Application of highly flowable strain hardening fiber reinforced concrete (HF-SHFRC) in new RC columns

The concept of New RC, which is upgrade of concrete and reinforcement strength, was proposed in Japan in 1989. The purpose of New RC project was aimed to reduce the member section sizes and increase the available space of high rise buildings by using high strength concrete (f’c > 70 MPa) and high strength rebars (fy > 685 MPa). However, the nature of brittleness of high strength concrete may be obstacles for further application. Addition of steel fibers provides more confinement and shear capacity to enhance the ductility, particularly under high axial loading demands. Highly flowable strain hardening fiber reinforced concrete (HF-SHFRC) has good workability in the fresh state and exhibits the strainhardening and multiple cracking characteristics of high performance fiber reinforced cementitious composites (HPFRCC) in the hardened state. This study presents the improvement of mechanical properties and confinement efficiency of high strength concrete by adding high strength steel fibers in New RC columns. Three 60×60×180cm New RC columns made of HF-SHFRC were subjected to cyclic loading to verify the enhancement of confinement and shear capacity. The test result shows that great deformation capacity is developed even stirrups spacing is increased to d/2 in New RC columns with 1.5% fiber volume fraction. The feasibility of steel fibers as a substitute for transverse reinforcement is further confirmed. Application of HF-SHFRC in New RC columns offers opportunities to significantly simplify the design and construction of columns, while ensuring adequate ductility and damage tolerance.