The definition of Bilinear material Timoshenko beam requires knowledge about the location of the neutral axis of the beam. However, in the case of existence of the axial force its location depends on the analysis result. The transverse shear stiffness for the Timoshenko beam element should be specified in advance and can not be changed through the analysis. The question is how to define the transverse shear stiffness in advance while there is no knowledge about the location of the neutral axis.
It's not trivial. You should look into the user subroutine USDFLD which set field variable values at material points as a function of current element states. You then define the material as a function of those field variables. I used it to have a pressure-stress-dependent elastic modulus for a soil model (stiffness depends on confining pressure). You may be able to set your transverse stiffness using a similar approach. I haven't looked into controlling the section properties this way but I think my colleague did something similar for cracked concrete columns.
You can also call ABAQUS (at least on a commercial license I can) and discuss the problem with their engineers.
- Badges
- Science topic