High Strength Concrete Corbels Research Articles

Shear Bearing Capacity Prediction of Steel-Fiber-Reinforced High-Strength Concrete Corbels on Modified Compression Field Theory

In order to analyze the shear mechanism of the steel-fiber high-strength concrete corbels, a calculation model for the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels was proposed based on the modified compression field theory. Considering the existence of residual tensile stress in steel-fiber-reinforced concrete at crack locations, the cracked steel-fiber-reinforced concrete was treated as a continuous material. The constitutive relation of cracked steel-fiber-reinforced concrete and the local stress equilibrium equation were modified. It was compared with the results of 34 steel-fiber high-strength concrete corbels, including those in this paper. The predicted results were compared with the experimental values and the predictions of the Fattuhi model, Campione model, and Russo model to validate the rationality of the proposed model. The results revealed that the mean value between the experimental values and the predicted results of the proposed model is 1.104, with a variance of 0.003, showing good agreement. The proposed model can accurately predict the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels.

Practical evaluation of high-strength concrete corbels reinforced with GFRP bent bars

Corbels, designed primarily as discontinuity-region structural elements, are often used as components of bridges and buildings to support beams and girders. There has been extensive research on steel-reinforced concrete (RC) corbels; however, there is a noticeable gap in research to investigate the behavior of glass fiber-reinforced polymer (GFRP)-RC corbels. Considering the linear stress–strain relationship up to failure of GFRP, the use of high-strength concrete (HSC) in lieu of the normal-strength concrete (NSC) in corbels would reduce their sizes considerably; yet it will aggravate their brittle nature. In this study, nine full-scale concrete corbels were constructed and tested until failure. One reference specimen was reinforced with steel bars, while the other eight were GFRP-RC corbels. The main test parameters were the type of concrete (HSC or NSC), the shear span-to-depth ratio, and the total reinforcement ratio of the main and horizontal bars. The tests showed that the principal mode of failure was concrete strut crushing for specimens with a shorter shear-span-to-depth ratio. The steel-RC corbels failed by tension tie yielding, which showed large ductility. The Canadian standards for FRP-RC building structures predicted a conservative mean capacity with Ppre/Pexp ratio of 0.59 compared to the American code and Eurocode, which overestimated the capacities with a ratio of 1.18 and 1.25, respectively.

Analysis of Shear Model for Steel-Fiber-Reinforced High-Strength Concrete Corbels with Welded-Anchorage Longitudinal Reinforcement.

According to the shear capacity test results of six steel-fiber-reinforced high-strength concrete (SFHSC) corbels with welded-anchorage longitudinal reinforcement under concentrated load, the effects of shear span ratio and steel fiber volume fraction on the failure mode, cracking load and ultimate load of corbel specimens were analyzed. On the basis of experimental research, the shear transfer mechanism of corbel structure was discussed. Then, a modified softened strut-and-tie model (MSSTM), composed of the diagonal and horizontal mechanisms, was proposed, for steel-fiber-reinforced high-strength concrete corbels. The contributions of concrete, steel fiber and horizontal stirrups to the shear bearing capacity of the corbels were clarified. A calculation method for the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels was established and was simplified on this basis. The calculation results of the model were compared with the test values and calculation results of the GB50010-2010 code, the ACI318-19 code, the EN 1992-1-1 code and the CSA A23.3-19 code. The results showed that the concrete corbel with small shear span ratio mainly has two typical failure modes: shear failure and diagonal compression failure. With the increase in shear span ratio, the shear capacity of corbels decreases. Steel fiber can improve the ductility of a reinforced concrete corbel, but has little effect on the failure mode of the diagonal section. The calculated values of the national codes were lower than the experimental values, and the results were conservative. The theoretical calculation values of the shear capacity calculation model of the corbels were close to the experimental results. In addition, the model has a clear mechanical concept considering the tensile properties of steel-fiber-reinforced high-strength concrete and the influence of horizontal stirrups, which can reasonably reflect the shear transfer mechanism of corbels.

Prediction of Shear Strength for Steel-Fiber High-Strength Concrete Corbels with the Softened Strut-and-Tie Model

On the basis of the test results of nine steel-fiber high-strength concrete corbel specimens subjected to a vertical load, the influence of the steel fiber content on the shear performance of corbels was analyzed. The softened strut-and-tie model (SSTM) was used to analyze the shear strength of steel-fiber high-strength concrete corbels, taking into consideration the shear contribution of steel fibers. A calculation model for the shear strength of steel-fiber high-strength concrete corbels is proposed, and a database for 26 steel-fiber high-strength concrete corbels was created by using the model. The results obtained according to the codes ACI318-19, EC2, CSA A23.3-19 and the softened strut-and-tie model were compared with the experimental values to verify the rationality of the model. The findings showed that steel fiber can effectively limit the crack width and improve the crack morphology. The overall average value of the ratio between the experimental and the predicted strengths of the model was 1.082, and the variance was 0.004. The values predicted with the proposed calculation model were closer to the experimental values than those calculated according to the codes. This study provides a definite mechanical model that can reveal the shear mechanism of steel-fiber high-strength concrete. It can reasonably predict the shear strength of steel-fiber high-strength concrete corbels.

