Tensile Reinforcement Research Articles

Flexural Performance of Reinforced Concrete Beams Strengthened with a Novel High-Strength and High-Toughness Epoxy Mortar Thin Layer

The flexural performance of RC beams strengthened with a novel high-strength and high-toughness epoxy mortar thin layer was investigated through four-point flexural tests on two contrast beams and two strengthened beams. The effects of this strengthening method on the failure modes, crack distribution, load–deflection curves, and bearing capacity of the RC beams with two reinforcement ratios were studied. The experimental results revealed that the contrast beams exhibited the typical bending failure modes where the failure mode of the reinforced beam is the yielding of the tensile reinforcement of the original beam and then fracture damage of the new epoxy mortar-reinforced thin layer. No debonding phenomenon was observed between the reinforced thin layer and the original concrete, and no visible cracks appeared before the tensile failure occurred in the thin layer. The cracks in the reinforced beams developed slowly, increased in number, and decreased significantly in width and spacing. The stiffness of the strengthened beam increased significantly, while its deformation ductility coefficient noticeably decreased. Compared to the corresponding contrast beams, the cracking load for strengthened beams A1 and B1 increased by 14% and 23%, respectively; the yield load increased by 32% and 40%, respectively; and the peak load increased by 18% and 17%, respectively. Finally, a calculation method for the flexural bearing capacity of RC beams strengthened with the novel epoxy mortar thin layer based on the flat section assumption was proposed. The calculated values showed a good agreement with the experimental values (with errors at −11.73% and 4.14%, respectively), providing a valuable reference for further research and application related to this kind of reinforcement method.

Sulphide stress corrosion in SAE 1070 steel wire used in the tensile armour of flexible pipelines: Effect of induced superficial defects

This research aims to investigate and quantify potential damage resulting from induced superficial defects on the surface of wires use on tensile armor of flexible pipes. Different values of kt factors and H2S concentration in aggressive gas mixtures with CO2, were analysed to determine the operational conditions that do not result in rupture of the tensile reinforcement during service, under the conditions studied. The tests were based on NACE TM0316 standard, using a 4-point bend test. Two superficial notches were created, which generated known stress concentration factor Kt values of 1.5 and 2.0, and three gaseous concentrations (220, 700, and 1100 ppm of H2S in CO2) were used. After bending tests, the samples were evaluated by metallographic and fractographic analysis, weight loss and liquid penetrant inspection. The results were then analysed using analysis of variance (ANOVA). Only the samples exposed to 220 ppm of H2S in CO2 did not rupture at both Kt values. However, for the Kt value of 2.0, cracks were observed in the longitudinal direction of the wires, originating from the machined notch. Additionally, the samples exposed to 700 ppm and 1100 ppm of H2S had a significantly higher damage score (approximately 15x) than the samples exposed to 220 ppm, regardless of the Kt value.

Moment redistribution in continuous reinforced concrete beams: Experimental study and analytical investigation

This paper presents the results of experimental and analytical studies carried out on continuous reinforced concrete (RC) beams to determine moment redistribution in statically indeterminate RC structures. For this purpose, continuous RC beams were produced with varying tensile reinforcement ratio at the intermediate support, which are shown as the parameters that affect moment redistribution the most in the literature. One of the main goals of this study is to check if the formulations in the design code provisions and in the literature give a safe estimate, and in order to perform this check, a dataset consisting of the experimental results of 141 beams in the literature has been used for validation and the moment redistribution ratios of this dataset have been estimated with all these formulations. The obtained results have been compared using various statistical indices such as the mean value (MV), standard deviation (SD), coefficient of variation (COV), the root mean square error (RMSE), mean absolute percentage error (MAPE). In particular, the formulations in the literature that take into account many parameters affecting the moment redistribution have been found to give better results than the formulations in the design code provisions. The results of this study confirm that elastic moment redistribution, which occurs in the process from the moment when the concrete cracks until the tensile reinforcement yields and constitutes a significant part of the total moment redistribution, is also important. Moreover, the properties of continuous RC beams related to their general behaviors, such as load-displacement relationships, ductility and moment-curvature relationships have been also investigated in detail.

