Due to high stress concentrations, welded joints represent the most common locations of fatigue crack initiation in steel structures that are prone to fatigue. Welding affects material properties by the process of heating, cooling, and combining basic and additional material. Since welding is the primary process of joining elements in steel structures, it is obvious that fatigue assessment during the design and maintenance process becomes inevitable. There are many fatigue assessment methods of welded joints, but their precision remains questionable. This paper represents a review of the most common fatigue assessment methods used for welded steel joints. As a result of this review, areas that require additional research are highlighted.

In the last few decades, the application of lightweight cold-formed composite steel–concrete structural systems has constantly been increasing within the field of structural engineering. This can be explained by efficient material usage, particularly noticeable when using cold-formed built-up sections and the innovative types of shear connections. This paper summarises an overview of the development of the cold-formed composite steel–concrete floor systems. Additionally, it provides the background, planned activities, and preliminary results of the current LWT-FLOOR project, which is ongoing at the University of Zagreb, Faculty of Civil Engineering, Croatia. The proposed structural system is formed of built-up cold-formed steel beams and cast-in-place concrete slabs that are interconnected using an innovative type of shear connection. Preliminary analytical and numerical results on the system bending capacity are presented. Obtained results are mutually comparable. The resistance of the fixed beam solution is governed by the resistance of the steel beam, while pinned beam solution is governed by the degree of shear connection without the influence of the increased number of spot welds in the steel beam.

<p>Built-up cold-formed steel elements are efficient structural elements, very attractive due to material savings, but also for ease of construction. The connection between the built-up beam components can be easily obtained by screws, but the developments in the welding process also led to other solutions like spot welding. The WELLFORMED research project, conducted within the CEMSIG Research Center of the Politehnica University of Timisoara, proposes to study a new technological solution for built-up beams made of corrugated steel sheets for the web and thin-walled cold-formed steel profiles for the flanges, connected by spot welding. Within the research project, the experimental work included tensile-shear tests on the lap joint welded specimens, where different combinations of steel sheets with various thicknesses were tested and, tests on two full-scale beams in bending. The paper briefly summarizes the results of the experimental program and extends the research by numerical analyses to demonstrate the potential of this solution for standardization and industrial manufacturing. Based on the validation of the numerical model, the paper presents the influence of several parameters i.e.: (1) the initial imperfections, (2) the number and distance between spot welding on flanges, (3) the thickness of the flanges, (4) the thickness of the corrugated web and (5) the thickness of the shear panel. From the parametric study, it results that the bearing capacity of the corrugated web beams made of cold-formed steel components is highly affected by the stability of the components and less affected by the configuration and the number of spot welding.</p>

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Researches show that composite systems made by combining cold‐formed steel (CFS) elements and concrete can produce excellent properties compared to traditional solutions. One of the solution which employs CFS elements and concrete is the subject of research within the LWT‐FLOOR project. The LWT‐FLOOR system consists of built‐up CFS beams with corrugated web, connected by spot welds and concrete slab with an innovative shear connection. This paper presents a numerical investigation of two types of shear connections suitable for the proposed composite solution. One type of shear connection is completed using bolts which provide a direct shear connection between the flange profiles of the steel girder and the concrete slab. The second type of shear connection is achieved using a composite dowel rib connector realised through a steel beam corrugated web. In this case, the connection between the profiles of the steel beam and the concrete flange is realised indirectly, i.e., through spot welds between C profiles and corrugated web. The results of FE simulations indicate that a solution with bolts ensures higher shear, but reduces its ductility. These results provide the basis for the conduction of experimental push‐out tests of the proposed shear connection types.