Amount Of Stirrups Research Articles

Flexural-shear strengthening of reinforced concrete T-beams subjected to asymmetric loading using CFRP system combined by NSM strips and U-wraps

This paper presents a developed three-dimensional (3D) finite element model (FEM) of flexural and shearstrengthening of reinforced concrete (RC) T-beams using a CFRP (Carbon Fiber-Reinforced Polymer) system combined by near-surface mounted (NSM) strips and U-wraps subjected by asymmetric loading. The 3D FEM was verified by experimental results. Concrete was simulated by a total-strain-based rotating smeared crack model. NSM CFRP strips and CFRP U-wrap sheets were modeled as shell elements. Steel reinforcement and NSM CFRP strips were embedded in concrete, corresponding to a perfect bond. U-wrap sheets were modeled as a shell element and bonded to the concrete surface using an interface element, considering appropriate bond properties. Four RC T-beams from an experimental work were analyzed, and predictions of the applied load-displacement curve and failure mode were presented to demonstrate the accuracy of the developed finiteelement analysis. It is shown that the finite element results of T-beams agree well with the experimental behavior in terms of applied load versus displacement and failure mode. Moreover, a parametric study was conducted to examine the influence of some design-oriented parameters such as concrete compressive strength, amount of longitudinal tension reinforcement, amount of stirrups, multiple layers of externally bonded (EXB) CFRP sheets, and flange width.

Analytical and Numerical Investigation of the Behavior of Engineered Cementitious Composite Members under Shear Loads.

This research discusses the performance of engineered cementitious composite (ECC) beams with and without transverse reinforcements using thorough analytical and finite element (FE) approaches under shear. The overall goal of this investigation was to assess the impact of various design characteristics, such as (i) shear span-to-effective depth ratio, (ii) transverse reinforcement ratio, etc., on the shear behavior of ECC beams. Nonlinear three-dimensional (3-D) FE analysis was performed with the commercial software ABAQUS to simulate the shear performance of ECC beams by employing the material properties obtained from the damage plasticity model. The correctness of the proposed FE model was validated with the benchmark experiments available in the literature. The developed FE model accurately computed the ECC beam’s overall load–deflection behavior and failure modes. In addition, the provision available in the Architectural Institute of Japan (AIJ) A-method was successfully employed to assess the shear load-carrying capacity of ECC beams. Furthermore, the effects of transverse reinforcement (pw) and shear span-to-depth ratio (a/d) on the behavior of ECC beams were also investigated. From a detailed parametric study, it was understood that a decreased a/d ratio exhibits enhanced load-carrying capacity for beams with and without stirrups for a particular cross-section. It was also observed that for the entire a/d ratio, the amount of stirrups had no substantial effect on the load-carrying capability of ECC beams.

Experimental investigation on behavior of splicing glass fiber–reinforced polymer-concrete–steel double-skin tubular columns under axial compression

Splicing glass fiber–reinforced polymer (GFRP)-concrete–steel double-skin tubular column (DSTC) is to set connection component at the joint of two or more separated GFRP tubes, and then pour concrete in the double-tube interlayer to form a continuous composite member. In this paper, the splicing DSTC composite members based on steel bar connection were designed and tested under axial compression to determine its mechanical performance. The main parameters include the connection steel ratio, the hollow ratio, and the thickness of GFRP tube. The results show that the GFRP tube presents apparent constraint effect on the concrete at about 60% of the ultimate load. The failure of splicing specimen occurred in the non-splicing section at a certain distance from the splice joint, and the stirrups at the splice joint provide effective constraint effect on the internal concrete. The proposed DSTC splicing method based on steel cage connection can satisfy the strength requirements of splice joint. Nevertheless, the increase of axial steel bar ratio cannot improve the bearing capacity of the splicing column, and the steel ratio of 2.44% is suggested for the splice joint of DSTCs under axial compression. The axial bearing capacity of splicing DSTCs significantly increases with the increase of GFRP tube thickness, but the amount of stirrups should be increased properly when a larger tube thickness is used. Two models were selected to calculate the bearing capacity of splicing members and it is found that Yu’s model is more accurate in predicting splicing DSTCs.