Numerical analysis of the local damage of RC beams under close‐in explosions based on the calibrated Karagozian & Case (K&C) concrete model

AbstractLimited research has been carried out to investigate the local damage features of reinforced concrete (RC) beams under close‐in explosions. To better capture the local damage features of rectangular cross‐sectional RC beams, a numerical study on the RC beams subjected to close‐in explosions based on the calibrated Karagozian & Case (K&C) concrete model was conducted in LSDYNA. First, a systematic calibration of the K&C model for concrete was performed in the single‐element numerical analysis. Calibration of the K&C model consists of parameter determination for the new strength surfaces, modification of the damage function to better feature the tensile behavior of concrete, elimination of the element size effect by introducing an element size factor and determination of the scaled damage factors. The new strength surfaces are verified and determined through both the approximation calculation method and the parameter fitting method. And the damage function was modified by reducing the termination of λ to better characterize the brittleness of concrete and feature the tensile failure. A comparison between the numerical results and the corresponding experimental results demonstrates that the calibrated K&C model and established FEM model of RC beams subjected to close‐in explosions can well characterize the local damage features of RC beams. On this basis, a further parameter analysis on the factors influencing the local damage response of RC beams was conducted by considering reinforcement details (stirrup spacing and longitudinal reinforcement diameter) and charge details (charge mass and aspect ratio). Results show that the close‐in explosions destroyed the concrete corners in the blast surface with shear stress first and the side shear failure of concrete corners weakens the concrete core strength and contributes to the greater loss of concrete core. Rear spalling damage was initially caused by the bond failure between the tensile longitudinal reinforcement and the surrounding concrete. Furthermore, increasing stirrup spacing, tensile longitudinal reinforcement diameter, and charge mass contribute to the increase in local damage sizes.

Effect of Bonding Type on the Failure of Reinforced Concrete Beam Strengthened with In-Situ High Performance Fibre Reinforced Concrete Layer

High performance fibre reinforced concrete (HPFRC) materials with tensile hardening behaviour can effectively be used for strengthening reinforced concrete beams. A perfect bond between the original and the reinforcing layer cannot be formed, the load-bearing capacity and ductility of the strengthened beam can significantly be affected by the interfacial bond strength between the contacting surfaces. In this paper, beam retrofitting with cast in-situ strengthening type is examined. The purpose of this experimental study is to investigate the impact of the different bond types on the load-bearing capacity, ductility, and failure mode of the strengthened beams in the case of cast in-situ strengthening. Twenty-four beam tests were performed with untreated and rough surfaced beams, with or without connecting elements. The effect of the bond type proved to be significant regarding the failure mode in the case of compression side strengthening, stronger bond resulted in higher load bearing capacity and ductility, too. When tensile side reinforcement was investigated no average increment was experienced in the maximal force and ductility due to the stronger bond. Based on the results, it can be concluded that the generally applied analytical models that assume perfect connection may lead to exaggerated results in the case of a compressed side HPC-strengthened beam. Therefore, it is necessary to develop a model that considers the effect of the imperfect bond.

Flexural behavior of reinforced concrete beams strengthened with gradually prestressed near surface mounted carbon fiber-reinforced polymer strips under static and fatigue loading

The near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique, combined with gradually anchored prestressed technique, is utilized to delay the occurrence of concrete cover separation (CCS) and enhance the ductility of reinforced concrete beams. The load-carrying capacity of fully prestressed beams and gradually prestressed beams are investigated under both static and fatigue loading conditions. The study focused on the effect of gradient prestress on flexural behavior of strengthened beams, analyzed the failure mode, characteristic load, ductility, and stress distribution at CFRP-concrete interface under both prestress and load conditions. Results indicate that gradually prestressed beams outperform fully prestressed ones in restraining crack development, delaying yield of tensile reinforcement, improving bearing capacity and avoiding CCS failure. Bearing capacity was significantly increased by up to 35.48%, while ductility was greatly improved by 100.33% with ultimate deflection for gradually prestressed beams compared to fully prestressed ones. The fatigue life of gradually prestressed beams, which experienced a transition from CCS failure mode to fatigue fracture of tensile reinforcement, was significantly extended. Additionally, their ductility at failure was also greatly enhanced, thus confirming the effectiveness of gradually prestressed NSM CFRP strengthening technique.

