This master's thesis explores lateral torsional buckling (LTB) in high-strength I-shaped welded bridge girders during the construction stage, addressing concerns about mid-span and intermediate support occurrences of LTB. Employing finite element modeling, various bridge girder geometries are designed and simulated to evaluate the performance of current design codes (SIA 263, EN 1993-1-1:2005) and the forthcoming EN 1993-1-1:2019. The research methodology involves finite element analysis to scrutinize geometric and material parameters, comparing results with established design codes. Notably, the study reveals the underestimation of LTB resistance in high-strength steel welded girders, particularly those made from flame-cut plates. Among the assessed codes, SIA 263 provides the most accurate yet imperfect predictions. Residual stresses in welded girders with rolled plates impact LTB capacity, with diminishing effects at higher steel grades, especially for slender sections with substantial depth. However, the same conclusion does not apply to welded bridges with flame-cut plates. Moreover, global geometric imperfections significantly influence LTB resistance, demonstrating a minimal impact for smaller spans and a pronounced effect for larger spans below a specific value of LTB normalized slenderness. Finally, the study identifies cost-efficient potential in hybrid sections where the web is of S355 grade and the flanges are HSS. LTB capacity is comparable to homogeneous systems, particularly for steel grades S460 and S690. However, for hybrid sections with S355 webs and S890 to S960 flanges, moment resistance stagnates at a lower value than that achieved by homogeneous systems, the web yields before the flanges reach their full strength. The thesis provides valuable insights into factors influencing LTB, aiding informed decision-making in bridge design and optimization.