Steel Reinforcement Ratio Research Articles

Shear strength of hybrid GFRP-steel reinforced concrete corbels without vertical stirrups: Experimental research and prediction models

This paper investigates the behavior and predicts the shear strength of concrete corbels reinforced with hybrid glass fiber reinforced polymer (GFRP)/steel reinforcement bars. For this purpose, the study consists of two main parts: the first part was an experimental study carried out on eight hybrid reinforced concrete corbels and four GFRP reinforced concrete corbels with a shear span to depth ratio (a/d) of 0.7 and 1.0; in the second part, a nonlinear finite element model (NFEM) was developed and validated against experimental results. Comprehensive parametric studies based on the validated NFEM were conducted to assess the impact of main parameters on the shear capacity. As a result, an empirical formula predicting the shear capacity of hybrid RC corbels was proposed. Furthermore, a softened strut-and-tie model (SSTM) was further developed to predict the shear capacity of hybrid RC corbels. The test results indicate that increasing the steel reinforcement ratio significantly enhances the shear strength. The width of the inclined crack band narrows as a portion of GFRP reinforcement is replaced with steel reinforcement. The NFEM shows good agreement with test results in terms of load-deflection curve, strain of rebar and failure modes. The proposed empirical formula and extended SSTM accurately predict the shear capacity of hybrid RC corbels compared to test results and numerical simulations.

Flexural behavior of RC beams externally strengthened with side-bonded CFRP laminates with variable internal reinforcement

This study investigates the flexural behavior of reinforced concrete (RC) beams externally strengthened with bottom- and side-bonded carbon fiber-reinforced polymer (CFRP) sheets with variable steel ratio. The choice of applying the CFRP sheets in a bottom- or side-bonded configuration depends on the accessibility of the beam. This experimental investigation is aimed at studying and comparing the efficacy of bottom- and side-bonded CFRP sheets for flexural strengthening of RC beams with variable internal steel ratios. The effect of steel reinforcement ratio, and the number of CFRP plies are examined by testing 10 RC beams under a four-point bending configuration. The results in terms of load-deflection response, ultimate load-carrying capacity, failure modes, and ductility are studied and compared with control unstrengthened beams. The study revealed that side-bonded beams provided flexural capacity comparable to the bottom-bonded beams for both ratios of internal reinforcement used in the study. The study also showed that both strengthening configurations were more effective when the internal steel ratio was low. In terms of ductility, the side-bonded scheme provided ductility indices comparable to the bottom-bonded beams. The findings of this study confirm the feasibility of using side-bonded fiber-reinforced polymer (FRP) sheets as a strengthening technique for RC beams when the soffit of the beam is inaccessible.

Application of Phenolic-based BFRP Rebars Adapted to High Temperature in Beam Strengthened by NSM Technique

Phenolic resin-based BFRP (P-BFRP) composites has been demonstrated to be superior to the commercial ones when being exposed to high temperature, while their strengthening effect for reinforced concrete (RC) components at ambient temperature has not been investigated. In this paper, exploration was conducted and experimental studies were mainly carried out on the flexural performance of reinforced concrete (RC) beams strengthened with P-BFRP rebars, including epoxy- (E-BFRP) and vinyl-based BFRP (V-BFRP) rebars as a comparison. Crucial characteristics of strengthened beams, especially strain variation of BFRP rebars, were analyzed, and flexural capacities were also calculated. The results showed that P-BFRP rebars can achieve a slightly better strengthening effect compared to commercial BFRP rebars. All BFRP rebars saw a less increase in strains at glue-strengthening zones, but an obvious change from cracking to failing at grouting-strengthening zone. The bonding scheme including both grouting and epoxy glue was reasonable, and sufficient to contribute a reliable anchorage to the BFRP rebars. The calculation in ACI 440.2R-08 was conservative in predicting the ultimate load capacity of the strengthened beam, while the trend of variation can be reasonably estimated. P-BFRP rebars were more effective in the case of higher concrete strength, or lower steel reinforcement ratio.

