RC Beams Research Articles

A REVIEW OF HYBRIDISED USE OF FIBRES IN SHEAR BEHAVIOUR OF FIBRE-REINFORCED CONCRETE BEAMS

Shear failure of the concrete beam is always disastrous due to unnoticed occurrences and is avoided in construction. Introducing fibres into concrete elements has provided significant shear support to reinforced concrete beam structures through stress redistribution after initial cracking and bridging mechanisms. Given their advantages over single fibre strengthening in past years, using hybrid fibres in an optimal combination as strengthening in cementitious materials has drawn much interest. However, research on this area remains inexhaustible based on the emerging various fibre combinations and the challenge of unnoticed concrete shear failure. Therefore, reviewed research articles on shear performances of Fibre Reinforced Concrete (FRC) beams considering the effect of fibre volume, lengths and orientation on the synergy. The findings reveal the possibility of synergising fibre to enhance reinforced concrete beam(RCB) shear performance for metallic-metallic, metallic-synthetic, synthetic-synthetic, and metallic-biofibre combinations, with varying performance. Using low-strength/modulus fibre with high strength has been effective for shear resistance. Also, beam type (deep/shallow), fibre type and volume fractions, length, aspect ratio, orientation and distribution remarkably affect the shear performance of RC beams.

Analysing the influence of ground granulated blast furnace slag and steel fibre on RC beams flexural behaviour

This study examines the effect of Ground Granulated Blast Furnace Slag (GGBS) and steel fibers on the flexural behaviour of RC beams under monotonic loading. Various percentages of GGBS were used to substitute cement, namely 0%, 20%, 40%, 60%, and 80% and fibers were added to the concrete mix as 0%, 0.5%, 1%, and 1.5% of the volume of concrete. The load–deflection behaviour of GGBS-incorporated RC beams with fibers was compared with the control RC beam. Beams were tested under load control for 28 days and 180 days. The ultimate load of the GGBS-incorporated RC beam up to 40% cement replacement was found to higher than that of the control beam. The strength of concrete is reduced by 28% and 19% when cement was partially replaced by 80% of GGBS at 28 and 180 days, respectively, compared to control concrete without fibres. Further, the analytical load–deflection response of GGBS-incorporated RC beams was determined by using several codes of practice, namely, ACI 318-11(2011), CSA A23.3-04 (2004), EC-04 (2004), and IS 456 (2000). The Codal provisions were primarily based on the effective moment of inertia, Young’s modulus, and modulus of rupture, stiffness, and cracking. Average load–deflection plots obtained from experiments were compared with the computed load–deflection of analytical studies. It was found that the analytically predicted load–deflection behaviour is comparable with the corresponding average experimental load–deflection response. Moment curvature relations were also developed for RC beams.

Shear capacity of miniature beams with continuous staggered spiral stirrups

Scaled-down-reinforced concrete beams with rectangular staggered continuous spiral stirrups are experimentally investigated. Scale-down RC beams were considered in the current research due to ease of construction and economic feasibility. As the brittle shear failure should be avoided, continuous research trials have been conducted to find an effective technique to improve shear failure mechanism. Twenty-two beams were investigated for shear behavior under 4-point static push-over load considering the normal stirrups and compared with continuous staggered spiral ones. Stirrup spacing, shear arm ratio a/d, and shear reinforcement configurations are the main variables. All beams were designed and scaled down to be one-eighth of the full-scale beams. To minimize the size effect of using small-scale models, mortar was used instead of conventional concrete. The focus in this study was related to improved shear capacity, dissipated energy, and shear cracks propagation. It was found that using spiral reinforcement instead of normal one leads to a significant enhancement in shear capacity and dissipated energy by 33% and 45%, respectively. Therefore, the prototype RC model expected capacities were detailed calculated considering the scale-down factor used by authors. The experimental results were compared by calculated values according to international standard and specifications.

