Longitudinal Steel Reinforcement Research Articles

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.

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.

Electrochemical Behavior of Reinforced Concrete Beams with Different Flexural Tensile Stresses in the Steel Reinforcement

In this work, the electrochemical and structural behavior of reinforced concrete beams subjected to flexure is studied. Eight beams with and without corrosion were considered. The study variable was the tensile stress in the longitudinal steel reinforcement. Stresses of 40% and 80% of the yielding stress of steel were considered. The beams were subjected to sustained loads using a post-tensioning system. Corrosion in the steel reinforcement was induced by chloride contamination of fresh concrete and wet and dry cycles. The corrosion rate of the steel, as well as the resistivity and concentration of chlorides of the concrete, were measured. The beams were tested two times using a four-point loading system. The first one before that corrosion was induced; a load associated with the target tensile stress in the steel reinforcement was applied to determine the initial structural parameters of the beams: crack pattern, crack resistance, and initial and postcrack stiffness. The second time after the corrosion was induced; incremental loads were applied until the failure of beams to determine the change in yielding and maximum strength, as well as the postyielding stiffness of the beams. It was found that the electrochemical behavior of the beams with corrosion was similar regardless of the tensile stress in the steel considered (40% or 80%). The measured electrochemical parameters indicated a high level of corrosion in accordance with Mexican standards; however, from the structural point of view, the strength and stiffness were not significantly affected by the corrosion status. Beams with electrochemical parameters associated with a higher level of corrosion are needed to study the initial degradation of the structural parameters, for example, strength degradation.

Circular concrete columns confined with GFRP tubes under repeated and sequential impact loads

The experimental work conducted in this study aims to develop more understanding of the dynamic response of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) columns under lateral impact load by testing 16 specimens. Three different types including reinforced concrete (RC), unreinforced CFFT and steel reinforced CFFT columns were tested. The specimens were tested under both repeated and sequential impact load testing protocols. Four parameters were investigated: the cross-section size, the thickness of the FRP tube, and the presence of longitudinal reinforcement. In addition, the effect of adding polypropylene fibers (PPF) to the concrete was also studied. Based on the experimental results, the damage mechanism, impact loads, deflections and strains were monitored and discussed. The results of this investigation confirmed that steel reinforced CFFT columns exhibited superior damage control characteristics when compared to RC columns. Increasing the thickness of the FRP tube decreased the displacement by up to 18 % and the residual displacement by up to 15 %. Adding PPF delayed the failure of the specimen and slightly enhanced its response. The experimental findings showed that longitudinal internal steel reinforcement played an important role in columns’ overall behavior and increased impact capacity.

Investigation of the effect of using geogrid, short glass, and steel fiber on the flexural failure of concrete beams

This research studies the flexural behavior of concrete beams reinforced with biaxial geogrids, distributed short glass and steel fibers. No longitudinal steel reinforcement bars were used. Therefore, an amount of short glass and steel fibers was used to improve the concrete beam behavior against flexural failure. Eleven specimens of single reinforced (flexural reinforcement) concrete beams and double reinforced (compression and flexural reinforced) concrete beams using two biaxial geogrids sheet layers, with randomly distributed short glass and steel fibers were cast. The samples were tested using two points of load along the beam specimen span with an increment of loading by 5 KN to evaluate several parameters. The studied parameters are using geogrids as a main flexural reinforcement, using geogrid sheet layers as a flexural and compression reinforcement, using short glass and steel fibers as an additional reinforcement of concrete with various ratios 0.25 %, and 0.75 %. The test results indicated that the use of geogrid layers as the main flexural reinforcement improved the behavior of the concrete beam specimens at failure. As well as; more enhancement of beam specimens at failure was observed when using short glass and steel fibers with geogrid reinforcement in concrete beams. The tested beam specimens which were reinforced by geogrids in the flexural and compression zone using 0.75 % of steel fibers gave better results due to modes of failure, toughness, failure load capacity, crack width, and post cracking stiffness.

