•Influence of steel fibre jacket on the flexural behaviour of recycled aggregate concrete beams;•Lack of suitable model to predict the bending performance of strengthened recycled concrete beams with ...concrete jacket;•Development of a new model to forecast the flexural resistance of jacketed RC beams with steel fibres concrete jacket.
In this study, the effect of steel fibres reinforced concrete (SFRC) jacketing on the flexural performance of coarse recycled aggregate reinforced concrete (CRARC) beams is studied. A total of 48 reinforced concrete beams, in two categories, were manufactured and tested. In the first category, 16 reinforced concrete (RC) beams were tested, then strengthened with a jacket and tested again. In another category, 16 specimens were strengthened with a jacket and then tested. All specimens were tested using a four-point flexural setup. Coarse recycled aggregate (CRA) was used at two mass replacement ratios, 0% and 100%, in both RC beams and concrete jackets (CJs). Steel fibres (SF) was also added at 0% and 2% (by volume) in both beams and CJs. In these tests, the flexural capacity, maximum displacement at mid-span and the ductility of specimens were measured. Moreover, a new modified model was proposed to predict the flexural behaviour of SF jacketed CRA and coarse natural aggregate (CNA) beams. The obtained outcomes indicate that the maximum flexural strength and displacement of 100% CRARC beams increased substantially by strengthening RC with 2% SF reinforced CJs.
Over the past few years, polyolefin fiber reinforced self-compacting concrete has shown high performance in both fresh and hardened state. