Flexural Behavior Research Articles

A study on the flexural behaviour and self-healing of fibre reinforced bacterial concrete beams

A study on the flexural behaviour and self-healing of fibre reinforced bacterial concrete beams

The confinement effect of basalt fibers for reinforced geopolymer composites: Flexural, shear and torsion capability for ductility and failure

Geopolymer concrete is a promising candidate to replace conventional concrete (CC), as geopolymer concrete is based on alkali-activated binders instead of Portland cement. The elimination of cement in the mix leads to a reduction in the release of greenhouse gases. It is known from the literature that the microscale properties of geopolymer concrete are similar to those of its counterparts. However, the structural performance of geopolymer elements should be investigated in detail. Therefore, in this study, the effect of basalt fiber ratio (%0 and %1), geopolymer mix type and stirrup (with and without stirrup) on flexural (four-point test), shear (overhanging test) and torsional (pure torsion test) behavior of RC beam were investigated. In these experiments, slag based geopolymer concrete with waste marble, geopolymer concrete with fly ash and geopolymer concrete with quartz powder were used in order to manufactured to the RC beams. The mechanical performances of RC beams were assessed by using load-deflection curves, stiffness, ductility, failure mode and crack propagations. Test results revealed that the use of basalt fiber tolerated the decrease in strength, although the shear, flexural and torsion capacity decreased if stirrups were not used in the beams. The use of fly ash in the mixture was more effective on the strength than other materials in terms of the aluminate and silicate it contained.

Finite element analysis of ductility and flexural capacity of FRP and steel bars hybrid reinforced concrete beams

AbstractTo study the flexural behavior of hybrid reinforced concrete (hybrid‐RC) beams with FRP and steel bars, this paper used ABAQUS finite element (FE) software to model and nonlinear analyze the hybrid‐RC beams and investigate the effects of effective reinforcement ratio, concrete strength, and FRP bars type on the flexural behavior of hybrid‐RC beams. In addition, the FRP bars stress, flexural bearing capacity, and ductility formulas for hybrid‐RC beams were fitted based on the FE results, and existing literature data were used to verify their accuracy. The FE model results indicated that the effective reinforcement ratio, FRP bars type, and concrete strength significantly impacted the flexural bearing capacity and deformation performance of hybrid‐RC beams. Increasing the strength of concrete improved the flexural bearing capacity and ductility of hybrid‐RC beams; increasing the effective reinforcement ratio and the elastic modulus of FRP bars increased the flexural bearing capacity of the hybrid‐RC beams but decreased its ductility. In addition, the fitted FRP bars stress, flexural bearing capacity, and ductility calculation formulas can quickly and conveniently predict the flexural bearing capacity and ductility of hybrid‐RC beams.

Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method

Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method

Flexural behaviour and shear capacity of RC flat plate sections during fire exposure

PurposeFire safety is a pivotal requirement in building codes. Prescribed design criteria have been the norm to achieve it, which imposes limitations on engineers, including the inability to accommodate new solutions/materials. The shift towards performance-based design offers the potential to address shortcomings of the prescribed design. However, this shift also significantly increases the workload on structural engineers without a corresponding increase in their engineering fees. Simplified design tools are needed to assist engineers in this transition.Design/methodology/approachThe paper is divided into sections investigating equivalent standard fire duration, thermal deformations, flexural behaviour and shear capacity of flat slabs when exposed to fire. The first section conducts a parametric study correlating equivalent and realistic fire durations using the average internal temperature profile (AITP) method, resulting in statistical equations estimating equivalent fire duration. The second section evaluates thermal deformations and flexural behaviour through a parametric study considering various parameters. This section results in statistical equations estimating thermal deformations and flexural behaviour of flat slab sections during fire exposure. The final section focuses on shear capacity, developing simplified heat transfer formulas and statistical equations predicting compression zone depth reduction. The section presents methodologies predicting flat slab sections' one-way and two-way shear capacities during fire exposure.FindingsStructural engineers can use the proposed methods for daily design work without applying complex heat transfer calculations. When the equivalent standard fire duration is utilized, a flat slab’s thermal deformations, flexural behaviour and shear capacity under an actual fire condition can be calculated. As such, the methods would be highly beneficial in assessing the structural integrity of a building during an active fire incident.Originality/valueThe paper provides engineers with the tools required to evaluate the safety of flat slab sections during fire exposure. The methodologies presented in the paper enable engineers to use performance-based design for slab sections by (1) converting any real fire scenario to a standard fire with an equivalent duration, (2) assessing their thermal behaviour, (3) evaluating their flexural behaviour and (4) evaluating their flexural and shear capacities. The paper concludes with a case study example demonstrating the detailed application of the developed methods.

