Ductility and moment redistribution capacity of two-span RC beams

The particular weaknesses of concrete buildings are brittle fracture and lack of material ductility, so using steel reinforcements and discrete fibers are an attempt to overcome this weakness. Strain hardening behavior under tensile force has made new material, High Performance Fiber Reinforced Cement Composite “HPFRCC” as a high performance material with high energy absorption capability and high cracking ability before failure. Therefore the structural application of this composite material in the structural members such as continuous beams to control cracks width and formation of multiple cracks, improve ductility, moment redistribution capacity have been investigated. In this paper, the effect of using HPFRCC containing 2 % steel fibers on the flexural performance of four large two-span reinforced concrete beams with similar dimensions and similar longitudinal reinforcement ratios has experimentally been investigated. Two beams were ordinary concrete with two different arrangements of stirrups in the middle support (hogging) and mid span (sagging) area and two other beams were companion but made with full HPFRCC composites. The specimens have rectangular cross section of 250 mm (height)×200 mm (width) and are continuous over two spans of 1800 mm each and two concentrated equal statically monotonic loads (from zero to the failure) are applied at the
mid-span of each beam. The experimental results showed that using HPFRCC layers in section beams and reducing the spacing of the stirrups, increased the ultimate load, ductility ratio, plastic hinge characteristics and moment redistribution capacity of these beams compare to reference beam. The greatest load carrying capacity values 42 % were observed in FHPS compared to RCN beam. Maximum moment redistribution values of around 23.31 % was observed in FHPS beam and maximum displacement ductility ratio 1.8 was observed in FHPS beam compare to reference beam. In HPFRCC beam, the sufficient shear strength is provided in beam without local shear cracks. This allows the formation of plastic hinge in beams and plastic hinge zone.