Predicting Failure Modes of RC Beams Strengthening with FRP-NSM System: A Statistical Approach

FRP strengthening using near surface mounted (NSM)is recognized as a highly effective method for strengthening structures using FRP material. However, there are some drawbacks associated with this technique. One of the challenges is concrete cover separation failure, which leads to premature material failure and restricts NSM technique applicability. To address this issue, multinomial logistic regression (MLR) analysis is used. This analysis aimed to investigate the factors (Total Equivalent Steel Ratio TESR%, Stirrup Steel Ratio%, and presence of an anchorage) that can be used to predict the failure modes of reinforced concrete beams strengthened with the FRP-NSM system using a previously published dataset consisting of 131 beam tests from 25 studies. By using odds ratios, which are exponential coefficients, the MLR results were interpreted. The study indicated that a reduction in the TESR% predictor or increase in Stirrup Steel Ratio%, deceases the probability of conversion from concrete cover separation to other failure modes such as flexural failure, FRP bar debonding, and FRP bar rupture. Moreover, the reinforced concrete beams strengthened with the FRP-NSM system with anchorage has a positive contribution on the expected the failure modes: flexural failure, FRP bar debonding, and FRP bar rupture compared to concrete cover separation. Based on the classification table analysis, the model’s correct classification rate was 51.1%. The model is accurate in predicting failure modes, as its rate is higher than the chance accuracy rate of 36.4%.

Uncertainty quantification of the flexural strengthening of RC beams with UHPC using improved metaheuristic algorithm

This study presents an artificial intelligence-based model to predict the flexural strengthening of RC beam/slab strengthened with UHPC (RC-UHPC) and perform uncertainty quantification of such values. Improved eliminate particle swamp optimization hybridized artificial neural network (IEPANN) was a model developed on artificial neural network (ANN) optimized by improved-eliminate-particle-swamp optimization (IEPSO). Experimental datasets were used to establish the hybrid ML model. The efficiency of IEPANN was compared against support vector regression (SVR) and multiple linear regression (MLR). The IEPANN demonstrates outstanding performance over MLR and SVR. The flexural strengthening of RC-UHPC depends on materials and geometrical configurations, which have stochastic characteristics. Convergence studies, sensitivity, and probabilistic analyses were conducted on each random parameter. Simulation results indicated that strengthening configuration is the most sensitive to flexural strengthening. Systematic assessment of uncertainties in flexural strengthening may lead to a higher confidence level in model outcomes, and RC-UHPC is examined and designed. It enhances construction reliability.

Flexural behavior of RC beams with multiple parallelogram openings

On account of the detrimental effects of the post-drilling holes in hardened RC beams, designing the beams with transverse openings before construction is becoming more popular in the last decades. The contribution of the transverse openings to the overall economy and efficiency of construction by reducing the unusable dead space in the floor height is a rather significant motivation behind the vast number of studies on this topic. In search for the opening geometries and reinforcement schemes with the least negative effects on the beam behavior, the present study focused on the parallelogram (diamond) opening geometry, which is thought to facilitate the transmission of diagonal compression forces in the beam web thanks to the inclination of the posts. Within this scope, a total of 12 beams, including two reference beams without openings, were tested under four-point bending. Circular, square and parallelogram (45°−60°−75°) opening geometries were adopted and the test results were evaluated based on the opening geometry and the longitudinal reinforcement ratio. In order to avoid various shear failure modes of beams with openings, different special reinforcement schemes were employed around the web openings. Two different longitudinal reinforcement ratios were used to understand if pure flexural failure can be reached in RC beams with openings without being affected by different shear failure modes (beam- and frame-type diagonal tension and diagonal compression). The inclination angle of the posts between the openings in parallelogram opening geometry was found to be the most crucial parameter in the final beam failure and beam ductility. The use of diagonal cables surrounding the openings and connecting the posts and chords was established to be obligatory in square and parallelogram opening geometries to reach a ductile beam behavior without being affected by Vierendeel panel action and different shear failure modes.

Shear Reinforcement of Existing Reinforced Concrete Beam Using Deep Embedment Method

The load capacity of old reinforced concrete structures must be increased to meet current standards. This might be due to increased load needs, inadequate shear provisions in the original design, material degradation, or rising demands for shear capacity related to flexural strengthening. This research demonstrates a method that effectively repairs RC beams using embedded steel bars. Loading history was reproduced in the form of cracking within the elastic range in 2000 x 150 x 200 mm beam. The beam was repaired and then reloaded to failure in the experimental test. The results show that the contribution of steel bars embedded in the core of the RC beam to the load capacity can be significant. The highest initial stiffness of the strengthened beam was 13,07 kN/mm, which was 69% higher than the control beam, while the maximum load of the strengthened beam was 43 kN with the deflection at 13,00 mm, 43% higher than the control beam. The cracks developed during the reinforced beam’s second load phase were identical to the first, and the shear capacity increased more than the control beam.