Phase-field anisotropic damage with bond-slip model for reinforced concrete beam under the service load

Concrete, as a quasi-brittle material, undergoes a latent damage accumulation preceding macroscopic crack formation, which is further complicated by the intricate interaction between steel reinforcements and concrete in reinforced concrete (RC) structures. Traditional approaches inadequately capture these nuances, especially when it comes to the seamless transition from numerous micro cracks to a visible macro cracks. Phase-field damage theory stands out as a sophisticated tool, integrating sharp cracks into a continuous damage field representation and detailing the entire process of micro-to-macroscopic cracking evolution. In this work, a phase-field damage model that accounts for bond-slip behavior is proposed, grounded in the principle of stress space decomposition to address the inherent tension–compression anisotropy. Newton’s method with a viscosity coefficient of 0.001 enhances simulation accuracy and robustness through optimal convergence. The comparison between rigid bond and bond slip mechanisms indicates a significant difference in their impact on crack modes, revealing the necessity of considering bond slip. As the steel reinforcement ratio increases, the RC beam’s load-bearing capacity increases incrementally, concurrently exhibiting a reduction in macroscopic cracks, steel reinforcement stress, and overall damage severity. However, the comparative advantage of rigid bond in improving RC beam’s resistance against cracking begins to wane as the reinforcement proportion rises. This study thus sheds light on the nuanced interplay between bond characteristics and the cracking behavior of RC beams, providing a comprehensive and advanced perspective.

Advanced analysis of intact, fire-damaged, and CFRP retrofitted bridge pier columns under vehicle collisions: Empirical equivalent static force equation and framework

A series of numerical simulations were completed to investigate the behavior of intact, fire-damaged, and Carbon Fiber-Reinforced Polymers (CFRP) retrofitted reinforced concrete (RC) bridge columns of varying sizes subjected to vehicle collisions. Three-dimensional finite element models of isolated RC columns and their foundation systems surrounded by soil volumes were developed using LS-DYNA. A comprehensive parametric study was carried out to investigate the effects of nine demand and design parameters on the performance of bridge columns. Studied parameters included: column diameter, column height, unconfined compressive strength, steel reinforcement ratio, fire duration, CFRP wrap thickness, wrapping configuration, vehicle’s mass, and vehicle’s speed. For each studied scenario, Peak Twenty-five Milli-second Moving Average (PTMSA) was employed to estimate the Equivalent Static Force (ESF) corresponding to each vehicle collision scenario. Resulting ESFs were then utilized to assess effectiveness of the current ESF approach available in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO-LRFD) Bridge Design Specification for analyzing and helping design bridge columns under vehicle collision. Multivariate nonlinear regression analyses were used to derive an empirically based, simplified equation to predict the ESF that corresponds to a vehicle collision. Rather than constant design force, this equation established a correlation between ESF and kinetic energy, column axial capacity, and column height. Results indicated that the proposed equation is reliable and can accurately predict ESFs over a diverse range of collision scenarios that included intact, fire damaged, and CFRP retrofitted columns. To facilitate realistic implementation of the derived equation, an ESF assessment framework was also devised.

Effects of steel reinforcement ratios on the flange effective width for reinforced concrete T-beams casting with recycled coarse aggregate

Effects of steel reinforcement ratios on the flange effective width for reinforced concrete T-beams casting with recycled coarse aggregate

A design methodology for fibre reinforced concrete elements in serviceability conditions integrating tension softening and stiffening effects

