  In this paper we derive the one-dimensional bending-torsion equilibrium model
modeling the junction of straight rods. The starting point is a
three-dimensional nonlinear elasticity equilibrium problem written as a
minimization problem for a union of thin rod-like bodies. By taking the limit
as the thickness of the 3D rods goes to zero, and by using ideas from the
theory of $\Gamma$-convergence, we obtain that the resulting model consists of
the union of the usual one-dimensional nonlinear bending-torsion rod models
which satisfy the following transmission conditions at the junction point:
continuity of displacement and rotation of the cross-sections and balance of
contact forces and contact couples.