Confined Effect of Spiral Steel on the Bond Strength of Tension Lap Splice in SCC Beam

This study investigates the bond strength of tension lap splice of self-compacted concrete (SCC) beam with various confining reinforcement. Four beam specimens were cast with SCC for test, in which three kinds of confined conditions were selected. Results indicate that the spiral steel at the tension lap splice presents similar confined effect as that of the transverse stirrups with same pitch. The beam reinforced with moderate stirrups in addition to the spiral steel may increase the confining effect. SCC beam should arrange proper amount of stirrups at the region of tension lap splice to preserve the flexural ductility of the beam.

Shear strength of recycled aggregate concrete beams containing stirrups

This paper reports the findings of an experimental study of the shear behavior of reinforced concrete beams produced using recycled coarse aggregates (RCA). A total of eighteen test results from three series of beams containing transverse and longitudinal reinforcement are presented. The variables in the tested beams were the percentage of replacement (PR) of natural coarse aggregates (NCA) with RCA in the concrete mixes, and the amount of stirrups provided.The percentage of replacement in the three series was 0%, 20% and 100%. The ratio of the longitudinal reinforcement in all the beams was 1.38%. The experimental results showed that incorporating RCA at the rates of PR = 20% and PR = 100% in the concrete caused 5% and 9% average reductions in the shear strength relative to the natural aggregate concrete (NAC) beams respectively. The results also showed negligible effects of PR on the shear cracking patterns, the critical shear cracks, the longitudinal steel strains and the mode of failure. However, the midspan deflections of the beams were increased considerably for PR = 100%. Beams that are reinforced with both longitudinal as well as transverse reinforcement are shown to be less affected by the incorporation of recycled aggregates than beams reinforced only with longitudinal reinforcement. The observed ultimate shear strengths were also compared with the calculations of shear equations from the ACI, CSA, MC2010 and EC2 codes. The calculations were conservative for the level of approximation II of the MC2010 model code, but were slightly unconservative for the rest of the methods checked, especially for the beams with recycled aggregates.

Confinement effects on high strength concrete under axial load: evaluation of International Standards prescriptions

Confinement effects on concrete behavior have been evaluated by many authors so far and some relationship is inserted in most of the International Standards and Guidelines in order to let the designers increase the properties of the material. A common behavior is shown by both normal and high strength mixtures, but the request of confinement forces is different and the results, in terms of design detailing and verifications, are different. The main problem shown in concrete is that, in order to obtain a significant increasing of rheological concrete performance, the designer is led to insert a large amount of stirrups in concrete columns. For high strength concrete (HSC) it has been found that a brittle behavior occurs when a great amount of confinement is not provided. This paper, focused on HSC columns, will show the limits of some international standard indications on confinement when this is provided in order to achieve high values of resistance, strain and hence ductility in the concrete.

Predicting diagonal cracking strength of RC slender beams without stirrups using ANNs

Numerous studies have been conducted to understand the shear behavior of reinforced concrete (RC) beams since it is a complex phenomenon. The diagonal cracking strength of a RC beam is critical since it is essential for determining the minimum amount of stirrups and the contribution of concrete to the shear strength of the beam. Most of the existing equations predicting the diagonal cracking strength of RC beams are based on experimental data. A powerful computational tool for analyzing experimental data is an artificial neural network (ANN). Its advantage over conventional methods for empirical modeling is that it does not require any functional form and it can be easily updated whenever additional data is available. An ANN model was developed for predicting the diagonal cracking strength of RC slender beams without stirrups. It is shown that the performance of the ANN model over the experimental data considered in this study is better than the performances of six design code equations and twelve equations proposed by various researchers. In addition, a parametric study was conducted to study the effects of various parameters on the diagonal cracking strength of RC slender beams without stirrups upon verifying the model.