The investigation and estimation of flexural strength in shear-critically designed RC beams considering the steel fiber content

Despite numerous studies investigating the effectiveness of steel fibers in RC members subjected to various loading conditions, the majority ignored the impact of the interaction between the tensile reinforcement ratio, compressive strength of fibrous concrete, and steel fiber dosage. This paper aimed to inspect and quantify the effects of hooked-end steel fiber dosage on the bending behavior of RC beams considering the interaction arising from various longitudinal reinforcement ratios. For this purpose, an extensive and hybrid investigation involving both experimental and numerical techniques was conducted. In the experimental part, an investigation was carried out to evaluate the contribution of a specific amount of fiber ratio and various aspect ratios to the behavior of large-scale RC beams having a shear-deficient design. Three beams with a 0.5% hooked-end steel fiber ratio and one without fibers but with a minimum amount of stirrups were produced, and three-point bending tests were conducted. All beams having fibers utilized full flexural strength as in the beam with stirrups. Once the experimental studies were completed, the numerical models were then developed and validated with those of experimental three-point bending tests using the non-linear finite element code VecTor2 to establish a basis for the comprehensive parametric study. The parametric study consisted of 33 analyses. Rebar and volumetric fiber ratios were selected to be variables, and the ratios adopted were within the typical range used in structural engineering applications. Based on the regression analysis a linear and a quadratic model were proposed for estimating the yield and peak strength depending on the steel fiber content. Finally, the obtained models were verified using work from the literature and found to be effective in forecasting the strength of shear-deficient RC beams with 0.8%, 1.0%, and 1.2% tensile reinforcement ratios and hooked end steel fibers (0.5 to 1.5%).

Comparative study on flexural performance of ultra‐high performance concrete beams reinforced with steel rebar and steel plate

AbstractTo enhance the mechanical and constructional performance of the ultra‐high performance concrete (UHPC) beams, the steel plate placed at the bottom surface of the UHPC beam is utilized to replace the ordinary steel rebars. In this paper, four 3.2 m UHPC T‐shaped beams with different reinforcement patterns of ordinary steel rebars and external steel plate were fabricated and comparatively tested under flexure loading. Their damage patterns, load versus deflection behavior, flexural capacity, load versus strain behavior, moment versus curvature behavior, stiffness, and crack development were investigated. The flexural experiments indicated that the external steel plate, positioned at the bottom surface of the UHPC members, could resolve the difficulty of installing ordinary steel rebars in slender UHPC components and improve its constructional performance. Compared with the inside steel rebar reinforcement, the employment of the steel plate at the bottom surface of the UHPC beam can effectively increase the distance from the neutral axis to the tensile reinforcement at the serviceability and ultimate states, thereby improving its flexural capacity and stiffness. Additionally, the configuration of the external steel plate was beneficial to reduce the tensile stress level of the tensile reinforcement and limit the opening of UHPC crack width, and thus their crack resistance can be effectively enhanced. Moreover, increasing the thickness of the steel plate or rebar ratio can also significantly improve the flexural capacity, stiffness, and cracking resistance of UHPC beams.

Time-dependent behavior of RC slab-column connections under high sustained loads

Reinforced concrete (RC) flat-plate slab-column connections may be exposed to high sustained stresses under gravity loads far exceeding the typical service-level stresses due to design errors, construction defects, or material deterioration. If the connections fail, then collapse of the structure could occur. Plain concrete can fail when exposed to sustained compressive stress in excess of 75% of its short-term strength. However, very little research has been conducted on the time-dependent strength and stiffness characteristics of RC slab-column connections under high sustained loads. This paper presents the experimental results of eleven aged slab-column connections under sustained concentric and eccentric gravity loading. The specimens were constructed at a 0.47-scale and had slab tensile reinforcement ratios of 0.64% and 1.0% without using shear reinforcement. Three specimens were loaded to failure in a short time, while eight specimens were tested for periods of approximately 45 days under high sustained loads (83% to 98% of their peak capacity). Test results showed that high sustained loads may lead to an eventual failure; however, the level of sustained load needs to be very close (∼95%) to the short-term capacity. Under the sustained loads, the deflection of specimens increased by 18% to 39% of the initial deflections. The deflection and steel strain creep rate approximately followed a logarithmic function, but there was a greater increase in deflection than steel strain. A sharp increase in deflection due to tertiary creep occurred only 2 to 3 min before failure, leaving little warning of the impending failure.

