Bar Reinforced Concrete Beams Research Articles

Comparative study on fracture evolution in steel fibre and bar reinforced concrete beams using acoustic emission and digital image correlation techniques

In recent decades, the demand for sustainable construction practices has increased, but raw materials such as reinforcing steel remain scarce. Therefore, steel fibres have emerged as a popular and sustainable choice in the construction industry, offering a cost-effective alternative to traditional steel bar reinforcement for both flatwork and elevated structures. The purpose of this study is therefore to compare the performance of fracture behaviour between steel fibre-reinforced concrete (SFRC) and steel bar-reinforced concrete (SBRC) beams subjected to three-point bending. The fracture process was monitored by using two non-invasive techniques: acoustic emission (AE) and digital image correlation (DIC). The damage level was identified by characterizing the parameter-based AE data such as hit rate, energy release, count, rise time, amplitude, and signal strength. DIC images were employed to visualise the crack propagation in parallel with the AE data. To further understand the fracture characteristics, the integration of 2D source localization of AE events (based on local AE fracture energies) with DIC results was investigated. The parameter-based AE results showed that SBRC beam experienced a high density of AE hits with large peak amplitude events that were accelerated during the pre-peak loading phase. The Ib-value analysis revealed that SBRC beam exhibited a higher degree of fracture magnitude during the primary crack development process than SFRC beam. Following the main cracking stage, SFRC beam demonstrated an improved post-cracking softening behavior and superior ability to arrest crack propagation compared to SBRC beam. The integration of local AE fracture energy and DIC results provided a novel approach for a better understanding of the fracture behaviour in both SFRC and SBRC beams. This study’s findings contribute to more precise monitoring of fracture evolution in SFRC and SBRC beams, ultimately improving the selection process for primary reinforcement in flatwork and elevated structures.

Investigation of Residual Strength of GFRP Bar Reinforced Concrete Beams with Recycled Materials Under Elevated Temperature

Investigation of Residual Strength of GFRP Bar Reinforced Concrete Beams with Recycled Materials Under Elevated Temperature

Flexural Behaviour of Hybrid Bar Reinforced Concrete Beams (GFRP Bars with Steel Wires): An Experimental Study

Flexural Behaviour of Hybrid Bar Reinforced Concrete Beams (GFRP Bars with Steel Wires): An Experimental Study

Flexural behaviour of steel–basalt fibre composite bar-reinforced concrete beams

The utilisation of steel–basalt fibre composite bars (SBFCBs) can effectively solve the corrosion problem of steel-reinforced concrete beams and avoid the poor ductility problem of pure FRP-reinforced concrete beams. However, the research on flexural performance of SBFCB-reinforced concrete beams is still rare. Eleven beams with different reinforcement methods were tested to study the flexural behaviour of SBFCB-reinforced concrete beams and provide reference for its design and application. The failure mode, ultimate bearing capacity and strain of concrete and reinforcement, as well as the crack distribution during loading, were studied. The effects of different reinforcement methods and equivalent reinforcement ratios on the flexural performance of the beams was discussed. In addition, the equivalent reinforcement ratio range of under-reinforced failure was determined, and the theoretical calculation formulas of the yield load and ultimate bearing capacity of the beams were deduced. Results demonstrated that the failure mode of SBFCB-reinforced concrete beams was affected by the equivalent reinforcement ratio; the cracking load values of the beams were close to each other, and the yield load and ultimate load increased with the increase in equivalent reinforcement ratio. The SBFCB-reinforced concrete beams have obvious secondary stiffness. Furthermore, the deflection of the beams at the late loading stage increased faster than that before the yield of the steel bar, which indicates that the beams have good ductility. Moreover, increasing the equivalent reinforcement ratio increased the crack number in the pure bending section of beams, reduced the average crack spacing and reduced the maximum crack width. The ultimate bearing capacity calculated by the deduced formulas were in good agreement with the measured values. The maximum strain of SBFCBs is recommended to be limited to 0.75 times the ultimate strain to prevent sudden brittle failure.