This paper proposes a design methodology to derive an analytical bilinear moment‒curvature diagram (Mana–χana) for the cross-section of fibre reinforced concrete (FRC) elements that also includes conventional steel flexural reinforcement (R/FRC). This bilinear diagram is obtained by determining the post-cracking tensile capacity of FRC (NtcFRC), which integrates not only the tensile stiffening capacity of the FRC surrounding the conventional flexural reinforcement due to the bond stress transference between this reinforcement and FRC, but also the tensile softening of the cracked FRC out of this zone. This Mana–χana is defined by two points, the first corresponding to the cracking moment and its corresponding curvature (Mcrana,χcrana), while the bending moment of the second point of this diagram (Muana) is a multiple of the analytical cracking moment (CuMcrana), where Cu is dependent on the fibre volume percentage (Vf). The curvature corresponding to Muana,χuana, is obtained by assuming the flexural stiffness of a fully cracked RC section. Therefore, the Mana–χana is determined by geometric and material properties of directly assessed by a designer.For demonstrating the applicability of the proposed design methodology, a database of beams of distinct cross-section aspect ratios and compressive strength classes, reinforced with different percentages of steel fibres and reinforcement ratios of conventional steel bars was established. By using the bilinear Mana–χana, and applying the principle of virtual work, the deflection of these beams was estimated with sufficient accuracy for design purposes, when compared to experimental records. Although the formulation has been applied to beams made by steel fibre reinforced concrete (SFRC), it is conceptually general and applicable to elements of concrete reinforced with other types of fibres.

Enabling efficient regional seismic fragility assessment of multi‐component bridge portfolios through Gaussian process regression and active learning

AbstractRegional seismic fragility assessment of bridge portfolios must address the embedded uncertainties and variations stemming from both the earthquake hazard and bridge attributes (e.g., geometry, material, design detail). To achieve bridge‐specific fragility assessment, multivariate probabilistic seismic demand models (PSDM) have recently been developed that use both the ground motion intensity measure and bridge parameters as inputs. However, explicitly utilizing bridge parameters as inputs requires numerous nonlinear response history analyses (NRHAs). In this situation, the associated computational cost increases exponentially for high‐fidelity bridge models with complex component connectivity and sophisticated material constitutive laws. Moreover, it remains unclear how many analyses are sufficient for the response data and the resulting demand model to cover the entire solution space without overfitting. To deal with these issues, this study integrates Gaussian process regression (GPR) and active learning (AL) into a multistep workflow to achieve efficient regional seismic fragility assessment of bridge portfolios. The GPR relaxes the probability distribution assumptions made in typical cloud analysis‐based PSDMs to enable heteroskedastic nonparametric seismic demand modeling. The AL leverages the varying standard deviation to select the least but most representative bridge‐model‐ground‐motion sample pairs to conduct NRHA with much‐improved efficiency. Both independent and correlated multi‐output GPRs are proposed to deal with bridge portfolios with seismic demand correlations among multiple components (column, bearing, shear key, abutment, unseating, and joint seal). Considering a single benchmark highway bridge class in California as the case study, the AL‐GPR framework and the associated component‐level fragility results are investigated in terms of their efficiency, accuracy, and robustness. The fragility results show that 70 AL‐selected samples would enable the GPR to derive bridge‐specific fragility models comparable to the ones using the multiple stripes analysis approach with 1950 ground motions considered for each individual bridge. The AL‐GPR model also successfully captures the physics of how bridge span length, deck area, column slenderness, and steel reinforcement ratio would change the damage state exceedance probabilities of different bridge components. The efficiency of AL stems from the fact that, with the multi‐output independent GPR, a stable and reliable fragility model can be achieved using 50 AL‐selected samples compared to at least 270 randomly chosen samples. The proposed methodology advances the state of the art in enabling more efficient and reliable regional seismic fragility assessment of multi‐component bridge portfolios.

Tensile characteristics of ultra-high-performance fibre-reinforced concrete with and without longitudinal steel rebars

Ultra-high-performance fibre-reinforced concrete (UHPFRC) specimens with and without longitudinal reinforcement were experimentally tested under direct tensile loading. The variables considered were the volume fraction of fibres (1.0% and 2.0%), the type of steel fibres (straight and hooked end) and the longitudinal steel reinforcement ratio (none and 1.2%). All of the specimens were tested using a servo-controlled fatigue testing machine in displacement control mode. The changes in displacement were monitored using linear variable displacement transducers and the digital image correlation technique. The strain profiles at different loading stages were used to identify the crack evolution process. The average localised strain was found to be 0.2–0.36%, with corresponding crack widths of 0.3–0.6 mm. A uniaxial tensile stress–strain model was developed based on the test results and data from the literature. Longitudinally steel-reinforced specimens showed both stiffening and strengthening effects. Tension-stiffened specimens with 1.0% fibres failed at a higher strain due to the formation of multiple macrocracks. In the specimens with 2.0% fibres, the rebar fractured in a brittle manner due to crack localisation. It is concluded that a higher longitudinal reinforcement ratio is needed to utilise UHPFRC effectively under tension-dominant loads.

