Experimental and analytical study of corroded shear-critical reinforced concrete beams

This paper presents the experimental results of two highly corroded shear-critical deep beams subjected to a chloride environment to assess the shear behavior of long-term-corrosion damaged beams. A 26-year-old reinforced concrete beam corroded by exposure to a chloride environment was cut into two small short-shear-span beams, or deep beams, which were tested under three point bending until failure, along with a control beam of the same age, same length and same cross-section (115 × 28 × 15 cm). Cracking and corrosion maps were drawn for the corroded beams in order to assess the corrosion. Force displacement curves were drawn for the corroded and control beams. After testing the beams until failure, the main steel bars and the stirrups were extracted from the beams and loss of mass was measured and plotted for both longitudinal and transverse reinforcement. It was noted that the loss of mass of transverse and longitudinal reinforcements had not had an important influence on the failure mode and it had not affected the load-bearing capacity of the beam. It was found that the stirrups came into action after the failure of the compression strut and thus decreased the ductility of the corroded beams. Analytical investigations were made to compare the experimental shear capacity with the theoretical value. Strut and tie model predictions were more accurate than the conventional sectional methods provided for in ACI 318-08 and Eurocode 2.     

Experimental study on the plastic rotation capacity of reinforced high strength concrete beams

This paper describes an experimental study on the plastic rotation capacity of reinforced high strength concrete beams. Thirty-six beams with various compressive strengths of concrete, tensile reinforcement ratios, compressive reinforcement ratios, and patterns of loading (1 point loading and 2-point loading) were tested to evaluate the plastic rotation capacity, extreme fiber concrete compressive strain and equivalent plastic hinge length, etc. The same quantities were also obtained from numerical analysis and compared with experimental data. According to the results, the yield curvatures obtained from experiments turned out to be quite close to those obtained from theoretical approach. However, the experimental results for ultimate curvatures were significantly larger than those of theoretical prediction based on the assumption of ε_cu=0.003. Based on these observations, a new formula for ultimate strain is proposed for high strength concrete beams. Also the test results for plastic rotation capacity were found to be closer to those obtained using moment-curvature relationship considering tension stiffening of concrete and shear effect than those obtained using equivalent plastic hinge length. This substantiates that for accurate evaluation of plastic rotation capacity the consideration of tension stiffening of concrete and shear effect is most important.     

Experimental evaluation of fiber reinforced concrete fracture properties

Concrete is now universally recognized a construction material vital and essential for the regeneration and rehabilitation of the infrastructure of a country. The last few decades have now shown that high strength concrete, with a compressive strength of 100–120 MPa can be readily designed and manufactured. There have also been several advances made in the development of fiber reinforced concrete to control cracking and crack propagation in plain concrete, and to increase the overall ductility of the material. However, there are now many types of fibers with different material and geometric properties, and the exact fracture behavior of fiber reinforced concrete materials is not clearly understood. The overall aim of this paper is to establish the fracture properties and fracture behavior of concrete containing two widely used types of fibers, namely, steel (high modulus) and polypropylene (low modulus). The experimental investigation consisted of tests on cubes and notched prismatic specimens made from plain concrete and fiber concrete with 1% and 2% of steel or polypropylene fibers. The cube tests and the three point bending tests on notched specimens were carried out according to RILEM specifications, and extensive data on their compressive and flexural tensile behavior and fracture energy were recorded and analyzed. The results obtained from the tests are critically assessed, and it is shown that fibers contribute immensely to the structural integrity and structural stability of concrete elements and thereby improve their durable service life.     

Experimental investigation of steel fiber reinforced concrete box beams under bending

Reduction of dead weight of a reinforced-concrete (RC) structure without too much concession in its load carrying capacity has always been an attractive study subject because it engenders (1) a decrease in dimensions of the members, (2) a decrease in the reinforcement steel, and (3) a decrease in lateral inertia forces during severe earthquakes. In this study, nine RC beams of outer dimensions of 300 × 300 × 2000 mm, six of which are box beams, designed and produced using a C20 class steel fiber concrete, (SFRC) with the commonly used steel fiber type of Dramix-RC-80/0.60-BN at a dosage of 30 kg/m³, are tested under bending. The mechanical behaviours of all these nine beams under bending are recorded from the beginning of the test till the ultimate failure of the tensile reinforcement in a two-point beam-loading setup. The proportions of (1) loss in ultimate load versus reduction in dead weight and (2) (ultimate experimental load)/(ultimate theoretical load) of the SFRC box beams are determined for two different box thicknesses. Dimensionless behaviour relationships of all the SFRC beams are determined, and the experimentally obtained relationship between the ratio of (actual ultimate load)/(theoretical ultimate load) and the ratio of (wall thickness)/(beam height) for the SFRC box beams is expressed diagrammatically.     

