Hello,
I'm joining 1D beam element to 3D solid elements using a transformation between the 6 dofs of the single node of the beam element, u = [u1, ..., u6], and 3n dofs of n nodes of the solid elements, U = [U1, ..., U3n], at the joint face using a linear transformation, S (6X3n), that I've derived from beam theory, which is essentially the continuity condition. Therefore:
u = S*U
Since S is a 6X3n matrix, I get six linear equations for u1, u2, ..., and u6 in terms of U1, U2, ..., U3n. For example the equation for u1 is like:
u1 - S1_1*U1 - S1_2*U2 - ... - S1_3n*U3n = 0
in which Si_j's are the components of the first row of the S matrix. When I run a general static analysis and compare the joint model with a full 3D model, the solutions converges and the displacements are quite acceptable, however, the stress and strain results close to the joint face are off, especially shear stress and strains, and they get better as you move away from the intersection. I was wondering if I'm doing something wrong. It's badly confused me and any help on this would be greatly appreciated.
Thanks,
Hanif