Bolted connections in prefabricated cantilevered cap beam-column structures: A comprehensive experimental and numerical study

Prefabricated cantilevered beam-column structures have gained popularity in mountainous road construction. However, a notable research gap exists regarding the beam-column connections. To fill this gap, a new bolted connection method was introduced for the cantilevered beam-column structure. The mechanical performance of this novel structure was systematically investigated through reduced-scale experiments and finite element analysis. The structure's response under three critical loading conditions was experimentally examined, revealing the efficacy of bolted connections in preserving structural integrity and highlighting pronounced strain concentration at the connection region of the cap beam. Furthermore, to enhance structural design, a finite element model of this beam-column structure was established to simulate the influence of various materials and structural parameters on structural response and damage. Simulation results indicated that the anchor rod angle and the number of bolts had a minor impact on load-bearing capacity and damage modes. In contrast, the choice of concrete material and steel reinforcement ratio significantly influenced load-bearing capacity. The insights derived from this study offer valuable guidance for optimizing and extending the application of this structural design.

Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams

Abstract This research aims to use numerical methods to analyze concrete beams with different reinforcement ratios. Two software packages – ABAQUS and OpenSeesPy – were employed to achieve this task. Empirical stress–strain relationships were utilized to forecast the concrete’s stress–strain behavior. The numerical analysis results were compared with previously published experimental results, and the findings showed a reasonable similarity. The results were consistent with the published laboratory results, particularly for ultimate and yield loads, with no more than 10% differences. However, the ultimate deflection variation was higher. For the first control beam, denoted as B 2−12, ABAQUS predicted a 24.64% difference in ultimate deflection, while OpenSeesPy predicted a 35.83% difference for the second beam, sampled as B 2–16. However, the ultimate deflection for the remaining beams differed by less than 10%. Meanwhile, the difference in yield deflection was greater than in ultimate deflection, with OpenSeesPy showing a maximum difference of 18.51%. The maximum ductility was found to occur at a reinforcement ratio equal to 0.0016. Additionally, OpenSeesPy was faster than ABAQUS in computation while still producing satisfactory agreement with experimental results.

The investigation on flexural performance of prestressed concrete-encased high strength steel beams

This paper reports an experimental on the flexural performance of prestressed concrete-encased high-strength steel beams (PCEHSSBs). To study the applicability of high-strength steel (HSS) in prestressed concrete-encased steel beams (PCESBs), one simply supported prestressed concrete-encased ordinarystrength steel beam (PCEOSSB) and eight simply supported PCEHSSBs were tested under a four-point bending load. The influence of steel strength grade, I-steel ratio, reinforcement ratio and stirrup ratio on the flexural performance of such members was investigated. The test results show that increasing the I-steel grade and I-steel ratio can significantly improve the bearing capacity of PCESB. Increasing the compressive reinforcement ratio of PCEHSSB can effectively improve its bearing capacity and ductility properties, making full use of the performance of HSS in composite beams. Increasing the hoop ratio has a small improvement on the load capacity of the test beams; setting up shear connectors can improve the ductile properties of the specimens although it does not lead to a significant increase in the load capacity of the combined beams. Then, combined with the test data, the comprehensive reinforcement index considering the location of reinforcement was proposed to evaluate the crack resistance of specimens. The relationship between the comprehensive reinforcement index and the crack resistance of specimens was given.