Investigation of the relationship between bending capacity and SMFL intensity of existing reinforced concrete hollow slab beams

This paper proposes a novel approach for monitoring the bearing capacity of RC beams using the spontaneous magnetic flux leakage (SMFL) effect. Three decommissioned reinforced concrete hollow slab (RCHS) beams underwent bending loading failure experiments to collect data on crack formation, deflection Y, concrete strain ε, steel bar strain ε and SMFL intensity Bx/y/z. The mechanical properties of concrete outside the structure and the magnetic properties of steel bars inside the structure during loading are investigated. The force-magnetic coupling effect of HRB400 steel bars is characterized. The SMFL parameter BC closely correlates with Y and ε variations in loading process, the quantitative relationship models between mechanical and magnetic parameters of the beam structures are established. A theoretical model predicted the ultimate bending capacity of RCHS beams. The relationship between beam bending capacity and SMFL intensity is clarified.

Flexural behavior of RC beam using industrial copper slag as a sustainable substitute for fine aggregate

Flexural behavior of RC beam using industrial copper slag as a sustainable substitute for fine aggregate

Flexural behavior of RC beams strengthened with CFRP sheets and ECC material

Premature debonding is a common failure mode of externally bonded fiber reinforced polymer (EB-FRP) strengthened reinforced concrete (RC) members, which leads to inefficient use of FRP. In this paper, engineered cementitious composite (ECC) with multiple fine cracks was introduced as a transition layer in FRP-concrete interface to delay CFRP sheet debonding. Four strengthened beams with CFRP sheet and ECC layer and one reference RC beam were tested under four-point bending. The effects of the type of strengthened scheme and CFRP sheet layers were investigated. The results showed that the beams strengthened with CFRP sheet and ECC layer had a significant improvement in crack load (71.8–105.1%), yield load (39.5–86.1%) and ultimate load (59.5–84.6%) relative to the reference beam. The introduction of the ECC layer could effectively delay CFRP debonding and had positive effect on the crack resistance. Fracture of CFRP sheet occurred when the beam was strengthened with one CFRP sheet layer. These findings are expected to provide better understanding on the FRP-ECC repair system.

Numerical analysis on rehabilitation material selection on RC beams with ultra-high-performance concrete: an application of sustainable construction

Numerical analysis on rehabilitation material selection on RC beams with ultra-high-performance concrete: an application of sustainable construction

Predictive modeling of shear strength in fiber-reinforced cementitious matrix-strengthened RC beams using machine learning

Predictive modeling of shear strength in fiber-reinforced cementitious matrix-strengthened RC beams using machine learning

Probabilistic model for cracking localization in reinforced fibrous concrete beams

This paper proposes a probabilistic model that explains the phenomenon of cracking localization (CL) in RC beams with addition of steel fibers. Quantification of the CL is defined as the ratio between the total number of cracks and the number of significantly wide cracks. The model considers both the fibers and conventional reinforcement ratios, as well as the steel stress hardening and the location of the rebars in the cross-section. The fiber distribution in the concrete mix is considered random while the conventional reinforcement—as deterministic. A cumulative function of the total steel distribution, and a binomial probability function are proposed for a newly defined variable that represents the distribution of the fibers effectiveness along the beam. The model was validated with available data from flexural experiments showing good agreement of the model’s prediction with the reported results. The model shows that the cracking localization level in beams is more pronounced in beams with low reinforcement ratios and relatively large fibers content and enables its quantification.

Modeling for torsional strength prediction of strengthened RC beams

Modeling for torsional strength prediction of strengthened RC beams

Experimental and Theoretical Studies on the Shear Performance of Concrete Beams Reinforced with Fiber-Reinforced Polymer Stirrups.

In this paper, the shear behavior of concrete beams reinforced with FRP stirrups is studied. The shear performances of six concrete beams with a size of 150 mm × 300 mm × 3000 mm under four-point loading up to failure were experimentally analyzed. The critical parameters included the shear span to depth ratio (λ) and stirrup spacing (S). The test results revealed that as λ increased from 1 to 2, 3, and 4, the ultimate shear capacity of the beam decreases by 50.5%, 67.7%, and 69.2%, respectively. Meanwhile, as S increased from 100 mm to 150 mm and 200 mm, the ultimate shear capacity decreased by 16.1% and 44.6%, respectively. A new shear capacity calculation model of concrete beam reinforced with FRP stirrups was also proposed, which further considered the shear capacity of the FRP stirrups on the basis of the shear capacity of an RC beam without stirrups using the strut-and-tie model. Finally, the experiment and calculation results of 56 beam specimens reinforced with FRP stirrups extracted from this paper and previous studies were compared using the calculation models proposed in this paper, in order to evaluate the accuracy of these calculation models.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Seismic performance of RC frame structures with infill CLT shear walls

