At RM Bridge inside OpenBridge Designer, at Modeler, in the Cross-section creation users have the opportunity to generate an FE-mesh. Though, the connections between elements must obey specific very basic FEM rules:

• Corner nodes must only connect to other corner nodes
• Elements must not overlap each other.

As all cross sections are plane finite element meshes built of 9-node-Lagrange elements; therefore, a topological error will occur in any of the above cases because the element edges of neighbor elements do not fit each other. It is an error and not a warning as it will be impossible to make a correct calculation later.

Normally the issue is the discontinuity between the nodes of the FEM elements in the deck and the beam connection, or the later addition of details in an existing cross-section. Another possibility is that the use of Variables affects the elements and then created this disconnection. In any way, it is required that the nodal points should be at the exact same location. See the images above from the RM Bridge User Manual for reference.

In the example above, the original red full wide FEM element needs additional subdivision at the blue and pink dashed arrow lines to be able to connect to his top slab subdivided elements in green, orange, and light green. A new purple FEM element, with 9 nodes, will be created or edited.