Proportion of High-Strength Steel Bars in Reinforced Concrete Ductile Piers

This paper mainly focuses on the affect factors of ductility of reinforced concrete pier with the high-strength longitudinal reinforcement and stirrups. By finite element software ANSYS, changed the amount of longitudinal reinforcement and high-strength stirrups in the piers, the ductility performance of concrete piers was studied. The results show that under certain conditions, the ductility coefficient of concrete piers with high-strength reinforcement can increase with the amount of stirrups. In addition, high-strength longitudinal reinforcement can improve the ductility performance of the concrete piers, but it should be controlled in a reasonable range. If there are too much high-strength longitudinal reinforcement in the concrete piers, the ductility performance will be lower, and structural seismic performance will also be affected.

Transverse Stirrup Configurations in RC Wide Shallow Beams Supported on Narrow Columns

This paper addressed the influence of stirrup configurations in wide beams on the effectiveness of stirrups in contributing to shear resistance as a ratio of the nominal shear stirrup strength. The evaluation was made by testing 16 continuous, wide, shallow, reinforced, concrete beams supported on interior narrow columns at their centers and simply supported at the ends. The 16 beams were composed of: three beams without stirrups, six beams having a constant amount of stirrups with either two-leg or four-leg configuration, and seven other beams with various configurations to verify the trend. The general trend is that reducing the transverse spacing of stirrups improves the stirrup efficiency to resist shear forces. For beams with a constant amount of stirrups, four-leg configuration showed a high increase in its efficiency to resist shear force over stirrups with two-leg configuration. Although code design equations assume that stirrups are fully effective, it was evident that wide shallow beams reinforced with two-leg stirrups were susceptible to becoming shear deficient if transverse spacing was not accounted for. On the basis of findings of this study, guidelines for computing the stirrup contribution in shear resistance were proposed and verified by comparisons with tested beams from the present study and a previous study by Serna-Ros et al. DOI: 10.1061/(ASCE)ST.1943- 541X.0000408. © 2012 American Society of Civil Engineers. CE Database subject headings: Beams; Columns; Configuration; Standards and codes; Reinforced concrete; Shear strength. Author keywords: Wide beams; Stirrups; Configurations; Standards and codes; Concrete; Reinforced; Shear strength.

SHEAR BEHAVIOR OF REDUCED-WEIGHT REINFORCED CONCRETE BEAMS

This paper presents an investigation to improve the understanding of the shear behavior of reinforced reduced-weight concrete beams made of light-weight expanded clay aggregate (LECA) as a partial replacement (by volume) to the normal-weight aggregates. Eleven reinforced concrete beams divided into two groups were fabricated and tested using the symmetrical two-point loads test. The tested beams consisted of seven reinforced reduced-weight concrete beams and four reinforced normal-weight control beams. The effects of several variables such as type of concrete according to its weight, shear span to depth ratio (a/d), concrete grade and the amount of stirrups were experimentally investigated. The behavior of the tested beams was analyzed in terms of mode of failure, load-deflection response, load-strains response, shear stress- shear strain relationships, first shear cracking loads, ultimate carrying capacity, stiffness and ductility. Furthermore, the test results were compared with the predictions using the Egyptian Code for Concrete Structures, (ECP 203). Despite the experimental results illustrated that the reduced-concrete beams were shown less load carrying capacity, stiffness and ductility than those of the comparative normal-weight concrete beams, the theoretical predictions using the Egyptian Code were quite conservative. This could be attributed to that the effect of arch action is still underestimated in the Egyptian Code.

