Numerous traffic bridges have been constructed over the last 150 years. Because bridges are commonly built based on an expected lifetime of 75 to 100 years, a large quantity of bridges are reaching the end of their design lifetime, or even are far overdue. To ensure these bridges remain operational without experiencing catastrophic failures, they have to be recalculated, and if need be, repaired, strengthened or replaced. Particularly older bridges are commonly constructed utilizing rivets. Their often overly complex geometries, the fact that riveting has become largely obsolete as a construction process, and old bridges are commonly not design for fatigue loading, engineers regularly face significant challenges when reassessing such bridges. While fatigue phenomena have been extensively investigated throughout the years, studies pertaining to the fatigue of riveted connections are relatively limited. The Eurocode on fatigue, EN-1993-1-9 includes only two detail categories. Additional guidelines, like RBK Steel expand upon these detail categories, but focus primarily on built-up beam cross-sections in riveted structures, rather than riveted connections. In order to attempt to more accurately assess the complex joints present in ancient steel bridges, this thesis attempts to answer the following question: What would be a suitable approach to model complex riveted joints and assess their fatigue life considering a balance between the level of complexity and applicability in design practice? A literature study is performed to identify the different factors that affect the fatigue resistance of riveted connections, as well as to highlight several of the available methods to perform a fatigue assessment. Through the investigation of experimental studies complemented with Finite Element (FE) Analyses, a design methodology for a full scale riveted model is drawn up, and finally a FE model of a joint of the John S. Thompsonbridge is constructed. A critical location within the joint is identified. On this critical locations, several stress- and strain-based fatigue life analyses are performed, namely the use of Stress Concentration Factors (SCF), Smith-Watson-Topper’s (SWT) strain-life equation, and the multiaxial shear strain criterion (MSSC) method, to investigate the effects of incorporating mean stress effects and multiaxiality. From these analyses, it is concluded that SCF appears to provide overly conservative fatigue life estimates, whereas SWT and MSSC provide more probable results. The increased life estimate through MSSC suggests a limited degree of multiaxiality present in the critical location. All three methods require a detailed FE model, complicating the fatigue assessment of the joint. While the SCF method is slightly simpler to use than SWT and MSSC, it does not weigh up to the conservativity of its life estimation. SWT is deemed the most suitable approach for the fatigue assessment of riveted joints, given that it is more widely applicable and relevant than MSSC.

This research aims to investigate the influence of Polyisocyanurate (PIR) insulation on small surface load distribution on corrugated steel roofing sheets. PIR foams are used for thermal insulation in industrial buildings. The distribution of surface loads induced by solar panels support structure might be altered by PIR foams. This is completely ignored in the design calculations according to current standard which might results in overconservative designs. In this study, the following main question is going to be investigated using experimental and numerical methods: ‘’What is the influence of PIR insulation on the transverse distribution of small surface loads on corrugated steel roofing sheets?’’. The methodology involves conducting bending experiments to obtain strains and deflection data, which then are validated using numerical models. The experiments have been conducted on corrugated steel sheets supported by rollers. The PIR insulation is connected to the steel sheet by bolts, and a loading cylinder applies vertical force at the PIR insulation panel side. Two loading configurations are selected to simulate the representative loading conditions in real-life structures. Vertical deflections and strains in the bottom flanges of the corrugated sheet are measured during the experiments. The experimental data are used for the validation of the numerical models that are created by using ABAQUS FEA. First, a linear F.E Model was developed and validated with experimental results up to the initiation of nonlinearities. The results of the linear models shows clearly that the PIR layer influence considerably the stress distribution in the adjacent ribs to the one of load application. A nonlinear analysis is conducted to determine the maximum load that the roof structure can resist. To capture geometrical nonlinearities more accurately, eigen buckling analysis was conducted to implement initial geometrical imperfections. Considering the imperfect initial geometry of the steel sheet and its plastic properties, maximum strength of the roof system could be estimated. As a note, the damage in the PIR insulation material was not considered as it is beyond the scope of this study, the material was assumed to be linear elastic. The experiments demonstrate that the behaviour of the roof structure is primarily governed by the rupture of the PIR insulation, occurring prior to any yielding in the steel sheet. The linear numerical model predicts the behaviour of the roof structure within the elastic phase. The linear model can be used to study the influence of the several influencing parameters such as the dimension, PIR material properties and the loading conditions. Expanding the span from 2 to 6 meters with a single mid-span surface load increases the adjacent rib contribution by 20%, meaning that their normalized strain values relative to the load location's maximum strain grow by 20% in the elastic phase. The nonlinear model is employed to establish the force vs. displacement curve and identify the strength of the roof. The non-linear numerical models show that the ultimate load is found to be 8000 N when a single surface load is applied directly on the steel sheet. The experiments show yielding of the steel at 7300 N after the loading jack ruptures both the PIR surface and layer, then the jack reaches the profiled steel sheeting. For design purposes, it is recommended to exclude the influence of the PIR insulation beyond its elastic phase. Compression tests conducted on the specimen revealed damage within the PIR material at a load of 6250 N, which is considered the upper limit for the PIR's elastic phase.

