Shear-critical Reinforced Concrete Beams Research Articles

A machine learning-based structural load estimation model for shear-critical RC beams and slabs using multifractal analysis

This paper presents a machine learning model for load-level estimation for shear-critical reinforced concrete (RC) beams and slabs using multifractal features of their characteristic crack patterns to automate and provide well-informed decisions for RC damage assessment. Multifractal analysis was conducted on a database of 508 images, of which critical features were extracted from the singularity and generalized dimension spectra. These features are used as predictors for the load-level estimation model. The extreme gradient boosting algorithm yielded the best performance among the four machine learning models considered. The mean of the predicted-to-true ratio for the developed model was 1.04 with a coefficient of variation of 0.27. Upon applying Shapley additive explanations, the fractal dimension, information dimension, correlation dimension and the area under the left branch of the singularity spectrum were the critical features influencing load-level estimation. The proposed model can be useful to RC building inspectors.

Verification of Truss-Arch model unified for RC beams with stirrups using shear database

A shear strength analysis model called “Truss-Arch Model Unified (TAMU)” was proposed for shear-critical reinforced concrete (RC) beams with transverse reinforcement. The TAMU has its roots in the Compatibility Strut-and-Tie Model (C-STM) which is a computational modeling approach for the overall force–deformation analysis of deep beams. The TAMU simplified the C-STM so that a limited analysis can be executed by hand methods of analysis to predict the maximum load-carrying capacity of RC deep beams. While the tensile stress of concrete is generally taken into account to evaluate the shear strength of RC beams, the TAMU limit analysis focuses on the strength reduction of the principal diagonal concrete arch due to the transverse principal tensile strain. In the present study, a shear database is assembled from previous works reported in the literature to further substantiate the validity of the TAMU approach. The shear database consists of tested RC beams with shear reinforcement whose shear span-depth ratios (a/d) are between 0.5 and 4.5. Comparative TAMU analysis results show satisfactory agreement with the ultimate strengths observed in 460 RC beam tests regardless of D- and B-regions, demonstrating the method’s ability to predict the maximum load-carrying capacity for shear-critical beams. Additionally, the TAMU approach shows better accuracy and consistency against the database compared to AASHTO sectional shear design methods. The probability of reasonable prediction of the TAMU method is 92% in d-regions and 78% in B-regions, respectively, which is significantly higher than those of AASHTO sectional shear design methods, especially in d-regions. Thus, the TAMU method may be a viable improvement as an alternative strength analysis method for shear-critical RC beams with transverse reinforcement.

Shear behavior of reinforced concrete beams repaired using a hybrid scheme with stainless steel rebars and CFRP sheets

Repairing corroded flexural-deficient reinforced concrete (RC) structures using a hybrid scheme with stainless steel (SS) rebars and carbon-fiber-reinforced polymer (CFRP) sheets revealed excellent structural performance and contributes to lower maintenance costs in the remaining service life of the repaired structure. However, although cutting the bottom arm of stirrups in a hybrid repair method could affect the structural performance of shear-critical RC beams since this effect was not investigated in the past research. In this paper, structural performance of a group of shear-deficient RC beams repaired using the hybrid method is investigated experimentally to examine the effect of cutting the bottom arm of stirrup on the shear capacity of the repaired beams. The test variables included the longitudinal reinforcement types (i.e. carbon and SS), shear reinforcement configurations, and CFRP sheet wrapping schemes. Experimental results demonstrate that cutting the bottom arm of stirrup for replacing the corroded tensile rebar could significantly reduce the shear capacity of the retrofitted beams. Therefore, strengthening using CFRP sheet is needed to restore the shear performance of the retrofitted beams. Test results revealed that complete wrapping of CFRP sheet is effective to overcome the shear deficiency due to cutting the bottom arm of stirrup in the shear-critical RC beams. In addition, the effectiveness of CFRP sheet wrapping schemes on shear performance of SS-RC beams is approximately identical with that of CS-RC beams. Finally, a design methodology to repair the corroded RC bridge using hybrid method is developed and presented based on bending and shear tests.

