Downsizing weight while upsizing efficiency: An experimental approach to develop optimized ultra-light UHPC hybrid beams

Abstract

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.