Flexural behaviors of a novel precast hollow UHPC composite beam reinforced with inverted T-shaped steel: Experimental investigation and theoretical analysis

To fully utilize the excellent mechanical properties and durability of ultra-high performance concrete (UHPC) as well as reduce the production cost, a novel UHPC encasing inverted T-steel (PUES) composite beam with hollow section is proposed in this paper. This paper aims to study the flexural behaviors of PUES beams, a bending test program consisted of one solid PUES beam and seven hollow PUES beams is carried out. The test parameters include thickness of inverted T-shape steel flange, tensile reinforcement ratio and stud spacing. The results showed that the PUES beams failed in the typical flexural failure mode and exhibited excellent ductility without obvious drop in load. Compared to composite beam with solid section, the hollow section had negligible influence on the flexural performance of PUES beams, while it saved 26 % UHPC used compared with the one with solid section. The increasing of the thickness of inverted T-shape steel flange and the reinforcement ratio effectively improved the stiffness and the flexural capacity of PUES beams, while the larger diameter of reinforcement incurred an obvious reduction of ductility. An excessively large stud spacing resulted in a poor composite behavior and a reduction of flexural capacity. Based on the analysis of the experimental results, calculating methods considering the shear connection degree between inverted T-steel and peripheral reinforced UHPC were developed to predict the ultimate flexural capacity of the hollow PUES beams. This study provides a reference for further research and practical engineering applications of this innovation composite beam.

Durability assessment of GFRP bars embedded in UHP-ECCs subjected to an accelerated aging environment with sustained loading

Ultra high-performance engineered cementitious composites (UHP-ECCs) have garnered significant attention in the field of civil engineering primarily due to their exceptional tensile strain-hardening performance and excellent compressive strength. To further enhance their tensile strength, particularly in meeting the rigorous environmental and mechanical demands frequently encountered in marine environments, fiber-reinforced polymer (FRP) bars can be employed as the internal tensile reinforcement for UHP-ECCs (referred to as “FRP-UHP-ECC members”). While numerous studies have focused on the durability of FRP bars in concrete environments, the durability of FRP bars embedded within UHP-ECCs, especially with sustained loads, remains unexplored. Glass FRP bars are commonly utilized in civil engineering due to their cost-effectiveness and favorable mechanical properties. Therefore, this paper investigated the durability performance of GFRP bars made from three different matrix resins (i.e. epoxy, vinyl ester and polyester). These bars were centrally embedded in UHP-ECCs and subsequently immersed in alkaline solutions at elevated temperatures while under sustained loads. Their tensile properties over a specified period were evaluated after exposure. The test results revealed a larger degradation in polyester-based GFRP bars compared to vinyl ester-based and epoxy-based bars. In addition, GFRP bars with UHP-ECC covers exhibited less degradation than the bare bars, but this protective effect diminished under sustained loads. Scanning electron microscope (SEM) and X-ray computed tomography (CT) analysis demonstrated that the degradation of GFRP bars was primarily attributed to matrix hydrolysis, which led to a reduction in stress transfer efficiency between fibers, contributing to the tensile strength reduction in GFRP bars.

