Load-deflection Relationship Research Articles

FLEXURAL PERFORMANCE OF REINFORCED CONCRETE BEAMS RETROFITTED USING FERROCEMENT WIRE MESH

Introduction: Ferrocement is a low-cost material that can be utilized as a replacement for expensive fiber-reinforced polymer (FRP), which is generally used for retrofitting structural and non-structural reinforced concrete members. The objective of this paper is to investigate the effectiveness of wire mesh in the retrofitting of flexural members such as reinforced concrete beams. It also investigated the flexural capacity of the beams, which are reinforced with wire mesh as a partial or complete replacement of regular rebar. The orientations and various forms of the wire mesh within the beam section are taken into consideration. The finite element method is used to model and analyze the beams. The structural performance of the studied beams, including the load-deflection relationship, first cracked and ultimate cracked loads, crack patterns, and flexural stress, were evaluated using the finite element method. The finite element model of the beam which is reinforced with wire mesh has been verified with experimental results. The results show that beams retrofitted with ferrocement or beams in which rebar is replaced by wire mesh have superior flexural performance and low crack depth. The beams retrofitted with wire mesh have a high ultimate load-carrying capacity and ductility. The confinement of three-sided wire mesh improves the flexural performance of the beam. It is observed that flexural performance remains the same when the length of the wire mesh exceeds half of the span length.

Implementation of Modified Compression Field Theory to Simulate the Behavior of Fiber-Reinforced Polymer Shear-Strengthened Reinforced Concrete Beams under Monotonic Loading

The numerical modeling of structures is a widely preferable approach to investigate the structural behavior of RC beams since it delivers inexpensive predictions for confirming the required goals concurrently with reducing casting, testing time, and effort. Shear-strengthening of reinforced concrete (RC) beams using externally bonded (EB) fiber-reinforced polymers (FRPs) has attracted much attention due to the fact that the FRP strengthening technique has the ability to alter the distribution of stresses between the structural elements and increase the load-carrying capacity. A significant number of experimental studies have been carried out to test the monotonic behavior of FRP shear-strengthened RC beams. Conversely, limited numerical research has been performed to investigate such performance. The VecTor2 software is developed based on the modified compression field theory (MCFT) and is directed to examine the monotonic behavior of retrofitted specimens using fiber-reinforced polymer (FRP) composites. To the authors’ knowledge, the behavior of FRP shear-strengthened beams has not been explored in the literature using the MCFT modeling approach. The main objective of this study is to detect the software’s capability of predicting the experimental outcomes of FRP shear-strengthened RC beams. This research study is carried out in two stages. Initially, the numerical study involves the development of an accurate finite element model to simulate the control specimens. The quality of this model is assessed by comparing the numerical results with the experimental outcomes. In the second phase of the numerical study, the control beam model is modified to accommodate the presence of external FRP composites. The accuracy of this model is again measured by comparing its predictions with the experimental measurements. The goal of these phases is to ensure that the numerical model captures the actual behavior of the tested beams. Additionally, two distinctive modeling approaches are investigated to represent the behavior of FRP composites. The accuracy of the numerical models is verified through comparisons of numerical predictions to experimental results in terms of ultimate loading capacity, load–deflection relationships, and failure modes. It can be stated that the validated numerical model provides alternate means for evaluating the monotonic behavior of both strengthened and non-strengthened RC beams. The predicted results compare very well with the test results of the control specimens when discrete truss elements are employed for the FRP composites. Furthermore, the numerical model provides useful information on the crack patterns and failure modes.

Experimental and Numerical Investigation of the Behavior of Steel Beams Strengthened by Bolted Hybrid FRP Composites