Experimental Study and Numerical Analysis of Flexural Strength of BFRP Bar Concrete Beams Reinforced with Bamboo Fiber and Steel Wire Mesh

To explore the effect of adding bamboo fiber and steel wire mesh to BFRP bar-reinforced concrete beams on their flexural performance, we designed and fabricated six test beams with different parameters. Through flexural tests and numerical simulations, the effects of bamboo fiber length and steel wire mesh layout on the crack resistance, deformation capacity, and flexural ultimate bearing capacity of BFRP bar concrete beams were assessed. The feasibility of the simulation and the calculation method of flexural capacity of such specimens were considered. The research results showed that the addition of bamboo fiber can increase the cracking load and global stiffness and reduce the deformation of the test beam, but this had little effect on the ultimate flexural bearing capacity of the test beam. The cracking load, global stiffness, and ultimate flexural bearing capacity of the test beams were improved by the addition of steel wire mesh, and the stiffness and ultimate flexural bearing capacity of the test specimens with steel wire mesh in the whole beam were improved. Although the composite effect of bamboo fiber and steel wire mesh showed some improvement in these indicators, the improvement effect was not ideal.

Prediction about Effect of Span-to-Depth Ratio on Shear Capacity for FRP Bar Reinforced Concrete Beams without Web Reinforcement

Most of the prediction models for the shear capacity of FRP bar reinforced concrete beams without web reinforcement in current codes are reported to be conservative and do not consider the effect of span-to-depth ratio. Grey relational analysis (GRA) method was used in this paper to investigate the relevance of span-to-depth ratio with the shear capacity, and the results shown that the span-to-depth ratio greatly affects the shear capacity of FRP bar reinforced concrete beams without web reinforcement. A prediction model which considers the effect of span-to-depth ratio was proposed for the shear capacity of FRP bar reinforced concrete beams without web reinforcement by regression analysis, which is more accurate and reasonable in comparison with the current models.

Flexural strengthening of fire-damaged GFRP-reinforced concrete beams using CFRP sheet: Experimental and analytical study

Since the strengthening of fiber-reinforced polymer (FRP) bar-reinforced structures after a fire incident has rarely been considered in research works, in this work, the flexural response of plain and fiber-reinforced concrete beam specimens with embedded glass FRP (GFRP) bars strengthened with carbon FRP (CFRP) sheets was examined after a fire. Variables understudy in 10 GFRP bar-reinforced concrete beams included the exposure temperature (20, 400, and 600 °C), percentage of steel fiber in volume (0 and 1%), ratio of rebars (0.00314 and 0.00872), and CFRP sheet layers (0, 1, and 2), together with the presence or absence of the U-shaped anchorage. After conducting the four-point quasi-static bending experiment on the non-heated and heated beams, several parameters including the ductility, cracking pattern, and failure mode of the beams, together with their load–deflection diagrams, were assessed. The results showed that the flexural strengthening using CFRP sheets improved the flexural capacity of the specimens and this performance improvement became more notable with an increase in the exposure temperature. In the end, the sectional analysis method was utilized to propose an analytical model capable of estimating the load–deflection response of beams strengthened with CFRP sheets; this model properly estimated the test results.

Flexural behavior of GFRP bar-reinforced concrete beams with U-shaped UHPC stay-in-place formworks

Poor durability of reinforced concrete structures in harsh marine environments is an intractable issue. Replacing steel bars with fiber-reinforced polymer (FRP) bars and utilizing ultrahigh-performance fiber concrete (UHPC) for the concrete cover can greatly increase the durability of such structures. A new hybrid GFRP bar reinforced concrete beam with a prefabricated U-shaped UHPC stay-in-place formwork was tested. Herein, nine beams—one reference beam and eight hybrid beams with prefabricated U-shaped UHPC stay-in-place formworks—were subjected to four-point bending tests. The test parameters included the existence of a U-shaped UHPC stay-in-place formwork, the GRFP bar reinforcement ratio, the core concrete strength, and the bottom longitudinal reinforcement type. Experimental results showed that the hybrid beams had approximately 93.8–228.2% higher cracking loads and the hybrid beams (except beams U2 and U5) had approximately 5.9–19.0% higher ultimate loads than the reference beam. Increasing the GFRP reinforcement ratio improved the cracking load and bearing capacity of the hybrid beams, and the ultimate load increased with increasing core concrete strength. Premature failures in some hybrid beams due to partial debonding occurred between the U-shaped UHPC stay-in-place formwork and core concrete. Thence, the partial debonding should be avoided in further studies by proposing a more effective interfacial bonding method for the hybrid beam.

