Abstract
There have been a large number of research programs dedicated to the investigation of stress concentration factor and its parametric design formulae for a variety of uniplanar and multiplanar tubular joints. However, for the multiplanar overlapped tubular joints, the related reports are very limited due to the fact that the combining effect between multiplanarity and brace overlapping is quite complex. In this paper, a novel bracket‐stiffened two‐planar overlapped tubular KT‐joint is proposed by adding two brackets between the upper diagonal and horizontal braces to alleviate the stress concentration at the brace‐to‐chord intersection area. As compared with the original KT‐joint and KT‐joint of larger brace gap, stress concentration reduction and fatigue strength enhancement at the most critical point of the proposed KT‐joint are significant under both axial and in‐plane bending (IPB) loads. The superiority of the proposed KT‐joint is further tested with a simplified fatigue life assessment of offshore jack‐up in field transit condition, when the KT‐joint corresponding to the upper guide level is most critical and fatigue‐sensitive. The obtained results with conservative assumptions may serve as guides or references in civil and offshore engineering practices.
Highlights
Circular hollow section (CHS) members are widely used as the primary components in civil and offshore engineering structures, such as jack-ups [1] as shown in Figure 1(a), due to high strength-to-weight ratio and low drag coefficient
A tubular joint is formed by joining the CHS members in which the profiled ends of brace members are welded onto the circumference of the chord member
For the purpose of fatigue design, the stress concentration factor (SCF), defined as the ratio of the local surface stress at the brace-to-chord intersection to the nominal stress in the brace [2], is used to quantify stress concentrations at various locations around the welded region. erefore, accurate estimation of the SCFs for tubular joints is of great importance to the fatigue life prediction of civil and offshore structures
Summary
Circular hollow section (CHS) members are widely used as the primary components in civil and offshore engineering structures, such as jack-ups [1] as shown in Figure 1(a), due to high strength-to-weight ratio and low drag coefficient. Cyclic wave loading on offshore tubular joints may induce localized fatigue damage and failure due to high stress concentration at the vicinity of brace-to-chord intersections. To the best of the authors’ knowledge, there is no report on the SCF and fatigue performance of multiplanar overlapped tubular joints in which the axis of the chord member resides in a plane different from the axes of overlapped brace members. By adding two brackets between the upper diagonal and horizontal braces for stress concentration alleviation at the vicinity of braceto-chord intersections, a novel bracket-stiffened overlapped KT-joint is firstly developed. Performances of the proposed KT-joint in stress concentration reduction and fatigue strength enhancement are investigated and compared with the original KT-joint and KT-joint with larger brace gap under different loading conditions. Recommendation for further improving the fatigue behavior of the proposed KT-joint is provided
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