Tensile Reinforcement Ratio Research Articles

Analysis of flexural and shear resistance of ultra high performance fiber reinforced concrete beams without stirrups

This paper analyzes failure characteristics of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) beams under flexural and shear loading. Four large scale beams, fabricated with a specially designed mix comprising of coarse aggregate, were tested to trace structural behavior of UHPFRC members. The beams had relatively low tensile reinforcement ratio and no shear reinforcement to take advantage of high tensile and shear strength exhibited by UHPFRC. The test variables included longitudinal reinforcement ratio and type of loading (flexure and predominant shear). Two beams were tested under flexural loading while the other two beams were tested under dominant shear loading. Results from these tests indicate that UHPFRC beams exhibit a distinct cracking pattern characterized by formation of multiple microcracks at initial stages, followed by propagation of a singular macrocack at the critical section with increased loading. Further, comparative results indicate that absence of shear reinforcement in UHPFRC beams did not lead to any reduction in either ductility or moment capacity of the beams even under dominant shear loading.

Flexural Behavior of RC Slabs Strengthened in Flexure with Basalt Fabric‐Reinforced Cementitious Matrix

This paper presents both experimental and analytical research results for predicting the flexural capacity of reinforced concrete (RC) slabs strengthened in flexure with basalt fabric‐reinforced cementitious matrix (FRCM). A total of 13 specimens were fabricated to evaluate the flexural behavior of RC slabs strengthened with basalt FRCM composite and were tested under four‐point loading. The fiber type, tensile reinforcement ratio, and the number of fabric layers were chosen as experimental variables. The maximum load of FRCM‐strengthened specimens increased from 11.2% to 98.2% relative to the reference specimens. The energy ratio and ductility of the FRCM‐strengthened specimens decreased with the higher amount of fabric and tensile reinforcement. The effective stress level of FRCM fabric can be accurately predicted by a bond strength of ACI 549 and Jung’s model.

Flexural behaviour of RC beams strengthened with near-surface-mounted BFRP bars

Basalt-fibre-reinforced polymers (BFRPs) are promising economical materials developed in recent years for strengthening or repairing reinforced concrete (RC) structures. The effectiveness of strengthening RC beams with near-surface-mounted (NSM) BFRP reinforcement was investigated in this study. One reference beam and six beams strengthened with NSM BFRP reinforcements were tested under four-point loading. The main test variables were the NSM reinforcement ratio, the tensile reinforcement ratio and the pre-cracking load. The experimental results indicated that, compared with the control beam, both the load-carrying capacity and flexural stiffness of the strengthened concrete beams increased due to use of NSM BFRP bars. For the NSM-strengthened concrete beams, the pre-cracked specimens failed by BFRP bar end cover separation while the directly strengthened specimens (not pre-loaded) were governed by concrete crushing. Analytical models based on the section analysis method were developed to predict the maximum bending moment and ultimate deflection at mid-span of the concrete beams strengthened with NSM BFRP bars. The analytical values of maximum bending moment and ultimate mid-span deflection were in good agreement with the experimental results.

Predicting shear strength of SFRC slender beams without stirrups using an ANN model

Shear failure of reinforced concrete (RC) beams is a major concern for structural engineers. It has been shown through various studies that the shear strength and ductility of RC beams can be improved by adding steel fibers to the concrete. An accurate model predicting the shear strength of steel fiber reinforced concrete (SFRC) beams will help SFRC to become widely used. An artificial neural network (ANN) model consisting of an input layer, a hidden layer of six neurons and an output layer was developed to predict the shear strength of SFRC slender beams without stirrups, where the input parameters are concrete compressive strength, tensile reinforcement ratio, shear span-to-depth ratio, effective depth, volume fraction of fibers, aspect ratio of fibers and fiber bond factor, and the output is an estimate of shear strength. It is shown that the model is superior to fourteen equations proposed by various researchers in predicting the shear strength of SFRC beams considered in this study and it is verified through a parametric study that the model has a good generalization capability.

Contribution of Steel that Holds Stirrups in Compression Zone to Bending Capacity

Theoretical investigation is performed to study the effect of the presence of steel bars at compression zone which are provided originally to hold stirrups and its contribution to the bending moment capacity of singly reinforced concrete sections. The study considers beam with specific geometry (b = 300mm, d = 442mm) and properties ( f y = 420 MPa & f ' c = 21 MPa) with tensile steel reinforcement ratio of (0.0111). The investigation arises that the enhancement of about (1.37% - 3.47%) in bending capacity may occur . Also, there is a possibility to decrease the amount of tension reinforcement by (1.64% - 3.16%). The idea presented here may be useful to be considered if the original design is found slightly not sufficient.