Machine learning-based shear capacity prediction and reliability analysis of shear-critical RC beams strengthened with inorganic composites

The application of inorganic composites has proven to be an effective strengthening technique for shear-critical reinforced concrete (RC) beams. However, accurate prediction of the shear capacity of RC beams strengthened with inorganic composites has been a challenging problem due to its complex failure mechanism and the interaction between the internal and external shear reinforcements. Besides, the predictive capabilities of the existing models are not satisfactory. Thus, this research proposed machine learning (ML) based models for predicting the shear capacity of RC beams strengthened in shear with inorganic composites, for the first time, considering all important variables. The results of the analyses evidenced that the proposed ML models can be successfully used to predict the shear capacity of shear-critical RC beams strengthened with inorganic composites. Among the ML models examined herein, the extreme gradient boosting (xgBoost) model showed the highest prediction capability. The comparison among the predictions of the proposed xgBoost and existing models evidenced that the efficacy of the xgBoost model is superior to the existing models in terms of accuracy, safety, and economic aspects. Finally, reliability analysis is performed to calibrate the resistance reduction factors in order to attain target reliability indices of 3.5 and 4.0 for the proposed model.

Prediction of Deflection of Shear-Critical RC Beams Using Compatibility-Aided Truss Model

This study proposes a method for predicting the deflection of shear-critical reinforced concrete (RC) beams. Shear deterioration of shear-critical RC beams occurs before flexural yielding. After shear deterioration occurs in the shear-critical RC beams, the deflection caused by shear is greater than the flexural deflection obtained from the elastic bending theory. To reasonably predict the deflection of shear-critical RC beams, it is necessary to evaluate deflections due to shear as well as flexure. In this study, the deflections produced by flexure and shear were calculated and superposed to evaluate the deflection of shear-critical RC beams. The method recommended by ACI 318-19 was employed to calculate the flexural deflection, and a compatibility-aided truss model able to calculate the shear stress and shear deformation at each load stage was used to consider the shear deflection. A comparison of the experimental and analytical results showed that the proposed analytical method can effectively predict the deflection of shear-critical RC beams.

Application of Nonlinear Finite Element Analysis on Shear-Critical Reinforced Concrete Beams

This paper presents the application of a smeared fixed crack approach for nonlinear finite element analysis of shear-critical reinforced concrete beams. The experimental data was adopted from tests undertaken on twelve reinforced concrete beams by Bresler and Scordelis in 1963, and from duplicate tests undertaken by Vecchio and Shim in 2004. To this end, all beams were modeled in 3D using the software package ATENA-GiD. In the modeling, the nonlinear behaviors of the concrete were represented by fracture-plastic constitutive models, which were formulated within the smeared crack and crack/crush band approaches. The applicability of nonlinear analysis was demonstrated through accurate simulations of the full load-deflection responses, underlying mechanisms, crack patterns, and failure modes of all 24 beams. Detailed documentation of the results is presented to demonstrate the potential and practical value of nonlinear finite element analysis in providing an informed assessment of the safety and performance of reinforced concrete structures.

Shear behaviour of RC beams strengthened using geosynthetic materials by external and internal confinement

The objective of the present article is to study the behaviour of shear deficient reinforced concrete (RC) beams strengthened with geosynthetic materials by the experimental and analytical investigation. Two types of geosynthetic materials viz. geogrid and geotextile were applied to strengthen the RC beam by external and internal confinement. In this experimental investigation, all the RC beam specimens tested under the three-point-bending load. The shear failure is noticed in the shear critical RC beams, which has turned into a flexural-failure after strengthening with geogrid and geotextile materials by external and internal confinement. A remarkable enhancement in load-carrying capacity, energy-dissipation capacity, ductility-factor, and post-yielding behaviour is observed in all the strengthened RC beams compared to the un-strengthened conventional specimens. Further, the performance of geogrid confined specimens on these parameters is better when compared to the geotextile confined RC beams, and it is maximum in the outer confined specimens. The economy index of all the geogrid and geotextile strengthened RC beam specimens is also increased in comparison with the conventional un-strengthened specimens. Hence, it is confirmed that geogrid and geotextile materials can be a very useful strengthening solution in the RC beam by external or internal confinement with very low cost. However, for new construction, these materials can be used as shear reinforcement instead of traditional reinforcing materials, which will be very cost-effective. Further, an analytical study is carried out to illustrate the ultimate load of all the RC beam specimens, where the analytical predictions are very close to the experimental findings and show very well agreement with the test results.

