Longitudinal Steel Reinforcement Research Articles

Performance of Bonded CRCP Overlay in Texas

As of 2012, there are 17,336 lane miles of Portland cement concrete (PCC) pavement managed by the Texas Department of Transportation (TxDOT), out of a total 196, 821 lane miles in Texas. Many miles of PCC pavement have approached or exceeded their design lives and need rehabilitation. PCC pavements that need rehabilitation now or in the near future were built thinner than today’s standard and are accordingly structurally deficient. Bonded concrete overlay (BCO) provides an optimal rehabilitation option for pavements that are structurally deficient. Over the years, BCO has been utilized in Texas to strengthen existing continuously reinforced concrete pavement (CRCP), with overlay thickness from 2 inches to 8 inches. In general, the performance has been satisfactory; however, in several projects, distresses occurred at early ages and forensic evaluations were conducted, which included continuous deflection testing using rolling dynamic deflection (RDD) and total pavement acceptance device (TPAD), deflection testing using Falling Weight Deflectometer (FWD), and other testing including bond strength testing. The findings include (1) BCO performance depends, to a large extent, on the structural condition of the existing CRCP as indicated by slab deflections evaluated by FWD or TPAD, (2) adequate amount of longitudinal steel reinforcement in BCO layer significantly improves CRCP BCO performance, (3) coarse aggregate type in BCO concrete has a significant effect on BCO performance, and (4) discontinuities in existing pavement, such as joints at bridge approach slabs, were problem areas with distresses in BCO. To ensure good performance of CRCP BCO on PCC pavement, it is recommended that (1) the entire project be evaluated with deflection testing device to identify areas with deflections more than 8 mils at 9,000 lbs for strengthening by removal of existing concrete and base layers and replacement with new concrete, (2) deflection threshold values be developed for CRCP BCO on jointed concrete pavement, and (3) longitudinal steel be provided in BCO.

The Effect of Steel Reinforcement Diameter on the Behavior of Concrete Beams with Corrosion

Corrosion is one of the main problems affecting reinforced concrete (RC) structures, yet there remains a lack of studies in which the electrochemical and structural behavior of corroded RC elements are studied together. In this work, four RC beams with and without corrosion were studied to evaluate their electrochemical and structural behavior via the variable of the diameter of the longitudinal tension steel reinforcement (LTR). The beams were initially tested to determine their initial structural behavior and then subjected to sustained loads and wetting and drying cycles by applying a NaCl solution. The beams were tested a second time to determine their final structural behavior. The variations in the corrosion potential and corrosion rate of the LTR with time, together with concrete resistivity, cracking patterns, and load–displacement curves of the RC beam, are presented. It was found that the electrochemical parameters of the beams with corrosion were similar regardless of the steel reinforcement diameter; these parameters indicated a high level of corrosion. The maximum flexural strength loss was observed for beams with an LTR of 10 mm compared to those with a 13 mm diameter. The maximum cross-sectional area loss associated with pitting corrosion was greater for the beam with an LTR of 10 mm.

A METHODOLOGY FOR EVALUATING THE COSTEFFECTIVENESS OF CRCP DESIGN FEATURES

Continuously reinforced concrete pavement (CRCP) evolved out of a desire to minimize joint-related distresses and improve long-term smoothness of the pavement by eliminating transverse contraction joints. In CRCP, longitudinal reinforcing steel is continuous throughout the pavement length to hold cracks tight. A methodology for evaluating the cost-effectiveness of key CRCP design features and optimizing CRCP design was developed and presented. In this methodology, performance and cost data are combined to evaluate the cost-effectiveness of pavement design features and to determine the optimum combination of these features which has lowest life cycle cost (LCC). The developed methodology was used to examine the cost-effectiveness of five of the more influential CRCP design features PCC slab thickness, longitudinal steel reinforcement content, base type and thickness, shoulder type and thickness, and PCC slab width. A detailed life-cycle cost analysis (LCCA) of 13 current CRCP designs utilizing different combinations of these five design features was conducted using best estimates of the relative costs and performance effects of each of these design features. The cost data were obtained from State and contractors surveys, as well as published cost data and bid tabs. The performance data were obtained from State and contractors surveys, as well as empirical and mechanistic-empirical pavement performance prediction models.