Experimental Investigation on Shear Capacity of Steel-Fiber-Reinforced High-Strength Concrete Corbels.

As short cantilever members, corbels are mainly used to transfer eccentric loads to columns. Because of the discontinuity of load and geometric structure, corbels cannot be analyzed and designed using the method based on beam theory. Nine steel-fiber-reinforced high-strength concrete (SFRHSC) corbels were tested. The width of the corbels was 200 mm, the cross-section height of the corbel column was 450 mm, and the cantilever end height was 200 mm. The shear span/depth ratios considered were 0.2, 0.3, and 0.4; the longitudinal reinforcement ratios were 0.55%, 0.75%, and 0.98%; the stirrup reinforcement ratios were 0.39%, 0.52%, and 0.785%; and the steel fiber volume ratios were 0, 0.75%, and 1.5%. According to the test results, this paper discusses the failure process and failure mode of corbel specimens with a small shear span/depth ratio and analyzes the effects of variables such as shear span/depth ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and steel fiber volume content on the shear capacity of corbels. The shear capacity of corbels is significantly affected by the shear span/depth ratio, followed by the longitudinal reinforcement ratio and the stirrup reinforcement ratio. Moreover, it is shown that steel fibers have little impact on the failure mode and ultimate load of corbels, but can enhance the crack resistance of corbels. In addition, the bearing capacities of these corbels were calculated by Chinese code GB 50010-2010 and further compared with ACI 318-19 code, EN 1992-1-1:2004 code, and CSA A23.3-19 code, which adopt the strut-and-tie model. The results indicate that the calculation results by the empirical formula in the Chinese code are close to the corresponding test results, while the calculation method based on the strut-and-tie model of a clear mechanical concept yields conservative results, and hence the related parameter values must be further modified.

Structural behavior of high-strength concrete corbels involving steel fibers or closed stirrups

A comprehensive experimental evaluation of the shear behavior of corbels made by high-strength concrete (HSC) with steel fiber or with stirrups was investigated. Thirteen samples were prepared and tested, the main variables in this research were steel fiber type, steel fiber content (Vf %), and amount of horizontal closed stirrups (Ah). The constants in this investigation were the area of the main steel reinforcement (As), ratio of shear span to depth (a/d) and cube concrete strength (fcu). The obtained results clearly showed that, the presence of fibers or closed stirrups enhanced the strength and decreased the deformation of the explored specimens. It was concluded that the horizontal shear reinforcement can be substituted by supplementation of steel fibers to RHSC corbels. A comparison was performed between the test results and estimated shear capacity by ACI code and other adopted equations. Very conservative shear strength values were obtained from ACI 318–19 for corbels prepared with high-strength concrete because the strut and tie method were influenced by concrete strength and did not take the contribution of closed stirrups into account. However, the shear friction method depends only on the quantity of the main steel reinforcement and closed stirrups. Russo [2] proposed a model that adequately predicted the ultimate force of high-strength RC corbels incorporating closed stirrups, but this model did not take the effect of steel fibers into account. Campione [3] added the effect of steel fibers by means of the residual tensile strength expression.

Modified prediction approach of strength of high strength polyolefin fiber reinforced concrete corbels

This paper aims to investigate the effect of polyolefin fibers on high strength reinforced concrete corbels using twelve specimens with different quantities of fibers and shear span-to-span ratios, all corbels were only tested vertically. Due to the addition of polyolefin fibers, the ultimate load-carrying capacity of corbels was significantly improved, according to the findings of this study and other relevant data. The limitations and insufficiency of the three techniques were proven by a comparison of current test results and anticipated values by the ACI 318 Code -19 rules for the tested specimens, the Strut and Tie Model, and the proposed method. The ultimate shear load of polyolefin fiber reinforced high strength concrete corbels with was determined to be best predicted by applying the Strut and Tie Model technique to account for the fibers' contribution to strength.