Flexural behavior of high strength concrete shallow wide beams reinforced by hybrid longitudinal reinforcement

ABSTRACT One of the most common statistical systems used in structures especially for wide span slabs are ribbed slabs with shallow wide beams (SWB). This experimental study aimed to investigate and enhance the flexural behavior of high-strength concrete SWB using hybrid longitudinal reinforcement from steel and advanced composite materials as a tensile main reinforcement in SWB. Longitudinal advanced composite bars locally manufactured from ribbed glass fiber reinforced polymer (GFRP) and the second type was ribbed basalt fiber reinforced polymer (BFRP). A group of six half scale SWB were examined in structures laboratory of American University in Cairo with dimensions 2.1 × 0.6 × 0.25 m for length (L), width (B) and depth (d) respectively with constant size effect (d/B). The first three specimens were completely reinforced at tension side with Steel, GFRP or BFRP ribbed bars to be considered a control specimen. Use of GFRP and BFRP bars enhanced the flexural capacity of SWB with 41% and 43% respectively compared to specimen completely reinforced with steel. But on the other hand, the crack propagation of specimens completely reinforced with GFRP and BFRP developed more quickly and had larger crack width compared to specimen completely reinforced with steel. Hybrid reinforcement from Steel with GFRP, Steel with BFRP and Steel with GFRP and BFRP specimens are used to enhance the crack pattern and mode of failure without a significant loss in flexural capacity of SWB. The flexural capacity of these three specimens was enhanced with 26%, 30% and 41% with a significant enhancement in crack pattern and ductility.

Rational prediction of moment redistribution in continuous concrete beams reinforced with FRP bars

In continuous fiber reinforced polymer (FRP) reinforced concrete (RC) beams, moment redistribution is typically not allowed in the design owing to the lack of ductility of FRP bars. However, this simplification cannot be justified as moment redistribution depends primarily upon the difference in stiffness along the beam length. This study aims at improving the current state-of-the-art redistribution quantification in continuous FRP RC beams. Redistribution behavior against neutral axis depth (c/d) of continuous FRP RC beams are numerically assessed, focusing on the impact of ρr1/ρr2 (ρr1, ρr2= tensile reinforcement ratios at positive, negative moment zones). It is shown that continuous FRP RC beams may experience marked positive or negative redistribution of moments, depending on ρr1/ρr2. However, the importance of ρr1/ρr2 is neglected in c/d-based code models (EC2, BSI and CSA). A modified BSI model is proposed to estimate the moment redistribution in continuous FRP RC beams. By introducing ρr1/ρr2, the proposed simplified model accounts for the structural characteristic and demonstrates a rational prediction of moment redistribution in these beams.

MODELING THE BENDING BEHAVIOR OF STEEL FIBER-REINFORCED CONCRETE BEAMS

In this study, modeling of the bending behavior of large-scale steel fiber-reinforced concrete beams (SFRC) was investigated using the Modified Compression Field Theory (MCFT) based non-linear finite element (NLFE) method and an analytical method. The two analysis methods included different modeling approaches for the contribution of steel fibers to the tensile strength of reinforced concrete. In the first approach, the residual tensile strength of fibrous concrete was related to the crack width and adopted into the MCTF-based NLFE method. However, the residual tensile strength was free from the crack width in the second approach, which was employed in the analytical method. The capabilities of the mentioned analysis methods were investigated on an experimental study selected from the literature. The experimental study included the four-point bending tests of five four-meter-long simply supported SFRC beams having various ratios of longitudinal reinforcement and fiber content. Results revealed that the MCTF-based NLFE method performed superior in representing the large-scale member responses (such as load-carrying capacity, crack profiles, and flexural stiffness) for the selected loading and boundary conditions while the simplified analytical tool was found to be always conservative in the determination of strength regardless of conventional reinforcement and fiber ratio. However, the rate of error was apparently proven to be highly dependent on the tensile reinforcement ratio.