Flexural and Shear Strengthening of High-Strength Concrete Beams Using near Surface Basalt Fiber Bars

Strengthening of reinforced concrete (RC) structures has become a primary challenge in civil engineering. Different materials and procedures have been used in order to repair or strengthen RC structures. In this research, the NSM-Basalt Bar (NSM-BFRP) technique was used to strengthen high-strength reinforced concrete beams in flexure and shear. Twelve beams were designed, constructed, and tested under four-point loads. Six of them were designed to have insufficient longitudinal steel reinforcement to make sure that the failure would be a flexural failure in the control beam. Whereas, the other six specimens were designed to have insufficient transverse steel reinforcement to make sure that the failure will be a shear failure in the control beam. All RC beams were strengthened using NSM-BFRP with different configurations except control specimens. The load deflection curve, the cracking pattern and the failure mode were evaluated. The experimental results reveal that NSM-BFRP bars significantly enhance the ultimate load capacity of high-strength concrete beams, with flexural capacity improvements of up to 33.33% and shear capacity enhancements of up to 63.5%. However, the use of BFRP bars also led to a shift in failure modes from flexural to shear, particularly in specimens with increased flexural reinforcement. The findings suggest that while NSM-BFRP bars are highly effective in strengthening concrete beams, careful consideration of the reinforcement configuration is necessary to avoid premature shear failure and ensure balanced structural performance.

Lateral Cyclic Response of Large-Scale Bridge Piers with Single and Double Layers of Longitudinal and Transverse Steel Reinforcements: An Experimental Study

Lateral Cyclic Response of Large-Scale Bridge Piers with Single and Double Layers of Longitudinal and Transverse Steel Reinforcements: An Experimental Study

Experimental and theoretical studies on the shear resistance of reinforced engineered cementitious composite beams with GFRP rebars and natural fibers

In this work, an attempt is made to produce a ductile construction system using natural fiber-based engineered cementitious composite (ECC) beams where the conventional longitudinal steel reinforcements are replaced using glass fiber-reinforced polymer (GFRP) bars. In total, sixteen medium-scale reinforced ECC beams were tested under an un-symmetric three-point bending configuration to generate shear failure. The parameters considered as a part of the experimental program include (a) type of longitudinal reinforcement (steel or GFRP) and (b) type of natural fiber (flax, hemp, kenaf and pineapple). In addition, a detailed analytical study was performed using the Architectural Institute of Japan (AIJ) method, and a modified equation was proposed for predicting the shear behavior of FRP reinforcement using ECC beams. Test results reveal that the use of GFRP reinforcements resulted in the reduction of peak load from 33.6% to 65.4% when compared to similar steel-reinforced R-ECC beams. However, the failure mode was highly ductile due to the excellent fiber bridging mechanism, multi-crack formation and effective stress redistribution at the crack tip. The predictions obtained from the modified AIJ method improved the accuracy of shear capacity FRP-reinforced ECC sections when compared to the experiments.

Investigation of plastic hinge length in high-ductility reinforced concrete shear walls

