma significativa capacidade de suporte de cargas. Estas secções transversais esbeltas proporcionam uma maior suscetibilidade à ocorrência de fenómenos de instabilidade local nos respetivos perfis enformados a frio. Adicionalmente, a instabilidade global dos elementos e a encurvadura distorcional relacionada com a existência de reforços na secção são também modos de colapso muito comuns nestes perfis. Estes fenómenos de instabilidade são intensificados quando os perfis estão sujeitos a elevadas temperaturas, tais como as que ocorrem em caso de incêndio. O presente estudo, que se foca na determinação das capacidades resistentes últimas de colunas, vigas e vigas-coluna em aço enformados a frio a altas temperaturas, é baseado em análises numéricas não lineares com imperfeições, aplicando o programa de elementos finitos SAFIR. Com o intuito de validar os diferentes modelos numéricos aplicados, foram analisados numericamente ensaios experimentais da literatura a diferentes perfis enformados a frio à temperatura normal e a elevadas temperaturas. Posteriormente foi realizado um estudo paramétrico para compreensão da influência de diferentes parâmetros para aferição dos modelos numéricos (como as imperfeições geométricas iniciais, as tensões residuais e os cantos com resistência aumentada) e para estabelecimento de casos de estudo, a considerar na validação de propostas de dimensionamento de colunas, vigas e vigas-coluna em aço enformados a frio. Através dos estudos paramétricos concretizados variando esbeltezas de secções, temperaturas, tipos de aço e tipos de carregamento, as cargas últimas obtidas numericamente são comparadas com as resistências fornecidas pelas prescrições do Eurocódigo 3, para estes perfis. E por fim, seguindo as observações obtidas com as referidas comparações, são propostas novas formulações de cálculo que melhoram a previsão analítica dos diferentes elementos estruturais a altas temperaturas
Programa Doutoral em Engenharia Civil

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
A construção com elementos de aço enformado a frio tem vindo a conhecer um desenvolvimento exponencial nas últimas décadas por se tratar de uma solução leve, de fácil aplicação e, consequentemente, vantajosa do ponto de vista económico. A grande maioria dos estudos já realizados no domínio das estruturas em aço enformado a frio incide sobre o desempenho e otimização de elementos estruturais principais, nomeadamente pilares e vigas em estruturas de pequeno porte, e de madres para suporte de elementos de revestimento em estruturas de edifícios de múltiplos pisos ou em pavilhões industriais. Por outro lado, e apesar da crescente utilização de chapas de revestimento em aço enformado a frio, o estudo do desempenho e otimização destes elementos estruturais secundários é uma área ainda pouco desenvolvida. As chapas de revestimento em aço enformado a frio, apesar do reduzido peso próprio do material, muitas das vezes correspondem a uma parcela significativa do peso da estrutura, por cobrirem grandes vãos e, por conseguinte, a utilização de secções otimizadas poderá contribuir de forma decisiva para a redução do custo global da estrutura. A crescente popularidade do aço enformado a frio impulsionou o desenvolvimento de métodos para o cálculo da resistência dos elementos neste material e depressa surgiram normas de dimensionamento de elementos estruturais neste tipo de aço, normas que deverão ser tidas em consideração aquando do estudo do desempenho e otimização dos elementos. Neste contexto, a investigação realizada no âmbito desta dissertação pretende a otimização da forma da secção transversal de chapas perfiladas e da secção transversal de madres Ω, com base em estudos analíticos apoiados nas Partes 1-3 e 1-5 do Eurocódigo 3. Nos estudos desenvolvidos foram tidos em conta os parâmetros geométricos das secções, a classe do aço, a espessura da chapa e a possibilidade de introdução de reforços, em particular no que se refere às suas implicações na resistência à flexão dos elementos. Como resultado destes trabalhos de investigação, apresenta-se uma série de secções economicamente mais competitivas do que as atualmente disponíveis no mercado e, tanto quanto possível, otimizadas ao nível das propriedades de resistência à flexão.