A comparative study of LightGBM, XGBoost, and GEP models in shear strength management of SFRC-SBWS

Steel fiber reinforced concrete (SFRC) was revealed to have superior mechanical properties compared to plain concrete, especially under shear loads. However, Due to a lack of prediction models for SFRC-Slender Beams without Stirrups (SFRC-SBWS) in the available literature, the application of SFRC-SBWS in reinforced concrete (RC) constructions is limited. This research aims to fill a literature gap by analyzing different Machine Learning (ML) algorithms, including Extreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), and Gene Expression Programming (GEP), to forecast the shear strength of SFRC-SBWS specimens. A database of 333 tested SFRC-SBWS specimens was collected and analyzed. The results revealed the LightGBM and XGBoost algorithms surpassed other studied algorithms with Coefficient of determination (R2) = 95.74% and 93.27%, Root Mean Square Error (RMSE) = 20.04 kN and 25.19 kN, respectively. A GEP-based closed-form model was suggested to forecast the shear strength, considering the most important factors, including beam depth effect, beam width, and longitudinal steel reinforcement ratio. The proposed GEP model has an R2 = 91.12% and RMSE = 101.44 kN, showing a slightly lower prediction accuracy. The effectiveness of the studied models was evaluated from various angles, and the results demonstrate the importance of managing new technological advancements to create reliable support methods. Engineers that use these approaches get a dependable tool for estimating shear resistance, which is crucial in guaranteeing the safety and lifespan of RC structures. The successful combination of classic engineering approaches and revolutionary ML strategies indicates the potential for improving accuracy and reducing bias in prediction-oriented investigations. As the engineering field supports technological improvements, combining robust and efficient prediction models, as described in this paper, can contribute considerably to resilient structure design and safety assurance. This leads to sustainable and robust management of structures with greater confidence in predictions.

Enhancement of punching shear behavior of reinforced concrete flat slabs using GFRP grating

The literature review showed insufficient relevant research on the application of Glass-Fiber-Reinforced-Polymers (GFRP) gratings in the structural elements, while GFRP bars, laminate, sheets, and strips, have been extensively explored. This research aims to present a proposal for a new reinforcing system using GFRP gratings to improve the punching shear resistance of RC flat slabs. Results of seven specimens tested experimentally under vertical static loading are displayed, taking into account the influence of the gratings variables. Test results revealed an improvement in the ultimate load ranging between 9.03% and 27.67% for the specimens strengthened by the proposed GFRP grating system. A Nonlinear Finite Element Analysis (NLFEA) was carried out using the ANSYS program with correlational evaluation using load-deflection response and cracking pattern, which resulted in a good convergence of numerical simulations and experimental performance results ranging from 1.0% to 8.0%. Key parameters, namely the concrete compressive strength, steel reinforcement yield strength, main steel reinforcement ratio, secondary steel reinforcement ratio, column dimensions, slab thickness, concrete cover, and GFRP gratings characteristics, were investigated through a parametric study adopting NLFEA by the ANSYS program, where the output results were compared to the recent code provisions.

FE Analysis on Size Effect in Torsional Behavior of Rectangular RC Beams with and Without FRP Strengthening

Although torsion is usually considered a secondary consideration in structural design, it can lead to failures, especially in structures with irregular geometry exposed to seismic forces or in unique situations. While some studies have explored the size effect on the torsional behavior of RC beams, none have addressed the impact of reinforcement. This paper investigates the size effect on the torsional behavior of RC beams with varying reinforcement ratios, including both FRP sheets and steel rebars. In this study, the torsional behavior of reinforced concrete (RC) beams with and without FRP strengthening was investigated numerically. Modeling was carried out by Finite element (FE) software ABAQUS and validated using experimental data from literature. The torsional behavior of 24 models with differences in cross-section size and reinforcement ratio were investigated. Concrete damage plasticity, Hashin damage criteria, and von Mises stress were used to investigate the damage in concrete, FRP, and steel, respectively. The cracking torsional moment, ultimate torsional moment, and torque-twist curve of the beams were evaluated and presented. The results indicated the presence of a significant size effect in the torsional strength of beams. After reinforcing the beams with FRP fabrics, the average cracking moment increased by a range of 1.72% to 36% across different groups of beams. An 8.2% increase in ultimate strength is observed with just a 0.4% rise in the FRP strengthening ratio. Post-cracking behavior was seen in 8 models with adequate steel and FRP reinforcement ratio.

