Hello,
I am beginning a Phd where I will have to use Abaqus so I am currently learning how to use it. Currently, I am studying the construction of stiffness matrices for Euler-Bernoulli beam elements with 2 nodes in 3D. In this case, there are 6 degrees of freedom (3 for rotation and 3 for translation) per nodes. For a single beam element, it gives a (12*12) elementary stiffness matrix (see theoretical_matrix.png). I tried to understand how this matrix was implemented for B33 elements (2-node cubic Euler Bernoulli beam element) in Abaqus. From the theory guide, I learned that cubic element have 2 additional variables for axial strain, so, the elementary stiffness matrix is now (14*14) instead of (12*12). How are these additional terms defined in the matrix ?
Also, when I compared the (14*14) stiffness matrices generated in Abaqus with my theoretical (12*12) matrix, I retrieve the sames results for the terms relative to bending and twisting but the terms relative to compression/traction seems different from the ones of my theoretical matrix ( = EA/L). Is this difference linked to the introduction of the 2 additional variables for the axial strain ?
Best regards,
Antoine