The use of welding is widely adopted to assemble structural components in the construction industry for many years. To ensure safety of these welded components, many fatigue tests have been conducted on many different shapes and configurations of welded connections to precisely assess the fatigue life. However, testing real-size structures and specimens is very limited due to it’s high cost and in-applicability. Thus, these full scale specimens are cut down into small scale specimens to allow applicability for testing. Different characteristics are exhibited between the full and the small scale specimens, as there are major difference in residual stresses induced by welding and cutting, which may give non conservative predictions for fatigue life. In this thesis, the objective is to forecast the evolution of the residual stress field originated by welding of a full scale and small scale specimens of a cruciform joint at the weld toe after breaking it down into smaller specimens using a cutting process by performing a numerical analysis using Abaqus finite element analysis software. To achieve this goal, first, a thermo-mechanical welding simulation was performed to obtain a welding residual stress field on a 910 mm long cruciform joint, which is done in two main parts, starting with the thermal model in which a temperature field is analysed. The temperature field from the thermal model is used as an input for the mechanical model in which the residual stress field is produced due to the temperature change and restriction of movement of material due to the shrinkage and expansion. Secondly, the 910 mm long full-scale cruciform joint was cut into five shorter specimens of 500, 210, 120, 75, and 20 mm. The welding residual stress (WRS) levels at the weld toe for each specimen was recorded and showed large stress losses and relaxations as the specimen gets shorter in length. a major longitudinal stress loss of 97% and 77% loss of maximum principle stresses when cutting down the 910 to a 20 mm long specimen, making it almost free of WRS, but only a 5-6% loss of longitudinal and Max. principal stresses when going from 910 to 500 mm. Thirdly, after generating multiple welded specimens with different lengths, a tension load of 186.2 is set in the x-direction of the attachment plate of the cruciform joint, and the stress level at the weld toe was analyzed due to the applied load and the WRS. A 40% increase of the stress occur due to the applied load, but a very slight decrease in longitudinal stresses for the 910, 500 and 210 mm due to depicting a plate-like behaviour in contraction due to poisson’s effect. Finally, the same specimens were analysed under the 186.2 MPa load but without including the WRS. Different shapes of stress distributions were found, and differences in stresses when comparing the models with and without WRS in the models. The difference in longitudinal z-direction reached up to 282 MPa, while only 77 MPa in the transverse direction. The maximum principle stresses insured the importance of including WRS when performing fatigue assessment as it showed the fatigue failure to occur in the weld root with a crack to happen at the middle part. The specimens that exclude WRS would start cracking at the edges of the weld root, but in the central part of the weld seam when including WRS. The model that included WRS showed similar fracture location at the weld root as the fractured specimen performed in tests at TNO’s laboratories. The next steps in this research is the modification of a modelling methods. The results can be improved and smoothed by modelling using the effective notch method were a radius is introduced at the weld toe and the root to eliminate the stress singularities. The welding simulation can be improved to get better results by modelling the full cruciform joint without symmetry conditions, and include a weld order for all four welds with proper cooling time in between each weld.