Influence of the proportion of FRP to steel reinforcement on the strength and ductility of hybrid reinforced concrete beams

Abstract

The present study pertains to the influence of variation of FRP (Fiber Reinforced Polymer) proportion in tension reinforcement on the flexural behavior of RC beams with FRP and steel reinforcing bars. A total of 25 beams, including FRP-, steel- and hybrid FRP-steel reinforced ones, were tested to failure under four-point bending. Two types of FRP bars, GFRP (Glass Fiber Reinforced Polymer) and BFRP (Basalt Fiber Reinforced Polymer), were used and both over- and under-reinforced beams were tested. The beams in each group were designed to have close flexural capacities to fully reveal the effect of FRP proportion in the tension zone on beam ductility for a fixed bending capacity. A new analytical model was developed for estimating the bending capacities of beams. Different deformation and curvature ductility definitions were adopted and an energy-based definition, revealing the expected tendency in beam ductility, was determined. The test results revealed that the presence of even a single FRP bar in the tension zone results in reductions up to 40% in beam ductility as compared to the beam with full steel reinforcement. Each additional replacement of a steel bar with FRP was found to cause a further decrease up to 20% in beam ductility.

Keywords:

• FRP rupture
• modulus of toughness
• modulus of resilience
• deformation ductility index
• ultimate deflection
• yielding of steel

Acknowledgments

The present paper is a condensation of a portion of the Ph.D. thesis of Dr. Saruhan Kartal under the supervision of Prof. Dr. Ilker Kalkan.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

The study was supported by Kırıkkale University Scientific Research Project Coordination Unit under the project number 2016/073. This support is gratefully acknowledged. The experiments were conducted in the Structural Engineering Laboratory of Atilim University.