This thesis treats virtual sensing for fatigue assessment of steel bridges. The purpose is to develop avirtual sensing method to use in the fatigue assessment process. The aim for the virtual sensing method is to only depend on strain measurements located on the bridge structure. The service life of bridges is often limited by fatigue and amending bridge design to improve fatigue resistance was developed in the 1970s. There are several bridges in Sweden, Europe and other countries that have exceeded their theoretical service life with regard to fatigue, and the need to replace them isboth a environmental and economical issue. The bridge over Rautasjokk north of Kiruna, Sweden is a specific example where the theoretical service life is limited by fatigue. Uncertainties in the theoretical fatigue assessment of bridges can be reduced by measuring strains atthe fatigue critical details, and therefore lead to a longer theoretical service life. Monitoring is, however,an expensive method and the procedure of installation and administration requires working time, and monitoring can only provide information at the gauge location. Hence, it is of great interest to optimizethe monitoring system. Virtual sensing is a method that could provide an alternative to conventionalmeasuring techniques. Virtual sensing combine measurement data with information from a model. Virtual sensing for fatigue assessment of the Rautasjokk Bridge was evaluated developing two methods. Both methods uses a finite element model of the bridge combined with strain measurements. The measurements were obtained on February 14 2018 and included a time signal and strain variations at six different locations of the structure. The accuracy of the virtual sensing methods were evaluated by comparing the fatigue damage of virtual sensing with the fatigue damage calculated using measured strains. The fatigue calculations were based on methods presented in the Eurocode EN-1993-1-9. The first method was based on the idea to find a relation between groups of stress ranges for two gauge locations on the bridge. The stress ranges were established by loading influence lines obtained from the finite element model with a fictitious train and the difference between two gauges was stored in a vector, the correlation vector. The correlation vector was applied on the measured stress ranges of the first gauge to estimate the actual stress ranges of the second gauge. No relation between groups of stress ranges for different loading cases was found and the correlation vector method for virtual sensing is not a sufficiently accurate method to apply in the fatigue assessment of the Rautasjokk Bridge. The second method was based on finding a relation between each stress range instead of a group of stress ranges. Influence lines from the finite element model were used to find a relation between each stress range of two gauges. Their relation was stored in a matrix, the correlation matrix. The matrix was applied on the measured stress ranges of the first gauge to estimate the actual stress ranges of the second gauge. The correlation matrix method for virtual sensing estimate the fatigue damage sufficiently accurate at the bridge locations where local stress ranges have the greatest impact on the fatigue damage. Results obtained through virtual sensing only include the same parameters that were used as inputs in the method. A credible virtual sensing method is crucial in order to achieve reliable results. In general, a virtual sensing method requires an extent amount of input data to validate its reliability. Further studies are required to investigate how the uncertainties of the correlation matrix affect the fatigue assessment.

In regular design practice, when it comes to conventional loading, such as uniaxial compression and bending, the local buckling of thin plates is taken care of through cross section classification. The effect of warping torsion, which also gives rise to normal stresses in the section, however, is typically not considered in the process. Present work aimed to uncover the influence of warping torsion on the phenomena of local plate buckling and to investigate the limitations of the effective width method when it was applied against its intended use. In the case of varying results, a simple correction to the calculation method was to be developed to improve accuracy. The examined I-sections were tested to failure and results were obtained with two different approaches: with finite element method and a Eurocode-based hand-calculation. The finite element models were refined to closely mimic physical experiments and their results were accepted as the true resistance of the sections, while the calculation method tried to capture the structural response in a practical, easily understandable way. The calculated results showed reasonably good accuracy with that of the finite element analysis. However, what really stood out was how similar the change in resistance was when the section parameters were manipulated. Through a properly chosen function, this allowed for the creation of an exponent that could modify the calculated results to achieve an even greater accuracy. The eccentricity of the applied load on the system was also manipulated to alter the proportion of normal stresses due to the two examined effects. It became clear that the stresses from warping in the applied calculation model were underestimated and the otherwise conservative method of effective width lost much of its safety margin when its application was extended to warping as well. Consequently, the consideration of stresses from warping in the regular design process and stability control of commonly used thin walled open sections seemed to be justified. The effective width method could not reliably cover the issue with retaining its original margin of safety.

This paper summarises the data from 1819 tests on concrete-filled steel tube columns and compares their failure load with the prediction of Eurocode 4. The full data is given on the website http://web.ukonline.co.uk/asccs2 . The comparison with Eurocode 4 is discussed and shows that Eurocode 4 can be used with confidence and generally gives good agreement with test results, the average Test/EC4 ratio for all tests being 1.11. The Eurocode 4 limitations on concrete strength could be safely extended to concrete with a cylinder strength of 75 N/mm2 for circular sections and 60 N/mm2 for rectangular sections.