Modified prediction approach of strength of high strength polyolefin fiber reinforced concrete corbels

This paper aims to investigate the effect of polyolefin fibers on high strength reinforced concrete corbels using twelve specimens with different quantities of fibers and shear span-to-span ratios, all corbels were only tested vertically. Due to the addition of polyolefin fibers, the ultimate load-carrying capacity of corbels was significantly improved, according to the findings of this study and other relevant data. The limitations and insufficiency of the three techniques were proven by a comparison of current test results and anticipated values by the ACI 318 Code -19 rules for the tested specimens, the Strut and Tie Model, and the proposed method. The ultimate shear load of polyolefin fiber reinforced high strength concrete corbels with was determined to be best predicted by applying the Strut and Tie Model technique to account for the fibers' contribution to strength.

Effect of Concrete Compressive Strength on Performance of Fibrous Reinforced Concrete Corbels

This paper presents an experimental investigation to study the behavior of fibrous high strength concrete corbels under the effect of static load. Totally six specimens with clear span to depth ratio equal to (0.7) were tested to failure. Three of the specimens provided with normal strength concrete with three different amounts of steel fibers (0%), (1%) and (2%) of total volume and three specimens provided with high strength concrete with same different ratios of steel fibers. The influence of concrete strength on the ultimate capacity, cracking capacity, load-deflection behavior, failure pattern and stiffness has been studied. Test results indicate that, the corbels with normal and high strength concrete were failed in diagonal shear mode. Also, the results showed that, the high strength concrete specimens generated higher ultimate capacity, cracking capacity, and stiffness than normal strength concrete.

Numerical analysis of reinforced high strength concrete corbels

This paper deals with comparisons of numerical results of reinforced high strength concrete corbels and experimental results obtained from the literature. The application of precast structures and high strength concrete have increased in the last years and taking into account the possibility of brittle failures using this solution, specific investigations are demanded to some structural details, as for example, corbels. It should be mentioned that brittle failures and complex regions are difficult to be analyzed by means of computational resources and for that reason it is argued if the available packages software are able to correctly describe the behavior of high strength concrete, specifically for corbels. In this way, the numerical simulations described in this paper have been conducted using the Finite element method. A parametric study was then carried out using the validated model to investigate the effect of the shear span-to-effective depth ratio, the main reinforcement rate and the compressive strength of concrete in the failure load and the contribution of secondary reinforcements. The main conclusions are: the numerical and experimental results showed a very close agreement, not only in the cracking and failure modes, but also in the load–deflection and load-reinforcement strain responses; there is a strong linear correlation of the failure load and shear span-to-effective depth ratio, the main reinforcement rate and the compressive strength of concrete; the horizontal secondary reinforcement improves the load capacity and could be considered in the design models; and the vertical secondary reinforcement only affects in the cracking distribution and ductility of the corbels.

Macro-mechanical strut and tie model for analysis of fibrous high-strength concrete corbels

Reinforced concrete (RC) corbels becoming a frequent attribute in the building construction with the increasing use of pre-cast high-strength concrete (HSC). The use of fibrous high-strength concrete (FHSC), increases corbel ductility and thus defines the mode of failure of the corbels, depending on the fiber parameters. In this paper a macro-mechanical strut and tie model is proposed for analysis of fibrous high-strength concrete corbels. In this model the fibers can be used as a replacement of horizontal stirrups, due to increasing of shear friction of (FHSC). The analytical macro-mechanical model takes into consideration the effect of fiber volume, fiber length, and fiber diameter, random distribution of fibers, fiber HSC interface and shear span-to-depth ratio, respectively. This model is compared with available experimental results found in literature and a good agreement is obtained. The parametric study is performed to examine for different parameters affecting the analysis of (FHSC) corbels using the proposed macro-mechanical strut and tie model.

Influence of Steel Fibers and Headed Bars on the Serviceability of High-Strength Concrete Corbels

Vertical loading tests are reported for six double-sided, high-strength concrete corbel specimens. The primary variables of the investigation were the percentage of steel fibers and the anchorage method of the main tension tie. The test results indicated that performance in terms of load-carrying capacities, stiffness, ductility, and crack width was improved, as the steel fibers were added and the percentage of steel fibers was increased. The corbel specimens with headed bars used as the main tension-tie reinforcement showed superior load-carrying capacities, stiffness, and ductility compared with the corbel specimens in which the main tension ties were anchored by welding to the transverse bars. From the test results, it is expected that the load-carrying capacities, serviceability, and durability of high-strength concrete corbels would be improved by using steel fibers and headed bars. Experimental results presented were also compared with various prediction models.

