Safety and risk assessment of damaged multi-planar square hollow section (SHS) TT-, YT- and KT-joints

Abstract

The provisions in the design guides such as BS7910 (2005) and RP579/ASME FFS–1 (2007) are applicable only for uni-planar tubular circular hollow section (CHS) joints, and it is strictly not applicable for cracked square hollow section (SHS) joints. In this study, a completely new and robust finite element (FE) mesh generator is developed to model cracked SHS joints. The new automatic FE mesh generator is validated using the previous experimental test data as well as with the existing commercial software results. The new FE mesh generator is able to overcome the drawbacks of the previous mesh generator approaches as well as achieves convergence of solutions even at a very high plastic deformation. The new FE mesh generator is further used in the parametric study and a new set of equations are proposed for determining the weld toe magnification factor of cracked double-sided T-butt joints and cruciform X-joints subjected to both axial and bending loading. Extensive parametric study is carried out for uni-planar SHS T-, Y- and K-joints and multi-planar SHS TT-, YT- and KT-joints subjected to axial tensile loading at the brace end. Subsequently, new equations for determining the reduction factor (FAR) of above mentioned SHS joints are proposed. The results reveal that the crack area and the brace to chord width ratio (β) have a significant influence on the plastic collapse load (Pc) of the cracked SHS joints. It is also concluded that the additional multi-planar brace increases the Pc load of cracked SHS joints. The highest level, Level 3C failure assessment diagram (FAD) curve of cracked SHS joints is constructed using the full numerical results of the elastic J-integral (Je), elastic-plastic J-integral (Jep) values and Pc load. It is found that standard Level 2A curve of the BS7910 (2005) is not always safe in assessing the safety and integrity of cracked SHS joints. Therefore, penalty factors of 1.2 and 1.1 for Pc load are recommended to move all the constructed Level 3C FAD curves above the standard Level 2A curve for cracked uni-planar and multi-planar SHS joints. These new Level 3C FAD curves are found to produce optimal solutions and they can be used to assess the safety and integrity of cracked uni-planar SHS T-, Y- and K-joints, and multi-planar SHS TT-, YT- and KT-joints.