Experimental study to evaluate the flexural behavior of concrete beams reinforced with CFRP grid

Fiber reinforced polymer (FRP) is evaluated as an excellent material to replace rebar in reinforced concrete due to its advantages such as high tensile strength-to-weight ratio and high corrosion resistance. Many studies have been conducted to use FRP as substitutes for steel rebar. However, most of these studies were conducted using FRP bars, and research on using FRP grids in the construction field is focused on the field of repair and strengthening. Therefore, this study reports the results of an experimental study to evaluate the flexural behavior of concrete beam with Carbon FRP (CFRP) grid tensile reinforcements as a basic study to evaluate the feasibility of using FRP grid as a as substitutes for steel reinforcement. Thirteen test specimens were prepared for the experiments. The CFRP grids were applied to the specimens as tensile reinforcement. The concrete cover thickness, layers of the CFRP grid and the spacing between the CFRP grids were considered as test variables. The experiment results showed that the specimens without spacing between the CFRP grids were destroyed by side CFRP grid fracture. Also, as the CFRP grid layer increased, the ultimate load increased by 53% to 94%, and when the cover thickness decreased by 10 mm, the ultimate load decreased about 10%. The ratios of the nominal flexural strengths calculated according to the CSA S806–12 and ACI 440.1R-15 standards were 1.004 and 1.09, respectively. Thus, the use of the CSA S806–12 standard enables a relatively accurate prediction of the nominal flexural strength of concrete beams reinforced with CFRP grids.

Stress analysis of assembled concrete structures with application of finite element modeling

Abstract In the paper, the finite element model of the assembled concrete structure is constructed based on the finite element method combined with ABAQUS software, including the specific definition of the model material, the boundary condition and contact setting, the analysis step and loading setting, and the validity of the constructed finite element model is verified. In order to deeply explore the stress changes of the assembled concrete structure, four aspects were analyzed, namely, concrete strength grade, load-mid-span displacement curve, stress of tensile and compressive reinforcement, and stress changes of frame combination beams respectively. The results showed that the larger the concrete strength grade, the relative stiffness ratio at the peak point gradually decreased from 0.44 to 0.27, and the specimen of concrete structure with higher steel content reached the maximum load at the mid-span displacement of 12.5 mm. The reinforcement at the end of the steel frame reaches the yield stress only when the lateral displacement is 25.8 mm, while the RC frame reaches the yield stress when the lateral displacement is 16.1 mm. When the load of the assembled concrete structural frame combination beams does not exceed 0.5 times the ultimate load, the stress change is elastic, which can ensure the stability of the assembled concrete structural building. Using the finite element model to model the assembled concrete structure numerically analyzes its stress change, which can better grasp the development of its structural stress during the actual casting process so as to ensure the safety of the building structure.

Intelligent prediction modeling for flexural capacity of FRP-strengthened reinforced concrete beams using machine learning algorithms

Fiber-reinforced polymers (FRP) are widely utilized to improve the efficiency and durability of concrete structures, either through external bonding or internal reinforcement. However, the response of FRP-strengthened reinforced concrete (RC) members, both in field applications and experimental settings, often deviates from the estimation based on existing code provisions. This discrepancy can be attributed to the limitations of code provisions in fully capturing the nature of FRP-strengthened RC members. Accordingly, machine learning methods, including gene expression programming (GEP) and multi-expression programming (MEP), were utilized in this study to predict the flexural capacity of the FRP-strengthened RC beam. To develop data-driven estimation models, an extensive collection of experimental data on FRP-strengthened RC beams was compiled from the experimental studies. For the assessment of the accuracy of developed models, various statistical indicators were utilized. The machine learning (ML) based models were compared with empirical and conventional linear regression models to substantiate their superiority, providing evidence of enhanced performance. The GEP model demonstrated outstanding predictive performance with a correlation coefficient (R) of 0.98 for both the training and validation phases, accompanied by minimal mean absolute errors (MAE) of 4.08 and 5.39, respectively. In contrast, the MEP model achieved a slightly lower accuracy, with an R of 0.96 in both the training and validation phases. Moreover, the ML-based models exhibited notably superior performances compared to the empirical models. Hence, the ML-based models presented in this study demonstrated promising prospects for practical implementation in engineering applications. Moreover, the SHapley Additive exPlanation (SHAP) method was used to interpret the feature's importance and influence on the flexural capacity. It was observed that beam width, section effective depth, and the tensile longitudinal bars reinforcement ratio significantly contribute to the prediction of the flexural capacity of the FRP-strengthened reinforced concrete beam.