Yes / This paper describes a sequence of experiments on a long-span asymmetric composite cellular beam. This type of beam has become very popular, combining the composite action between the steel and concrete with the increased section depth, compared with more commonly used solid-web I sections. Openings in the steel web also reduce the self-weight and can accommodate the passage of service ducts. Eurocode 4 recommends a high degree of shear connection for asymmetric composite beams despite the practical difficulties in achieving this. Recent research suggests that the required degree of shear connection could be reduced, particularly for beams that are unpropped during construction. However, little test data exists to verify the behaviour of unpropped composite cellular beams. Therefore two series of tests were conducted on a 15.26 m long asymmetric composite cellular beam with regular circular openings and an elongated opening at the mid-span. The degree of shear connection was 36%, less than half of that recommended in Eurocode 4, and the beam was unpropped during construction. The beam was subjected to uniformly distributed loading and shear load during the tests. The end-slip, mid-span vertical deflection, shear connector capacity and strain distribution were examined. The beam failed at an applied uniform load of 17.2 kN/m2 (3.4 × design working load 5.0 kN/m2). The member withstood an applied shear load that was 45% higher than predicted, and exhibited a Vierendeel mechanism at the elongated opening. Overall, these tests demonstrated the potential of unpropped composite cellular beams with low degrees of shear connection. / RFCS

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.

Yes / This paper presents experimental and numerical investigation on an innovative composite floor system with deconstructability. In this system, a composite slab formed with metal profiled decking is connected to a steel beam using demountable shear connectors. A series of push tests was conducted to investigate the behaviour of this form of shear connectors. In addition to the push tests, a full-scale composite beam was tested to failure in the laboratory under a number of cycles of monotonic loading. For direct comparison, a similar composite beam test was conducted using same section size, concrete strength, but using the conventional welded headed stud connectors. Test results showed that the behaviour of the composite beam with demountable shear connectors is comparable with the specimen with welded shear connectors. After the test was terminated, the demountable shear connectors were unfastened and the composite floor can be easily lifted off from the steel beam. Test result showed that these demountable shear connectors possess high ductility in comparison with the equivalent welded shear connectors. Simple design rules currently use in Eurocode 4 for the welded shear connections and Eurocode 3 for bolts are proposed to predict the shear resistance of this form of demountable shear connectors.

Yes / A full-scale composite floor plate was tested to investigate the flexural behavior and in-plane effects of the floor slab in a grillage of composite beams that reduces the tendency for longitudinal splitting of the concrete slab along the line of the primary beams. This is important in cases where the steel decking is discontinuous when it is orientated parallel to the beams. In this case, it is important to demonstrate that the amount of transverse reinforcement required to transfer local forces from the shear connectors can be reduced relative to the requirements of Eurocode 4. The mechanism under study involved in-plane compression forces being developed in the slab due to the restraining action of the floor plate, which was held in position by the peripheral composite beams; while the secondary beams acted as transverse ties to resist the forces in the floor plate that would otherwise lead to splitting of the slab along the line of the primary beams. The tendency for cracking along the center line of the primary beam and at the peripheral beams was closely monitored. This is the first large floor plate test that has been carried out under laboratory conditions since the Cardington tests in the early 1990s, although those tests were not carried out to failure. This floor plate test was designed so that the longitudinal force transferred by the primary beams was relatively high (i.e., it was designed for full shear connection), but the transverse reinforcement was taken as the minimum of 0.2% of the concrete area. The test confirmed that the primary beams reached their plastic bending resistance despite the discontinuous decking and transverse reinforcement at the minimum percentage given in Eurocode 4. Based on this test, a reduction factor due to shear connectors at edge beams without U-bars is proposed.

Yes / In recent years, a new low nickel content stainless steel (EN 1.4162) commonly referred as ‘lean duplex stainless steel’ has been developed, which has over two times the tensile strength of the more familiar austenitic stainless steel but at approximately half the cost. This paper presents the finite element analysis of concrete filled lean duplex stainless steel columns subjected to concentric axial compression. To predict the performance of this form of concrete filled composite columns, a finite element model was developed and finite element analyses were conducted. The finite element model was validated through comparisons of the results obtained from the experimental study. A parametric study was conducted to examine the effect of various parameters such as section size, wall thickness, infill concrete strength, etc. on the overall behaviour and compressive resistance of this form of composite columns. Through both experimental and numerical studies, the merits of using lean duplex stainless steel hollow sections in concrete filled composite columns were highlighted. In addition, a new formula based on the Eurocode 4 was proposed to predict the cross-section capacity of the concrete filled lean duplex stainless steel composite columns subjected to axial compression.

