Although modern technologies such as smartphones with GPS functionality make navigation substantially easier, automobilists still rely on traffic signs to inform them which exit to take or which lane to follow. These traffic signs on highways are of substantial size rendering them, and their support structures, extremely susceptible to aerodynamic load induced fatigue damage.

In this thesis traffic sign support structures in the form of steel portal frames consisting of square hollow sections are considered. Antea Group designs such structures using conservative generalized methods prescribed by the Eurocode and ROK norms. In order to investigate whether or not the structures may be optimized with respect to fatigue, a more elaborate load and dynamic response model is formulated.

Aerodynamic loads are primarily considered as these are the most significant dynamic loads, which are governing for fatigue damage. The two types of aerodynamic loads that are considered are traffic induced pulse loads generated by large vehicles passing close to the sign, and stochastic turbulent wind flow. The former is in the form of a pulse load, while the latter is in the form of a super-position of sinusoidal waves based on the Solari wind turbulence spectrum. These loads are applied to a dynamic finite element method developed in Python specifically for this thesis, consisting of one dimensional Euler-Bernoulli beam elements. The dynamic response is evaluated using a modal analysis. The resulting dynamic cross-sectional signals are transformed into weld-stress signals using a finite element model in \textit{IDEA StatiCa}. Finally the Rainflow Cycle Counting algorithm is used in combination with the Palmgren-Miner rule and SN-curves provided by the Eurocode in order to estimate the fatigue damage of the structure during its lifetime.

This methodology is applied to an existing reference structure, and an optimized design. The optimized design is optimized according to the Eurocode with respect to the ultimate and serviceability limit state, but fails in the fatigue limit state. From the results it is established that the calculation model presented in this thesis yields much lower magnitudes of stress range cycles compared to those found in the design norms, leading to significantly reduced fatigue damage. However this model does not take instantaneous wind gust loads into account, reducing its range of applicability. It is suggested to utilize the simulation model for loads that occur more than 10e5 times in a 50 year life time, but utilize the existing design norm models for loads that occur less often. The traffic induced pulse loads are found to be of significant size under the current assumptions, but due to a lack of research in this field the validity of the magnitude of the pulse loads remains uncertain.

Ultimately it is show that there is potential for optimization with respect to fatigue, but the simulation model should be used on more structures and should be further evaluated in order to create a more simplified and generalized analytical model that may be applied quickly to any design or even structure.

Higher strength steels (HSS) hollow sections with steel grades from S460 up to and including S700 are becoming increasingly competitive in long span structures. Reduction of self weight is accomplished with the smaller wall thickness of the hollow section, leading to fabrication, transport and execution benefits. The use of HSS has a positive effect on the CO2 equivalent emission, which is aligned with the European Green Deal for the future development of the construction sector. Lack of experimental evidence is identified as one of the main reasons to propose rather pessimistic material factors in the revised version of EN1993-1-8 [5] for design in tubular joints. The revised version, published in 2020, recommends material reduction factors for the design of joints made of steel with yield strength larger than 460 and up to 700 MPa, in the range from 0.9 to 0.8.
In this thesis, the behaviour of the X-joints made of steel grade S355, S500 and S700 are investigated experimentally and numerically, and the proposed material reduction factors are discussed. Five full-scale welded X-joints in tension with rectangular hollow section were tested Stevin Lab II, TUD. Additionally, base material and butt-welded coupon specimens are tested to obtain the engineering stress-strain relationship of the base material, weld and heat affected zone (HAZ).
Based on the results of coupon tests, finite element software ABAQUS is used to model X-joint and to supplement the limited number of experiments. Furthermore, result of a parametric study is presented in which effects of three parameters: the yield strength, the parameter β (ratio of the width of the brace member to that of the chord member) and the thickness of the chord are investigated to analyse their influence on the structural performance of X-joints. Following properties are thoroughly examined: static strength, stiffness, ductility and failure mode. Finally, conclusions are drawn on the validity of the material reduction factors.