The strengthening of steel beams using hybrid fiber-reinforced polymers (HFRPs) has gained enormous attention over the last decades. Few researchers have investigated the effectiveness of the fastening techniques without a bonding agent to overcome the undesirable debonding failure of the bonded FRP–steel system. This paper reports the outcomes of experimental and numerical investigations conducted on steel beams strengthened by HFRP using steel bolts. Twenty-two steel beams were tested in four-point loading to investigate the effect of the HFRP length and the bolt arrangement on the flexural behavior of the strengthened systems. The observed failure modes, load-deflection relations, deflection profiles, and strain measurements were also studied. The tested beams showed a ductile behavior, with 15.1 and 22.2% enhancements in the yield and ultimate flexural capacities, respectively. Simplified empirical equations were developed to predict the ultimate load of the bolted HFRP–steel beams. ANSYS software was used to model the beams’ behavior and investigate the effects of the HFRP thickness, bolt spacing, steel grade, loading scheme, and beam length on the effectiveness of the adopted fastening technique. Increasing the HFRP length enhanced the utilization of HFRPs as well as the beam’s ductility, with a reduction of up to 51.2% in the mid-span deflection. Moreover, the strain compatibility of the HFRP–steel beams was improved with an 87.2% reduction in the interfacial slippage. The bolt arrangement showed an insignificant effect on the overall performance of the beams. The numerical results verified the effectiveness of the fastening technique in enhancing the flexural performance of the steel beams, with gains of up to 16.7% and 34.5% in the yield and ultimate load-carrying capacities, respectively.

Effects of structural size and corner radius on eccentric failure of rectangular CFRP-wrapped RC columns: Meso-scale modellings

The strengthening and retrofitting technique with fiber-reinforced polymer (FRP) composites on reinforced concrete (RC) columns has been widely popular. Compared with concentric compression behaviors of rectangular FRP-confined concrete columns, there are only limited investigations on their eccentric behaviors. Additionally, the applicability of existing design codes obtained from tested small-size columns in calculating load capacity of large-size columns has not been reasonably explained. In view of this, this paper developed a meso-scale numerical analysis method using a random aggregate model based on consideration of concrete heterogeneity. A series of rectangular carbon FRP (CFRP)-confined RC columns having different cross-sectional heights were modelled to investigate the influences of corner radius and size effect on their eccentric compression behaviors. Simulated results showed that there was a transformation of failure mode from brittle compression failure to ductile tensile failure with the increasing load eccentricity. An identical globally failure mode for rectangular columns having different cross-sectional heights was observed whereas crack widths became larger obviously with the increasing cross-sectional height. Regarding the axial load versus mid-height deflection relationship, the corner radius had a significant influence on maximum axial load and softening stage, especially at smaller load eccentricities. One can see that from nominal interaction diagrams, small-eccentrically-loaded columns exhibited more obvious size effect than large-eccentrically-loaded columns. The safety factor of load capacity decreased with the increasing cross-sectional height compared with existing design codes of ACI 440.2R-17 and GB 50608, illustrating that design codes appear to be not conservative for large-size specimens. Taking the influence of size effect into account, the design equations suggested by ACI 440.2R-17 were modified in this study, and the rationality of this correction methodology was verified against simulated data and results of tested large-size rectangular columns.

Postbuckling behavior of functionally graded porous toroidal shell segments with surrounding elastic media subjected to combined mechanical loads

AbstractBuckling and postbuckling behavior of toroidal shell segment (TSS) made of functionally graded porous material (FGPM), exposed to a thermal environment, surrounded by an elastic medium and subjected to combined action of axial compression and lateral pressure are investigated in this paper. Material constituents are varied across the thickness according to power‐law functions, while porosities are distributed in the TSS in the form of cosine functions of thickness variable. Governing equations in terms of deflection and stress function are derived based on classical shell theory taking into account geometrical nonlinearity and interactive pressure from surrounding elastic media. Multi‐term analytical solutions are assumed for simply supported TSSs and Galerkin method is used to obtain nonlinear load–deflection relations from which buckling loads can be derived. Parametric studies are carried out to access the influences of material and geometry properties, porosity coefficient and distributions, preexisting loading conditions, thermal environments and surrounding elastic media on the buckling resistance and postbuckling load carrying capabilities of FGPM TSSs.

Experimental Study on the Bending Resistance of Hollow Slab Beams Strengthened with Prestressed Steel Strand Polyurethane Cement Composite

In order to explore the toughening performance and failure mechanism of hollow slab beams strengthened with prestressed steel strand polyurethane cement composite, three test beams (L1–L3) were strengthened and one test beam (L0) was used as a comparison. The influence of different tensile stresses of steel strand and fiber additions on the flexural bearing capacity of the hollow slab beams, was studied. The cracking characteristics, load deflection relationship, ductility and strain of each test beam were compared and analyzed. The test results showed that the toughened material was well bonded to the hollow slab beam and the steel strand, which effectively inhibited the development of cracks in the test beams. The flexural bearing capacity of the strengthened test beams was significantly improved. The use of prestressed steel strand polyurethane cement composite material effectively improved the flexural bearing capacity of the test beams, and this reinforcement process can be further extended to engineering applications.

Experimental investigation on flexural performance of polyester polyurethane concrete steel bridge deck composite structure

In this study, the results of an experimental investigation on the flexural behavior of composite specimens are presented, with the objective to simulate the performance of Polyester Polyurethane Concrete (PPUC)-steel bridge deck composite structures with different pavement layer thicknesses. Four groups of composite specimens with paving layer thicknesses of 20, 30, 40, and 50 mm are prepared, which are subjected to four-point bending tests with positive and negative moment loading, to obtain the failure mode, crack distribution, load-deflection relationship, and load-strain relationship. The test results indicate that under the action of a positive bending moment the specimens demonstrate two different failure modes, i.e. compressive failure and shear compression failure, whereas under the action of negative bending moment failure due to tensile failure occurs. Both the flexural stiffness and ultimate load-bearing capacity of the specimens increase with the increment of the paving layer thickness, in which the flexural stiffness under a positive bending moment loading state is higher than that under a negative bending moment loading state. Moreover, the specimens with lower stiffness can withstand a greater vertical displacement than those with higher stiffness. The strain of both PPUC and steel plates decreases with the increment of paving thickness, and this strain decrease is greater under the action of a negative bending moment compared to the strain under the action of a positive bending moment. Finally, the flexural performance of PPUC-steel plate composite structure is successfully simulated based on the cohesive zone model (CZM), which is verified by the test results. In addition, the parametric analysis, including the thickness of steel plate, the thickness of PPUC layer and the PPUC compressive strength, is conducted to reveal the flexural performance of PPUC-steel plate composite structure. This work can be used as a resource for the initial design of a PPUC-steel bridge deck.

Experimental Research on Fatigue Performance of Reinforced Concrete T-Shaped Beams under Corrosion-Fatigue Coupling Action.

Highway bridges in coastal areas are seriously affected by the marine environment, while most of the existing test methods for bridge-reinforced concrete beams considering both corrosion and fatigue factors are carried out in an alternating manner, which cannot reflect the actual service conditions of the bridge structure. This paper focuses on an experimental study of the coupled influence of reinforcement corrosion and fatigue loading in reinforced concrete T-shaped beams. A novel loading test device that can realize the corrosion-fatigue coupling effect is designed, and then six reinforced concrete T-shaped beams are fabricated and tested. For the corrosion-fatigue coupling test beams, the variation law of beam cracks, failure modes, steel strain development law, load-deflection relationship, and fatigue life are analyzed and compared with that of the simple fatigue test beams. The test results show that the cracks of the test beam develop continuously with the fatigue loading times under the corrosion-fatigue coupling environment. The fatigue failure modes are all brittle fractures of the main steel bars, which present the shape of uneven oblique section tearing. The new testing device and approach can provide direct insights into the interaction of reinforcement corrosion and cyclic loading on the fatigue behavior of T-shaped RC beams, which can be further used to understand the long-term performance of bridge structures under complex marine environments.

Flexural behaviour of RC one-way slabs reinforced using PAN based carbon textile grid

Textile reinforced mortar (TRM) is mainly used for strengthening of existing structural members whereas, on the other hand Textile reinforced concrete (TRC) is a technology implied in construction of new members for enhancing the structural behaviour. Application of TRM on the tension zone of the reinforced concrete (RC) slabs to improve the flexural capacity has been investigated by many researchers in the past. However, the effectiveness of textile fabrics, used as internal reinforcement in the RC slab (TRC technology) needs to be studied. The paper, therefore, presents the experimental research conducted on three one-way RC slabs specimens reinforced using textile grid. An innovative Polyacrylonitrile (PAN) based carbon textile grid was used as internal reinforcement in combination with the steel bars. Two textile-reinforced RC slabs having one and two layers of textile grid (SRC + 1T and SRC + 2T respectively) and one reference slab (SRC) was fabricated to investigate the flexural behaviour under a four-point loading system. The internal textile reinforcement layer(s) was confirmed to be effective, particularly in terms of improving the cracking load, ductility, deformability and toughness. The material ductility of SRC + 1T and SRC + 2T slabs were increased by 41% and 44% compared to SRC slab. Also, the deformability ratio was found to be greater than 4, indicating a ductile failure of textile-reinforced slabs. Further, based on the load-deflection relation, moment-curvature curves were derived. Moreover, these curves were also developed using Eurocode two prediction model. The experimental and the predicted moment-curvature curves showed good agreement.

Torsional instability of functionally graded porous toroidal shell segments including elastic edge constraints and elevated temperature

This article aims to analyze the nonlinear instability of toroidal shell segment (TSS) made of functionally graded porous material (FGPM), exposed to elevated temperature and subjected to uniform torsion. The volume fraction of two material constituents is varied through the shell thickness according to a power-law function, while porous distribution into FGPM is modeled in forms of cosine functions. Governing equations in terms of deflection and stress function are established within the framework of classical shell theory incorporating geometrical nonlinearity. Two edges of the TSS are assumed to be simply supported and elastically restrained. Multi-term analytical solutions are assumed to satisfy boundary conditions and Galerkin method is applied to derive closed-form expressions of nonlinear load–deflection relations and buckling loads. Parametric studies are carried out to analyze the separate and combined influences of material and geometry properties, porous coefficient and distributions, degree of edge constraint and elevated temperature on the buckling resistance and postbuckling strength of torsionally loaded FGPM TSSs.

Study on the load-carrying capacity of an innovative cold-formed steel floor system

To account for the higher structural ductility requirement and higher load-bearing capacity and stability requirements of floor-to-wall connections of mid-rise cold-formed steel (CFS) structures, an innovative CFS floor system with gridded beams and filler blocks (BB-based CFS floor system, where BB stands for “beams” and “blocks”, respectively) was first proposed. Then, experimental and refined numerical simulation studies were performed to investigate the flexural behaviour of the floor system. Afterwards, a simplified calculation method of the load-carrying capacity of the floor system was deduced based on its mechanical mechanism. The results show that (1) the deformation of the floorboard-to-beam screw connections and the relative buckling of the compression beam flange and adjacent web are the primary reasons for the nonlinear load-deflection relationship and bending failure of the floor system. (2) Compared with the existing CFS composite floor systems, the combination effect of each component in the BB-based CFS floor system prevented the beams from unstable failure after losing the restraint of floorboards, thereby effectively improving the load-carrying capacity and nondeformability of the floor system. (3) After decomposing the BB-based CFS floor system into composite floor beams, the load-carrying capacities of the floor system can be determined simply according to the cumulative flexural bearing capacities of these composite floor beams based on plasticity theory, the relative errors between the deduced load-carrying capacities and the test results and simulated results of different BB-based CFS floor systems are within 10%, and the calculated results are relatively safe.

Performance of hybrid glass/steel fibre self-compacting concrete beams under static flexural loading

In this paper, it is proposed to study the static flexural performance of hybrid (glass and steel) fiber reinforced M30 grade self-compacting concrete (SCC) beams made with glass fiber reinforcement polymer (GFRP) re-bars. Nan Su mix design approach is adopted to develop the M30 grade plain SCC (PSCC) mixes. Glass fibre SCC (GFRSCC), steel fibre SCC (GFRSCC) and hybrid fibre SCC (HFRSCC) mixes are prepared using the optimum dosages of glass (0.05%) and steel fibres (1%) by volume fraction. HFRSCC reinforced beams of size 1200 *200*150 mm will be casted with steel and GFRB rebars and tested to study the flexural properties such as ultimate flexural strength, load at first crack, deflection at the center, crack width and crack patterns. For the above fibred beams, load-deflection relations will be established. The HFRSCC beam made with GFRP rebars have the load carrying capacity 37.03% more than HFRSCC beam made with steel rebars. The deflection for the HFRSCC beam made with GFRP rebars is 61.52% more than beam made with steel rebar HFRSCC beam made with GFRP rebars increases the load at first crack, ultimate flexural strength, and deflection at the centre at failure and the crack width for same HFRSCC beam made with steel rebars

Experimental Studies on the Fire Flame Behavior of Reinforced Concrete Beams with Construction Joints