I detta arbete görs en jämförelse av KL-bjälklag med hänsyn till svikt och vibrationer utifrån den nuvarande och den preliminära uppdateringen av Eurokod 5 som förväntas tas i bruk år 2026. Syftet med denna studie är att undersöka och analysera konsekvenserna av uppdateringen av Eurokod 5 för KL-bjälklag med avseende på svikt och vibrationer, samt uppdateringens påverkan på dimensioneringsprocessen för konstruktörer. Beräkningar utförs på fyra olika skivtjocklekar (160 mm, 170 mm, 180 mm och 200 mm) med och utan tjock pågjutning av betong enligt båda standarder för att utreda hur den nya normen påverkar vilka bjälklag som är godkända i flerbostadshus samt om beräkningsmetoderna innebär en förändring i tidsåtgång. Arbetet visar på en stor förändring i vilka bjälklag som är godkända för flerbostadshus enligt de olika standarderna. Enligt nuvarande Eurokod 5 måste egenfrekvensen strikt hålla sig över gränsvärdet 8 Hz, vilket gör att endast de skivorna med tillräcklig böjstyvhet utan pågjutning av betong är godkända, det vill säga skivorna med tjocklekarna 180 mm och 200 mm. Enligt den preliminära Eurokod 5 kan däremot bjälklag med egenfrekvensen under gränsvärdet 8 Hz godkännas med krav på vibrationsacceleration. Kraven i den preliminära Eurokod 5 bygger till stor del på valet av prestandanivå varpå skivorna med tjocklekarna 170 mm, 180 mm och 200 mm med tjock pågjutning av betong uppfyller kravet för ”kvalitetsval” för flerbostadshus. Utöver det uppfyller samtliga beräknade bjälklag förutom den 160 mm tjocka skivan med tjock pågjutning av betong den lägsta tillåtna prestandanivån för flerbostadshus, det vill säga ”ekonomival”. Tidsåtgången för de olika beräkningarna är snarlik. Den första beräkningen, som utfördes enligt den preliminära Eurokod 5, tog en timme längre tid än för den nuvarande, men de övriga beräkningarna som utfördes när beräkningsmallen väl var gjord tog exakt lika lång tid enligt båda standarder. Slutsatser som arbetet givit är att den preliminära Eurokod 5 kan förväntas ge en positiv effekt både för begränsningen av svikt och vibrationer hos KL-bjälklag och för användningen av KL-trä som bjälklagsmaterial i större utsträckning utifrån vilket val av prestandanivå som görs. Därmed kan uppdateringen av Eurokod 5 anses stödja både FN:s Globala mål 2030: punkt 3-God hälsa och välbefinnande samt punkt 13-Bekämpa klimatförändringarna. Problemet kan dock vara att begränsa svikt och vibrationer i största möjliga utsträckning och samtidigt minska bjälklagens miljöpåverkan, eftersom tjock pågjutning av betong anses vara en god lösning för att begränsa vibrationer hos bjälklag med stora spännvidder. Utifrån konstruktörens synpunkt ses endast fördelar med uppdateringen av Eurokod 5 eftersom ökningen av tidsåtgång för beräkningarna till följd av fler kontroller kan ses som försumbar, samtidigt som den nya standarden har en betydligt förbättrad tydlighet och trygghet i beräkningsgången och de kontroller som skall utföras. / This study presents a comparison of CLT- floor systems regarding deflection and vibrations based on the current and the preliminary updated of Eurocode 5, expected to be implemented in 2026. The purpose of this study is to investigate and analyse the consequences of the Eurocode 5 update för CLT- floor systems concerning deflection and vibrations, as well as the impact of the update on the design process för engineers. Calculations are conducted on four different slab thicknesses (160 mm, 170 mm, 180 mm and 200 mm) with and without a thick concrete floor layer according to both standards to investigate how the updated Eurocode 5 affects which floor systems are approved for use in multi-family residential buildings and whether the calculation methods entail a change in time consumption. The study reveals a significant shift in the approval of floor systems for multi-family residential buildings between the different standards. According to the current Eurocode 5, the fundamental frequency must exceed the limit of 8 Hz, resulting in approval only for floors with sufficient floor bending stiffness without a thick concrete floor layer, in other words thicknesses of 180 mm and 200 mm. However, according to the preliminary Eurocode 5, floor systems with a fundamental frequency below the 8 Hz limit can be approved with requirements for floor vibration acceleration. The criteria in the preliminary Eurocode 5 largely depends on the choice of performance levels, whereby floors with thicknesses of 170 mm, 180 mm and 200 mm with a thick concrete floor layer meet the requirements for ”Quality choice” for multi-family residential buildings. Additionally, all calculated floor systems, except for the 160 mm thick floor with a thick concrete floor layer, meet the minimum performance level for multi-family residential buildings, i.e., ”Economy choice”. The time consumption for the various calculations is similar. The initial calculation performed according to the preliminary Eurocode 5 took 1 hour longer than for the current one, but the subsequent calculations, once the calculation template was established, took the same amount of time according to both standards. Therefore, conclusions drawn from the study indicate that the preliminary Eurocode 5 can be expected to have a positive effect on both limiting deflection and vibrations in CLT-floor systems and the utilization of CLT as a floor system material to a greater extent, depending on the performance level chosen. Thus, the update of Eurocode 5 is considered to support several of the UN’s Sustainable Development Goals for 2030. However, the challenge lies in both limiting deflection and vibrations to the greatest extent possible while simultaneously reducing the environmental impact of floor systems, as a thick concrete floor layer is deemed the optimal solution for limiting vibrations in floor systems with large spans. From the perspective of the structural engineer, only advantages are seen in the update of Eurocode 5, as the increase in calculation time due to additional checks can be considered negligible, while the new standard provides significantly improved clarity and confidence in the calculation process and the checks to be performed.