Performance evaluation of reinforced concrete beams with corroded web reinforcement: Experimental and theoretical study

This study investigated the effect of corroded web reinforcement on the shear behavior of reinforced concrete (RC) beams. In this study, nine shear-critical RC beams were cast and tested. Six of these beams were corroded stirrups, while the remaining three beams were uncorroded stirrups serving as control samples. An accelerated corrosion technique was employed to corrode the stirrups in the beams. After the accelerated corrosion process, the beams were tested in three-point bending over a simply supported span. The shear span-to-depth ratio was kept constant at 3 for all beam specimens. The effects of the corrosion level, the type of steel stirrups (smooth or deformed), and the stirrup diameter were considered in the tests. The corrosion damage could easily be observed in the form of rust stains and corrosion cracks, which developed parallel to the stirrups. The beams with higher corrosion levels showed a reduction in their shear capacities. This reduction was more apparent in the beams with deformed steel stirrups. The shear capacities of the test beams were analyzed using a theoretical model that considers the effects of corrosion of the stirrups. The results of the analysis showed a good correlation between the experimental and theoretical shear strengths of the beam specimens.

Impact Resisting Mechanisms of Shear-Critical Reinforced Concrete Beams Strengthened with High-Performance FRC

Reinforced concrete (RC) structures typically present brittle failures by shear or punching under impact loading. High-performance fiber-reinforced concrete (HPFRC) has great potential due to its superior strength and energy absorption. The higher price and environmental cost of HPFRC compared to conventional RC can be effectively overcome by partially strengthening impact-sensitive RC members with HPFRC. To study the feasibility of this technique, HPFRC was applied as a tensile layer at the bottom of RC beams. Drop weight impact tests were carried out on beams with two values (35 and 55 mm) of HPFRC thickness, in addition to companion RC beams. Results show that the impact response can be divided into two stages: a first stage governed by local effects and shear plug formation at midspan, and a second stage governed by global beam behavior with formation of shear web cracks. A new resisting mechanism was observed for beams strengthened with HPFRC, as the strengthening layer worked similarly to a stress ribbon retaining the damaged RC and reducing fragmentation-induced debris. Such mechanism was fully achieved by the specimens with 35 mm HPFRC layer but was limited for the specimens with 55 mm HPFRC layer due to impact-induced interface debonding.

Shear strengthening of RC beams with FRP grid-reinforced ECC matrix

Fabric reinforced cementitious matrix (FRCM) composites are increasingly used for flexural and shear strengthening of reinforced concrete (RC) beams. This paper presents the results from an experimental study on the effectiveness and performance of a new FRCM system made of FRP grid-reinforced ECC matrix (referred to as “FGREM” for brevity) for shear strengthening of RC beams. A total of twelve shear-critical RC beams were constructed and tested. The parameters varied between the tests included the type of FRP grids, the type of cementitious matrix, the installation method of the shear strengthening system (prefabricated or cast-in-place), and the shear span-to-depth ratio of the beams. The crack patterns of all the tested beams were monitored using the digital image correlation (DIC) technique. Test results indicated that interfacial debonding of the shear strengthening layer and separation of the concrete side covers were two typical failure modes for the beams strengthened with the cast-in-place method and the prefabricated method, respectively. The gains in the shear capacity of the strengthened beams ranged from 50.9% to 160.6% with respect to the reference beams. Compared to the cast-in-place installation method, the prefabricated FGREM was demonstrated to be more efficient for shear strengthening of the RC beams.