This study was experimentally investigated experimentally, investigating the effect of such mechanical properties and deflection behavior on the performance of reinforced concrete beams with construction joints exposed to fire flame. These beams were built using a slanted connection at a 45° angle in the middle of the beams. Four beams were for a wide temperature range (25–800°C) for the fire flames used on the concrete beams. Two temperature levels (600°C and 800°C) were chosen, with (1 and 2) hrs. period time, respectively. One beam wasn't burnt (Reference specimen). When put through a fire, flexural strength drastically decreased. The experimental program's results suggested the worst effect on construction joint beam for temperature 800°C with 2 hrs. period time because that heating reduces the bonds between two surfaces in the joint and makes like slip and disconnect between the joint after exposure to load. After 1 and 2 hours in a fire at 600°C, the residual flexural strength was 85% and 72%, respectively, whereas, after 1 and 2 hours in a fire at 800°C, it was 41% and 28%, this is showed that the stiffness of beam its decrease when exposed to fire flam with raising temperature and time and increase the deformation by cracks that appear on the beams. It was noticed that the load-deflection relation to beams exposed to fire flame is flat, representing softer load-deflection behavior than that of the control beam.

Experimental and Numerical Investigation of Aluminum Beams: Flexural Behavior Section Shape Effect

Advanced technology and other aspects of life aim to use the available and efficient materials. Due to their high strength-to-weight ratio and durability, aluminum alloys are used in a variety of structural engineering applications. This paper describes the experimental and numerical flexural behavior investigation of the aluminum beams. The main variables considered in the study are related to section shape, which are the shape configuration, depth, and thickness of the aluminum section. The finite element three dimensional models are used to analyze the tested beams in order to check the ability of the models to predict the overall behavior and to obtain more information about the stresses and strains that developed. The results show that the larger the value of the section shape factor, the fiber is still in the elastic range, and the smaller the plastic deformation of the beam. And the web plates slenderness ratio has a significant influence on the load-deflection relationship because of local deformation as well as the plastic deformation of box beams is relatively smaller than that of the I-section beam. The constraint of the flange for box beams is greater than that for I-section beams. Besides, the adopted nonlinear numerical modeling gives acceptable agreement with the experimental results besides the load-deflection responses, the ultimate strength convergence ratios varied between 1.1-0.93.

Flexural performance of steel-reinforced geopolymer concrete one-way slabs: Experimental and numerical investigations

This paper investigated the out-of-plane flexural performances of ambient-cured steel-reinforced slag and fly ash-based geopolymer concrete one-way slabs, in which the activator was the blend of NaOH and sodium silicate solutions (SiO2/Na2O = 3.1–3.3). Twelve specimens were prepared and tested, which included six OPC concrete specimens. The test parameters were concrete type (i.e., geopolymer and ordinary Portland cement (OPC) concrete), concrete compressive strength (i.e., 30 MPa, 40 MPa, and 50 MPa) and longitudinal tensile reinforcement ratio (i.e., 0.82 % and 1.20 %). The failure modes, crack patterns, load–deflection relationships and load–strain relationships of all specimens were carefully studied and reported. Further, a two dimensional (2D) finite element (FE) analysis was conducted to validate the test results. The results of the study indicated that: (1) the geopolymer concrete specimens presented lesser crack width and crack spacing owing to the improved bond between rebar and geopolymer concrete; (2) the cracking load and initial stiffness of geopolymer concrete specimens were slightly lower than that of OPC concrete counterparts; (3) the current Codes of Practice GB50010-2010 and ACI 318-19 provided reasonable predictions of the cracking load and flexural load capacity of the steel-reinforced geopolymer concrete specimens; (4) the developed FE model provided a good prediction of the flexural performance of the tested slabs, and could be used for further parametric investigation.

Thermal nonlinear stability of functionally graded porous material nearly cylindrical shells with surrounding elastic media and tangentially restrained edges

This paper aims to investigate the influences of surrounding elastic media and tangential edge constraints on the buckling and postbucking behaviors of nearly cylindrical shell (NCS) made of functionally graded porous material (FGPM) and subjected to uniform temperature rise. Three different types of porosity distributions are considered and assumed to be in forms of cosine functions of thickness variable. The volume fractions of material constituents are assumed to vary through the shell thickness according to power‐law functions. Temperature‐dependent material properties and elasticity of tangential constraints of boundary edges are included. Governing equations are established within the framework of classical shell theory taking into account von Kármán–Donnell nonlinearity and interactive pressure from surrounding elastic media. Multiterm analytical solutions for simply supported NCSs are assumed and Galerkin procedure is utilized to derive expressions of buckling load and nonlinear load–deflection relation. An iteration process is adopted to determine critical thermal loads and postbuckling temperature–deflection paths. Numerous parametric studies are carried out to assess many different effects on thermal buckling resistance and postbuckling load carrying capabilities. The study reveals that porosity and tangential edge constraint have beneficial and deteriorative influences on the thermal stability of the NCSs, respectively. Furthermore, the obtained results demonstrate that surrounding elastic media have significantly beneficial influences on the thermal nonlinear stability of FGPM NCSs.

