Shear Performance Of Concrete Beams Research Articles

Effects of carbonation modification on shear performance of recycled aggregate concrete beams: Test and mechanism analysis

The effective use of recycled aggregates (RAs) in construction significantly contributes to environmental preservation and the conservation of non-renewable natural resources. However, RAs typically exhibit inferior performance relative to natural aggregates (NAs). To improve the quality of RAs, carbonation modification has been introduced as an eco-friendly and practical method. This study explores the shear performance of concrete beams that incorporate various replacement ratios (30 %, 50 %, 70 %, and 100 %) of carbonated recycled aggregates (CRAs). The experiment employed Digital image correlation (DIC) system to evaluate the stress distribution on the concrete surface within the shear span section. The evaluation of shear performance was conducted through comprehensive analysis includes load-deflection curve, steel strain, the width of the primary diagonal crack, average principal tensile strain, orientation of principal directions, average shear strain, and shear deflection. A practical approach was adopted to separate the shear strength contributions of transverse steel (Vs) and concrete (Vc), based on transverse steel strains along the primary diagonal crack. Results indicate that carbonated recycled aggregate concrete (CRAC) beams demonstrate enhanced shear performance in comparison to recycled aggregate concrete beams. Shear strength significantly decreases with replacement rates exceeding 70 %. Furthermore, the experimental results were compared against shear strength with the design codes, and shear deflection with existing models.

Prediction of the shear strength of lightweight concrete beams without web reinforcement based on a machine learning model optimized by a genetic algorithm

The shear performance of concrete beams is affected by several factors, and some of effective variables and control mechanisms should be considered in predicting shear strength. Compared with ordinary concrete, lightweight concrete (LWC) is more unique, which greatly increases the difficulty of prediction. This is also why it is necessary to introduce machine learning (ML) technology with stronger data processing capabilities to predict the shear performance of LWC. Therefore, the aim of this study is to employ four well-known machine learning methods to predict the shear performance of LWC beams, namely, support vector machine (SVM), artificial neural network (ANN), radial basis function (RBF) neural network and random forest (RF). First, the shear test results of 220 LWC beams were collected, and the corresponding datasets were established based on possible influencing factors. Then, the optimal dataset partitioning methods for four different ML models were explored and determined. The parameter search process of the four models under the optimal dataset partitioning ratio was optimized using a genetic algorithm (GA), and four GA-ML prediction models were developed. The results show that the developed GA-RF model achieves a train set accuracy of 95.3 % and a test set accuracy of 93.3 %. The GA-ML technology significantly improves the accuracy of the prediction of shear strength compared to the formulaic model based on current international design standards. The prediction mechanism of the model is further analyzed to ensure that the model is reliable. The results indicate that it can be applied to predict the shear strength of LWC. In summary, the GA-RF model and importance analysis proposed in this article are practical methods for predicting and explaining the shear strength of LWC.

Experimental Study on Shear Performance of Concrete Beams Reinforced with Externally Unbonded Prestressed CFRP Tendons

To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites.

Experimental Study on the Flexural and Shear Performance of Concrete Beams Strengthened with Prestressed CFRP Tendons

To investigate the influence of external prestressing with carbon fiber-reinforced polymer (CFRP) tendons on the flexural and shear performance of reinforced concrete beams, a total of six simply supported beams with a length of 3.5 m and two two-span continuous beams with a length of 7 m were studied. The influences of the prestressing level of CFRP tendons, the pattern of straight-line and flexural reinforcement of externally prestressed CFRP tendons, and the existence of initial cracks in the beams on the flexural bearing capacity of the reinforced beams were explored through modeling tests. The calculating equation for anticipating the ultimate flexural bearing capacity of concrete beams reinforced with externally prestressed CFRP tendons was modified based on the test results. The findings indicate that the flexural bearing capacity of the test beams was significantly enhanced through both flexural and straight-line reinforcement. Specifically, the ultimate flexural bearing capacity of the simply supported beams exhibited improvements of approximately 160% and 170%, respectively, whereas the ultimate flexural bearing capacity of the continuous beams was enhanced by approximately 113% through the reinforcement of flexural arrangement. Additionally, the shear resistance capacity of the concrete beams was notably improved through the flexural arrangement reinforcement, and the shear resistance capacity of the beams exhibited a substantial increase as the prestressing level of the CFRP tendons increased. The flexural moments in the vicinity of the support point of the reinforced beam exhibited an increase ranging from 41.7% to 112.5% when the stirrup strains started to escalate rapidly. Additionally, the rigidity of the test beams showed a close correlation with both the prestressing level and the existence of initial cracks.