Experimental Study on Seismic Performance of Precast Concrete Shear Walls with Hybrid Connections

ABSTRACT Seismic performance of full-scale precast concrete shear walls with grouting sleeve/grouting-anchor hybrid connection was tested under low cyclic loading and compared with the cast-in-place shear wall. The tested parameters include the longitudinal steel reinforcement connection mode and the number of the connection row. The results show that all precast walls have a flexural failure under low cyclic loading, with the yielded longitudinal steel reinforcement and crushed concrete at the bottom of the walls. The ultimate interlayer displacement angle of each wall is in the range of 1/59 ~ 1/50, which meets the requirement of the elastic-plastic interlayer displacement angle limit. The hysteretic curves of the four shear walls are similar. The positive and negative average bearing capacity of precast walls PW1, PW2 and PW3 are 1.07, 1.02 and 1.2 times higher than that of the cast-in-place wall SW1, respectively; their ductility coefficients are 0.77, 0.74 and 0.96 times that of SW1, respectively, and their cumulative energy dissipation rate are 0.89, 0.64 and 0.87 times that of SW1, respectively. Besides, the four walls have a similar stiffness degradation trend. The shear deformations of PW2 and PW3 are significantly smaller than those of SW1 and PW1. The seismic performance of PW2 (double-row hybrid connection) is close to that of PW1 (grouting sleeve connection) but is poorer than PW3 (single-row hybrid connection).

Structural behavior of reinforced concrete incorporating glass waste as coarse aggregate

ABSTRACT Most of the previous work related to using waste glass as aggregate in concrete focused on mechanical properties, so this investigation focused on the structural behavior of reinforced concrete (RC) beams incorporating waste glass as a partial replacement of aggregate. This research investigated the influence of waste glass as a replacement for coarse aggregate in the following percentages: 0% (reference), 25% and 50%, on the structural behavior of RC beams. This work uses six beams (cross-section 150 × 150 mm and span length of 900 mm). In addition to the effect of glass aggregate content on structural behavior, another parameter was considered, which is the effect of longitudinal steel reinforcement ratio (2Ø10 mm, ρ = 0.0083; 2Ø16 mm, ρ = 0.0222). The beams containing waste glass aggregate (WGA) showed a more ductile behavior and were less stiff compared to reference beams. Beams containing WGA showed good strength and satisfactory structural performance compared with the reference beam.

The analysis of numerical self-compacting concrete wall panel models with variations of shear reinforcement

Reinforced concrete wall critical zones are the responsive areas of dissipated earthquake loads. They are formed in the connection of the wall panels and the fixed restraints. The longitudinal and transversal steel reinforcements with certain spacing are designed according to the required nominal strength at the connections. Under certain conditions, the reinforcement distance becomes very tight, making working on castings using normal concrete difficult. This condition also occurs in boundary elements consisting of longitudinal and transversal reinforcements in tight spaces. A concrete material that flows easily and solidifies itself is required to avoid segregation. One type of this material is Self-Compacting Concrete (SCC). The SCC performance as a wall panel material that withstands gravity and cyclic lateral loads still require further research. This study aimed to analyze the hysteretic performance of reinforced SCC wall panels with variations of shear reinforcement in resisting cyclic lateral loads. The analysis used software based on numerical analysis. The drift ratios, hysteretic curves, stress patterns, ductility, and stiffness of the wall panels were analyzed. The SCC wall panel with ordinary shear reinforcement resisted lateral positive and negative loads of 152.32 kN and 143.09 kN, respectively. In comparison, the wall panel with boundary elements and tighter shear reinforcements could withstand the positive and negative lateral loads of 187.62 kN and 145.98 kN, respectively. The SCC wall panel reached the best ductility of 21.38 with ordinary shear reinforcement because the yield occurred faster than in other wall panels. The results showed that the boundary elements and shear reinforcements of reinforced SCC wall panels affected the performance in resisting cyclic lateral loads.