The Behavior of Slab-Column Joints of Reactive Powder Concrete under Cyclic Load

Experimental work on four specimens of reinforced concrete slab- column connection sub-assemblages using reactive powder concrete (RPC) was conducted. The specimens were subjected to a combination of gravity and cyclic loading. The gravity loading was represented by a number of concrete cubes hung on the slab bottom surface and the cyclic lateral loading was applied on the upper end of the columns. The specimens consisted of two variables, i.e tensile flexural reinforcement ratio (0.65% and 1.8%) and slab span (2.0 m and 3.0 m). Shear reinforcement was not used in the slab. The displacement history consisted of three repeated cycles, starting from 0.07 to 5.00 percent drift ratio, covering the elastic and the inelastic response of the specimens. The RPC mixture proportion for the specimen’s material was developed using local materials and normal concrete technology methods. The average RPC compression tests results were 136.0 MPa at 28 days and 141.0 MPa at the time of the first specimen, tested at 56 days. The tests results showed that up to 5.0 percent drift all specimens had stable hysteresis loops without any significant degradation of strength and stiffness. The specimen with a larger tensile flexural reinforcement ratio developed more strength, stiffness and energy dissipation.

Experimental and Analytical Investigations of a Locally Developed Ultrahigh-Performance Fiber-Reinforced Concrete

AbstractThis paper presents the experimental investigations and analytical modeling of the strength and flexural characteristics of a locally (Las Cruces, New Mexico) developed fiber-reinforced ultrahigh-performance concrete (UHPC). High-strength steel fibers were used to improve the strength and flexural properties of the UHPC. Mean compressive strength of the UHPC mixture was obtained as 138 MPa. The UHPC beams also exhibited favorable flexural responses with the deformational ductility indexes ranging between 6 and 10 and the performance factor between 4 and 6. The longitudinal tensile reinforcement ratio was 0.7%, and no transverse reinforcement was present. The moment versus curvature response was modeled analytically by considering the microscopic stress-strain relationship of the concrete and steel. This response was then integrated with a force-based distributed plasticity beam element. The analytical model thus created captured the experimental moment-curvature and force-deformation responses wit...

FLEXURAL DUCTILITY OF LIGHTWEIGHT-AGGREGATE CONCRETE BEAMS

This paper describes an experimental study on the flexural ductility of lightweight-aggregate concrete beams in­cluding concretes with compressive strengths between 22.0 and 60.4 MPa and dry densities between 1651 and 1953 kg/m3. Nineteen simply supported beams were tested until failure. Two symmetrical concentrated loads were applied at approxi­mately one third of the span. Ductility was studied by defining ductility indexes. The main variables are the concrete compressive strength and the longitudinal tensile reinforcement ratio. It is shown that the parameter with higher influ­ence on ductility is the longitudinal tensile reinforcement ratio. The test results are also compared with the requirements from some codes of practice. It is shown that ACI Code requirements give more guaranties as far as ductility is con­cerned, when compared with European codes.

Chord rotation demand for effective catenary action of RC beams under gravitational loadings

Many experimental and analytical studies have been conducted with beam-column subassemblages composed of a two-span beam to investigate the progressive collapse resistance of RC frames. Most study results reveal a strength-decreased transition phase in the nonlinear static load-deflection curve, which may induce dynamic snap-through response and increase the chord rotation demand for effective catenary action (ECA). In this study, the nonlinear static response is idealized as a piecewise linear curve and analytical pseudo-static response is derived for each linearized region to investigate the rotation demands for the ECA of the two-span RC beams. With analytical parameters determined from several published test results, numerical analysis results indicate that the rotation demand of 0.20 rad recommended in the design guidelines does not always guarantee the ECA. A higher rotation demand may be induced for the two-span beams designed with smaller span-to-depth ratios and it is better to use their peak arch resistance (PAR) as the collapse strength. A tensile reinforcement ratio not greater than 1.0% and a span-to-depth ratio not less than 7.0 are suggested for the two-span RC beams bridging the removed column if the ECA is expected for the collapse resistance. Also, complementary pseudo-static analysis is advised to verify the ECA under realistic dynamic column loss even though the static PAR is recovered in the nonlinear static response. A practical empirical formula is provided to estimate an approximate rotation demand for the ECA.