Combined bending-torsion and compression-bending-torsion behaviours of reinforced concrete-filled thin-walled corrugated steel tubes

Reinforced concrete-filled thin-walled galvanized corrugated steel tube (RCFCST) is a novel composite member that has application potential in extremely corrosive environments and seismic activity regions. A series of preliminary works have been conducted on its compressive, flexural, shear, and torsional behaviour. However, the combined loading condition is almost inevitable in practice. The correlations between the flexural and torsional behaviour of RCFCSTs are unique due to the special spiral corrugated profile, which is unclear and needs to be addressed. This paper, therefore, presents an experimental investigation of the RCFCST under combined bending-torsion and compression-bending-torsion loads, encompassing the main test variables of torsion-to-bending ratios, torsional directions, and axial compression ratios. The loading set-up and instruments have been introduced in detail. The failure modes, lateral load versus lateral displacement curves, bending moment versus flexural lateral displacement curves, torsion moment versus torsional angle curves, and strain distributions are carefully addressed. The working mechanisms of the RCFCST under monotonic combined loads are discussed, with a particular explanation of the dependent behaviour on the torsion-to-bending ratios and torsional directions. The applicability of the existing design methods for the bearing capacity of RCFCST specimens under combined loads is examined carefully, with specific design suggestions proposed.

A size‐dependent model of strain gradient elastic laminated micro‐beams with a weak adhesive layer

AbstractA size‐dependent model for a laminated micro‐beam with a soft adhesive is developed in the framework of strain gradient elasticity theory. The layered beam is constituted by two Euler–Bernoulli strain gradient elastic isotropic beams, joined through a strain gradient spring‐type contact law at the adhesive level. The governing bending and extensional equations and boundary conditions are obtained by using the variational principle. The differential system shows a coupling between the flexural and axial behaviors of the upper and lower beams, due to the presence of interface terms related to shear and peeling stresses. Two benchmark problems have been presented through their closed‐form solutions, namely a simply‐supported laminated beam subjected to a uniform distributed load and a mode 2‐type loading configuration of a layered axially deformable beam. Size effects and non‐local phenomena, due to high strain concentrations, are highlighted. Though simple in their features, the examples prove the efficiency of the proposed approach in designing micro‐scale layered beams.

On Numerical Flexural Behaviour of Hybrid Composite Shallow Shell Panels with Experimental Validation

On Numerical Flexural Behaviour of Hybrid Composite Shallow Shell Panels with Experimental Validation

Flexural cracking behavior of steel-NC-UHPC composite beam under negative bending moment

Steel-concrete structures are widely applied in bridge engineering due to their superior mechanical performance and cost-effectiveness. However, normal concrete (NC) decks often suffer cracking problems, adversely affecting their serviceability. Ultra-high performance concrete (UHPC) can be used to partially replace the top of NC decks to enhance their post-cracking behavior because UHPC shows high tensile strength, strain-hardening characteristics in tension, and strong bond strength with NC. To this end, this paper focused on the flexural behavior of steel-NC-UHPC composite beams regarding their failure mode, stiffness, strain development, cracking behavior, crack width, etc. Test results indicated that the test specimens mainly exhibited two types of failure modes: shear failure of the NC layer and local buckling of the compressive flange at the steel girder, which were mainly determined by the reinforcement ratio. Flexural stiffness was controlled by the steel girder, and the reinforcement ratio had a notable effect on the reinforcement strain and crack propagation. Additionally, cracks can be categorized into three types: through cracks, connecting cracks, and separate cracks. These cracks in the UHPC layer and NC layer would affect each other, especially those near the roughening interface. The sectional nonlinear analysis was employed to calculate the strain of reinforcement and the steel girder accurately. Finally, the prediction methods of crack width for the NC layer and UHPC layer were discussed. Formulas in NF P18–710 were verified to be feasible for the prediction of UHPC crack width. The UHPC influence factor was introduced to modify the calculation results of the NC crack width by the Chinese NC code.