Seismic Behavior and Bearing Capacity Calculation of the Three-Layer-Closed-Restraining Stirrups Coupling Beam with Small Span-to-Depth

Seismic behaviors of the nine coupling beam specimens that three-layer-closed-restraining stirrups arranged in the coupling beam section depth direction were investigated experimentally. Effects of span-to-depth, amount of stirrups and longitudinal bars of coupling beam on its failure mode are studied, as well as the hysteretic behavior, stiffness degradation, and deformation capacity. Coupling beams with span-to-depth ratio of 0.75－1.5 were observed to suffer shear failure or flexural-shear failure, no matter whether longitudinal reinforcements yield or not. The existing of three-layer-closed-restraining stirrups along the section depth of coupling beam effectively improved its deformation and energy dissipation capacity. According to the experimental results, the formulae for estimating shear strength of the coupling beams were suggested considering the effect of longitudinal reinforcements. Estimated shear strength of coupling beams agreed well with the experimental data.

Shear design procedure for reinforced normal and high-strength concrete beams using artificial neural networks. Part II: beams with stirrups

In order to re-evaluate the current shear procedures of different codes of practice for normal-strength and high-strength beams with web reinforcement an extensive research study was performed. An Artificial Neural Network was developed to predict the shear strength of reinforced beams failing on diagonal tension failure and, based on its results, a parametric study was carried out to study the influence of each parameter affecting the shear strength of beams with web reinforcement. Some important influences are highlighted, for example the non-linear relationship between the amount of stirrups and the shear strength. Finally, new design expressions are proposed, taking into account the observed behaviour for the design of high-strength and normal-strength reinforced concrete beams with shear reinforcement. The new expressions correlate much better with the empirical tests than EC-2 or ACI procedures.

Structural behaviour of steel fibre reinforced concrete

Results of an experimental study on 21 fibre reinforced concrete beams indicate that steel fibres do not only increase shear capacity but also provide substantial post-peak resistance and ductility in conventionally reinforced beams as well as in prestressed pretensioned concrete beams. The tests were carried out on 2 m long beam specimens reinforced with longitudinal bars and fibres. Test variables were amount and type of fibres, amount of stirrups and type of longitudinal reinforcement (prestressed or non-prestressed).

Predicting the failure modes of monotonically loaded reinforced concrete exterior beam-column joints

This study aims at postulating a simple methodology for predicting the failure modes of monotonically loaded reinforced concrete beam-column joints. All the factors that affect the failure modes of joints are discussed in detail using an experimental database of monotonically loaded exterior beam-column joints. The relative contributions of the strut and truss mechanisms to joint shear strength are determined based on the test results. A simple design equation for the beam longitudinal reinforcement ratio for joints with low, medium and high amount of stirrups is developed. The factors influencing the failure modes of monotonically loaded exterior beam-column joints are investigated in detail. Design charts that predict the failure modes of exterior beam-column connections both with and without stirrups are developed. Experimental data are compared with the design charts. The results show that the simple methodology gives very accurate predictions of the failure modes.

Shear behaviour and shear analysis of reinforced concrete beams containing steel fibres

An investigation of the shear behaviour of reinforced concrete beams containing steel fibres is presented. The major test variables were the amount of steel fibres and the volume of shear stirrups. The fibre content was varied from 0% to 2% by volume, and the amount of stirrups from zero to full reinforcement using code-required values. The test results show that the cracking shear strength increases significantly as the fibre content increases, and that improvement in ultimate shear strength is also achieved. It is seen that the steel fibres play an important role in reinforced concrete beams by curbing crack occurrence and reducing the crack width. This effect greatly enhances the serviceability and durability of reinforced concrete structures. The mode of failure changed from shear to flexure when the volume fraction of fibres exceeded 1%. This means that fibre reinforcement greatly increases the shear capacity. The ductility is also enhanced remarkably by the addition of fibres. The present study indicates that fibre reinforcement can reduce the amount of shear stirrups required, and that a combination of fibres and stirrups may be used to achieve both strength and ductility requirements. An analytical method for predicting the shear strength of reinforced concrete beams containing steel fibres is proposed. Good correlation was obtained between calculated and test data. The proposed method allows a more realistic shear analysis of reinforced concrete structural members containing steel fibres.