In this study, the plastic hinge lengths of reinforced concrete (R/C) cantilever shear walls were analytically determined considering various design parameters. Nonlinear static (Pushover) analyses were conducted on R/C shear wall models and their nonlinear behavior was examined using ABAQUS software. In the study, 72 shear wall models with different parameters were analyzed under the influence of vertical and horizontal loads. Parameters whose effects on plastic hinge length were investigated height/length ratio (Hw/Lw), axial load ratio (N/No), and horizontal web reinforcement ratio (ρsh). The load-displacement graphs of the modelled shear walls were obtained. The plastic hinge height of shear walls was determined according to the heights of the deformations in the concrete and longitudinal steel reinforcement in the section when the shear walls lateral load decreased by 15%. The analytical plastic hinge lengths (Lpz) were determined with respect to the location of the yield occurred at the longitudinal steel reinforcement of the shear wall. The observed plastic hinge lengths (Lp) were determined based on the height of observed the crush as of the foundation top level in the concrete shear wall model. The relationship between the findings of this study and empirical formulas in the literature was determined. It was determined that there is greater closeness between the values obtained from empirical formulas in the literature and the observed plastic hinge length values. It was observed that the plastic hinge length generally increases as the shear span increases. It was observed that the change in ρsh was not a very effective parameter in plastic hinge formation. As the N/No decreases, the plastic hinge length values ​​ generally increase. The Lp/Lpz ratio varied within the range of 0.15-0.50. In addition to ductility (μ) values were determined by using the displacements determined according to both the crushing occurred in the shear wall concrete and the yield observed in the steel reinforcement. The observed that the ductility value depends more on Hw/Lw ratio as N/No ratio decreases.

Analytical Modeling Approaches for the Cyclic Behavior of Concrete-Filled Circular Filament Wounded GFRP Tube Columns

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) offer an alternative to traditional reinforced concrete columns for new construction applications due to their high strength, ductility, and corrosion resistance properties. Despite their popularity, there is a lack of accurate analytical models for the cyclic/seismic performance of CFFT columns. This is due to the absence of precise stress–strain models for FRP tubes and confined concrete under cyclic loading. Previous experiments on CFFT columns suggest that even minimal reinforcement (≤1%) provides essential energy dissipation for extreme events. However, existing stress–strain models for FRP-confined concrete often neglect the contribution of longitudinal and transverse steel reinforcement. While some researchers have proposed material models to address this issue, the analytical modeling of confinement effects from both steel reinforcement and FRP tubes, especially under lateral cyclic loading, continues to pose a significant challenge. This study aims to use previously collected experimental data to evaluate current analytical modeling approaches in OpenSeesPy3.5.1.12 to simulate the lateral cyclic behavior of CFFT columns with ±55° glass fiber-reinforced polymer (GFRP) fiber orientation. Both the lumped inelasticity and the distributed inelasticity modeling approaches are applied. The performance of various FRP confinement models is compared. The effect of plastic hinge length is also considered in the lumped plasticity approach. The findings suggest that integrating a fiber element section into the plastic hinge zone enhances the efficiency of the distributed inelasticity approach. This method accurately captures the non-linear behavior in the critical region and precisely predicts the shape of the hysteretic curve, all while reducing computational costs. Conversely, the lumped inelasticity modeling approach effectively forecasts energy dissipation and peak load values across the entire cyclic hysteresis curve, offering significant computational savings. Finally, a generalized modeling methodology for predicting the response of CFFTs under cyclic lateral load is proposed and subsequently validated using experimental results found in the existing literature.

Experimental Investigation of Ductility in GFRP RC Beams by Confining the Compression Zone

Nowadays, building structures in corrosive environments requires some considerations. Being lightweight, high tensile strength, and corrosion resistance are the features that make fiber-reinforced plastic (FRP) bars an alternative component for longitudinal steel reinforcement of concrete. On the other hand, the linear elastic behavior of FRP bars, alongside the brittle behavior of concrete, makes brittle members without considerable ductility. In this paper, the effect of compression region confinement with CFRP sheets on the FRP-reinforced concrete beams was experimentally investigated. Eight GFRP reinforced beams with 2 m length, including one reference beam and seven confined beams, were constructed and tested under a four-point bending test. Based on the type of confinement, specimens are categorized into four groups. Flexural behavior improvements, including load carry capacity, energy dissipation capacity, and ductility, were observed in at least one specimen of each confined group. According to the results, the specimen that was spirally confined with a 30 mm ribbon width and angle of 10° had the best total energy absorption up to about 110% improvement in comparison to the unconfined specimen. On the other hand, vertically confined specimens with 50 mm ribbon width showed the highest improvement in ductility indices and load carrying capacity up to 60% and 11% in comparison to unconfined specimens, respectively. Due to concrete compression zone fractures in flexural failure mode, the over-reinforce method is considered the design philosophy. Results indicate that regardless of the confinement type (discrete vertical, discrete spiral, or continuous spiral confinement), there is an optimal amount for width, blank space between ribbons, and depth of confinement to achieve the best flexural behavior.