강섬유 및 헤디드 바를 활용한 고강도 콘크리트 내민받침의 성능 향상

Technology Research Center, Samsung C&T Corporation, Seoul 137-956, KoreaABSTRACT High-strength concrete corbels with varying percentage of steel fibers and two different anchorage types (weldingto transverse bar, headed) for the main tension tie were constructed and tested. The results showed that performance in terms ofload carrying capacities, stiffness, ductility, and crack width was improved, as the percentage of steel fibers was increased. In addi-tion, the corbel specimens in which headed bars were used as the main tension tie reinforcements showed superior load carryingcapacities, stiffness, and ductility compared to the corbel specimens in which the main tension ties were anchored by welding tothe transverse bars. From the test results, it is expected that load carrying capacities, durability, and constructibility of high strengthconcrete corbels would be improved by using steel fibers and headed bars. Experimental results presented in this paper were alsocompared with various prediction models proposed by researchers and presented in codes. The truss model proposed by Fattuhiprovides fairly good predictions for fiber reinforced high-strength concrete corbels.Keywords : corbels, steel fibers, headed bars, high strength concrete

강섬유 및 폴리프로필렌 섬유로 보강된 고강도콘크리트 내민받침의 구조 거동 평가

Institute of Tech., Samsung Engineering & Construction Co., Ltd., Seongnam 463-771, KoreaABSTRACT In this study, high strength concrete corbels reinforced with steel fibers and polypropylene fibers, and subjected tothe vertical and horizontal loads were constructed and tested. The results showed that performance in terms of load carrying capac-ities, stiffness, ductility, crack width, and number of cracks was improved, as the steel fibers and polypropylene fibers were added.The polypropylene fiber reinforced concrete corbels resulted in higher ductility in presence of horizontal loads, but showed largercrack width than the steel fiber reinforced concrete corbels. And, the heads of the headed bars provided excellent end anchorageof the main tension tie reinforcement. Experimental results presented in this paper are also compared with various prediction mod-els proposed by codes and researchers. The refined strut-and-tie model showed more accurate and conservative predictions in pres-ence of horizontal loads, and the truss model proposed by Fattuhi provides fairly good predictions for fiber reinforced concrete corbels.Keywords : corbels, steel fibers, polypropylene fibers, high strength concrete, headed bars

Design of high performance concrete corbels

Currently, concretes of higher compressive strengths have been produced and increasingly used by designers and contractors for both reinforced and prestressed concrete construction. The design of concrete corbels using the strut-and-tie model considers two failure modes: failure by crushing concrete in the strut and by yielding of the main steel reinforcement. To consider the failure by diagonal tension, a third equation is included in the truss plastic model proposed by Rogowsky and MacGregor. To use the truss plastic model, an efficiency factor is applied to reduce the effective concrete strength. An efficiency factor is proposed in this paper for high performance concrete. The proposed model using the new efficiency factor gives an improved correlation with experimental data. Based on the test results reported from literature review, the design method proposed by AFREM for high stregth concrete corbels is modified in this paper to make design of high strength concrete corbels more reasonable. The comparison with experimental data shows that the modified AFREM model predicts fairly well the shear capacity of the corbels.

Performance of High-Strength Concrete Corbels

Investigators tested 30 high-strength concrete corbels to destruction. Variables considered in the investigation were shear span-to-depth ratio, concrete strength, and the provision of secondary reinforcement. The investigation examined corbel behavior in the context of the previous parameters and compared the experimental results with the American Concrete Institute (ACI) 318-89 design method and the plastic truss model of Rogowsky and MacGregor. Particular attention was given to determining the concrete efficiency factor for members failing in compression, and the results were compared with the efficiency model proposed by Warwick and Foster. The findings revealed that good load predictions can be obtained using the plastic truss model when combined with the Warwick and Foster efficiency factor. Researchers concluded that the design method given in ACI 318-89 is not appropriate for corbels fabricated using high-strength concrete.

Precompressed Concrete Corbels

Abstract Very short members such as concrete brackets, corbels, and ledger beams are exposed to direct shear force. While much research has been done on reinforced concrete corbels, experimental data on the performance of precompressed concrete corbels and high-strength concrete corbels are limited. This study was designed to verify the shear-friction theory of design as suggested in the American Concrete Institute (ACI) Code. Nine corbels, divided into three series with the average concrete strength ranging between 33.23 MPa (4820 psi) and 65.72 MPa (9530 psi), were subjected to varying compressive forces and light confining steel. The corbels were loaded monotonically to failure and studied at the California State University at Fullerton. In all cases, the shear span to depth ratio (a/d) was less than 0.5. Incremental static load was gradually applied until the specimen failed. The study indicated that the ACI Code provisions are conservative and the shear friction theory needs modification.