Flexural performance of lightweight reinforced-concrete slabs

Recent advances in high-performance/high-strength lightweight concrete (HP/HSLWC) have had limited application in structural construction because of the lack of design and construction guidelines and concerns about material properties and their impact on performance. Research is needed to address the factors that significantly influence the design, constructability and performance of HSLWC slabs. After reasonable validation with experimental test results of companion slabs, non-linear finite-element analysis was conducted with the aim of providing a better understanding of the effect of concrete compressive strength, ratio of tensile steel reinforcement, ratio of compression steel reinforcement and slab thickness on the performance of the slabs. The results show that the current ACI 318-08 provisions for the serviceability requirements of ultimate strength and maximum deflection are underestimated, although they are adequate for cracking load requirements.

PLASTIC ROTATION CAPACITY OF LIGHTWEIGHT-AGGREGATE CONCRETE BEAMS

This article describes a study on the plastic behaviour of lightweight-aggregate concrete beams. The experimental results of nineteen simply supported beams previously tested by the authors were used in this study. The experimental plastic rotation capacity of the tested beams was characterized by a parameter called Plastic Trend Parameter (PTP). The main variables studied were the concrete compressive strength and the longitudinal tensile reinforcement ratio. It was found that plastic rotation capacity slightly increases as the concrete compressive strength increases. An appropriate range for the longitudinal tensile reinforcement ratio to ensure plastic rotation capacity is proposed. The results of this study were also compared with the requirements from some codes of practice. From this analysis, it was shown that ACI Code requirements give more guaranties as far as plastic rotation capacity is concerned, when compared with European codes. First published online: 28 Jan 2016

Flexural and Thermal Properties of Novel Energy Conservation Slotted Reinforced Concrete Beams

Conventional solid reinforced concrete (RC) beams were modified to slotted beams for consideration as thermal insulation structural components. The slotted beam consisted of an outer and an inner beam, respectively, with a slot located near the middle of the beam along its width direction for filling thermal insulation material. Flexural and thermal behavior of the slotted beams were investigated. Three RC reference solid beams and six slotted beams were fabricated and tested under four-point bending tests. The test results indicated that the failure mode of both slotted beams and the solid beams was flexural failure. However, the damage process of the slotted beams was different from that of the solid beams at the final loading stage. The moment curvature analysis indicated that the tensile reinforcement ratio of the outer and inner beams had an important effect on the flexural behavior, especially the ductility of the slotted beams. Thermal study indicated that the heat transfer coefficient of the slotted beam was greatly reduced and the thermal inertia factor increased a lot, compared with the solid beam. In addition, FE simulation results showed that a new frame structure using slotted beams exhibited obvious and attractive thermal insulation property.

Satisfactory margin of safety against shear failure of lightweight reinforced concrete beams: 3D finite element modeling

In concrete structures a satisfactory margin of safety should be ensured against shear failure that might occur under the forces that act upon the structure during its lifetime. Therefore, knowledge of the design and construction guidelines for shear of normal and high strength Lightweight Concrete (LWC) beams is desirable to better understand the structural design and performance of LWC beams. Thus, research is required to address and investigate the contribution of concrete compressive strength, shear span to depth ratio, tensile reinforcement ratio, and shear stirrups spacing as well as the failure mechanisms in situation of using LWC beams. As a result, this paper presents Nonlinear Finite Element Analysis (NLFEA) results of reinforced LWC beams because of the main benefits of NLFEA by providing substantial savings in the cost, time, and effort compared with the fabrication and experimental testing of structure elements as well as the ability to change any parameter of interest and the capability of demonstrating any interesting behavior at any load value and at any location in the system. After reasonable validation of NLFEA with the experimental test results, the NLFEA was expanded to provide a parametric study of fourteen hundred LWC beams that correlates the ultimate shear stress to studied parameters. Results indicated that the lower bound was for the beams with shear span to depth ratio, concrete compressive strength, and tensile reinforcement ratio of 5, 27.5 MPa, and 0.71%, respectively, and the upper bound was for the beams with shear span to depth ratio, concrete compressive strength, and tensile reinforcement ratio of 1, 68.8 MPa, and 2.21%, respectively. In addition, the performance of simulated models was investigated in terms of ultimate load capacity, ductility and energy absorption. Finally, a new parametric model is introduced in this paper to compute the shear strength of reinforced LWC beams without stirrups. The proposed equation was compared with numerous previous analytical models and founded that some models to be in a good agreement.