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.

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.

Investigation of shear response due to variation of fiber volume fraction, transverse steel, and placement method on short span R/UHPC beams

This study investigates the response of small-scale, reinforced ultra high performance concrete beams. Seven specimens were cast and experimentally tested. Steel fiber volume fraction, amount of longitudinal and transverse steel reinforcement, and casting direction varied between specimens. High longitudinal reinforcement ratios of 4.1% and 9.5% were expected to drive relatively large shear demands and low steel fiber volume fractions of 0.5% and 1% were expected to decrease the UHPC’s ability to resist tension, shear, and compression. Specimens were either cast at one end or mid-span. All specimens failed in shear, as expected. R/UHPC beams with only 0.5% fibers and a stirrup spacing equal to half the beam’s depth carried more ultimate load than beams with 1% fibers and twice the stirrup spacing. At a 0.5% fiber volume fraction, UHPC performed well, exhibiting fiber bridging in tension and resisting spalling in compression. As longitudinal reinforcement ratio increased from 4.1% to 9.5%, load carrying capacity generally increased, but not proportional to the increase in steel. Placement method did not influence fiber orientation in the R/UHPC beams when measured in 2D planes transverse or longitudinal to the specimens’ major axis. The longitudinal and transverse reinforcement interrupted fiber flow and prevented significant fiber alignment; combined with the short span of the beams, these factors mitigated the influence of placement method.

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.

Full-scale and half-scale fibreglass-confined concrete columns for seismic resilience

Steel corrosion is by far the biggest durability issue for many reinforced concrete bridge structures worldwide. The columns in these bridges can be critical, especially for seismic resistance. In this study, glass-fibre-reinforced-polymer bars were investigated as an alternative to steel for sustainable and resilient bridge construction. As lateral reinforcement is more susceptible to corrosion, and structures fully reinforced with fibreglass bars display softer responses with lower shear and flexural capacity, fibreglass spirals and longitudinal steel reinforcement were used in the tested columns. The experimental programme included the design, construction and seismic testing of full-scale (508 mm diameter) and half-scale (356 mm diameter) columns. The other variables investigated were the axial load and the amount and spacing of spirals. For both column sizes, fibreglass spirals provided increasing confining pressure to the concrete core with increased deformations. For the full-scale columns, no adverse size effects were observed in comparison to the half-scale columns. The columns produced large ductility and energy dissipation. Results from selected representative specimens are presented here to establish the feasibility of using fibreglass spirals in circular bridge columns. Resilience can thus be built into new columns through innovative durable fibreglass lateral reinforcement, with similar if not superior behaviour to steel-reinforced columns.

RC beams externally strengthened by steel plates: experimental database and preliminary analysis

External steel plating is a popular technique for the flexural strengthening of RC beams thanks to the ease of application which does not require skilled labor, the relatively low-cost and the optimal mechanical properties of the steel material. Research on externally plated RC beams is much older than the literature related to the strengthening methods employing fiber reinforced (FRP) materials which were more recently developed. Despite this, the number of FRP applications is far greater than those available for steel applications, as also corroborated by the widespread of several international guidelines for the FRP strengthening design of RC structures. Conversely, the in-situ applications with steel plates are still very common and often preferred to FRPs, but they are not well supported by clear design indications. This paper contributes to filling this knowledge gap by presenting the results of a preliminary study on the flexural performance of steel-plated RC beams. A large experimental database was compiled from the literature, which includes three/four- point bending tests performed on RC members variably reinforced with external steel plates. The database is in-depth examined by considering the following main parameters: layout of the external steel plating, shape of beam’s cross section, mechanical percentages of both external steel plate and beam’s longitudinal steel reinforcement in tension, and failure mode. The collected data is useful for a theoretical study on beams’ flexural performance, which is under preparation.

