Hi,
I have exported the mass and stiffness matrices for a 2D euler-bernoulli beam element (B23 in ABAQUS). These elements have three degrees of freedom for each node (two translation, one rotation), therefore, for a single element I would've expected a 6x6 matrix for both matrices, however, I have an 8x8 matrix for both.
Can anyone tell me where these extra DOF are coming from?
I have attached the input file I used to extract the matrices as well as the mass and stiffness matrices. The beam material properties are:
L = 1m
b = 0.01 m
h = 0.01
E = 70e9 Pa
rho = 2700 kg/m^3
v = 0.3
Hi Kyle,
I can only make an observation. It seems that half of the elements in the stiffness and mass matrices are zero. This means that 36 are non-zero and that would be the total number of elements in a 6x6 matrix.
Simon
.dat file reports that:
NUMBER OF ELEMENTS IS 1
NUMBER OF NODES IS 3
NUMBER OF NODES DEFINED BY THE USER 2
NUMBER OF INTERNAL NODES GENERATED BY THE PROGRAM 1
TOTAL NUMBER OF VARIABLES IN THE MODEL 8
From Abaqus theory manual (sect.3.5.3. Euler-Bernoulli beam elements, Interpolation): “To eliminate the unwanted axial strain constraint, in Abaqus the stretch at the node of each such element is taken as an internal variable, local to the element (a third internal node is created for this purpose, and so it is not shared with neighboring elements.)”
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