Experimental study on the seismic behavior of seawater sea sand concrete beams reinforced with steel-FRP composite bars

This study offers a new solution to improve the durability of steel-reinforced seawater sea sand concrete (SWSSC) beams without reducing their energy-dissipation capacity under seismic loads. Thus, an investigation of beams reinforced with steel-FRP composite bars (SFCBs), hybrid reinforced with SFCB bars and basalt fiber reinforced polymer (BFRP) bars was conducted. The effects of incorporating 1% minibar in concrete on the seismic behavior of reinforced concrete (RC) beams were also studied. These behaviors included the failure mode, hysteretic response, stiffness degradation, energy-dissipation capacity, strain variation, and curvature of the pedestal. Results showed that chloride ions in seawater and sea sand concrete caused steel bars to corrode and adversely affected the seismic response of RC beams. In addition, the SFCB bars and hybrid RC beams exhibited a more pronounced pinching effect and smaller residual displacement as compared with the steel RC beams. The total cumulative dissipated energy of the SFCB RC beams was approximately the same as that of the steel bar RC beams due to increased deformation. The seismic behaviors of the SFCB bar reinforced minibar-concrete beams were significantly improved under low cyclic loads due to a stable confinement of minibar on concrete. Their load-carrying capacity and energy consumption increased by 27.0% and 36.5%, respectively, as compared with those of the steel RC beams. Similar improvements could be observed in the response of the lateral load versus curvature in the pedestal relationship. Based on these seismic behaviors, structures reinforced by SFCB bars and hybrid reinforced by SFCB and BFRP bars are recommended as means of reinforcement for seawater and sea sand concrete structures.

Shear performance of short-span FRP-reinforced concrete beams strengthened with CFRP and TRC

This paper presents an experimental program to study the shear performance of short-span GFRP (glass fiber reinforced polymer) bar-reinforced concrete beams strengthened in shear with CFRP (carbon fiber reinforced polymer) laminates or TRC (textile reinforced concrete). Seven short-span concrete beams reinforced with GFRP bars, which have an aspect ratio of 1.7, are strengthened in shear with various schemes. Two un-strengthened beams, which have limited and no transverse reinforcements, are used as the controlled specimens. Two commonly used strengthening methods, namely CFRP strip and TRC are applied to the tested specimens. The number of textile layers is investigated in this experimental program. The U-wrapping strengthening configuration is used for both CFRP and TRC methods. The experimental results indicate that both TRC and CFRP schemes effectively enhance the shear strengths of short-span FRP-reinforced concrete beams. The number of textile layers slightly affects the shear strengths of the tested beams because the failure is controlled by the crushing of the concrete struts in short-span beams. A simple strut-and-tie method is used in the last part of the paper to predict the shear strengths of the tested specimens.

Theoretical and Experimental Flexural Behavior of Steel Bars-Reinforced Concrete Beams Strengthened with Cementitious Mortars Based on Dune Sands

This paper presents theoretical and experimental investigations to analyze the flexural behavior of reinforced concrete beams strengthened with a cementitious mortar based on the dune sand varying the cover thickness and the reinforcement ratio. After a suitable cure of beam specimens in the laboratory, they submitted to progressive loadings until the failure. The results obtained show that the flexural capacity of the strengthened beam is about 134.44 KN, which is 96% of that of the reference beam for a reinforcement ratio of 1.2% environ (over-reinforcement section). However, for ratios of 0.5% and 0.8% environ (under-reinforcement section), the flexural peak load and the failure load of the strengthened beam and those of the reference beam are similar. Deflections of strengthened beams are in general reduced compared to those of reference beams. The repair dune sand mortar could be used to enhance the flexural capacity and the ductility of damaged reinforced concrete beams strengthened with dune sand mortars. Theoretical results compared to those obtained from experimental tests, in terms of deflections and ductility, are generally in good agreement.

