Structural behavior of tubular T/Y-joints with collar plate under static in-plane bending

• Ultimate capacity and failure mechanism of tubular T/Y-joints with collar plates under IPB load were investigated.
• 210 FE models were developed and validated for parametric study.
• Geometrical effects on the ultimate strength and failure modes were studied.
• Collar plates significantly increase the ultimate strength and improve failure modes of T/Y-joints under IPB load.
• A static design formula was proposed to calculate ultimate strength of collar plate reinforced T/Y-joints.

This paper investigates the static strength of collar plate reinforced tubular T/Y-joints subjected to in-plane bending (IPB) load. At the first step, a finite element (FE) model was developed and validated against the data available from 12 experimental tests. Afterwards, 210 FE models were generated and analyzed to evaluate the effect of joint geometry and collar plate size on the ultimate strength and failure modes of T/Y-joints reinforced with collar plates subjected to IPB load. Results show that the collar plate reinforcement method can significantly increase the ultimate strength and improve the failure mechanisms of tubular T/Y-joints under in-IPB load. Despite the considerable effect of the collar plate on the static strength and in spite of the frequent usage of CHS T/Y joints in offshore jacket-type platform, the ultimate strength and failure modes in collar plate reinforced T/Y-joints subjected to IPB load have not been investigated so far and no design equation is available to determine the ultimate capacity of IPB-loaded joints of this type. Therefore, after the parametric investigation, a new formula is proposed, through nonlinear regression analysis, for determining the ultimate strength of T/Y-joints reinforced with collar plate subjected to IPB load.