Finite-element study of the diagonal-tension failure in reinforced concrete beams

In this work, we aim to tackle one of the most devastating failure modes in reinforced concrete (RC) structures: the diagonal-tension failure. In order to study this phenomenon numerically, a model capable of dealing with both static and dynamic crack propagation as well as the natural transition of these two regimes is necessary. We chose a discrete cohesive model for concrete fracture, an interface bond-slip model for the deterioration between concrete and steel rebar, both combined with an insertion algorithm. The static process is solved by a dynamic relaxation (DR) method together with a modified technique to enhance the convergence rate. The same DR method is used to detect a dynamic process and switch to a dynamic calculation. The methodology is applied to model the experimental results of Carmona et al. (Engineering Fracture Mechanics 74:2788–2809, 2007), where the recognition of the transition to a dynamic fracture in a presumably static calculation is essential to reproduce the diagonal-tension failure observed.     

Behaviour of shear-strengthened reinforced concrete beams

A large experimental programme was developed to study the behaviour of shear-strengthened, simply-supported reinforced concrete beams. This paper presents the shear strength of these beams by combining new reinforcement and shotcrete or pre-packed mortar jackets. The behaviour in service and ultimate state, along with bond aspects, are taken into consideration. Three different types of strengthening stirrups were tested.

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Résumé Un vaste programme expérimental a été élaboré pour étudier le comportement de poutres en béton à appui simple qui ont été renforcées au moyen d'armatures d'efforts tranchants. Cet article discute de la résistance au cisaillement de ces poutres après leur renforcement par une nouvelle armature conjuguée soit avec du béton projeté soit avec du mortier spécial préconditionné. Le comportement en service et à l'état limite ultime, ainsi que certains aspects de l'adhérence, sont pris en considération. Trois différents types d'étrier ont été l'objet d'essais.

     

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.     

Flexural performance of FRP reinforced concrete beams

A numerical method for estimating the curvature, deflection and moment capacity of FRP reinforced concrete beams is developed. Force equilibrium and strain compatibility equations for a beam section divided into a number of segments are numerically solved due to the non-linear behaviour of concrete. The deflection is then obtained from the flexural rigidity at mid-span section using the deflection formula for various load cases. A proposed modification to the mid-span flexural rigidity is also introduced to account for the experimentally observed wide cracks over the intermediate support of continuous FRP reinforced concrete beams.     

Anti-vibration characteristics of rubberised reinforced concrete beams

The flexural and vibration properties were examined in order to evaluate the anti-vibration characteristics of rubber modified reinforced concrete beam. The rubberised mixtures were produced by replacing 5, 7.5, and 10 % by mass of the fine aggregate with 1–4 mm scrap truck tyre crumb rubber particles. A series of reinforced concrete beam (1,200 × 135 × 90 mm³) was tested in a free vibration mode and then subsequently in a four point flexural tests. The input and output signals from vibration tests were utilised to calculate various dynamic parameters such as natural frequencies, frequency response function, dynamic modulus of elasticity and damping ratio. The results showed that compared to control mixture, gradual reductions of natural frequencies in first six modes of all rubberised beams with the highest being in the mixture with 10 % rubber contents. In addition, despite the reduction in overall strength, rubberised mixtures showed flexibility under loading due to the higher energy absorption capacity of rubber particles. Compared to control mixture, the results also showed a uniform global decrease in the dynamic modulus over the span. The reduction was found as high as 26 % in the mixture with 10 % rubber content. The results indicated that the rubberised concrete exhibits better anti-vibration properties and could be a viable alternative to use as vibration attenuation material where resistance to impact or blast is required such as in railway buffers, jersey barriers (a protective concrete barrier used as a highway divider and a means of preventing access to a prohibited area) and bunkers.     

Flexural behaviour of strengthened reinforced concrete beams

A large experimental research programme has investigated the flexural strength of simply supported reinforced concrete beams. The beams were first damaged so that they could be strengthened by means of jackets (cast-in-place shotcrete or pre-packed special mortar plus additional new reinforcement). This paper analyses the flexural strength of these beams. The behaviour in service and ultimate state as well as the bond characteristics are studied.