A Model for Shear Strength of FRP Bar Reinforced Concrete Beams without Stirrups

The shear failure of a reinforced concrete beam generally occurs when the principal tensile stress near the neutral axis is equal to or greater than the tension strength of concrete. In order to set up a model for shear strength for FRP bar reinforced concrete beams without stirrups by the mechanical method, this paper equivalently transformed the FRP bar reinforced concrete rectangular beam with cracks as one composed of ideal elastic material to facilitate the analysis and proposed a new and more reasonable model of shear strength for FRP bar reinforced concrete beams without stirrups. Then, an experimental database including 235 FRP bar reinforced beams without stirrups was compiled to verify the validity of the proposed model. It was found that the values from the proposed model are in better agreement with the experimental results of shear strength of FRP bar reinforced concrete beams without stirrups in comparison with the models in codes.

Prediction of shear behavior of steel fiber-reinforced rubberized concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars

A combination of fiber-reinforced polymer (FRP) reinforcing bars and steel fibers can be employed in locations of a structure with reinforcement congestion instead of the conventional combination of steel rebars and stirrups. In this study, first, the shear performance of the FRP bar-reinforced concrete beams containing steel fibers and crumb tire rubber without shear reinforcement was evaluated, and then an analytical model was proposed to predict their shear capacity and achieve a relationship between the first cracking moment and the shear capacity. Furthermore, an empirical equation was derived from the experimental data of 30 beams of the present research together with a database extracted from the results reported in other research to calculate the share of concrete in the shear capacity of this type of beam. Through evaluating the proposed equation against those given by different codes and those developed by other researchers, it was revealed that most existing shear strength prediction equations give an underestimated value for this parameter in beams having FRP reinforcing bars, while the present equation provides more accurate results. These results make the proposed model suitable for accurately designing FRP bar-embedded concrete beams containing steel fibers and crumb tire rubber.

Shear Strength Prediction Model of FRP Bar-Reinforced Concrete Beams without Stirrups

The shear strength prediction model for fiber-reinforced polymer (FRP) bar-reinforced concrete beams without stirrups in ACI440.1R-2015 does not consider the “size effect” and the effect of shear span-to-depth ratio and predicts the zero-shear strength for concrete members without longitudinal reinforcement. A modified shear strength prediction model for FRP bar-reinforced concrete beams without stirrups was presented in this paper. The proposed model takes into account the effect of concrete strength, size of the beam, shear span-to-depth ratio, reinforcement ratio, and modulus of elasticity of the longitudinal reinforcement and the “size effect.” The superiority of the proposed model has been evaluated by comparing the calculated shear strength of FRP bar-reinforced concrete beams without stirrups by the proposed model with the experimental results and calculated values by the models in design codes, respectively. It confirmed that the shear strength of FRP bar-reinforced concrete beams without stirrups by the proposed model was in better agreement with the experimental results.

Numerical Analysis of Behavior of Glass Fiber-Reinforced Polymer Bar-Reinforced Concrete Beams under Impact Loads

Numerical Analysis of Behavior of Glass Fiber-Reinforced Polymer Bar-Reinforced Concrete Beams under Impact Loads

Experimental study on the durability of FRP bars reinforced concrete beams in simulated ocean environment

Abstract In this paper, the flexural performance of fiber-reinforced polymer (FRP) bars reinforced concrete (RC) beams after conditioning in a simulated seawater wet-dry cycling environment for 6, 9 and 12 months is experimentally investigated. Two types of FRP bars, i.e. basalt FRP (BFRP) bars and steel-FRP composite bars (SFCBs), are adopted. Steel bars are employed for comparison. During the conditioning, a constant load is coupled to the beams. A total of 24 simply supported beams are tested. In addition, microscopic damage to the conditioned BFRP bars is detected by scanning electron microscopy (SEM). The test results indicated that total corrosion was observed at the surface of the bottom longitudinal steel bars after a maximum exposure of 12 months. However, the degradation of the macro-mechanical properties of the steel bars RC beam was not distinct. The ultimate load of the BFRP bars RC beams after 6 months, 9 months and 12 months was reduced by 22%, 33% and 42%, respectively. The yield load and ultimate load of the SFCBs RC beams were reduced by a maximum of 18% and 38%, respectively. The SEM observations revealed that there were distinct damages at the outer layer of the BFRP bars after 12-month conditioning.

