In the current paper, continuous damage mechanics is adopted to predict the fracture failure in the circular hollow section (CHS) joints, with the chord member reinforced using ultra-high strength grout. Isotropic damage is assumed and a single scalar damage variable has been adopted to describe the evolution of damage in the steel materials. The parameters for damage initiation and fracture are verified by a coupon test. FE models combining material damage effects are analyzed for grouted X joints under brace in-plane bending. The geometric parameters of these models are based on previous tests conducted in National University of Singapore (NUS). The numerical results show very close agreement with the experimental data. Further analyses regarding the effect of damage initiation strain, fracture strain, loading rate are also carried out.
As a result of Hurricanes Katrina and Rita in 2005, existing platforms will be required to resist significantly higher environmental actions than the originally design loads. This imposes a correspondingly higher demand on the strength of the critical tubular members and joints. For older platforms therefore, strengthening of the critical structural joints, through a viable engineering approach, becomes necessary to ensure the structural safety. Grouting technology proves to be an efficient method to strengthen or repair tubular joints. Experimental evidence (Tebbett, 1979; Choo and Chen, 2007) reveals that ductile fracture or punching shear failure are the most popular failure mechanisms for grouted joints under brace bending action or brace axial tension. However, conventional numerical approaches based on continuum mechanics do not represent the ductile fracture failure which involves material separation and thus invalidates the primary assumption in continuum mechanics. At the micro-scale level, material fracture is characterized by the nucleation, growth and coalescence of voids.