Minimum longitudinal reinforcement in rectangular and flanged reinforced concrete walls

The amount of longitudinal steel in reinforced concrete walls is a key point in the damage distribution along the wall, although it is usually associated mainly with the prevention of temperature and shrinkage problems. A recent earthquake in New Zealand pointed out its relevance after the observation of a localized failure mode found in walls due to insufficient longitudinal steel reinforcement. Low amounts of longitudinal steel reinforcement prevent the correct distribution of the damage and can even lead to an early fracture of the reinforcement. The following study analyzes walls with different sections, such as T, L, and C-shaped walls, among others, subjected to pushover analysis, where the amount of longitudinal boundary reinforcement is varied, using values close to the minimum provided by ACI 318-19 code. The main parameter under analysis was the strain at the boundaries, revealing different behavior depending on the amount of boundary steel. When using steel amounts less than the minimum provided by the code, a greater growth for the tensile strain is observed, which in turn localizes the damage in a few zones along the wall height at low drift levels. This is overcome when using the recommended minimum steel amount. In addition, regarding the strength-to-cracking moment ratio (Mn/Mcr), although related to the growth of tensile strains, there is no specific value that can be recommended for all wall cross-sections.

Cyclic behavior of recycled-lump-concrete-filled GFRP tubular columns: Experimental investigation and numerical modeling

A fiber-reinforced polymer (FRP) tube offers the advantages of lightweight formwork, external confinement, and non-corrosive reinforcement for recycled lump concrete (RLC), creating an attractive opportunity for structural applications of this green material. While prior research has predominantly focused on the axial compressive behavior of RLC-filled FRP tubular columns, this study addresses the implications of using such members in seismic areas. Six large-scale RLC-filled Glass FRP (GFRP) tubular columns were tested under constant axial compression and quasi-static reversed lateral loading to examine the impact of crucial parameters on their cyclic behavior. Additionally, the study discusses the numerical modeling of such columns using a fiber beam element approach. The findings indicate that the replacement rate of recycled lumps (<33%) has limited impact on the cyclic behavior of the columns. Reducing the GFRP tube thickness and simultaneously adding a minimum amount of longitudinal steel reinforcement can improve the hysteretic response. An off-axis tube with a fiber orientation close to 50° appears more suitable for structural use compared to 80°. Moreover, even with a tube diameter-to-thickness ratio of 100, the columns still meet the code requirement for lateral drift limit of flexural-dominated members. Overall, the study contributes to instilling confidence in the scaling-up applications of RLC-filled GFRP tubular columns in earthquake-prone areas.

Machine learning-based models for predicting the shear strength of synthetic fiber reinforced concrete beams without stirrups