Flexural Behaviour and Environmental Impact of African Fan Palm Reinforced Concrete Beams under Symmetrical Loading Conditions

The paper presents the results of investigation on reinforced beams adopting eco-friendly materials for sustainable concrete. The use of African fan palm is explored to mitigate the environmental impact aimed at reducing carbon emissions associated with the production and use of steel reinforcement. The beams were tested under a four -point loading system with the ends simply supported. The test comprised twenty-three beams that were reinforced with African fan palm bars whilst two beams were reinforced with mild steel bars to serve as control beams. The study investigated the flexural strength and deformation characteristics of the beams under monotonic loading. Two concrete strengths of 15.34N/mm2 or 22.37N/mm2 were adopted and proposed optimal tensile ratios for an under reinforced fan palm section. The parameters considered included the tension bars ratio (ρ), concrete compressive strength, span-to-effective-depth ratio and loading conditions. A linear elastic behaviour of both fan palm and steel reinforced concrete beams was observed to the point of first crack load beyond which the beam stiffness continued to reduce until failure. A comparison of the experimental results with results of theoretical analysis of the beams revealed that a 1.22% increase in the tensile ratio of steel in the control beams increased the cracking moment (Mcr) to 36%, while the fan palm beam of the same size and same concrete strength with a higher tensile ratio of 9.69% exhibited a lower Mcr of 11.86%. This shows a significant effect of reinforcing steel bars on concrete cracking compared to the fan palm. The averages of experimental to theoretical failure loads of fan palm to steel were compared with failure loads of 36.52kN to 20.19kN and 32kN to 19.78kN respectively. These results of the study based on the failure mode, and failure loads, highlights the suitability of using African fan palm as substitute reinforcing material for low rise buildings. Furthermore, the study also proposed minimum and maximum tensile ratio of 0.76% and 5.60% respectively for fan palm reinforced concrete beams based on the Indian Standard and modulus of elasticity of steel.

Effects of Anisotropic Mechanical Behavior on Nominal Moment Capability of 3D Printed Concrete Beam with Reinforcement

In this study, 3D-printed reinforced concrete beams were tested for flexural performance and compared with the analytical model based on the material test results. Two cementitious mixes (PSU and GCT) were designed for concrete printing and were mechanically tested and compared. Anisotropies in the compressive strength and modulus of elasticity of printed concrete were observed, applied to the analytical prediction of flexural bending behavior, and validated by actual test results. Significant differences between analytical predictions and experimental tests of the bending behaviors of the printed concrete beams were observed. Furthermore, higher compressive strengths and moduli of elasticity were observed when the loading direction was perpendicular to the printed layers or with the PSU mix. The effect of anisotropic mechanical properties on a reinforced beam was compared to the flexural bending tests for both mixes. The analytical model based on the material test results was compared to the flexural bending test results. The significant errors in the prediction of printed concrete’s structural performance, from 10% to 50%, suggest that factors other than reduced compressive strengths may influence the structural behaviors of printed concrete beams.

Post impact flexural behavior investigation of hybrid foam-core sandwich composites at extreme Arctic temperature

This study explores the post-impact bending behavior and failure mechanisms in hybrid sandwich composites made of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). Flexural tests conducted at both ambient room temperature and low temperature Arctic conditions reveal a significant enhancement in flexural performance when GFRP layer is incorporated on the outer side of the hybrid composite. The investigation utilizes images from testing to elucidate damage modes, including fiber and matrix cracking in the composite facesheet, as well as core shearing and debonding in the Polyvinyl Chloride (PVC) foam core. Residual flexural properties are notably influenced by stacking sequence, facesheet compressive properties, pre-existing impact damage and temperature conditions. Analytical predictions, validated experimentally, highlight the effect of stacking sequence, low temperature, and impact energy on flexural collapse modes, with competing failure modes such as indentation and core shear. Collapse maps indicate that room temperature specimens predominantly collapse through indentation, while diverse collapse mechanisms emerge due to facesheet thickness, rigidity, and degraded tensile strength. The study aims to provide fundamental insights for future composite designs tailored for Arctic applications.

Punching shear behavior for flat slabs with CFRP and openings

This study is devoted to investigate the flexural behavior of geopolymer flat slab that have transverse web openings with CFRP. The shear reinforcement is considered one of the important solutions to increase the resistance of the slabs to the failure of the punching shear and it is also possible through the use of these collars to provide service openings next to the columns. Three molds made of wood were prepared to examine 15 samples of geopolymer concrete under concentrated conditions, Dimensions of section are of total (70*70*7 cm) and Dimensions of column (15*15*15 cm). Three groups of models comprise the models for this research: the first group looks at the impact of the column's location; the second group looks at the impact of an opening next to the column or not; and the third group looks at the impact of CFRP. The findings demonstrated that the presence of transverse web openings affects the general flexural behavior of flat slab geopolymer reinforced concrete as a result of the reduction of concrete within the geopolymer concrete section. CFRP specimens demonstrated superior due to the inherent mechanical properties of the material. Among the various repairing procedures used, the full wrapping technique yielded the best results after the repairs.