In recent decades, the use of cold-formed steel (CFS) in structural members faced a significant growth due to their unique characteristics and wide range of structural applications. It allows the design of light structures, easy to build, resulting in economic solutions. Most of the available studies related to CFS structures focus on structural performance and optimization of main structural elements, such as beams and columns in small buildings, as well as purlins to support sheeting in multiple store and industrial buildings. On the other hand, and despite of the increasing use of steel sheeting, performance and optimization studies of these secondary elements is still an underdeveloped area. Sheeting profiles, in spite of the reduced weight of the material itself, often make up a significant portion of the structure’s weight, as they withstand very large spans, and therefore the use of optimized sections may give a crucial contribute for the reduction of structure´s overall cost. The growing popularity of CFS structures led to the development of calculation methods to predict the structural response of their members; consequently, some design standards for CFS structures have already been published and may be taken into account when studying the performance and optimizations of CFS elements. In this context, this research aims the optimization of CFS sheeting and CFS Ω purlins cross sections, based on analytical studies supported in Parts 1-3 and 1-5 of Eurocode 3. In these studies, the cross sections’ geometric parameters were taken into account, as well as the steel class, the plate thickness and the possibility of introducing reinforcements, in particular their implications on the elements’ flexural strength. As a result of this research, a series of cross sections more competitive than those currently available in the market and, as far as possible, with enhanced flexural strength, were presented.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
O trabalho realizado no âmbito desta dissertação teve como objetivo analisar o comportamento mecânico de soldaduras feitas em aço estrutural S355 J2 em situação de fogo e pós-fogo. Para fabricar as soldaduras, utilizou-se um processo de soldadura muito comum na indústria de construção metálica, ou seja, o processo de soldadura MAG utilizando fios sólidos e fios fluxados como material de adição.A caraterização das soldaduras compreendeu a realização de testes de análise metalográfica, ensaios de dureza e ensaios de tração. Os ensaios de tração foram efetuados à temperatura ambiente e a temperaturas elevadas (300ºC; 600ºC e 900ºC). Foi ainda testada a resistência das soldaduras em condições pós-fogo, testando provetes pré-aquecidos e arrefecidos a ar. As curvas de tensão-deformação à temperatura ambiente demonstraram que o input de calor utilizado no processo de soldadura condicionou a tensão máxima das amostras soldadas. Os ensaios de tração a temperaturas elevadas revelaram um aumento de resistência a 300ºC, ocorrendo a sua degradação após o aumento da temperatura, ou seja, para 600ºC e 900ºC. Este comportamento também foi verificado nas amostras testadas em situação pós-fogo. Os ensaios de dureza permitiram verificar que a dureza das soldaduras começava a degradar-se a partir dos 600ºC, não ocorrendo nenhuma alteração até 300ºC. A análise metalográfica revelou que a 300ºC ocorria o aumento de carbonetos precipitados, o que contribuía para a redução do tamanho de grão e, posteriormente, ao aumento da resistência mecânica. Por outro lado, a partir de 300ºC, verificou-se que ocorria uma diminuição dos carbonetos precipitados e um aumento do tamanho de grão, sendo máximo para 900ºC. Os fatores de redução obtidos através das curvas dos ensaios de tração a temperaturas elevadas e em situação pós-fogo foram comparados com os disponibilizados pelo Eurocódigo 3, tendo sido observado que, de um modo geral, é seguro a utilização da norma no projeto de estruturas metálicas.
