A multi-structure is a compound domain that consists of several substructures such as solid bodies, thin shells and slender rods. In this thesis we consider different mixed boundary value problems in multi-structures. In the formulations of these problems a small perturbation parameter c is introduced, e.g., the thickness of a shell. The common objective of the papers in this thesis is to analyse the junctions between the substructures and to construct the asymptotics of the solution as ε tends to zero.