Finite Element Model of Concrete-Filled, Fiber-Reinforced Polymer Tubes for Small-Scale Wind Turbine Towers

The finite element method was used to study the feasibility of concrete-filled, fiber-reinforced polymer tubes (CFFTs) for small-scale wind turbine towers in remote areas. Although CFFTs have been successfully employed for a variety of structural applications, their use for wind turbine towers is novel and has yet to be investigated in detail. The objective of the study was to identify, for the first time, the most important parameters for design and compare the behavior of CFFT towers versus conventional steel and concrete towers. The model was first validated using experimental results reported in the literature followed by a series of parametric studies to evaluate the importance of several key parameters. In the first phase, the effect of different geometric properties (taper and concrete filling ratio) and reinforcement configurations (FRP laminate configuration, steel reinforcement ratio, and prestressing level) were investigated for cantilever tower models with concentrated lateral loads. A 10 m high CFFT wind turbine tower model was subsequently modeled and studied under different loading configurations. The influence of the height-to-diameter (h/D) ratio on cantilever CFFT models was also studied and a conservative preliminary design that can be refined for specific turbine systems and wind conditions was adopted using the h/D ratio. The CFFT tower model was compared to concrete and steel tubular models with similar geometry to study the advantages of CFFT towers and showed that CFFTs can be an efficient alternative.

Punching shear capacity of fiber-reinforced concrete suspended slabs: Database analysis and models assessments

The punching shear capacity is critical in the design of suspended slabs. Fiber reinforcement has been introduced to improve the punching shear capacity of these slabs. Several models have been used to predict the punching shear capacity of fiber-reinforced concrete slabs (FRCS). Some of these models accounted only for the contribution of concrete (e.g., ACI 318–19 and CSA-19), while others also accounted for the contribution of reinforcing steel (e.g., JSCE-07 and Eurocode-2 and/or fibers (e.g., fib MC-10). In the present study, experimental results from 240 FRCS and 78 control slabs (without fibers) were collected and analyzed to assess the effect of various parameters and the extent to which these parameters affect the predicted punching shear capacities by various models. Four main parameters, concrete compressive strength, steel reinforcement ratio, fiber reinforcement, and punching shear perimeter, were considered in the assessment of various design and theoretical models. The study revealed that most design-based models underestimate, to varying degrees, the punching shear capacities with large variability. To better capture the dependence of the punching shear capacity on the four main parameters, a new model was proposed for FRCS. The proposed model considers the critical shear perimeter at a distance d from the face of the column and accounts for the fiber contribution as a function of the residual strength parameter obtained from standard beam tests (ASTM C1609). Predictions of the proposed model were characterized by high accuracy and low coefficient of variation (CV).

Effect of main reinforcement on box girder flexural and shear behavior

The primary goal of the current study is to determine, in a lab setting, how the main longitudinal reinforcement ratio affects the behavior and load capacity of single-cell box girders made of reinforced concrete. Three specimens were cast and tested, each with a length of 1600 mm, top and bottom slab has a uniform thickness of 50 mm, an upper flange width of 430 mm, a bottom flange width of 300 mm, and a height of 230 mm. The three box girders are reinforced by having three distinct ACI 318–19 reinforcing ratios: the minimum, the maximum, and average of them, i.e., the reinforcing ratios were 0.0033, 0.0184, and 0.00591, respectively. All three specimens were subjected to 2-concentrated forces. For the tested box girders, the cracking load, crack pattern, failure load, deflection, average strain values on the concrete surface, strain values in steel bars, and failure mode were recorded and discussed. Experimental work has proven that increasing the ratio of the main steel reinforcement from minimum to maximum, passing through the average between them, i.e. 79-425%, leads to higher load capacity by about 66.67-99% and midspan deflection decrease by about 28-36%. It was also concluded that steel reinforcement yield occurred at both minimum and average main reinforcement resulting in flexural failure. While at the maximum of the main reinforcement, yield did not urge but rather a failure occurred in another place which is the shear, whose stirrups suffered from yield this time