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.

Experimental study on shear performance of basalt fiber concrete beams without web reinforcement

In this study, we report the results of an experimental investigation conducted under a four-point bending loading in order to evaluate the shear performance of concrete beams reinforced with basalt fiber without web reinforcement. According to the experimental results, it is evident that the final failure morphology of concrete-basalt fiber concrete composite beams and conventional concrete beams was shear failure, whereas the failure morphology of concrete beams reinforced with full basalt fiber was bending failure. Moreover, the results also indicate that the cracking load and ultimate bearing capacity of concrete composite beams reinforced with concrete-basalt fiber are lower than those of conventional concrete beam. This is mainly due to the interface between ordinary post-cast concrete and concrete reinforced with hardened basalt fiber. Due to the superior tensile properties of fiber, composite beams and all basalt fiber concrete beams exhibit a higher degree of ductility than conventional concrete beams. Utilizing the existing calculation theory for concrete beams reinforced with fiber, it was calculated that the cracking load and ultimate load of basalt fiber beams were calculated, and the calculation results were consistent with the experimental results. Based on the results of the evaluation and the theoretical analysis, this study proposes a finite element modeling method for basalt fiber composite beams. The results of the analysis were consistent with the experimental results of all investigated beams. The established model was employed in order to investigate the influence of shear span ratio on the shear performance of basalt fiber beams.

Shear Performance of Concrete Beams with a Maximum Size of Recycled Concrete Aggregate

The use of concrete mixes with recycled materials has gained traction in research communities. However, the major drawback of the recycled concrete aggregate (RCA) has been the contribution of the cement paste mortar attached to the surface. The quantity of surface-attached mortar on the virgin aggregate dominates and defines the shear performance of concrete beams. Concrete shear failure is usually abrupt and catastrophic, especially in concrete beams without shear reinforcement. The effectiveness of the maximum size of RCA for the performance of untreated and treated with pozzolanic cement and rice husk ash (RHA) slurry was investigated. A total of sixteen (16) beams containing RCA of four (4) maximum sizes, 10, 14, 20, and 25 mm, were prepared and tested after 28 days. The beams were loaded in shear using shear span-depth ratios of 1.25 and 2.50. The results showed that the shear strength of the beams increases as the aggregate size increases to a maximum size of 20 mm, beyond which the shear strength reduces. It was attributed to the attached mortar, which increased as the size of the aggregate increased, creating a weak zone for shear failure in the concrete. In addition, RCA pretreatment using slurry-containing cement and RHA strengthened the attached mortar on the aggregate surface. It resulted in a dense and more compact aggregate that slightly improved the shear strength by about 2.2% for beams containing 20 mm RCA size. The ultimate shear strength of the experimental work in the study was predicted using eight (8) selected models from the literature. Models that account for the aggregate size and shear span to depth ratio resulted in shear strength ratios of 1.29, 0.91, 1.08, and 1.20 for Bažant and Becq-Giraudon, 2002, Zsutty, 1968, Xu et al., 2012, and Gastebled and May, 2001, which are almost similar outcomes to the experimental results.