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Résumé Au cours d'un vaste programme expérimental, on a étudié la résistance en flexion de poutres en béton armé à appui simple. Ces poutres ont d'abord été endommagées, pour ensuite être renforcées par du béton projeté ou par du mortier spécial préconditionné, avec l'adjonction de nouvelles armatures. Cet article discute de la résistance en flexion de ces poutres. Le comportement en service et à l'état limite ultime, ainsi que les caractéristiques d'adhérence, sont étudiés.

     

Experimental and analytical assessment of the behavior of stainless steel reinforced concrete beams

This paper reports the results of a comprehensive experimental test program on high performance and standard AISI 316L stainless, steel reinforced concrete beams. Experimental results were compared with theoretical analysis data using current reinforcement mechanical feature standards and experimental testing-based ones, to identify any resistance, ductility and membrane collapse mode difference. It is also proved the importance of establishing a specific standard on the use of stainless steel reinforcement, in order to enable its more widespread, structural use, and not only for its corrosion resistance.

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Résumé Dans ce travail sont présentés les résultats d'un vaste programme d'essais expérimentaux réalisés, sur des poutres en béton armé normal et à haute résistance; toutes les poutres sont renforcées de barres d'acier inoxydable. Les résultats obtenus à partir de l'analyse expérimentale ont étés comparés avec ceux obtenus par une analyse théorique dans laquelle on a utilisé les valeurs des caractéristiques mécaniques de l'acier, soit standardisées, soit obtenues à partir de l'expérimentation, afin de mettre en évidence pour les poutres, les différences en termes de résistance, de ductilité et de mode de rupture.

     

Experimental investigation into flexural retrofitting of reinforced concrete bridge beams using FRP composites

End cover separation and shear crack debond are the two most critical debonding modes in beams retrofitted with fibre reinforced polymer composites due the brittle nature of the failures. However, these failures are still not fully understood. A testing program including 18 rectangular reinforced concrete beams is carried out to investigate the failure mechanisms and the influence of several parameters on these debond modes. Testing shows that end cover separation starts from FRP ends and fails in the form of shear failure at steel reinforcement level at the root of the concrete teeth between shear cracks. Shear crack debond failure is due to the opening of one of those inclined cracks. Several debond prediction models are then verified with the experiment proving to work relatively well.     

Shakedown with softening in reinforced concrete beams

Critical softening parameters for first-formed highes at any location in a two-span beam are derived, and the relationship between positive load increments and softening parameter less than critical for midspan or interior support highes are also determined. The effect of non-critical softening on the well known static collapse and shakedown loads for an elastic-plastic beam is found. It is shown that the combined effect of softening and residual moments (such as caused by differential settlements) on the static collapse and shakedown loads may be dramatic.     

Eight-year deformation tests on reinforced concrete beams

In 1981 the author reported on the long-term testing of nine reinforced concrete beams. The beams had then been under load for five years. The present article is a report on the next three years of tests on the same nine beams and on the unloading of the beams. The beams all had a rectangular cross-section 170 mm by 280 mm and were simply supported with a span of 7.5 m. The loading varied from self-weight only to the same plus 18 kN. The deflections were measured for 8 years. The tests also included measurements of the shrinkage of control specimens and of the humidity in the room, where the beams were stored. This report describes the experimental procedure and presents the test results.     

Viscoelastic analysis of FRP strengthened reinforced concrete beams

External bonding of FRP plates or sheets has become a popular method for strengthening reinforced concrete structures. Stresses along the FRP-concrete interface are critical to the effectiveness of this technique because high stress concentration along the FRP-concrete interface can lead to the FRP debonding from the concrete beam. Although the short-term stress distribution along the FRP-concrete interface has been studied extensively, very few studies have been conducted on the long-term stress distribution, which closely simulates the behavior of the structure during the service-life. In this study, we develop a viscoelastic solution for the long-term interface stress distribution in a FRP plate strengthened reinforced concrete beam. In this solution, the RC beam and the FRP plate are modeled as elastic materials; while the adhesive layer is modeled as a viscoelastic material using the Standard Linear Solid model. Closed-form expressions of the interface stresses and deflection of the beam are obtained using Laplace transform and calculated using the Zakian’s numerical method. The validation of this viscoelastic solution is verified by finite element analysis using a subroutine UMAT based on the Standard Linear Solid model.     

