Wind-induced or current-induced torsional vibration is a long-neglected issue for offshore engineering (e.g., offshore wind turbines, offshore oil platforms, etc.). As the dimension of the pipe pile implemented offshore increases dramatically, the one-dimensional rod theory can no longer precisely compute the dynamic torsional impedance. This paper proposes a novel 3D torsional soil-pile interaction model and derives the corresponding analytical solution for the 3D dynamic torsional impedance at the pile cross-section with the adoption of the Laplace transform, variable separation, and impedance transfer method. The solution is then validated by comparisons against some widely-accepted existing solutions. The main conclusions of this study can be drawn as follows: (1). Classic one-dimensional theory overestimates the impedance of the pipe pile, which could result in severe disasters if the dynamic design is radical; (2). Even for small diameter pipe piles, the impedance would vary in the radial direction at the pile cross-section. Usually, the impedance at the outer radius would be slightly larger than that at the inner radius; (3). For large-diameter pipe piles or pipe piles with high-strength soil plugs, the most significant impedance could appear at the inner radius, indicating the resistance provided by the soil plugs can not be overlooked for large-diameter pipe piles.

风致或电流引起的扭转振动是海上工程（例如海上风力涡轮机、海上石油平台等）长期被忽视的问题。随着海上实施的管桩尺寸急剧增加，一维杆理论不再能精确计算动态扭转阻抗。本文提出了一种新的3D扭转土-桩相互作用模型，并采用拉普拉斯变换、变量分离和阻抗传递的方法，推导出了桩截面处3D动态扭转阻抗的相应解析解。然后通过与一些被广泛接受的现有解决方案进行比较来验证该解决方案。本研究的主要结论如下： (1)．经典的一维理论高估了管桩的阻抗，如果动态设计激进，可能会导致严重的灾难；(2)。即使对于小直径管桩，阻抗也会在桩截面处沿径向变化。通常，外径处的阻抗会略大于内径处的阻抗；(3)。对于大直径管桩或高强度土塞管桩，最显着的阻抗可能出现在内径处，说明土塞提供的阻力对于大直径管桩是不可忽视的。