Development of welded tubular joints and comparison of fatigue behaviour

In order to compare the fatigue behaviour of different types of welded tubular joints, the structural development and innovation on welded tubular joints were introduced and the corresponding statistics on stress concentration factor (SCF) and fatigue life were conducted. The Sh-N curves based on hot spot stress method of different welded tubular joints were developed for practical fatigue design. The comparisons of fatigue behaviour for different welded joints were made based on Sh-N curves and SCFs. The results show that as for Sh-N curves of joints with thickness t≤4 mm, the weld defects become the critical effects, leading to lower fatigue life. In the current design guidelines, the Sh-N curve in CIDECT design guide No.8 is unsafe for all joints. The Sh-N curve in DNV-RP-C203 can be used for square bird-beak SHS joints and diamond bird-beak SHS joints, but it is unsafe for the other joints. In APIRP 2A-WSD, the so called X' Sh-N curve is lower than X Sh-N curve. The X' curve can be applied for bird-beak joints (both square bird-beak SHS joints and diamond bird-beak SHS joints), conventional CHS-CHS, RHS-RHS joints and the corresponding joints with concrete infill in the chords. The X curve is unsafe for all joints. Under the same geometrical parameters β,2γ,τ (where β,2γ,τ are the brace-to-chord width ratio, width-to-wall thickness ratio of the chord and brace-to-chord thickness ratio, respectively), fatigue resistance decreases with following order, CHS-CFCHS joints, CHS-CHS joints, RHS-CFRHS joints, and RHS-RHS joints. The fatigue behaviour of CHS-CFRHS is slightly better than RHS-RHS joints. The fatigue behaviour of CHS-RHS joints is worse than RHS-RHS joints. The square bird-beak SHS joints and diamond bird-beak SHS joints are recommended for practical fatigue design when β≤0.7. © 2019, Editorial Office of Journal of Building Structures. All right reserved.