Flexural performance of RC beams using hybrid anchored ​CFRP sheets with bond defects

Hybrid anchorage technique can effectively prevent end debonding and impede intermediate debonding of CFRP sheet in strengthened reinforced concrete (RC) beams. However, its effectiveness in the presence of bond defects at the CFRP-concrete interface is unclear. Therefore, this study conducted four-point bending tests on CFRP-strengthened RC beams, considering two factors: bond defects (with and without) and strengthening methods (externally bonded and hybrid anchorage). The results showed that bond defects can lead to premature intermediate debonding of the CFRP sheet, resulting in a 22.49% decrease in debonding load due to local stress concentration around them. Owing to the effectiveness of the hybrid anchorage method, the propagation of the intermediate debonding is significantly impeded, leading to a 4.32% and 21.61% higher in ultimate load and deflection, respectively. This is because the hybrid anchorage can control the distribution of local cracks and improve the overall stress distribution of CFRP. A finite element analysis was performed and compared against the experimental results which shows good agreement. Then, parametric analyses were conducted to further analyze the flexural behavior of the strengthened beams with bond defects. Finally, an analytical model was proposed to predict the flexural capacity of the hybrid strengthened beams with bond defects.

Experimental study on the flexural behavior of reinforced concrete beam strengthened with novel prefabricated HSSM-UHPC thin plate

Ultra-high performance concrete (UHPC) has been used to strengthen reinforced concrete (RC) structures recently. Although UHPC has high compressive strength, the tensile strength is still low and, the high curing condition on site requirements of UHPC may hinder the further application in complex condition. In this study, a novel prefabricated UHPC thin plate, which is reinforced with high-strength steel wire strand meshes (HSSM), is proposed for rapidly strengthening RC beams. In order to understand the flexural performance of RC beams strengthened with the prefabricated HSSM-UHPC thin plate, four-point bending tests were conducted on three beams including one unstrengthened RC control beam (CB), one cast-in-place HSSM-UHPC strengthened beam (SUB) and one prefabricated HSSM-UHPC strengthened beam (PSUB). The failure modes of the beams were investigated and, the crack development process of the test beams was detailly observed by digital image correlation (DIC). Experiment results showed that compared with CB, the cracking, peak load of SUB and PSUB increased by 25.30%, 28.5% and 19.8%, 26.4%, respectively. However, the deflection ductility of the strengthened beams slightly decreased. Finally, calculation model and theoretical equation for predicting the cracking as well as peak flexural capacity of HSSM-UHPC plate strengthened beams were proposed. Comparison between theoretical and test results showed that the proposed model can accurately predict the cracking and peak capacity of the strengthened beams, and can be used for strengthening design.

Trio/hybrid fiber effect on the geopolymer reinforced concrete for flexural and shear behavior

AbstractGeopolymer concrete (GC) is an innovative and sustainable type of composite resulting from the chemical reaction between waste materials containing and alkaline activators. The researchers have been focused to reduction of the greenhouse‐gas release, especially during the production of cement. Although numerous studies have been conducted on alkali‐activated cement or GC at the material level, there is limited research in the literature on the structural performance of reinforced GC members. The aim of this study is to investigate the effect of fiber combination on the shear and flexural performance of RC beams with maximum and minimum reinforcement ratio. To investigate the shear and flexural behavior of GC beam, four‐point and three‐point tests were performed on 12 GC with hybrid fibers, 4 GC with trio fibers, and 2 GC fiber‐free as references beams. The test parameters were the combination of fibers (steel, glass, carbon, and basalt), the longitudinal reinforcement ratio, and loading type. The key test results include the load‐deflection behavior, characteristics of the cracks, the effect of fiber type on the shear and flexural performance, ductility and stiffness properties, microstructure, the strain in the concrete, and the bars and code predictions. The test results showed that as expected, reducing the longitudinal reinforcement ratio decreased the strength, but the decrease in strength was tolerated by using different types of fibers. The use of trio fibers in beams under bending increased the strength capacity, considerably. Finally, the capacity prediction performance of current codes, that is, GB50010, EuroCode‐2, TS500, and ACI318, were also examined, and the calculations resulted that the current code equations had a percentage error of approximately 25% and 82% on average for flexural and shear, respectively, although EuroCode‐2 equations performed slightly better.

