Strength analysis of steel structures using finite element analysis

Throughout the service life of Canadian Naval Vessels damage occurs to the structure of the ships. This damage could be caused by regular wear and tear, specific incidents like accidents, or even design flaws. To determine the severity and/or cause of the damage to the ships a finite element model (FEM) and a finite element analysis (FEA) are typically conducted.; Hull surveyors of the Canadian Navy discovered cracks on the Iroquois (IRO) Class Destroyers. The cracks were in the vicinity of the major transverse bulkhead at frame 29 (Bhd 29). There were three locations where the cracks were located: the intersections of the port side, starboard side and centreline longitudinal bulkheads with Bhd 29. The suspected cause of the cracks was due to misalignments of the longitudinal bulkheads in the vicinity of Bhd 29 which created stress concentrations.; Due to these cracks, structural modifications to repair the areas of damage as well as to improve the structural performance were conducted under the guidance and recommendations of the IRO Class hull surveyors.; The objective of this thesis was two-fold. The first objective was to conduct FEA of the original structure in the port, starboard and centreline areas to gain an understanding of the root cause of the cracks. The relative magnitude of the stress concentrations that were causing the cracks was determined and an understanding of how the structure performs under loading was determined. The second objective was to modify the FEM to include the structural modifications that were implemented by the hull surveyors and to conduct another FEA to determine the effectiveness of the modifications of reducing the stress concentrations. Reducing the stress concentrations in the structure in the vicinity of Bhd 29 will greatly minimize the number of future cracks forming.; For the Port side analysis, the von Mises stress concentration factor (SCF) in the localized region at the intersection of the 6-Ft flat and the 8'7" OCL bulkhead was approximately 2. On the Starboard side, the region of high stress was identified at the intersection of the 9' OCL bulkhead, the 5-Ft flat and Bhd 29. The SCF in the 9' OCL bulkhead and 5-Ft flat was approximately 4.7. The substantial bracket modifications that were made to the Starboard side were very effective and reduced the SCF in the 5-Ft flat to approximately 2 and on the 9' OCL longitudinal bulkhead to 1.3. For the Centerline analysis, the stress concentration in the horizontal stiffeners at the intersection with the CL bulkhead was approximately 1.6 and the installed bracket reduced the stress concentration factor to approximately 1.1.