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A three‐phase topology optimization is applied to a conventional reinforced concrete (RC) beam loaded in four‐point bending. The aim is to reduce material amounts to a minimum while preserving load bearing capacity and stiffness. The optimization result is converted into two alternative designs, namely a RC truss structure and a hybrid concrete‐steel (HCS) truss structure. The RC truss structure is constructed in conventional reinforced concrete. By contrast, the HCS truss structure is designed using ultra‐high performance fiber‐reinforced concrete (UHPFRC) and S355 structural steel. Experimental studies demonstrate a 53% reduction in weight of the RC truss structure compared to the reference beam, while achieving a similar load bearing capacity and a significantly higher stiffness, albeit by increasing the structure's height. For the HCS truss structure, the weight saving is considerably higher, namely 83%, whereas the load bearing capacity can be increased by 10%. The stiffness remains comparable to that of the RC truss structure by increasing the structure's height likewise, while a more ductile type of failure is achieved.

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Optimization-based design Concrete is freely formable. And reinforcements can be placed anywhere in the concrete. Nevertheless, this potential is rarely used. Reinforced concrete structures are commonly rectangular shaped with reinforcement meshes parallel to the surfaces and thus possess large mass. This article shows how topological optimization can be used to create concrete structures affine to the flux of forces. Material consumption decreases rapidly. External shaping, effective cross-section designs, and trajectory-oriented reinforcement layouts are presented. First the very basic equations of the associated structural optimization problem are derived. Then a novel material-specific control mechanism towards tensile or compressive dominant designs is introduced. It is discussed how this enables to account for structural robustness. Numerous examples illustrate application on bridges, pylons, shells, beams, girder grids or support details and quantify the potential material reduction in concrete construction arising thereof.