Improvement of shear capacity of RAC beams by adopting identical mortar volume method of mix-design along with dual-stage mixing approach

The shear performance of concrete beams produced from construction and demolition (C&D) waste is evaluated by considering two different shear-span to depth ratios (a/d). A total of twelve beams are cast, in which four beams of natural aggregate concrete (NAC) of conventional mix-design procedure (denoted as NAC), four beams of recycled aggregate concrete (RAC) of identical mortar volume (IMV) mix-design procedure in conjunction with normal mixing procedure (NMP) (denoted as RAC/NMP), and rest four beams of RAC of IMV mix-design procedure in conjunction with proposed dual-stage mixing procedure (DSMPSiC) (symbolized as RAC/DSMPSiC). Out of four beams of each of the above categories, two beams are tested by considering a/d = 2.5 and the other two are tested by considering a/d = 3. The load-deflection curve, ultimate load carrying capacity, and crack propagation parameters are also evaluated. The results are compared with different empirical relations proposed in codes and published literature. Analysing critically, it is observed that the shear strengths of RAC/NMP beams are reduced by 19% for a/d = 2.5 and 13.5% for a/d = 3 as compared to corresponding NAC beams. However, after following the proposed DSMPSiC, the above reduction percentages are reduced by 11.2% and 5.2%, respectively.

Experimental Study on the Shear Strength of Reinforced Concrete Beams with Various Integrated Shear Reinforcements

The purpose of this study was to evaluate the shear performance of concrete beams with integrated shear reinforcements made of steel plates and rebar bent in an N shape (N-type rebar), and to evaluate the applicability of the current relevant design standards. For this purpose, four concrete beam specimens were manufactured. Four-point loading tests were performed with all the specimens. The experiments confirmed that both types of shear reinforcements had a shear-reinforcing effect (an about 60% increase in shear strength), but the N-type rebar did not exceed the nominal shear strength, probably because the rebar did not yield sufficiently. A sufficient number of steel-plate-type shear reinforcements yielded in the shear crack. When evaluating the shear performance of a new shear reinforcement, it is necessary to calculate the design strength by actually reflecting whether the shear reinforcements’ yields are due to the angle of the diagonal crack. Calculating the shear contribution based on the strain of the shear reinforcements and comparing this shear strength with those five design standards, the shear strength of the shear reinforcements were evaluated conservatively. It is considered that there will be no problem in structural safety even if the shear design is carried out according to the current design standards.

Shear performance of basalt fiber-reinforced concrete beams reinforced with BFRP bars

This paper reports on the experimental and analytical investigation of the shear performance of concrete beams cast with basalt fiber-reinforced concrete (BFRC) and longitudinally reinforced with basalt fiber-reinforced polymer (BFRP) bars. Fourteen hybrid (BFRC-BFRP) beams with no stirrups were tested to failure under a four-point loading setup. The investigated parameters included the volume fraction, Vf, of the added fibers (0.75 and 1.5%), the reinforcement ratio of the BFRP bars,ρ, (0.31, 0.48, 0.69, 1.05, and 1.52%), and the shear span-to-depth ratios, a/d, of the beams (3.3 and 2.5 for slender and short beams, respectively). The tests results showed that adding 0.75% of basalt macrofibres (BMF) improved the shear capacity of the slender and short beams by 46 and 43 %, respectively, compared to 81 and 82% when 1.5% of BMF were added. The impact of adding the BMF on the shear strength of the beams diminished as the longitudinal reinforcement ratios increased. The existing models overestimated the shear strength of the tested beams with an average predicted-to-experimental ratio ranging between 1.15 ± 0.03 and 2.48 ± 0.29. A shear model that accounts for the type of the longitudinal reinforcement and the added fibers was proposed to predict the shear strength of the BFRC-BFRP beams. A good agreement between the predicted and experimental shear strength was evident with a predicted-to-experimental ratio that ranged between 0.98 ± 0.11 and 0.88 ± 0.02 for the slender and short beams, respectively.