Stirrups can be added to reinforced concrete (RC) beams made of plain concrete to increase the shear strength providing better performance against embrittlement. If the need for shear stress is less than the strength of RC beams, reinforced with the minimum number of stirrups, then this choice might not be the most cost-effective. Synthetic Fiber Reinforced Concrete (SyFRC) in Reinforced Concrete (RC) structures is limited due to the lack of predicting models for this emerging material in current literature. However, recent advances in concrete technology have revealed more significant benefits of SyFRC, including high deformation capacity and less corrosive concrete. This study predicts shear strength of SyFRC beams without stirrups using the ACI 318-19 equation in addition to Machine Learning (ML) methods such as LightGBM, XGBoost, and Gene Expression (GEP). A database of 102 tested SyFRC specimens were compiled, processed, and evaluated. With R2 values of 98.91% and 97.22%, respectively, the LightGBM and XGBoost outperformed the other examined algorithms by having the least predictions discrepancy and highest accuracy values. As the ACI 318-19 equation does not account for the fibers volume ratio and shear span-to-depth ratio effects on the shear strength contribution, it projected shear strength with the lowest degree of accuracy, with R2 = 75.5%. The feature importance analysis revealed that these two factors, in addition to the effective beam depth, beam width, longitudinal steel reinforcement ratio, and concrete compressive strength should not be negligible in shear strength prediction. For forecasting the shear strength, a closed-form GEP-based model was suggested. The proposed GEP model has a little lower prediction accuracy with R2 = 88.4%. The performance of the four examined models was evaluated from various perspectives. The analysis shows that, apart from the ACI equation, all considered models effectively predict the effects of shear span-to-depth ratio. This is critical for investigating deep and slender beams, and size effect, which are critical for beams with high effective depths. The current study's findings should give practitioners a solid platform for making precise and straightforward assessments of shear strength.

Experimental investigation on ultra high-performance concrete beams without shear reinforcement

Seven ultra high-performance concrete (UHPC) beams without shear reinforcement are tested in this work to examine their structural behavior as shear failure is a major concern in such members. Coarse aggregate was not used in two of the beams while the other five are made with coarse aggregate as 50% replacement of fine sand. Three longitudinal steel reinforcement ratios (1.14%, 1.64% and 2.46%) and three steel fiber ratios (0, 1% and 2%) are used. Results show that UHPC beams with coarse aggregate show higher ultimate loads (4.7% − 11.5%) than UHPC beams without coarse aggregate and incorporating 1% and 2% steel fiber raises ultimate loads by 60% and 131%, respectively for beams with coarse aggregate. Also, using 2% steel fiber changes failure mode from brittle shear failure by diagonal crack in beams of 0 or 1% steel fiber to ductile flexural failure by yielding of longitudinal reinforcement. Higher stiffness and toughness and lower deflections are observed with the increase of longitudinal reinforcement, steel fiber or coarse aggregate. Using 2% steel fiber highly improved toughness by more than 17 times. Lower rates of improvement are recorded for longitudinal reinforcement and coarse aggregate. However, it is recommended to perform more research to examine more parameters such as fiber types.

Sustainability of Using Steel Fibers in Reinforced Concrete Deep Beams without Stirrups

Reinforced Concrete (RC) deep beams perform better structurally when steel fibers are added, as this reduces the need for web steel reinforcements, boosts shear strength, and helps to bridge cracks. The current ACI 318-19 code does not include predicting shear strength models to account for the added steel fibers in Steel Fibers Reinforced Concrete (SFRC) deep beams without stirrups; therefore, structural engineers are less motivated to use them. To fill this gap, the databases of 281 RC and 172 SFRC deep beams were compiled, and the preliminary investigation of the collected databases revealed that (1) Longitudinal steel reinforcement significantly increases the shear strength of SFRC specimens, as the steel fibers make deep beams better at carrying loads by assisting them in bridging cracks; and (2) Although shear stress and span-to-depth ratio are inversely related, SFRC deep beams encounter larger shear loads than RC deep beams because when the span-to-depth ratio of beams increases, the failure mode switches from crushing struts to diagonal shear failure. To help structural engineers adopt SFRC deep beams, a nonlinear regression-based model was developed to estimate the shear strength of SFRC deep beams using the experimental database of SFRC beams. Three factors—feature selection, data preprocessing, and model development—were considered. Additionally, the model’s effectiveness was evaluated and compared with other models found in the literature. The proposed shear strength model of SFRC performed better than the other models in the literature, providing the lowest Root Mean Square Error (RMSE) of 1.58 MPa. The results of this study give practitioners a strong platform for establishing precise and useful estimations of shear strength in SFRC deep beams without stirrups.