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FAQ 003316 | I have entered a line hinge in the center of the surface, and the bending moment is ...

Figure 01 - Two Equal Surfaces with Line Hinge in Center

Figure 02 - Distribution of Basic Internal Force m-x

Figure 03 - Error Message after Calculation

Figure 04 - Deformations of Structure Corresponding to Error Message in Figure 03

Figure 05 - Incorrectly Defined Line Supports in Bottom Structure

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003316

Finite Element Analysis

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. What is the reason?

Answer

If the line hinge has been defined correctly, the problem may be in the incorrect support definition.

Figure 01 - Two Equal Surfaces with Line Hinge in Center

Although the structural system (see Figure 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.

Figure 02 - Distribution of Basic Internal Force m-x

In the present case, the cause can already be derived from the error message after the load case calculation.

Figure 03 - Error Message after Calculation

There are very large deformations resulting in the bottom structure, so that this already indicates an incorrect support of the surface.

Figure 04 - Deformations of Structure Corresponding to Error Message in Figure 03

When checking the line supports, it becomes clear that the bottom structure is rotated about the global Y-axis due to the missing restraint. In the end, this leads to the non-meaningful distribution of internal forces in the basic internal force m-x.

Figure 05 - Incorrectly Defined Line Supports in Bottom Structure

If you adjusted the line support, you will get the expected result.