Experimental Research On Shear Performance Of Rc Beam Reinforced With Glass Steel-fiber Composite Bars(GSFCBs)

Steel-fiber composite bars(SFCBs)have been proposed as a new form of reinforcement for concrete structural elements.SFCBs have high initial elastic stiffness provided by the inner steel bars before yielding,positive postyield stiffness owing to the outer FRP after the inner steel bars yield,and superior anti-corrosion performance.Furthermore,the postyield stiffness of SFCBs can be fully tailored by changing the steel-to-FRP ratio.In order to expand the use of SFCBs in new structures,a satisfactory degree of understanding is required for the behavior of members reinforced with SFCB rebar.The purpose of this study is to investigate the shear strength of concrete beams with a rectangular cross-section of 150mm widths and 250mm heights reinforced with glass steel-fiber composite bars(GSFCBs).51 beams were tested under a four-point loading configuration.27 beams reinforced with GSFCBs while the other 12 beams were reinforced with steel and 12beams with GFRP.The investigated parameters included variables shear span-to-depth ratio,a/d,stirrup spacing,s,and longitudinal reinforcement ratio,ρ.A Steel-FRP composite bar(SFCB)is a new and modern reinforcing rebar made of an inner steel bar and outer FRP integrated in a pultrusion process.For the purpose to promote the application of this new reinforcing rebar,this paper explores the Experimental research on shear performance of RC beam reinforced with SFCB bars.Test results of these bars under cyclic tensile and uniaxial loading show that SFCB has high elastic modulus,a high ultimate strength and a stable post-yield modulus.The characteristics of tensile strength of SFCBs calculated according to the mixture law are found to be in good agreement with test results.The failure modes of SFCBs are depends on factors like the steel/FRP ratio,concrete strength,and effective bond length.Basically,the reinforced concrete beams fail in two modes:flexural and shear.It is evident that in contrast with flexural failure mode which is a ductile one,the shear failure mode of the concrete beam is sudden and with brittle nature.In addition,its time of occurrence is not easily predictable and the shear failure does not present much warning before failure.Therefore,shear failure is more dangerous than flexural failure.As a result,the reinforced concrete beams should be designed in a way that they can attain their total flexural capacity and under maximum loads,these beams must represent a ductile flexural failure mode.The flexural failure is preferred to shear failure due to brittleness of the latter because in regard to soft failure.For the specimen beam in this test,the diagonal crack width increased slowly when it just cracked.As stated before,the causes of shear failure are likely to be associated with the stress conditions in the region of the path along which the compressive force is transmitted to the supports after the occurrence of diagonal cracking;an analytical description of these conditions could lead to the formulation of a lower bound criterion for failure.As the applied load increases,the width of the diagonal crack increases faster.When the stirrups intersect oblique cracks in the beam of a yielded specimen,the crack growth rate increases rapidly.The shear behaviour of reinforced concrete beams is playing an important role in reinforced concrete structures.For this reason,reinforced concrete beams are needed to be tested under various loads.The results indicated that the shear capacities of GSFCBs-reinforced beams are lower than that of reinforced with ordinary steel beam but slightly stronger than beams reinforced with GFRP.Therefore,for the specimen beams reinforced with GSFCBs have wider and deeper cracks than beams reinforced with steel but have smaller cracks than beams reinforced with GFRP with the same properties.Furthermore,the shear capacity of reinforced concrete beams with low shear strength can be increased by reducing the spacing of stirrups.Beams,being an important part of structural support system,transfer loads from structural elements like floor and loads directly coming upon them to columns.Fracture mechanism that may occur on beams against loads affecting structures is quite important in terms of building behavior.That’s why;beam elements should be tested under various loads.Stirrups developed length can directly influence on shear strength while closed stirrups may have a significant influence on the strength contribution attributed to the stirrups.This paper also presents the experimental results of shear behaviour of reinforced concrete beams,longitudinally reinforced with glass Steel-fibre composite bars(GSFCBs),glass fibre polymer(GFRP)and steel.All beams were provided with steel stirrups as shear reinforcement within the shear region with different spacing.The beams were prepared with varying test variables,such as shear span-to-effective depth ratios(a/d),amount and types of longitudinal reinforcement bars,length of beam and stirrup spacing.The effect of longitudinal reinforcement ratio,Stirrup reinforcement ratio,stirrup spacing and effect of reinforcement type on shear capacity are discussed and compared with conventional beams reinforced with GSFCB,GFRP,and steel reinforcement.All beams were provided with steel stirrups as shear reinforcement within shear region with deferent spacing.The beams were prepared with varying test variables,such as shear span-to-effective depth ratios(a/d),amount and types of longitudinal reinforcement bars,length of beam and stirrup spacing.The effect of longitudinal reinforcement ratio,ρ_f and effect of reinforcement type are discussed and compared with conventional beams reinforced with GFRP and steel reinforcement.The test results were compared with predictions recommended by ACI 440.1R-06 design guidelines and modified proposed equation.Other performance in terms of compressive strain in concrete and tensile strain in longitudinal and stirrups reinforcement was analyzed.Based on the test results,it is shown that the shear resistance of GSFCBs RC beam is influenced by elasticity modulus of GSFCB bars that resulted in low shear strength compared to conventional steel reinforced beams and high shear strength compared to GFRP reinforced beams.Moreover,due to specific properties of GSFCB materials,shear behavior of beams with GSFCB bars is different to beams with steel and GFRP reinforcement.While the current modified equation was found to be very conservative compared with experimental results.The experimental results show that the ratios of a/d and stirrup spacing significantly influence the ultimate shear capacities of the beams.Moreover,more closely spaced diagonal shear cracks were resulted in GSFCB reinforced concrete beams compared to GFRP and steel RC beams.