Impact of developed hybrid polypropylene fiber inclusion on the flexural performance of concrete beams reinforced with innovative hybrid bars

This paper investigates the impact of incorporating a hybrid combination of structural polypropylene fibers on the flexural behavior of concrete beams reinforced with steel, GFRP, and innovative hybrid bars. A new ductile hybrid bar with equivalent bilinear stress-strain characteristics has been developed to address steel corrosion and FRP ductility issues. Fourteen half-scale RC beams were fabricated and tested under four-point loading configuration to study the flexural response. The tensile reinforcement types (steel, GFRP, and hybrid), hybrid reinforcement ratios (0.85 %, 1.26 %, and 1.70 %), reinforcement hybridization schemes (hybrid-hybrid, hybrid-GFRP, and GFRP-steel), and hybrid fiber ratio (0.0 %, 1.0 %, and 2.0 %) are the major parameters studied. The test results were recorded and analyzed in terms of mid-span deflection, cracking load, flexural capacity, and failure mechanism. The results demonstrated that the addition of hybrid fibers and using hybrid bars significantly improved the peak strength, ductility index, and bending stiffness. Moreover, the hybrid-reinforced concrete beams exhibit large inelastic deformations similar to steel-reinforced concrete beams. The inclusion of hybrid fibers improves the post-peak response of the tested beam due to fiber bridging capabilities. For design purposes, a simplified formula proposed by ACI 544 for predicting the nominal flexural capacity of hybrid fiber concrete beams reinforced with hybrid bars was presented, compared with experimental results and validated with 44 specimens from other studies. The predicted and test results were in good agreement with a standard deviation of 0.12. Additionally, 3D nonlinear finite element analysis was developed to validate the test results, demonstrating reasonable accuracy in predicting the flexural behavior of the beams.

Bearing capacity of UHPC‐NC connection structure in negative moment zone of PC beam bridges

AbstractA new type of UHPC‐NC (normal concrete) structure in the negative moment zone was proposed to improve the bearing capacity of the connection structure in the negative moment zone of prefabricated prestressed concrete (PC) beam bridges. First, the distribution characteristics of the crack, cracking load, ultimate moment, and ductility coefficient of the new structure were obtained by the 1:4 scale model tests. The feasibility of the connection structure is verified. Then, the value ranges of critical structural parameters affecting the bearing capacity of the connection structure based on the plane section assumption analysis, including the reasonable thickness of the UHPC layer, the reinforcement ratio of the longitudinal tensile reinforcement, and the diameter of the reinforcement, are obtained. At the same time, based on the verification of the finite element model, the influence of crucial research parameters on the bending capacity of the connection structure is obtained by using the finite element method. Finally, a theoretical method for the bending moment capacity of the connection structure of the UHPC‐NC structure is proposed, considering the high ductility characteristics of UHPC materials. The average relative error between the calculation results and the finite element method is within 7.2%, which verifies the reliability of the calculation method in this paper and provides a reference for its design and engineering application.

A Theoretical Analysis of Shear Failure of a Reinforced Self- Compacting Concrete Beam without Shear Reinforcement was Experimentally Validated

Abstract: Failures linked with reinforced concrete include axial, flexural, shear, torsion, and deflection (as well as cracking in the case of RC as a material) beyond specified allowed limitations. Failure due to shear (including shear related with torsion) is the most severe and can occur with little or no notice. To prevent the brittle character of shear failure with little or no forewarning, an examination was conducted to determine the size effect, and the diagonal shear failure of reinforced concrete beams without stirrups was analysed in terms of the effective depth of the section. The test beams are made of two types of concrete: conventionally vibrated concrete and self-consolidating concrete, both having nominal compressive strengths of 30, 60, and 70 at 28 days. Given the limitations of the laboratory, three beam sizes with overall depths of 200, 300, and 500 mm, a set shear span to effective depth ratio (a/ d) of 3.50, and a constant tensile reinforcement content of 3% are utilised as test specimens. The experimental results were compared to the acceptable shear stress requirements of IS 456 and ACI 318. The size, concrete type, and concrete strength were determined to have a substantial influence on beam shear strength