MODELING AND TESTING OF WELDED STRUCTURAL JOINTS MACHINED WITH LASER CUTTING TECHNOLOGY

This doctorate thesis focuses on the impact of using different welding techniques on the performance and failure mechanisms of Hollow Structural Section (HSS) joints manufactured by Laser Cutting Technology (LCT). In mid-high-rise steel structures, Circular or Rectangular Hollow Structural Sections (CHS/RHS) have emerged as recommended structural members. Nonetheless, the complexity of beam-to-column joints of these members often necessitates extensive use of materials and labour force. Using LCT to fabricate HSS joints can offer highly precise, simplified, yet robust beam-to-column joint solutions. This thesis presents comprehensive material tests, 35 monotonic tensile test results, and over 77 numerical simulations on various hollow section LCT welded joints (HSS-LCT-W), including full and partial penetration groove welds (CJP/PJP) as well as full and partial strength fillet welds (FSFW/PSFW) specimens, to evaluate capacity, failure mechanisms, and compare performance across aforementioned welding processes. Each specimen consists of an HSS half-column and a passing-through plate made of S355 mild steel joined using the GMAW (Gas Metal Arc Welding) welding process. Subsequently, finite element (FE) models validated by experimental results, are used to conduct parametric studies and stress-strain analyses, and then, design recommendations are proposed for HSS-LCT-W joints. Relevant findings highlight that whilst both the PJP and FSFW techniques can provide adequate capacity for the joints, HSS-LCT fillet welded joints (HSS-LCT-FSFW) represent the most efficient and sustainable solution compared to joint penetration groove weld (butt weld) joints, particularly for HSS columns with thick walls. Moreover, the effects on the PJP welded joints due to repeated thermal cuts to realize bevel geometry was investigated. In general, CHS joints exhibit higher initial axial stiffness than RHS joints due to their specific arch resistance mobilization against tensile loading. Some extra processes such as pre-welding surface oxidation removal and using additional welding passes, called special welding in this research, have been shown to be unnecessary for these passing-through LCT joints. Finally, to develop design capacity equations for HSS-LCT-FSFW joints that integrate effective weld length concept, the most influential parameters are first identified from the joint performance and failure mechanisms and then incorporated into a regression analysis based on experimental/numerical data. The results of this thesis can serve as a guideline for the optimal design of HSS-LCT welded joints.