Explicit rules for safety verification of open cold-formed lightweight beam-to-tubular column joints are missing in the current EC3-1-8. By developing economical detailing, with design guidance based on Eurocodes, the market share for new buildings, renovation and for additional storeys on existing buildings will increase. Within the INNO3DJOINTS project an innovative plug-and-play joint is developed, allowing for modularity and industrialization for low to mid-rise buildings. This solution will increase the competitiveness and sustainability of steel construction. The goal of this MSc thesis is to characterize the behaviour of the plug-and-play joint using the component test; T-plug bending around weak axis. The strength, stiffness and deformation capacity following the EC3-1-8 component method approach are investigated.

An experiment is designed for testing in the Stevin-II laboratory at Delft University of Technology. This work includes both the design of the set of test specimens and laboratory set-up. Secondly, a numerical study is performed to predict the experimental results and an extending parametric study is performed to derive new components, using the finite element software of ABAQUS. The influence of geometrical properties; thickness ratio (reverse channel vs. T-plug web), use of stiffeners, use of tubular sections and length of the T-plug web, is studied for a steel grade S355. The numerical study is validated for three configurations using the component test; T-plug in tension, provided by the INNO3DJOINTS project. As the parametric study is based on an elasto-plastic material model, these numerical results are directly used to derive new analytical expressions/models and characterize new components and component interactions for design verification. The numerical study resulted in the identification of seven active components for the plug-and-play joint, consisting of basic EC3-1-8 components and tubular components from the CIDECT report 16F: Component method for tubular joints. In addition, two new components are introduced namely, the reverse channel in bending and T-plug in bending. Based on a total of 127 unique joint configurations, new analytical expressions are derived to characterize the behaviour of the new components for resistance and stiffness. The component interaction is established by proposing a physical spring model and a component model suitable for Eurocode implementation. This results in the characterization of the joint behaviour for the experimental configuration C-SHS200 with a 7.5% deviation on the resistance and a 20.5% deviation on the stiffness compared to the numerical result. The accuracy of the joint stiffness can be improved if the component stiffness derivation also includes non-governing configurations and a wider range of parameters is studied, such as the position of the bolt holes along the net-section and the use of tubular section. The results, derivations and the physical spring model contribute to the INNO3DJOINTS project and could be used for implementation in the software tool, to be developed by the French Institute CTICM. Besides, the Eurocode aligned component model is recommended for practical use in design standards, but further research should be performed on the verification of the rotational stiffness on the joint level.

Standardized column splices consist of bolted end-plate connection or bolted/welded cover plate splice connection. In this thesis a non-symmetrical column splice connection that uses a combination of bolted end-plate splice and cover plate splice is studied. End-plate column splice may interfere with installation of cladding elements and may interfere with architectural requirements. Proposed column splice provides a solution to the underlying issue with space optimization. Splice connections are modeled on Abaqus using solid elements. Based on the location in the building non-symmetrical column splice connections are classified as non-symmetrical corner splice connection and non-symmetrical intermediate splice connection.

Aim of this thesis is to study the structural behavior of non-symmetrical column splice connections with the aid of moment-rotation curves, individual component behavior and force distribution obtained from finite element analysis. A quasi-static analysis is conducted on software package Abaqus using dynamic explicit solver. In addition, an attempt is made to characterize the non-symmetrical column splice connection based on component method. Stiffness coefficients of end-plate in bending produced too high stiffness when used for hollow-section end-plate connection. A modified stiffness model for end-plate in bending and bolts in tension are considered for the component characterization of current connections. Effects of end-plate thickness, cover plate thickness and bolt edge distances on overall moment-rotation behavior and initial stiffness was studied.

Non-symmetrical column splice connections are studied under bending and tensile behavior. Due to uneven force distribution in the connection, torsion is noticed in bending cases of non-symmetrical corner splice and intermediate splice. Eurocode stiffness model for end-plate in bending and bolts in tension produced high stiffness compared to the results obtained from Abaqus. Stiffness was overestimated by at least 2 times. Whereas, acceptable values of initial rotational stiffness were obtained using modified stiffness model for end-plate in bending and bolts in tension. Increase in thickness of end-plate and cover plate had a positive effect on the resistance of non-symmetrical column splice connection. However, local failure in column cross-section was noticed when the thickness of end-plate and cover plate was 10 mm. Bolt distance from the column face and edge distance was varied. Overall resistance and initial rotational stiffness increased when the bolts were moved closer to the column face and the opposite was noticed when bolts were moved away from the column face. Similar behavior was also noticed in case bolts in end-plate were moved close to each other.