Analytical solutions for flexural design of hybrid steel fiber reinforced concrete beams

Hybrid reinforced concrete (HRC) is referred to as a structural member that combines continuous reinforcement with randomly distributed chopped fibers in the matrix. An analytical model for predicting flexural behavior of HRC which is applicable to conventional and fiber reinforced concrete (FRC) is presented. Equations to determine the moment–curvature relationship, ultimate moment capacity, and minimum flexural reinforcement ratio are explicitly derived. Parametric studies of the effect of residual tensile strength and reinforcement ratio are conducted and results confirm that the use of discrete fibers increases residual tensile strength and enhances moment capacity marginally. However improvements in post-crack stiffness and deformation under load is substantial in comparison to conventional steel reinforcement. Quantitative measures of the effect of fiber reinforcement on the stiffness retention and reduction of curvature at a given applied moment are obtained. The approach can also be presented in a form of a design chart, representing normalized moment capacity as a function of residual tensile strength and reinforcement ratio. Numerical simulations are conducted on the steel fiber reinforced concrete (SFRC) and HRC beam tests from published literature and the analytical solutions predict the experimental flexural responses quite favorably.

An evolutionary fuzzy modelling approach and comparison of different methods for shear strength prediction of high-strength concrete beams without stirrups

In this paper, an Adaptive nerou-based inference system (ANFIS) is being used for the prediction of shear strength of high strength concrete (HSC) beams without stirrups. The input parameters comprise of tensile reinforcement ratio, concrete compressive strength and shear span to depth ratio. Additionally, 122 experimental datasets were extracted from the literature review on the HSC beams with some comparable cross sectional dimensions and loading conditions. A comparative analysis has been carried out on the predicted shear strength of HSC beams without stirrups via the ANFIS method with those from the CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94 codes of design. The shear strength prediction with ANFIS is discovered to be superior to CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94. The predictions obtained from the ANFIS are harmonious with the test results not accounting for the shear span to depth ratio, tensile reinforcement ratio and concrete compressive strength; the data of the average, variance, correlation coefficient and coefficient of variation (CV) of the ratio between the shear strength predicted using the ANFIS method and the real shear strength are 0.995, 0.014, 0.969 and 11.97%, respectively. Taking a look at the CV index, the shear strength prediction shows better in nonlinear iterations such as the ANFIS for shear strength prediction of HSC beams without stirrups.

An evolutionary fuzzy modelling approach and comparison of different methods for shear strength prediction of high-strength concrete beams without stirrups

In this paper, an Adaptive nerou-based inference system (ANFIS) is being used for the prediction of shear strength of high strength concrete (HSC) beams without stirrups. The input parameters comprise of tensile reinforcement ratio, concrete compressive strength and shear span to depth ratio. Additionally, 122 experimental datasets were extracted from the literature review on the HSC beams with some comparable cross sectional dimensions and loading conditions. A comparative analysis has been carried out on the predicted shear strength of HSC beams without stirrups via the ANFIS method with those from the CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94 codes of design. The shear strength prediction with ANFIS is discovered to be superior to CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94. The predictions obtained from the ANFIS are harmonious with the test results not accounting for the shear span to depth ratio, tensile reinforcement ratio and concrete compressive strength; the data of the average, variance, correlation coefficient and coefficient of variation (CV) of the ratio between the shear strength predicted using the ANFIS method and the real shear strength are 0.995, 0.014, 0.969 and 11.97%, respectively. Taking a look at the CV index, the shear strength prediction shows better in nonlinear iterations such as the ANFIS for shear strength prediction of HSC beams without stirrups.