Centrifugal concrete poles for transmission lines reinforced with prestressed FRP rebar

Reinforced with steel rebar concrete centrifuged conical poles for power transmission poles receive corrosion damage to steel reinforcement during operation. These damages can lead to the failure of structures. Complete replacement of both longitudinal and transverse steel reinforcement by composite one is a way to increase the reliability and durability of such structures. This method also allows the use of cost-effective concretes with a low cement content. The research results have shown the viability of such solutions, but the use of composite reinforcement requires its prestressing. This article discusses the Russian practice of testing concrete centrifuged conical poles for strength, crack resistance and rigidity. A brief description of the prototypes and methods of their testing is given. The main results of bending tests of full-scale test samples are presented in the form of diagrams of their deformation. Analysis of the results showed that the test samples of poles are correspond to requirements of Russian norms for deformability, crack resistance and strength. According to the results the studied centrifugal concrete poles with prestressed longitudinal GFRP rebars and transverse spiral GFRP rebars are like traditional ones with steel reinforcement (in standardized strength, crack resistance and deflection values) and, therefore, can be used in building construction.

Experimental analysis of timber-concrete composite behaviour with synthetic fibres

With the growing importance of the principles of sustainable construction, the use of load-bearing timber-concrete composite structures is becoming increasingly popular. Timber-concrete composite offers wider possibilities for the use of timber in construction, especially for large-span structures. The most significant benefit from combining these materials can be obtained by providing a rigid connection between the timber and concrete layers, which can be obtained by the adhesive timber-to-concrete connection produced by the proposed stone chips method. A sustainable solution involves the abandonment of steel longitudinal reinforcement. The use of such a solution in practice is often associated with fears of a fragile collapse. Therefore, the issue of how to increase the safety factor of the proposed material is topical now. The experimental investigation is made to determine the effect of synthetic fibre use on timber-concrete composite behaviour by testing a series of timber-concrete composite specimens with and without fibres in the concrete layer. The obtained results show that adding 0.5 % of synthetic macro fibres allows to abandon the use of longitudinal steel reinforcement and prevents the formation of large cracks in concrete and the disintegration of the concrete layer in case of collapse.

Shear Strength of Concrete Beams without Stirrups Made with Recycled Coarse Aggregate

Eco-friendly concrete that considers waste material and requires less energy for production is in demand because it produces less carbon dioxide, reduces the consumption of raw material, and can be a cheaper option to conventional concrete. The objectives of this study are to investigate the shear behavior of reinforced concrete beams made with locally produced recycled coarse aggregate from construction demolition waste, study the important parameters that affect the shear strength and ductility, and check the applicability of the available theoretical shear strength predictive equations to recycled concrete. An experimental program that involved the testing of fifteen half-scale beams in shear without stirrups was carried out with a theoretical component. Results of the study showed that recycled concrete beams employing 50% recycled coarse aggregate had on average 27% lower shear strength than corresponding beams made with natural aggregate when tested at a shear span-to-depth ratio equal to 1.15, and almost the same strength as the natural aggregate beams when subjected to a shear span-to-depth ratio equal to 2.5. On the other hand, the average shear strength of beams utilizing 100% recycled aggregate was lower by 5% than the strength of their natural aggregate counterparts, irrespective of the shear span-to-depth ratio. The longitudinal steel reinforcement ratio had less effect on the shear strength provided by recycled concrete beams than on those made with natural aggregate, possibly due to the reduced ability of such concrete to develop strong dowel action. Although the use of higher strength concrete improved the shear strength of recycled aggregate beams, there was no clear correlation between the square-root of the concrete compressive strength and the shear strength provided by the concrete. The theoretical part of the study showed that the ACI 318 code and the strut-and-tie method can be reliably used to predict the shear strength of concrete made with recycled coarse aggregate employed in shallow and deep beams, respectively.