Experimental investigation on the seismic performance of steel–polypropylene hybrid fiber reinforced concrete columns

• The effects of steel–polypropylene hybrid fiber on the seismic performance of reinforced concrete columns were investigated.
• Favorable improvements in failure modes, bearing capacity and deformation capacity of HFRC specimens were observed.
• Analytical predictions for evaluating the seismic bearing capacity of HFRC specimens were proposed.

Addition of fibers into cementitious composites has raised concern over decades, which enables considerable improvement in mechanical and dynamic properties of reinforced concrete (RC) members. In this paper, we present an experimental study on the seismic performance of steel–polypropylene hybrid fiber reinforced concrete (HFRC) columns, which is of vital significance to postearthquake serviceability of structures. A total of 24 specimens subjected to combined constant axial load and cyclic lateral force were investigated. The main variables involve fiber type, shear span ratio, axial compression ratio, and reinforcement ratio (longitudinal and transverse). The failure modes, ultimate bearing capacity and deformation capacity were analyzed. The experimental results showed that the presence of hybrid fibers in RC columns had positive influence on improving the seismic bearing capacity. The improvement ratio could reach to 15–20% when a relative high axial compression was applied. Moreover, in comparison to RC columns, HFRC columns exhibited a notable synergetic effect in terms of ductility and energy dissipation capacity, particularly for columns with a higher axial compression ratio. Subsequently, on the basis of principles of equilibrium and compatibility, analytical equations to estimate the seismic bending moment capacity and shearing force capacity were developed, which took into account the synergetic effect of hybrid fibers. The analytical solutions were then validated by the test results, and the correlations were observed in reasonable accuracy.