Structural complexity as a new paradigm in construction cost optimization

Structural optimization in engineering has traditionally focused on minimizing material weight to enhance efficiency and performance. However, due to fabrication, transportation, and assembly requirements, minimizing material consumption does not necessarily minimize total construction cost. Lightweight designs may involve increased nodal connectivity, a higher diversity of cross-sections, or the use of oversized or overweight members, thereby raising production effort, installation complexity, and logistical costs. To address this issue, three dimensionless indices are proposed in this study, namely typological complexity, nodal complexity, and logistical complexity. These indices enable a quantitative assessment of structural complexity to be performed alongside material weight. When embedded into a multi-objective optimization framework, they allow structural designs to be evaluated in terms of material efficiency, manufacturing standardization, topological simplicity, and logistical convenience. In this way, trade-offs among these competing design aspects can be systematically explored. The applicability of the proposed framework is demonstrated through three case studies: a planar cantilever truss, a three-dimensional geodesic dome, and an industrial steel building. The results show that the proposed indices can provide complementary information beyond material weight and enable a more comprehensive evaluation of alternative structural designs. Consequently, the framework supports more informed decision-making during early design stages