U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design

The application of externally bonded fiber-reinforced polymer (EB-FRP) as shear transverse reinforcement applied in vulnerable reinforced concrete (RC) beams has been proved to be a promising strengthening technique. However, past studies revealed that the effectiveness of this method depends on how well the reinforcement is bonded to the concrete surface. Thus, although the application of EB-FRP wrapping around the perimeter of rectangular cross-sections leads to outstanding results, U-jacketing in shear-critical T-beams seems to undergo premature debonding failures resulting in significant reductions of the predictable strength. In this work, five shear-critical RC beams with T-shaped cross-section were constructed, strengthened and tested in four-point bending. Epoxy bonded carbon FRP (C-FRP) sheets were applied on the three sides and along the entire length of the shear-strengthened T-beams as external transverse reinforcement. Furthermore, the potential enhancement of the C-FRP sheets anchorage using bolted steel laminates has been examined. Test results indicated that although the C-FRP strengthened beams exhibited increased shear capacity, the brittle failure mode was not prevented due to the debonding of the FRP from the concrete surface. Nevertheless, the applied mechanical anchor of the C-FRP sheets delayed the debonding. Moreover, the design provisions of three different code standards (Greek Code of Interventions, Eurocode 8 and ACI Committee 440) concerning the shear capacity of T-shaped RC beams retrofitted with EB-FRP jackets or strips in U-jacketing configuration are investigated. The ability of these code standards to predict safe design estimations is checked against 165 test data from the current experimental project and data available in the literature.

Experimental study on shear strengthening of shear critical RC beams using iron-based shape memory alloy strips

Shape memory alloys (SMAs) have been introduced into structural engineering in recent years. This paper presents research results about developing a new methodology to actively strengthen reinforced concrete (RC) beams by low-cost iron-based SMA strips (Fe-SMA). These strips can transversally prestress, or confine, the cross-section of beams thanks to the shape memory effect of Fe-SMA, without having to apply prestressing force. Activation of strips is carried out by heating them up to 160 °C and then cooling them. An experimental campaign was carried out at two levels: characterization of Fe-SMA strips, and the practical application of the strengthening technique on small-scale beams without internal stirrups. The retrofitted beams with activated strips failed by bending, and the appearance of shear cracks was clearly delayed. Meanwhile, the reference beams failed due to shear.

Experimental and analytical study on strengthening of reinforced concrete T-beams in shear using steel reinforced grout (SRG)

The use of steel reinforced grout (SRG) has emerged as a promising technique for the strengthening and retrofitting of reinforced concrete (RC) structures, however, the experimental evidence on its application for shear-critical RC beams is rather limited. Accordingly, this study focuses on the structural performance of SRG-strengthened RC beams critical in shear. At this aim, an experimental investigation has been conducted on eleven RC T cross-section beams. Eight beams were strengthened with different types of SRG (different for the density, namely 1.57 and 3.14 cords per centimeter) comprised of ultra-high tensile strength steel fabrics, and three, which were unstrengthened, were used as reference specimens. The test parameters investigated were as follows: (a) steel fabric density, (b) bond scheme, and (c) amount of internal shear reinforcement within the critical shear span, SRG/stirrups interaction. The experimental results revealed the high potential of SRG system for the strengthening of shear-critical RC beams. It has significantly improved the shear capacity and deformation characteristics of the strengthened beams. The percentage increase in the load-carrying capacity over the reference beam of up to 71% was observed. In addition, an analytical model based on the simplified modified compression field theory (SMCFT) has been proposed to predict the shear capacity of SRG-strengthened beams. The SMCFT-based model has resulted in an accurate and safe prediction of the shear capacity of the SRG-strengthened beams with an average ratio of Vth/Vex of 0.92 and a standard deviation of 4.07%.

Steel-Reinforced Grout (SRG) strengthening of shear-critical RC beams

Abstract This paper investigates the effectiveness of Steel-Reinforced Grout (SRG) jackets to strengthen shear critical reinforced concrete (RC) beams. Eleven RC beams were tested in three-point bending. Key parameters of investigation were the strengthening configuration (U- and fully-wrapped jackets), the density of the fabric (1.57 and 4.72 cords/cm) and the number of the strengthening layers (one and two). The test results demonstrated the efficiency of SRG jacketing in increasing both strength (up to 160%) and deformation capacity (up to 450%) of the shear critical beams. Expressions are proposed for estimating the effective strain of the SRG jacket.

