  Here, we address a dimension-reduction problem in the context of nonlinear
elasticity where the applied external surface forces induce bending-torsion
moments. The underlying body is a multi-structure in $\mathbb{R}^3$ consisting
of a thin tube-shaped domain placed upon a thin plate-shaped domain. The
problem involves two small parameters, the radius of the cross-section of the
tube-shaped domain and the thickness of the plate-shaped domain. We
characterize the different limit models, including the limit junction
condition, in the membrane-string regime according to the ratio between these
two parameters as they converge to zero.
