关于梁单元的主惯性轴方向的问题

seaplanet

我建了一个空间梁单元的模型，所有杆件的主惯性轴方向都是0,0,1。因为有斜的杆件，所以这个0,0,1不可能是精确地方向，我理解的是：在杆件轴线方向与0,0,1方向的外积平面上，确定主惯性轴的方向。经过梁单元的实体显示（方钢管）也确实如此。可是在data check 的时候总是警告：
For 300 beam elements either the average curvature about the local 1-direction differs by more than 0.1 degrees per unit length as compared to the default curvature or the approximate integrated curvature for the entire beam differs by more than 5 degrees as compared to the approximate integrated default curvature. This may be due to a user-specified normal or due to the nodal averaging routine used by Abaqus. This difference may cause unexpected behavior of the beam and you may want to verify that the beam normals are correct for your problem. The elements have been identified in element set WarnBeamCurvature1.
求高人知道，谢谢