Shear behaviour of steel fibre reinforced concrete beams

The possibility of substituting traditional transverse reinforcement (stirrups) for steel fibres in precast elements can significantly reduce production costs. In the present paper, the shear behaviour of prestressed elements has been investigated by means of experimental tests on full scale beams. Tests concern beams with conventional as well as steel fibre reinforcement. Experimental results show that the shear behaviour of fibre reinforced concrete beams without conventional reinforcement is similar to, or even better than that of beams with stirrups. When used in beams with stirrups, steel fibres significantly improve their shear strength. A discussion on the contribution of steel fibres on the shear strength is also presented, with reference to the latest RILEM provisions.

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Résumé La possibilité de remplacer des armatures transversales traditionnelles par des fibres d'acier dans des éléments pré-tendus peut apporter des améliorations considérables sur les performances structurales. Dans ce rapport, le comportement en cisaillement des éléments précontraints a été étudié à l'aide de tests expérimentaux sur des poutres à échelle grandeur nature. Les essais portent aussi bien sur des poutres avec armatures traditionnelles que sur des poutres renforcées à l'aide de fibres. Les résultats expérimentaux montrent que les performances des poutres en béton de fibres sans armatures traditionnelles sont similaires, sinon meilleures, à celles des poutres avec armature ordinaire de cisaillement. Lorsqu'elles sont utilisées dans des poutres avec armatures traditionnelles les fibres d'acier améliorent considérablement leur résistance en cisaillement.

     

Shear strength of reinforced concrete beams with stirrups

This study presents alternative shear strength prediction equations for reinforced concrete (RC) beams with stirrups. The shear strength is composed of the contribution of the nominal shear strength provided by stirrups and the nominal shear strength provided by concrete. For the concrete contribution, cracking shear strength values estimated by Arslan’s equations are almost same those obtained with ACI 318 simplified equation in terms of coefficient of variation (COV). However, mean values estimated by ACI 318 tend to be more conservative comparing to the mean values obtained with Arslan’s equations. Thus, for the consideration of concrete contribution to shear strength, Arslan’s equations are used. To obtain the shear strength of RC beams, shear strength provided by stirrups is added to the concrete shear strength estimated by Arslan’s equations. Results of existing 339 beam shear tests are used to investigate how accurate proposed equation estimates the shear strength of RC beams. Furthermore, ACI 318 and TS500 provisions are also compared to the aforementioned test results. It is found that proposed equations for beams with shear span to depth ratios (a/d) between 1.5 and 2.5 are also conservative with a lower COV than ACI 318 and TS500. However, when a/d ratios exceed 2.5 (both normal and high strength concrete beams), ACI 318, TS500 and proposed equations give similar COV value.     

Deflections of concrete beams reinforced with FRP bars

The aim of this study is to experimentally and theoretically investigate the flexural behavior of concrete beams reinforced with fiber reinforced polymer (FRP) bars. In this research, three types of experiments were made. First, the tensile properties of FRP and steel bars were tested, then the bond-slip behavior between bars and concrete was tested on standard specimens and, in the end, three series of concrete beams reinforced with GFRP, CFRP and steel bars were tested up to failure. The theoretical model for calculating deflections was developed, which included bond-slip behavior of FRP bars. The theoretical results were compared to the test results of beam deflections, as well to deflection results obtained by theoretical models developed by other authors.     

BFRP筋钢纤维高强混凝土梁受弯承载力试验与理论

通过11根玄武岩纤维增强聚合物复合材料（BFRP）筋钢纤维高强混凝土梁的受弯性能试验,研究了钢纤维混凝土层厚度、钢纤维体积分数和BFRP筋配筋率对BFRP筋钢纤维高强混凝土梁受弯破坏形态及其承载力的影响。结果表明,BFRP筋钢纤维高强混凝土梁的破坏模式可分为受压破坏、受拉破坏和平衡破坏3种;钢纤维混凝土层厚度和钢纤维体积分数的变化对于BFRP筋钢纤维高强混凝土梁受弯承载力具有一定程度的影响,当BFRP筋配筋率为0.77%时,掺加体积分数为1.0%钢纤维的梁受弯承载力较无钢纤维梁提高了22.7%,在受拉区0.57倍截面高度内掺加1.0vol%钢纤维的梁受弯承载力达到全截面钢纤维混凝土梁受弯承载力的86.7%;增大BFRP筋配筋量可显著提高BFRP筋钢纤维高强混凝土梁的受弯承载力,BFRP筋配筋率为1.65%的试验梁受弯承载力较配筋率为0.56%的试验梁提高了39.4%。针对不同的破坏模式,提出了BFRP筋钢纤维高强混凝土梁受弯承载力和平衡配筋率的计算方法,并结合安全配筋率的概念对试验梁的破坏模式进行了预测,试验结果与分析结果吻合良好。