Bent-up Bars Research Articles

Performance Study and Efficacy of Steel Plate Reinforced Concrete Composite Beam with Prefabricated Cage and Bent-Up Bars: An ANN-Based Approach

Performance Study and Efficacy of Steel Plate Reinforced Concrete Composite Beam with Prefabricated Cage and Bent-Up Bars: An ANN-Based Approach

Experimental investigation and mechanical modelling of shear failure in reinforced concrete members with plain and ribbed bent-up bars

Using bent-up bars as shear reinforcement was state of the art in reinforced concrete (RC) construction until the 1970s. Since the approach to shear reinforcement design has changed since then, the structural assessment according of structural members to current structural codes often yield insufficient theoretical shear capacities. In this paper, a series of twelve shear tests on members with plain and ribbed bent-up bars is presented. Despite the beams only containing plain bars or widely spaced bent-up bars, the test results show higher shear capacity compared to reference beams without any shear reinforcement, and the formation of pronounced localised shear cracks. The contribution of the bent-up bars to the shear strength is evaluated by combining the constitutive laws of various shear transfer mechanisms along an idealised shear crack. The model approach is validated by a comparison with detailed test measurements. It is shown that the interaction of the bent-up reinforcing bars with other shear mechanisms in a localised shear crack is highly dependent on the bond behaviour of bent-up and longitudinal bars. The great potential of this approach for the refined assessment of existing structures with bent-up bars is confirmed by the accuracy of its predictions.

Study on the Mechanical Performance of H-Shaped Steel-Concrete Laminated Plate Composite Beams under Negative Bending Moment

To make the construction of assembled steel-reinforced truss concrete laminated plate composite structure faster, safer, and more efficient, this paper proposes an H-shaped steel-reinforced truss concrete laminated plate composite structure with new angle connectors embedded in the precast bottom panel. Through experimental studies on the H-shaped steel-concrete laminated plate composite beams with precast bottom panels protruding from the bent-up bars, precast bottom panels with embedded new angle connectors and laminated whole cast slab, the similarities and differences of load-deflection, deflection distribution, interface slip, crack distribution and cross-section strain distribution of three groups of composite beams under negative bending moment were analyzed and compared. Using ABAQUS finite element software, we established a finite element model and found the numerical simulation results were in good agreement with the experimental results. Based on this, five groups of finite element models were established for parametric analysis to investigate the effect of concrete strength on the flexural load capacity and flexural stiffness of the steel-laminated plate composite beams with embedded angle connectors. The results of the study show that the combined performance of the H-shaped steel-concrete laminated plate composite beams with the new angle connection embedded in the precast bottom panel was better and the flexural stiffness was greater. The slippage of the H-shaped steel-concrete laminated plate composite beams with embedded new angle connectors in the precast bottom panel was less than the slippage of the precast bottom slab bent-up bars protruding and the laminated cast plate, with the maximum slippage being only 1/2 of the precast bottom panel bent-up bars protruding. In the composite structure of H-shaped steel-concrete composite slabs under negative bending moment, shear angle connectors can replace the bent-up bars protruding from the laminated bottom panel to achieve without extending the reinforcement of the laminated bottom panel.

Performance of a novel bent-up bars system not interacting with concrete

Increasing the bending and shear capacities of reinforced concrete members is an interesting issue in structural engineering. In recent years, many studies have been carried out to improve capacities of reinforced concrete members such as using post and pre-tensioning, Fiber Reinforced Polymer and other techniques. This paper proposes a novel and significant technique to increase the flexural capacity of simply supported reinforced concrete beams. The proposed method uses a new reinforcement bar system having bent-up bars, covered with rubber tubes. This technique will avoid interaction of bent-up bars with concrete. They are located in the zone where compressive and tensile forces act against one another. The compressive force in the upper point of the bent-up bars is exerted to the end point of these bars located under neutral axis. Moreover, the tensile stress is decreased in reinforcements located under the neutral axis. This will cause the Reinforced Concrete (RC) beam to endure extra loading before reaching yield stress. These factors may well be considered as reasons to increase bending capacity in the new system. The laboratory work together with finite element method analysis were carried out in this investigation. Furthermore, bending capacity, ductility, strength, and cracking zone were assessed for the new proposed system and compared with the conventional model. Both the FEM simulation and the experimental test results revealed that the proposed system has significant impact in increasing the load bearing capacity and the stiffness of the RC beams. In the present study, an equation is formulated to calculate bending capacity of a new reinforcement bar system beam.

