Load-Deflection Behavior of Over- and Under-Reinforced Concrete Beams with Hybrid FRP-Steel Reinforcements.

Saruhan Kartal,Ahmet Beycioglu,Ilker Kalkan,Magdalena Dobiszewska

doi:10.3390/ma14185341

Saruhan Kartal, Ahmet Beycioglu + Show 2 more

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https://doi.org/10.3390/ma14185341

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Abstract

The present study pertains to the load-deflection behavior and cracking moments of concrete beams with hybrid FRP-steel reinforcement. Under and over-reinforced hybrid beams were tested for failure along with reference beams with only steel or FRP reinforcement. The first-cracking moments of the beams were estimated analytically by using different uncracked moments of the inertia and modulus of rupture definitions. The uncracked moment of inertia definitions include the gross and uncracked transformed moments. The adopted modulus definitions are comprised of the experimental values from tests on prisms and the analytical values from the equations in different concrete codes. Furthermore, analytical methods were developed for estimating the deflections of concrete beams with hybrid FRP-steel or only FRP reinforcement. Two different types of elastic moduli, namely the secant modulus corresponding to the extreme compression fiber strain and the ACI 318M-19 modulus, were used in deflection calculations. Closer estimates were obtained by using the secant modulus, particularly in hybrid-reinforced beams. In the post-yielding region of the steel tension reinforcement, the deflection estimates were established to lay in closer proximity to the experimental curve when obtained by adding up the deflection increments instead of directly calculating the total deflections from the elastic curve equation. Accurate estimation of the cracking moment was found to be vital for the close prediction of deflections.

Highlights

The loss of the reinforcing bar cross-section and the reduction in the bond strength of rebars in concrete due to the formation of debonding cracks are among the most deleterious effects of reinforcement corrosion on reinforced concrete (RC) members and structures
Ductility problems associated with the brittle material properties and serviceability problems originating from the low elastic modulus values of FRP materials are among the leading shortcomings of the use of FRP as the sole reinforcement material in concrete flexural members
The load-deflection curves of hybrid FRP-steel RC beams can be approximated into three linear segments, meaning that sudden changes in slope took place at two points along the curve

Summary

Introduction

The loss of the reinforcing bar (rebar) cross-section and the reduction in the bond strength of rebars in concrete due to the formation of debonding cracks are among the most deleterious effects of reinforcement corrosion on reinforced concrete (RC) members and structures. RC members are always liable to cracking due to chemical and physical events, such as alkali–silica reactions and the carbonation and restrained shrinkage of concrete. These cracks form paths for the aggressive agents and air to reach the steel rebars, which can exacerbate the corrosion problem during the service lives of structures. There has been a proliferation of studies on the use of composite materials in strengthening concrete beams [1,2,3], the direct use of polymers as a concrete reinforcement is a fairly new concept Despite their major advantages, various drawbacks arise when concrete members are reinforced with only FRP bars. The ductility and serviceability concerns receive particular attention in the design of FRP RC members [4]

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