In Computer Aided Drafting three groups of three-dimensional geometric modelling can be recognized: wire frame, surface and solid modelling. One of the methods to describe a solid is by using a boundary based representation. The topology of the surface of a solid is the adjacency information between vertices, edges and faces. To develop a design model, however, topological information on all relevant elements (vertices, edges, faces and solids) is required. The design model presented consists of two representations: the Edge Based representation (E.B-rep) to describe the boudary of a solid and the Face Based representation (F.B-rep) to describe the boundary relations between solids. The topology of both representations can be represented by the qual edge data structure, that is, embedding of graphs in surfaces. One of the applications of the bipartite design model is parametric design. The E.B.-rep can be used for representing parametric objects. With the F.B-rep we can also define parametric relations between (parametric) objects to realise Computer Aided Design. To support the design process of a structural engineer, for instance to design prefabricated concrete constructions, we introduce three phases: the grid, the structure and the construction. Other applications for the developed design model will be a connection with production assembly and information-exchange.