Shear resistance of welded inclined bars in rectangular reinforced concrete beams

The bent-up bars have not been used as shear reinforcement in beams since the past 40 years or so. In all cases of design and construction nowadays, shear forces are resisted by vertical links only. Some complications in installing the multiple set of bent-up bars, the less opportunity to have sufficient number of bent-up bars due to small number of flexural reinforcement provided at the mid-span of the beams and also the large anchorage required for the horizontal portion of the bars beyond the upper end of the bend could be the reasons behind this. This paper presents the results of tests on five rectangular reinforced concrete beams in which the effectiveness of welded inclined bars (WIB) as shear reinforcement was studied. Two of the beams were controlled specimens, with no shear reinforcement in one, and full design vertical links in another. The other three beams were provided with three different quantities of WIB, measured in terms of area to distance ratio, Asw / S as shear reinforcement in the shear spans. All beams were tested to failure under two point loads with a shear span to effective depth ratio of 2.34, which would ensure that the failure was due to shear unless their shear capacities were larger than the flexural capacity. The performances of the beams were measured in terms of deflection, crack formation, strains in WIB and on the concrete surfaces in the shear region, ultimate loads and failure modes. The results show that WIB alone is capable of carrying the whole shear forces in the beam, and larger shear capacities are achieved with a larger quantity of WIB, and a higher grade of the bars used. The beam with WIB requires 22% less in the quantity of Asw / S compared to that with vertical links to achieve the same shear resistance. These suggest that WIB can be used as an effective system of shear reinforcement in beams.

Experimental investigation on hybrid GFRP-concrete decks with T-shaped perforated ribs subjected to negative moment

This paper proposes a hybrid glass fiber reinforced polymer (GFRP)-concrete deck consisting of pultruded GFRP plate with T-shaped perforated ribs in tension part and reinforced concrete in compression part. To better understand the structural behavior of the proposed hybrid deck over main girders in the transverse direction (perpendicular to the traffic direction), static tests on five full-scale deck models were conducted under negative bending moment. The main parameters of these experimental deck models were reinforcement ratio and the presence/absence of bent-up bars. The load-displacement relationship, ultimate capacity, strain distribution of GFRP plates and steel bars, and crack development were measured during the test. Experimental results indicated that flexural and shear failure modes occurred depending on the reinforcement ratio and the presence/absence of bent-up bars. The arrangement of the bent-up bars near the negative moment region can increase the ultimate loading capacity especially with respect to shear strength, but has little influence on the stiffness of the hybrid deck. GFRP T-shaped ribs are effective in controlling cracking. Simplified calculation methods were proposed to evaluate the flexural and shear strength and to predict the average crack spacing, which were calibrated by experimental results. The agreement of theoretical results with experimental ones demonstrates the accuracy and effectiveness of proposed equations for estimating the ultimate capacity and cracking behavior of such hybrid GFRP-concrete decks.

Design Issues about the Bar Lay-Out at the Dapped Ends of Simply-Supported One-Way R/C Slabs

Directly-or indirectly-supported R/C slabs are frequently used in the covers of small-to-medium underground facilities, where the service loads are often rather limited, but very severe loads cannot be ruled out in accidental situations.To have fresh information on the structural performance and cracking of R/C slabs simply supported along their short sides via corbels (dapped ends), four rectangular slabs subjected to transversely distributed or concentrated loads have been recently tested in Milan (b x L = 1.30 x 2.20 m; simply-supported span = 2.10 m; thickness = 15 cm). The load was applied either at mid-span (in the bending tests, not presented in this paper), or at 1/10 of the span (in the shear tests).Two bar arrangements were investigated with straight or bent-up bars in the main body, and straight bars or hooks in the corbels.In the D zones of the slabs tested in shear, the concentrated load induces a rather complex 3-D crack pattern, with a limited reduction in the bearing capacity, compared with the cross-wise distributed load.Rather simple strut-and-tie models applied to the slabs with bent-up bars and hooks, and the equations provided by European and North-American codes for the beams devoid of transverse reinforcement are shown to yield realistic predictions for the bearing capacity at the ultimate limit state. In the former case, however, modelling the bond along the tension reinforcement of the corbel requires some care, because of bond local and global effects. Last but not least, refining bar layout confirms – once more – that slab performance can be markedly improved with little extra effort.

