Different types of issues can occur with the connection between different parts. One issue occurs when both parts are the same element type; the issue is whether the nodes are connected together as desired or not. Another issue occurs when the parts are different element types. In addition to the concern of whether the nodes are connected or not, there is an issue of what type of load is transmitted between the parts. This page will discuss some of these issues. See the previous page, , for the types of contact.
The issue here is related to the degrees of freedom for each part are different. Bricks have only the three translational degrees of freedom (Tx, Ty, Tz) while plates (and shells) have all degrees of freedom except for rotation about the direction normal to the element. Therefore, the bricks cannot apply a moment to the plates that prevent the plates from rotating. Without special considerations, a connection between plates and bricks along a straight line of nodes will result in a hinge. This is depicted in Figure 1. In the case of linear stress, this may not be a statically stable configuration.
The black arrows represent the hinge line. The schematic on the right shows a side view and how the plate deflects; note the rotation at the hinge line. If the free end of the plate was not supported, the plates is free to rotate around the hinge line which would result in a statically unstable situation.
In the top method, the plate is embedded one element deep into the bricks. (The elements are shrunk to show the space between them.) In the bottom method, a tee connection of plates is created on the surface of the bricks. In the schematics on the right which show the side view, visualize the arrows as the reactions provided by the bricks on the plate. (These are in fact the forces that are transmitted between the nodes of the bricks and plates.) Since the force couple can resist a moment load, the plate is now statically stable.
The connected between beams and bricks has a similar problem to the plate-to-brick connection: the bricks cannot prevent the beams from rotating. The solution is likewise similar: make a web of beams (or spokes) to connect to the bricks. The beams must connect to the bricks at three or more points, not in a straight line, to form a statically stable solution. Figure 3 shows an example.
The left side of the figure shows the beams and bricks together; the middle shows the beams only. Note how the vertical member is connected to four other beams that tie to the bricks at multiple points. If a torque were applied to the beams, such as in the schematic on the right side, then the black arrows represent the reactions provided by the bricks.