This paper focuses on the newly proposed RC-CLT hybrid wall systems used in residential buildings. Cyclic loading tests were conducted using 2-storey specimens, to confirm the seismic performance and behavior of the hybrid system and also to investigate the behavior of the RC beams in mid-level and the transmission of shear stress by the CLT wall from upper to lower level. The experimental results showed that CLT could potentially be more superior than RC wall infill in terms of ductility, due to CLT exhibiting higher inter-story drift during shear failure. Furthermore, this study proposes numerical models to simulate the experimental results of the hybrid systems. The RC structural members were modeled using linear elements with MS model inserted at the ends to consider for the N-M interactions. As for the CLT wall, it was modeled using several braced models. The numerical results generally show good agreements with the experimental results. As a result, the numerical model proposed in this study can contribute to better predict the structural behavior of CLT shear wall infilled RC frame with concealed steel plate and drift pin connections.

Integrating Image Processing and Machine Learning for the Non-Destructive Assessment of RC Beams Damage

Non-destructive testing (NDT) is a crucial method for detecting damages in concrete structures. Structural damage can lead to functional changes, necessitating a range of damage detection techniques. Non-destructive methods enable the pinpointing of the location of the damage without causing harm to the structure, thus saving both time and money. Damaged structures exhibit alterations in their static and dynamic properties, primarily stemming from a reduction in stiffness. Monitoring these changes allows for the determination of the failure location and severity, facilitating timely repairs and reinforcement before further deterioration occurs. A systematic approach to damage detection and assessment is pivotal for fortifying structures and preventing structural collapse, which can result in both financial and human losses. In this study, we employ image processing to categorize damaged beams based on their crack growth and propagation patterns. We also utilize support vector machine (SVM) and k-nearest neighbor (KNN) methods to detect the type, location, and extent of failures in reinforced concrete beams. To provide context and relevance for the laboratory specimens, we will compare our findings to the results from controlled experiments in a controlled laboratory setting.

Flexural behavior of SFRC-NC composite beams: An experimental and numerical analytical study

In this study, the flexural behavior of SFRC-NC composite beams cast with normal concrete (NC) and steel fiber-reinforced concrete (SFRC) were investigated. Nine SFRC-NC composite beams were designed and tested through four-point bending (FPB) experiments, including one reference beam with normal concrete (NC) and eight beams with different SFRC layer thicknesses. The effect of the designed parameters, including the SFRC layer thickness, diameter of steel rebar, and fiber content, on the flexural behavior of the beams was investigated experimentally. Compared to beams cast with normal concrete, the experimental results showed that the application of SFRC can effectively improve the bearing capacity of RC beams. These improvements include the crack-initial load, yield load, ultimate load, and ductility. Based on the experimental results, an FE macro-model was developed, and a series of numerical analyses were conducted to investigate the flexural behavior of SFRC-NC composite beams.

Scaling laws of low-velocity impact response for RC beams: Impact force and reaction force

Predicting the low-velocity impact response of the prototype based on the scaled test results is one of the significant topics in structural design and protection. Thus, reliable similarity laws are required to bridge the dynamic similarity between models and prototypes. In this study, numerical modeling was carried out by considering plastic damage and strain rate effects. Then, the impact responses of four series reinforced concrete beams satisfying traditional similarity laws were analyzed. The largest beam section size reached 600 mm × 1000 mm. The scaling effects on the impact force profiles (comprising three Types) and reaction force profiles of the beam were investigated. Several characteristic points were defined for the available simplified profiles of impact and reaction forces. It is shown that the scaling effects on each characteristic are not consistent. As the theoretical scale factor increases, the characteristics such as the peak impact force, the positive peak of the reaction force, and its plateau satisfy the traditional similarity law, whereas the characteristics such as the impact force duration and the negative peak of the reaction force do not. Therefore, modified dynamic scale factors for the characteristics of impact and reaction force profiles from models to prototypes were proposed. Based on the suggested scaling laws, the simplified profiles of impact and support reaction forces of the prototype can be predicted. It is expected that it will help researchers to conduct experimental studies and optimized designs on structural impact resistance.