The work carried out within the scope of this dissertation had the objective of analyzing the mechanical behavior of welded joints made of structural steel S355 J2 in a fire and post-fire situation. For this, the two most common welding processes in industry, solid wire (GMAW) and fluxed wire (FCAW) welding were used.The welding characterisation process comprised metallographic analysis tests, hardness tests and tensile tests at room temperature, at high temperatures (300ºC, 600ºC and 900ºC) and post-fire with air cooling, because it is the most unfavorable method of cooling. The tensile tests were performed using a strain rate of 0.01 mm/s. Samples tested at high temperatures and in a post-fire condition were heated with a heating rate of 5 ºC/min. The stress-strain curves at room temperature showed that the heat input used in the process of welding conditioned the maximum stress of the welded samples. Subsequently, tensile tests at high temperatures showed an increase of resistance at 300ºC and the degradation of the mechanical properties after the increase of the temperature up to 600ºC and 900ºC. This behavior was also verified in the samples tested in a post-fire situation. The hardness tests allowed to verify that the hardness of the welded joints began to degrade from 600ºC, with no change occurring up to 300ºC. The metallographic analysis revealed that at 300ºC the increase of segregated carbides occurred, which contributed to the reduction of the grain size and, later, to the increase of the mechanical resistance. On the other hand, from 300ºC, it was verified that a decrease of the segregated carbides occurred and an increase of the grain size, being maximum at 900ºC. The reduction factors obtained through the tensile test curves at high temperatures and in the post-fire situation were compared with those provided by Eurocode 3, and it was observed that, in a general mode, it is safe to use the standard in the projection of metallic structures.

Στην παρούσα εργασία αναπτύχθηκαν καμπύλες τρωτότητας οδικών και σιδηροδρομικών γεφυρών οπλισμένου σκυροδέματος που συναντώνται στην Ευρώπη. Οι κατηγορίες που εξετάστηκαν ήταν αυτές των κανονικών γεφυρών, με συνεχές κατάστρωμα συνδεδεμένο με τα βάθρα είτε μονολιθικά είτε μέσω ελαστομεταλλικών εφεδράνων. Άλλες παράμετροι που θεωρήθηκαν όσον αφορά στην τυπολογία των γεφυρών είναι το μήκος της γέφυρας, το ύψος των βάθρων και η διατομή τους, ο αριθμός των υποστυλωμάτων ανά βάθρο και το επίπεδο αντισεισμικού σχεδιασμού. Ο σχεδιασμός, η διαστασιολόγηση και οι λεπτομέρειες όπλισης έγιναν βάσει του Ευρωκώδικα 2 για γέφυρες που δεν υποβάλλονται σε σεισμική φόρτιση και του Ευρωκώδικας 8 για γέφυρες που σχεδιάζονται αντισεισμικά. Για την εκτίμηση στη συνέχεια των αντισεισμικών απαιτήσεων πραγματοποιήθηκε γραμμική ελαστική ανάλυση σύμφωνα με το μέρος 3 του Ευρωκώδικα 8 χρησιμοποιώντας την επιβατική δυσκαμψία των βάθρων και το ελαστικό φάσμα απόκρισης. Εν τέλει ότι οι συναρτήσεις τρωτότητας κατασκευάστηκαν έχοντας λάβει υπόψη την αβεβαιότητα του μοντέλου όσον αφορά στην σεισμική απόκριση και αντοχή, την διασπορά στην αντοχή των υλικών και τα γεωμετρικά χαρακτηριστικά και την αβεβαιότητα των φασματικών τιμών.
This study presents first a literature review of existing fragility functions for bridges and then new fragility curves that were produced for European road and railway RC bridges. Regular bridges with continuous deck, connected to the piers either monolithically or through elastomeric bearings, were studied. Other variable parameters were: bridge length, pier height and cross-section, number of columns per pier and level of seismic design. Each bridge was designed, dimensioned and detailed according to Eurocode 2 and, for bridges with seismic design, according to Eurocode 8. Linear elastic analysis was subsequently performed according to Part 3 of Eurocode 8 to estimate the seismic demand. Fragility functions were then constructed accounting for the model uncertainty for demand and capacity, the dispersion of material and geometric properties and the uncertainty of spectral values.