Crack Mapping on Shear-critical Reinforced Concrete Beams using an Open Source Digital Image Correlation Software

Three reinforced concrete beams, one with no shear reinforcement and two others with shear reinforcement ratios of 0.4% and 1.1%, were tested to investigate the influence of stirrup spacing on the mode of failure, overall strength and ductility. The results show that the beam reinforced with closely-spaced shear reinforcement failed in a ductile manner, whereas the other two beams with large stirrup spacing and no stirrup exhibited only a small measure of ductility and failed in a brittle manner. The importance of the provisions of maximum spacing is highlighted to ensure adequate anchorage for the stirrups and prevent a premature shear failure to occur. The application of a non-contact monitoring system employing the open source digital image correlation software Ncorr, an ordinary digital camera and a smartphone is demonstrated to provide a visualization of the cracking process throughout the load history.

Nonlinear Finite Element Modeling of Shear-Critical Reinforced Concrete Beams Using a Set of Interactive Constitutive Laws

Complex nature of diagonal tension accompanied by the formation of new cracks as well as closing and propagating preexisting cracks has deterred researchers to achieve an analytical and mathematical procedure for accurate predicting shear behavior of reinforced concrete, and there is the lack of a unique theory accepted universally. Shear behavior of reinforced concrete is studied in this paper based on recently developed constitutive laws for normal strength concrete and mild steel bars using the nonlinear finite element method. The salient feature of these stress–strain relations is to account the interactive effects of concrete and embedded bars on each other in a smeared rotating crack approach. Implementing the considered constitutive laws into an efficient secant-stiffness-based finite element algorithm, a procedure for the nonlinear analysis of reinforced concrete is achieved. The resulted procedure is capable of predicting load-deformation behavior, cracking pattern, and failure mode of reinforced concrete. Corroboration with data from shear-critical beam test specimens with a wide range of properties showed the model to predict responses with a good accuracy. The results were also compared with those from the well-known theory of modified compression field and its extension called disturbed stress field model which revealed the present study to provide more accurate predictions.

Nonlinear finite element study on the improvement of shear capacity in reinforced concrete T-Section beams by an alternative diagonal shear reinforcement

In the study a new shear reinforcement configuration named as diagonal shear reinforcement (DSR) is proposed as an easily applicable, economical and alternative technique to improve the shear capacity and ductility of shear critical reinforced concrete (RC) beams under monotonic and cyclic loadings. For this objective a numerical nonlinear finite element (FE) study is performed by considering two tested beams with flexural and shear failure modes. These two tests results are first verified numerically then DSR is included to existing FE model to start a parametric study for highlighting the efficiency of proposed DSR shear reinforcement configuration.The numerical results demonstrate that there is a significant increase in shear and ductility capacity of RC beams when proposed DSR is included. Moreover, with an increase in diameter and yield strength of DSR, the shear capacity further improves and failure mechanism shifts from shear to flexure. Thus, more ductile behavior for shear critical RC beams is achieved by the proposed DSR reinforcement configuration.

Predicting the Response of Shear-critical Reinforced Concrete Beams using Response-2000 and SNI 2847:2013

This study investigates the accuracy of Response-2000 in predicting the response of shear-critical reinforced concrete beams. The experimental data selected was that obtained by Vecchio and Shim in 2004 on twelve reinforced concrete beams which sought to replicate beams originally tested by Bresler and Scordelis in the early 1960s. This study also aims to compare the results obtained to the predictions of SNI 2847:2013. It is demonstrated that Response-2000 is capable of providing accurate predictions of load-deflection responses up to the peak load, but underestimates the ductility of beams that exhibit a mixed flexure-shear failure mode. It is also shown that both methods provide conservative predictions of the shear strength of beams with no shear reinforcement, with the software providing more consistent and reliable predictions of shear strength of beams containing shear reinforcement.

Behavior of Shear-Critical Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer—Analytical Method

Behavior of Shear-Critical Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer—Analytical Method

Behavior of Shear-Critical Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer—Experimentation

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