­­Performance of Punching Shear Reinforcement under Gravity Loading: Influence of Type and Detailing

The performance of 11 different shear reinforcement systems against punching of inner slab-column connections under gravity loading was compared on the basis of experiments on 12 full-scale specimens, 8 of them newly reported. The slab geometry and flexural reinforcement ratio (1.5%) were kept constant. The shear reinforcement systems included different layouts of double-headed studs, individual links, bent-up bars and bonded post-installed reinforcement. All the systems were found to increase both the strength and the deformation capacity of the members but exhibited varying performances. The factors influencing the maximum punching strength of different systems, such as the layout and the anchorage conditions of the transverse reinforcement units, are described and analyzed. The mechanical model of the Critical Shear Crack Theory is used to explain the observed differences and provide design guidance. Comparisons to the codes of practice (ACI 318, Eurocode 2 and Model Code 2010) are also presented.

Shear effectiveness of shallow-angle bent-up bars for reinforced concrete beams

Recently there has been a renewed interest in reinforced concrete research to re-look into the shear effectiveness of shallow-angle bent-up bars. In the early years of reinforced concrete construction, considerable attention was directed to the use of this type of reinforcing system. Despite such popularity, however, there has been only limited research reported in this area. Two test series, with shear span to effective depth ratios of 2·86 and 4·00, respectively, were conducted in this study. The results obtained indicated that the performance of shallow-angle bent-up bars was superior in both strength and deformation characteristics, and they were able to achieve total steel saving of up to 18% compared to stirrup reinforcement. The shear effectiveness of bent-up bars depends greatly on the shear span to effective depth ratio, the angle of inclination and its position. It is recommended that current code provisions should revise the shear contribution of bent-up bars to minimum 75% and the optimum angle to be equal to 25°.

Structural Weaknesses of the Hennebique Early Reinforced Concrete System and Possible Retrofitting

One of the most popular reinforced concrete patterns used in many countries until the First World War was the system of François Hennebique (1842–1921). The best known characteristics of the Hennebique design, which was used in buildings as well as in bridges, are the monolithic structure with continuous T-beams reinforced with bent-up bars overlapping the supports and the use of flat open U-shaped stirrups as transversal reinforcements. The reasons for the success of his company have been extensively studied. However, so far, the assessment of the carrying capacity of the system remains incomplete. The first part of this paper deals with the results of experimental bending tests up to failure performed on three full-scale T-beam segments removed from a narrow gage railway viaduct built in Braine-l’Alleud (Belgium) in 1904. They aim at identifying the mechanisms of failure. The second part of the paper presents retrofitting actions to counteract the observed principal structural weakness—the too short overlapping length of the tensile rebars over the supports.

Punching shear testing of reinforced concrete slabs, and design implications

The paper presents results from an extensive testing programme involving a total of 30 reinforced concrete (R/C) slabs with and without shear reinforcement, subjected to a concentrated load in the middle. Shear reinforcement consists of either bent-up bars or closed stirrups. Measured punching shear strengths were compared with strengths predicted from two major design codes (the American, ACI 318, and the European, Eurocode 2), as well as from two models from the literature, the plasticity model and a recent multi-parameter empirical model. It was found that predictions by both codes were conservative in the case of slabs without shear reinforcement; Eurocode 2 and ACI 318 predictions are generally similar in this case. Less conservative predictions were found in the case of slabs with shear reinforcement, particularly in the case of Eurocode 2 that overestimated measured strengths of slabs with stirrups. The plasticity model tended to overestimate punching strength, whereas the multi-parameter empirical model gave the best overall predictions. Finally, bent-up bars appeared to be more efficient than stirrups in increasing the punching shear strength.

