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This paper presents an efficient scheme to filter structures out of ground structures, which is implemented using a nested elastic formulation for compliance minimization. The approach uses physical variables and allows control of the minimum ratio between the minimum and maximum areas in the final topology. It leads to a singular problem which is solved using a Tikhonov regularization on the structural problem (rather than on the optimization problem). The filter allows a multiple choice solution in which the user can control the global equilibrium residual in the final structural topology and limit variations of the objective function between consecutive iterations (e.g., compliance). As a result, an unambiguous discrete solution is obtained where all the bars that belong to the topology have well-defined finite areas. This filter feature, with explicit control of member areas, allows the user (e.g., engineer or architect) to play with different alternatives prior to selecting a specific structural configuration. Examples are provided to illustrate the properties of the present approach and the fact that the technique does not always lead to a fully stressed design. The method is efficient in the sense that the finite element solution is computed on the filtered structure (reduced order model) rather than on the full ground structure.

Topology optimization can be divided into continuum and discrete types, the latter being the emphasis of the present work. In the field of discrete structural topology optimization of trusses, the generation of an initial ground structure is crucial. Thus, this paper examines the generation of ground structures for generic structural domains in two and three dimensions. It compares two methods of discretization, Voronoi-based and structured quadrilateral discretizations, and proposes two simple and effective ground structure generation approaches: the macroelement and macropatch approaches. Both can be implemented with either type of discretization. This work presents several features of these approaches, including the efficient generation of initial ground structures, a reduction in matrix bandwidth for the global stiffness matrix, finer control of bar connectivity, and a reduction in the number of overlapped bars. Generic examples and practical structural engineering designs are presented. They display the features of the proposed approaches and highlight the comparison with results from either the literature, the traditional ground structure generation, or the continuum optimization method.

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