Numerical modelling of carbon fibre‐reinforced polymer and hybrid reinforced concrete beams in fire

ABSTRACTInvestigation on the fire resistance of fibre‐reinforced polymer (FRP) reinforced concrete (RC) is essential for increased application of FRP bars in the construction industry. Experimental tests for determining the fire resistance of RC elements tend to be expensive and time‐consuming. Although numerical models provide an effective alternative to these tests, their use in case of FRP RC structures is hindered because of the insufficient constitutive laws for FRP bars at elevated temperatures. This paper presents the details of a numerical modelling work that was carried out for simply supported carbon FRP (CFRP) and hybrid (steel‐FRP) bar RC beams at elevated temperatures. Constitutive laws for determining temperature‐dependent strength and stiffness properties of CFRP bars are proposed. Numerical models based on finite element modelling were employed for the rational analysis of beams using the proposed constitutive laws. The behaviour of concrete was simulated by means of a smeared crack model based on the tangent stiffness solution algorithm. The employed numerical models were validated against previous experimental results. The theoretical rebar stresses were calculated in both the FRP and steel bars, and the differences are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

Effect of steel and synthetic fibers on flexural behavior of high-strength concrete beams reinforced with FRP bars

Six high-strength concrete beam specimens reinforced with fiber-reinforced polymer (FRP) bars were constructed and tested. Three of the beams were reinforced with carbon FRP (CFRP) bars and the other three beams were reinforced with glass FRP (GFRP) bars as flexural reinforcements. Steel fibers and polyolefin synthetic fibers were used as reinforcing discrete fibers. An investigation was performed on the influence of the addition of fibers on load-carrying capacity, cracking response, and ductility. In addition, the test results were compared with the predictions for the ultimate flexural moment. The addition of fibers increased the first-cracking load, ultimate flexural strength, and ductility, and also mitigated the large crack width of the FRP bar-reinforced concrete beams.

이질 보강근 및 섬유와 함께 보강된 FRP 보강근 보강 고강도 콘크리트 보의 휨 거동

이질 보강근의 조합 및 섬유의 혼입을 변수로 한 10개의 고강도 콘크리트 보를 제작하고 구조 실험을 수행하고 균열 후 강성, 처짐, 균열 양상, 연성에 대한 거동을 살펴보았다. 6개 부재는 철근, CFRP 보강근, GFRP 보강근의 조합으로 2단 휨 배근되었고, 4개 부재는 CFRP 보강근 혹은 GFRP 보강근으로만 2단 배근되고 강섬유 및 합성 섬유를 혼입하였다. FRP 보강근 내측에 철근을 처짐 및 균열 제어용으로 하이브리드 배근함으로써 FRP 보강근 보강 보의 낮은 강성, 큰 처짐, 낮은 연성, 깊은 균열 및 넓은 균열폭을 제어할 수 있었다. 또한, 섬유의 혼입을 통해 FRP 보강근 보강 보의 빠르고 깊은 균열이 제어되고 연성 및 내하력이 향상되었다. 섬유 혼입된 FRP 보강근 보강 콘크리트 부재 설계 시 섬유 혼입에 의해 증가된 콘크리트의 극한 압축 변형률에 대한 고려가 필요함을 알 수 있었다.

Evaluation of Thermal Resistance of FRP Reinforced Concrete Beams in Fire

Fibre reinforced polymer (FRP) bars are made of innovative materials and establishment of the fire resistance of FRP reinforced concrete (RC) is necessary for their widespread application. Experimental behaviours of Carbon FRP (CFRP) and Glass FRP (GFRP) bar RC beams at elevated temperatures have been investigated in this paper. Data are presented from fire tests of six simply supported beams that were fabricated using normal-weight concrete. The effects of varying load levels and FRP bar type were studied. The beams were designed over-reinforced and were tested in a floor furnace. A steel bar reinforced beam was used as control specimen. A rebar temperature of 500°C was selected as failure criterion for the beam. Non-linear temperature distribution across the beam cross section was observed. Temperature rise in the compression concrete was found insignificant and its mechanical properties were nearly unaffected. All beams met the failure criterion of critical rebar temperature of 500°C. The stiffness reduction in the GFRP and steel RC beams was nearly the same at elevated temperatures and was independent of load levels and/or bar modulus. The CFRP bar reinforced beams showed better stiffness characteristics compared to other beams.