Experimental study on concrete beams without web reinforcement based on fractal theory

Based on the development and distribution of cracks, we explored the shear performance of concrete beams without web reinforcement under different shear span ratios and longitudinal reinforcement ratios. Nine groups of concrete beams without web reinforcement with shear-span ratios of 1.5, 2, 2.5 and longitudinal reinforcement ratios of 1.28%, 1.62%, and 1.99% were used for four-point loading shear tests. The cracks on the surface of the test beam were analyzed by applying fractal geometry theory, and the box counting method was used to calculate the fractal dimension of the cracks on the surface of the beam under the effect of the graded load and the ultimate load. The relationship among the fractal dimension of the beam surface, the ultimate load, the graded load and the span was discussed. The results show that the shear-span ratio is inversely proportional to the ultimate load and cracking load, while the longitudinal reinforcement ratio is directly proportional to the ultimate load and exhibit a small influence on the cracking load. Concrete beams without web reinforcement have obvious fractal characteristics under the effect of graded loading or ultimate load. The fractal dimension under the effect of graded load is 0.964–1.449, and the fractal dimension under the effect of ultimate load is around 1.33. The graded load, mid-span deflection and fractal dimension show a good logarithmic relationship. The change curve of graded load and fractal dimension is affected by the shear-span ratio and the beam longitudinal reinforcement ratio. The intermediate deflection is less affected by the shear-span ratio. Under the effect of the longitudinal reinforcement ratio, the curvature of the curve shows a trend of first increasing and then decreasing, but the relationship between the ultimate load and the fractal dimension has certain differences. The ultimate load first increases and then decreases with the increase of the shear span ratio, and the difference is greater with the increase of the longitudinal reinforcement ratio.

Fatigue shear performance of concrete beams reinforced with hybrid (glass-fiber-reinforced polymer + steel) rebars and stirrups

Fatigue shear performance of concrete beams reinforced with hybrid (glass-fiber-reinforced polymer + steel) rebars and stirrups

Shear performance of reinforced concrete beams incorporating stiff slender elements

The present work investigates the shear performance of concrete beams reinforced longitudinally with steel rebars incorporating randomly distributed stiff elements known as “needles”. Compared to commonly used fibers, needles function differently in concrete members that carry increasing internal stresses. To measure the effect of needles on the mechanical performance of concrete, 32 longitudinally reinforced concrete (RC) beams and 96 non-reinforced concrete prisms were tested. Among numerous possibilities, the dimensions of the needles used in the present study were selected based on a number of practical considerations. The results showed that the needles increased the peak and residual shear capacity of the reinforced beams significantly. However, the improvements were not greater than those achieved by using the same volumetric content of fibers made of the same material as that the needles were produced from. Based on the measured results and the observation of cracking patterns, guidance for optimizing the geometry of needles and test specimens are provided for future research.

Experimental Investigation of the Shear Behavior of a Concrete Beam without Web Reinforcements Using External Vertical Prestressing Rebars

The shear performance of concrete beams is known to be an important mechanical feature; hence, enhanced shear resistance is critical for determining a beam’s performance in terms of security and service life. This paper presents a study on the shear behavior of concrete beams without web reinforcement strengthened by external vertical prestressing rebars (EVPRs). Experimental data were obtained from seven test beams with varying influencing factors (stirrup ratio ρsEP, arrangement spacing s, prestressing force Fp, and compressive stress degree γp of the EVPRs) to determine their effects on the shear behavior. The results reveal that the EVPRs can significantly improve the shear capacity and ductility of concrete beams without web reinforcement. Furthermore, the failure mode is changed from brittle diagonal tension to relatively ductile shear compression, and the flexural cracks and shear cracks are more fully developed. The shear capacity becomes enhanced as the ρsEP and γp are increased; vertical compressive stress provided by the EVPRs can reduce the principal tensile stress of the concrete structure to prevent the shear cracking and enhance the shear resistance of the concrete. Meanwhile, in the stage from the formation of the critical shear crack (CSC) to the shear failure, the EVPRs can be used as stirrups to share the shear load. It can be concluded that EVPRs can effectively improve the shear performance of concrete beams.