Longitudinal reinforcement ratio in lightweight aggregate concrete beams

The development of lightweight aggregate concrete (LWAC) has brought new design opportunities. The high strength and simultaneous low densities can lead to economically competitive structural solutions, which has immediate impact on seismic construction and on the strengthening of existing structures. Currently, most studies are focused on the mechanical properties and the structural behaviour under ultimate limit states, lacking experimental and numerical data concerning the serviceability of LWAC members. In this scope, a parametric study was undertaken to address the serviceability LWAC beams under flexural loading for a complete range of longitudinal reinforcement ratios. An advanced finite element technology was validated in the simulation of the overall and localised response of the members, the latter including crack openings and patterns. It was observed that the tensile reinforcement ratio should be kept bellow 2% when the durability of the LWAC is important. Nevertheless, reinforcement ratios bellow 1% might not fulfil the design requirements for aggressive environments. The numerical findings also point out that the characteristic crack openings evaluated according to the Eurocode 2 might underestimate the actual value for LWAC beams.

Moment redistribution in RC beams – A study of the influence of longitudinal and transverse reinforcement ratios and concrete strength

In this paper, the results from an experimental programme, aimed at investigating moment redistribution in statically indeterminate reinforced concrete structures, are presented and compared with theoretical analysis of the structural behaviour. Due to the nonlinear structural behaviour of reinforced concrete structures, linear elastic analysis can lead to an inaccurate assessment of the behaviour and, therefore, it can become necessary to use more advanced methodologies to achieve sufficiently accurate analysis. Furthermore, more advanced methods can enable a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. In order to assess the load-carrying capacity at the ultimate limit state (ULS), a model combining plastic and nonlinear analysis is presented. The evolution of moment redistribution to structural collapse was studied experimentally for continuous two-span beams. The focus of the experiments was on the influence of the longitudinal tensile reinforcement ratio at the intermediate support, the transverse reinforcement ratio and the concrete strength. The experimental response at the ULS was further compared with the predicted distribution of internal forces according to the theoretical model. Evaluation of the experimental study indicated a highly nonlinear structural behaviour of the tested beams with the distribution of moment differing from linear elastic analysis, even for low load levels. The evolution of moment redistribution and the moment redistribution at the ULS were appreciably dependent on the arrangement of longitudinal reinforcement, whilst the transverse reinforcement ratio had a marginal impact up to yielding of the longitudinal reinforcing steel, with the concrete strength slightly reducing the degree of moment redistribution. For those beams which failed in flexure, predictions from the theoretical model presented were in good agreement with the experimental results. However, several beams collapsed in shear-related failure modes.

탄소섬유보강재로 보강한 순환골재 콘크리트보의 휨보강효과에 관한 실험적 연구

Recycled coarse aggregates (RCAs) made by construction waste can be used as concrete aggregates. Nevertheless, some studies have indicated that increasing the RCA replacement ratios of the reinforced concrete (RC) structures resulted in a decrease in failure load capacity, in strength degradation, and in severe cracking. In this study, the use of carbon fiber reinforcement polymer (CFRP) sheets and CFRP plates in RC structures was evaluated for their effect in suppressing cracking and in adding strength to the structure. Twelve specimens including five control beams were fabricated, using various recycled coarse aggregate substitution rates, to compare and analyze the CFRP material's reinforcement effects. All specimens were fabricated with stirrups as simple beams with fixed span to effective depth ratio of 3.88 to 1 (i.e., a/d=3.88). The main variables studied in this investigation are (1) replacement level of recycled coarse aggregates (0, 15, 30 and 50%), (2) tensile reinforcement ratio (0.8, 1.27%), and (3) the incorporation of CFRP sheets and/or CFRP plates.

FE modeling of inelastic behavior of reinforced high-strength concrete continuous beams

A finite element model for predicting the entire nonlinear behavior of reinforced high-strength concrete continuous beams is described. The model is based on the moment-curvature relations pre-generated through section analysis, and is formulated utilizing the Timoshenko beam theory. The validity of the model is verified with experimental results of a series of continuous high-strength concrete beam specimens. Some important aspects of behavior of the beams having different tensile reinforcement ratios are evaluated. In addition, a parametric study is carried out on continuous high-strength concrete beams with practical dimensions to examine the effect of tensile reinforcement on the degree of moment redistribution. The analysis shows that the tensile reinforcement in continuous high-strength concrete beams affects significantly the member behavior, namely, the flexural cracking stiffness, flexural ductility, neutral axis depth and redistribution of moments. It is also found that the relation between the tensile reinforcement ratios at critical negative and positive moment regions has great influence on the moment redistribution, while the importance of this factor is neglected in various codes.