Cette contribution, en s’appuyant sur expérimentation et modélisation numérique vise à une meilleure compréhension du comportement des dalles en béton armé sous sollicitations de cisaillement. Une campagne expérimentale a été réalisée sur des dalles épaisses à pleine échelle de centrales nucléaires. Ces dalles sans armatures d’effort tranchant sont soumises à une sollicitation de cisaillement en chargement quasi-statique. Les essais sont réalisés en faisant varier différents paramètres qui peuvent influencer le comportement au cisaillement. Sont ainsi étudiés : résistance en compression du béton, épaisseur, taux d’armatures longitudinales et transversales, taille des granulats, longueur de la plaque de chargement. L’influence des efforts de membrane, de compression ou de traction, sur le comportement au cisaillement a également été analysée. Les résultats des essais sont ensuite comparés aux prédictions des codes de calcul. Ces résultats ont d’abord permis d’apporter une réponse aux divergences qui existent entre l’Eurocode 2 et l’Annexe Nationale Française quant à la prédiction du cisaillement. Ont également été évalués le niveau de précision donné par d’autres normes de dimensionnement au cisaillement: la norme américaine ACI 318-14, le code nucléaire AFCEN ETC-C 2010, le fib-Model Code 2010 et l’approche par la théorie de la fissure critique de cisaillement CSCT. Ensuite est évalué la possibilité d’analyses non-linéaire par élément finis (EF) pour reproduire le phénomène du cisaillement dans les dalles. Un modèle de béton élastoplastique avec endommagement est combiné à une analyse quasi-statique à schéma de résolution explicite. Des lois de comportement non linéaires appropriées du béton avec des comportements post-pic associés à un critère énergétique ont été considérées. La bonne concordance entre le modèle proposé et les résultats expérimentaux en termes de résistance au cisaillement et de modes de rupture permet de valider la modélisation proposée. Une étude paramétrique a été réalisée sur la base du modèle proposé avec les mêmes propriétés mécaniques de béton. Des lois simplifiées permettant d’estimer les capacités en cisaillement en fonction des différents paramètres étudiés sont finalement proposées. / This study, based on experiments and numerical modeling, aims at a better understanding of the shear behavior of reinforced concrete slabs. An experimental campaign was carried out on full-scale thick slabs typical of nuclear power plant slabs. These slabs without shear reinforcement are subjected to a quasi-static shear loading. The tests are carried out by varying different parameters that can influence the shear behavior: the concrete compressive strength, the slab depth, the bottom longitudinal and transverse reinforcement ratio, the concrete aggregate size, the loading plate length. The influence on shear behavior of compression or tension membrane forces has also been analyzed. The results of tests are then compared with the predictions of the calculation codes. These results first of all helped to answer the differences between the Eurocode 2 and the French National Annex concerning the prediction of the shear capacity of reinforced concrete slabs. The level of accuracy given by other shear dimensioning standards was also assessed: The American standard ACI 318-14, the AFCEN ETC-C 2010 code used for nuclear buildings, the fib-Model 2010 and the Critical Shear Crack Theory. Next, we evaluate the possibilities of a non-linear finite element analysis (EF) to reproduce the phenomenon of shear in slabs. An elastoplastic concrete model with damage was used and combined with a quasi-static analysis using an explicit resolution scheme. Appropriate nonlinear behavior laws of concrete with post-peak behaviors associated with an energy criterion were considered. The good agreement between the proposed model and the experimental results in terms of shear strength and failure modes allowed validating the proposed modeling. A parametric study was conducted based on the numerical proposed model with the same mechanical properties of concrete. Simplified laws allowing estimating the shear capacities according to the different parameters studied are proposed.