Flexural behavior of RC beams strengthened with BFRP bars and CFRP U-jackets: Experimental and numerical analysis

The strengthening of concrete structures is an inevitable requirement throughout their service life. This study proposed a hybrid strengthening method of combining near-surface mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars and carbon fiber-reinforced polymer (CFRP) end anchors. To verify the proposed method, four-point bending test and corresponding numerical analysis were implemented on four reinforced concrete (RC) beams. One beam was the reference beam, while the other three were strengthened with NSM BFRP bars with or without CFRP end anchors. After validating the numerical model, it was employed to systematically investigate the impact of hybridization strengthening details on the flexural performance of RC beams. The results showed that the bearing capacity of the NSM strengthened specimens increased by more than 64 % compared to the reference beam. The addition of CFRP U-jacket end anchors significantly enhanced beam ductility. Regarding failure mode, the reference beam, BFRP strengthened beam, and the BFRP and CFRP hybrid strengthening beam were controlled by the concrete crushing, concrete cover separation, and concrete cover separation (CCS) along with CFRP-jacket rupture, respectively. Proposed numerical models by considering the effects of interfacial normal stress and shear stress on the debonding behavior of epoxy resin and concrete, which could predict theCCS of the NSM strengthened beam, and results compared between the numerical analysis and experiments verified the accuracy of the model with the errors around 2 %. Further investigations using numerical models demonstrated that the ultimate strain of BFRP bars in the presence of CFRP U-jacket is higher than that without CFRP U-jacket. It confirmed the contribution of CFRP U-jacket to improve the flexural strength of the NSM strengthened beams, while also facilitating the utilization of the tensile strength of the BFRP bars. In summary, both experimental and analytical evaluations confirm the effectiveness of the proposed strengthening technique.

Experimental research on the flexural behavior of Basalt fiber‐reinforced polymer (BFRP) and steel bars hybrid reinforced concrete beams

Experimental research on the flexural behavior of Basalt fiber‐reinforced polymer (<scp>BFRP)</scp> and steel bars hybrid reinforced concrete beams

Evaluation of mechanical properties of natural fiber based polymer composite

Natural fiber based polymer composites are eco-friendly alternatives to synthetic materials, with greater mechanical properties, biodegradability, availability, ease of access, and affordability. Jute fiber is widely recognized as one of the most important and beneficial natural fibers due to its strength, durability, and biodegradability. In this study, the jute composite is designed and fabricated using a 5-layer jute and epoxy resin, utilizing the manual hand lay-up technique. The combination of 52.5 % jute and 47.5 % of epoxy resin and harder is found optimized to achieve the goals of improving the tensile strength and flexural strength, reducing the cost of epoxy resin, and promoting eco-friendliness and sustainability. Tensile testing was performed on a universal testing machine, while flexural testing was done with a three-point bending test. Experimentally, the composites reinforced with jute and epoxy resin were capable of achieving the required levels of tensile strength (42.91 MPa) and bending strength (69.30 MPa). To validate and visualize specimens, numerical analysis was performed on the ABAQUS simulation software. The numerical simulation utilized ASTM D3039 and ASTM D7264 as the specified requirements for tensile and flexural behavior. For validation, these tensile and flexural test results were then numerically analyzed and compared to the experimental data. Finally, composite design, fabrication, and optimization can improve mechanical properties, reduce composite weight, lower resin cost, and increase sustainability. The proposed design and composition can be implemented to achieve lightweight properties in various applications, such as car components, door handle sheets, bicycle seat backs, and luggage covers.

Comparative analysis of flexural strength prediction in SFRC using frequentist, Bayesian, and Machine Learning approaches

Steel fiber reinforcement significantly enhances the flexural strength of concrete, which is vital for structural integrity. Annex L of the new Eurocode 2 classifies steel fiber-reinforced concrete by its flexural performance, aiding engineers in designing resilient structures. This study investigates the flexural behavior of steel fiber-reinforced concrete (SFRC) using three data-driven methodologies: Frequentist Inference (FI), Bayesian Inference (BI), and Machine Learning (ML). A comprehensive database was constructed from three-point bending tests on SFRC specimens, encompassing various compressive strengths, fiber quantities, and geometric parameters, to identify key factors influencing material properties.The findings indicate that all three methodologies yield comparable predictive capabilities for flexural responses in SFRC. Notably, FI models emphasize the importance of compressive strength and fiber volume fraction, along with fiber properties such as non-dimensional length and tensile strength. BI models enhance predictive stability by integrating prior knowledge and quantifying uncertainty, demonstrating their advantage, particularly in data-scarce situations. Additionally, ML analysis reveals that linear regression (LR) models can achieve accuracy similar to or greater than that of more complex models. This research provides novel insights into the application of BI and ML in concrete technology, emphasizing their potential to enhance predictive modeling. Additionally, it offers practical guidelines for optimizing SFRC design through a case study that compares residual flexural strengths obtained via Bayesian analysis, classifying the material in accordance with Annex L of the new Eurocode 2.