Supplementary Evaluation Method for Maximum Deflection of Pipeline Systems with Expansion Joints under Bending and Axial Tension

Pipeline systems that transport oil, gas, and water are essential infrastructure components and must effectively absorb joint deformations caused by ground movements to maintain operational integrity. However, in assessing ground deformation components orthogonal to the pipe axis, the current ISO 16134 procedure estimates maximum deflection solely based on the bending limit angle, neglecting axial tensile behavior. Monotonic loading tests on bellows expansion joints of various sizes conducted in this study revealed that, for a standard pipe length of 6 m, the tensile limit angle was consistently smaller than the bending limit angle. This finding indicates that tensile deformation reaches its limit state before bending under such conditions. To address this limitation, we propose a supplementary maximum-deflection formula based on the tensile limit angle. When applied in parallel with the ISO 16134 procedure, the proposed formula reduces the risk of overestimating maximum deflection under permanent ground deformation. Consequently, it enhances the safety and reliability of pipeline systems design.