[ANSWERED] 1. The plane stress element only allows for in-plane displacements, while the frame or beam element.

1. The plane stress element only allows for in-plane
displacements, while the frame or beam element resists displacements and
rotations. How can we combine the plane stress and beam elements and still
ensure compatibility?
2. Compute the stiffness matrix of element 1 of the two-triangle
element model of the rectangular plate in plane stress shown in Figure P6–23.
Then use it to compute the stiffness matrix of element 2.