Punching shear testing of reinforced concrete slabs, and design implications

The paper presents results from an extensive testing programme involving a total of 30 reinforced concrete (R/C) slabs with and without shear reinforcement, subjected to a concentrated load in the middle. Shear reinforcement consists of either bent-up bars or closed stirrups. Measured punching shear strengths were compared with strengths predicted from two major design codes (the American, ACI 318, and the European, Eurocode 2), as well as from two models from the literature, the plasticity model and a recent multi-parameter empirical model. It was found that predictions by both codes were conservative in the case of slabs without shear reinforcement; Eurocode 2 and ACI 318 predictions are generally similar in this case. Less conservative predictions were found in the case of slabs with shear reinforcement, particularly in the case of Eurocode 2 that overestimated measured strengths of slabs with stirrups. The plasticity model tended to overestimate punching strength, whereas the multi-parameter empirical model gave the best overall predictions. Finally, bent-up bars appeared to be more efficient than stirrups in increasing the punching shear strength.

FLAT SLABS WITH FIBRE OR LINK REINFORCEMENT AT SLAB-COLUMN CONNECTIONS.

Keywords BIRMINGHAM UNIVERSITY, SOUTHAMPTON UNIVERSITY CONCRETE, SLABS, FLAT, FIBRES, LINK, REINFORCEMENT, COLUMNS, CONNECTIONS, RATIOS, STRENGTH, DUCTILITY, SHEAR, PUNCHING, FIBROUS, CRACKS, CONTROL, FLOORS, STEEL, RIGS, EXPERIMENTS, BEHAVIOUR, LOADS, DEFLECTION, FAILURES, MODES, DESIGN, CONSTRUCTION, CRACKING, RESISTANCE... Show All

Punching Shear Behavior of Reinforced Slab-Column Connections Made with Steel Fiber Concrete

Punching shear failures occur suddenly and produce catastrophic results. The effect of fiber reinforcement on the deformation and strength characteristics of punching shear failures is discussed in this paper. The fibers were used throughout the slab or in the punching shear zone of the column head, and comparative tests were carried out on connections with bent-up steel bars. The results show that fibers reduce deformations at all stages of loading, increase ultimate punching shear loads, and produce ductile shear failures. Substantial increases in ductility and energy absorption can be obtained by using fiber concrete. Fibers can not only produce flexural failures for the same load capacity in shear but can achieve it with considerable saving in flexural steel. Bent-up bars are clearly more effecti•·e than fiber reinforcement but are very labor-imensive.

Comparative Study of Bent-up Bars with other Forms of Secondary Reinforcement in Beams

ALTHOUGH CONSIDERABLE RESEARCH HAS BEEN DEVOTED TO THE EFFECTS OF STIRRUPS AS SHEAR REINFORCEMENT, BENT-UP BARS, WHICH HAVE BEEN USED FOR MANY YEARS AND ARE INCLUDED IN THE RECOMMENDATION OF ALL CODES OF PRACTICE, HAVE RECEIVED LITTLE SYSTEMATIC STUDY. THIS PAPER PRESENTS A DIRECT COMPARISON OF THREE FORMS OF WEB REINFORCEMENT, VERTICAL AND INCLINED STIRRUPS, AND BENT-UP BARS, AND IT IS FOUND THAT THE WEB REINFORCEMENT RATIO PROVIDES A SATISFACTORY BASIS FOR THE EVALUATION OF THE RELATIVE EFFICIENCY OF THESE TYPES. /ACIJP/

Reducing the shear reinforcement in reinforced concrete beams and slabs

Summary The shear tests reported in the present paper were carried out in Stuttgart from 1961 to 1963. The mechanism of failure at ultimate shear load is explained in terms of the truss analogy, and the ratio between the width of the compression flange and the thickness of the web is shown to have a considerable influence on the inclination of the top chord and of the diagonal struts of the truss and, consequently, on the tensile forces in the web. From the results, a simple method for reducing the shear reinforcement is derived. For short beams with a slenderness ratio l/d < 8 or for concentrated loads close to the supports, a further reduction in shear coverage is possible. The determination of the points for cut-off and bent-up bars must be adapted to the variations in the compression members of the truss. The tests showed clearly that stirrups are preferable to bent-up bars for shear reinforcement, particularly if high-tensile steel is used.