Use of hybrid fibers and shrinkage mitigating materials in SCC for repair applications

Self-consolidating concrete (SCC) is used to repair structural elements with congested reinforcement or restricted access to placement and consolidation. In addition to adequate flowability, passing ability, filling capacity, and stability, adequate bonding to the substrate and reinforcing bars, low shrinkage and cracking resistance are required for successful repair. This study employs various shrinkage mitigating materials, including expansive agent (EA), coupled use of EA with shrinkage reducing admixture (SRA), and EA with pre-saturated lightweight sand (LWS) to fulfill these requirements. The effect of these materials on the performance of SCC made with a hybrid synthetic (PP) fiber and a hybrid steel-synthetic (STPP) fiber is investigated. The investigation included key fresh and hardened concrete properties and flexural performance of composite beams repaired using these materials. Test results show that the investigated fiber-reinforced self-consolidating concrete (FRSCC) mixtures can secure adequate workability and mechanical properties and low shrinkage, limited to 600 µstrain after 224 days. High EA content (10% by mass of binder) can lead to excessive expansion at early ages resulting in microcracking and drop in mechanical properties. The FRSCC made with 5% EA and 0.5% SRA, by mass of binder (5EA0.5SRA mixture), had superior mechanical properties (50 MPa compressive strength and 36 GPa modulus of elasticity). The cracking potential due to restrained shrinkage of this mixture is very low. The 5EA0.5SRA mixture made with hybrid synthetic fibers is successfully used to repair reinforced concrete beams prepared with various reinforcement ratios in the tension zone. The results indicate a 48% increase in first crack load, 4% gain in peak load, and 33% increase in flexural toughness compared to the monolithic beam cast with the conventional concrete. A comparison between the cracking load and ultimate flexural capacity of the repaired beams with estimated values by ACI 544 reveals the estimated to experimental ratio of 0.36–0.70 for cracking load and 0.56–0.74 for the flexural capacity. This can stem from the promotion of FRSCC concrete by the effect of hybrid synthetic fibers and the development of internally induced stress in the presence of shrinkage mitigating materials and fibers that led to higher mechanical properties and enhanced performance of FRSCC for repair. Reinforced beams repaired using FRSCC made with 0.5% hybrid synthetic fibers and combination of EA-SRA can reduce the steel reinforcement ratio by 21% to 27%, depending on the primary steel reinforcement.

Flexural improvement of reinforced concrete beams strengthened with self-prestressing shape memory alloys

The study reported here aims to investigate the application of shape memory alloys (SMAs) in the form of strips for strengthening cracked reinforced concrete (RC) beams. The study proposes an innovative technique for prestressing RC beams by utilizing the shape recovery property of the alloy. Nine full-scale RC beams with a length of 3.75 m and a cross-section of 200 mm × 300 mm were categorized into three groups based on the steel reinforcement ratio, and tested under static loading. Three RC beams were used as control specimens and the other six were retrofitted with either one layer or two layers of SMA strips. The beams to be strengthened were exposed to an initial applied load before the installation of the SMA strip to simulate the deterioration scenario. SMA strips were retrofitted on the soffits of the deteriorated beams and activated by applying temperature from an external heat source while the temperature-deflection-strain measurements were monitored. Specimens were tested again up to failure to evaluate the strength improvement of the retrofitted specimens. Beams retrofitted with one layer of SMA experienced a deflection recovery up to 2.3 mm upon activation and an additional service load of up to 62%, whereas beams retrofitted with two layers experienced a deflection recovery up to 2.8 mm and an additional service load of up to 95%. In general, the deflection recovery was proportional to the ratio of the total reinforcement ratio after strengthening to the initial reinforcement ratio before strengthening. Therefore, tested specimens with two SMA layers experienced less improvement than specimens with one SMA layer. Finally, the experimental results were evaluated with two analytical methods: ACI method and the non-linear sectional analysis proposed by Oukaili.