• Steel and Composite Structures
• /
• v.4 no.2
• /
• pp.149-167
• /
• 2004

Offshore platforms have to serve in harsh environments and hence are likely to be damaged due to wave induced fatigue and environmental corrosion. Welded tubular joints in offshore platforms are most vulnerable to fatigue damage. Such damages endanger the integrity of the structure. Therefore it is all the more essential to assess the capacity of damaged structure from the point of view of its safety. Eight internally ring stiffened fatigue damaged tubular joints with nominal chord and brace diameter of 324 mm and 219 mm respectively and thickness 12 mm and 8 mm respectively were tested under axial brace compression loading to evaluate the reserve capacity of the joints. These joints had earlier been tested under fatigue loading under corrosive environments of synthetic sea water and hence they have been cracked. The extent of the damage varied from 35 to 50 per cent. One stiffened joint was also tested under axial brace tension loading. The residual strength of fatigue damaged stiffened joint tested under tension loading was observed to be less than one fourth of that tested under compression loading. It was observed in this experimental investigation that in the damaged condition, the joints possessed an in-built load-transfer mechanism. A bi-linear stress-strain model was developed in this investigation to predict the reserve capacity of the joint. This model considered the strain hardening effect. Close agreement was observed between the experimental and predicted results. The paper presents in detail the experimental investigation and the development of the analytical model to predict the reserve capacity of internally ring stiffened joints.

• Journal of the Korean Wood Science and Technology
• /
• v.42 no.4
• /
• pp.367-375
• /
• 2014

A simplified material model, which was efficiently implemented in a three-dimensional finite solid element (3D FE) analysis for wood was developed. The bi-linear elasto-plastic anisotropic material theory was adopted to describe constitutive relations of wood in three major directions including longitudinal, radial and tangential direction. The assumption of transverse isotropy was made to reduce the requisite 27 material constants to 6 independent constants including elastic moduli, yield stresses and Poisson's ratios in the parallel, and perpendicular to grain directions. The results of Douglas fir compression tests in the three directions were compared to the 3D FE simulation incorporated with the wood material model developed in this study. Successful agreements of the results were found in the load-deformation curves and the permanent deformations. Future works and difficulties expected in the advanced application of the model were discussed.