Question:
I have entered a line hinge in the center of the surface, and the bending moment is not equal to zero at the line hinge. Why?
Answer:
If the line hinge has been defined correctly, the problem may lie in the incorrect support definition.
.
Although the structural system (see Image 01) would seem to be the same, there is a moment in the mid-span resulting from the determination of internal forces on the surface.
In the present case, the cause can be derived from the error message after the load case calculation.
There are very large deformations resulting in the bottom structure, so this already indicates an incorrect support of the surface.
When checking the line supports, it becomes clear that the bottom structure is rotated about the global Y-axis due to the missing restraint. This ultimately leads to the inconclusive distribution of internal forces in the basic internal force m-x.
If you adjust the line support, you will get the expected result.