Flexural Behavior of RC Beams with an Abrupt Change in Depth: Experimental Work

The most crucial components in the case of roofs with two levels or a variable floor height are variable depth beams. In order to investigate the flexural behavior of reinforced concrete (RC) beams with varying depths under static loads, experimental research was conducted. Under the four-point bending flexural test, two reference beams with constant depth, six dapped beams at the soffit, and four dapped beams at the top were tested. For all beams with a 150 mm depth, a 100 mm increase in depth occurred at the middle span of the beams. The primary characteristics included the impact of increasing depth, the impact of stirrups’ absence and their various ratios, and the characteristics of the longitudinal bars at the locations of sudden depth changes in either the top or bottom bars. Both the cracks’ progression and the load-deflection relationship along the beam’s length were observed. The ultimate carrying load (Pu) was reduced by 23.56% and 27.35% as a result of the 100 mm increase in the half-span of the beam over the constant depth in case of changes at the top and soffit, respectively. The Pu was increased by a ratio ranging from 20.9% to 31.35% for the bottom dapped beams and by a ratio of 29.79% for the top dapped beams due to the various stirrup ratios in the dapped area. The ductility was significantly impacted by the elevated stirrup ratios in the dapped area. The predicted results and the experimental results matched when the Pu of the tested beams was evaluated using the strut and tie model.

Experimental tests and analytical model for reinforced polyvinyl alcohol‐engineered cementitious composite beams in bending

AbstractPolyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship.

Fatigue response of RC beam strengthened by BFRP laminate

Strengthening RC structures become more essential due to its deterioration, updating in new design codes, lack of quality control, and changes in the use of the structure. The technique of external bonding fiber reinforced polymer is recognized as a convenient method for repairing existing reinforced concrete structures and provides immediate shelter rather than replacement of the whole existing structure. Basalt Fiber Reinforced Polymer gaining more demand in recent research due to its eco-friendly properties. In this regard, this research investigates the efficaciousness of externally bonded Basalt Fiber Reinforced Polymer (BFRP) laminates in the reinforced concrete beam under repeated load. BFRP is externally bonded at the soffit of reinforced concrete (RC) beams to enhance its fatigue resistance. The load-deflection relationship, stiffness, crack pattern, and energy dissipation capacity of the BFRP-reinforced concrete beams are experimentally investigated and validated with the ANSYS simulated results. The experimental results exhibits that the BFRP reinforced concrete beams enhances the fatigue response, load carrying capacity and prevention of premature failure. The numerical results are validated with the experimental results which are found to be correlated with negligible deviation. Also, both investigations reveal the failure mode of RC beams, which helps fatigue life prediction in its application.

Stress–strain relationship of ductile materials and flexural behavior of ductile over-reinforced concrete beams

This paper aimed to investigate the effect of using ductile materials in the compression zone on the flexural performance of over-reinforced concrete beams. In order to avoid brittle compression failure, partial replacement of concrete with ductile materials layer in the compression zone was used. Four over-reinforced concrete beams of size 120 × 180 × 1,300 mm were cast and tested under three-point loading conditions. The steel fibers reinforced concrete (SFRC), slurry infiltrated fiber concrete (SIFCON), and ultra-high performance fiber reinforced concrete (UHPFRC) were used as ductile materials. The flexural capacity of the beams, failure modes, crack patterns, load-deflection relationships, ductility index, and toughness were investigated. The results showed that using ductile materials in the compression zone is an effective technique to increase the ultimate load, ductility, and toughness by up to 52.46, 84.78 and 279.93%, respectively, compared to the reference beam. In addition, the failure mode changed from brittle to ductile failure. Noting that the use of SFRC layer enhanced the ductility of over-reinforced concrete beams more than using UHPFRC and SIFCON layers. Also, one of the main advantages of this technique is led to increase the tensile reinforcement ratio up to 8.548% without needing the compressive reinforcement. Thus, ductile composite beams with a high flexural capacity were generated using an economical amount of ductile materials.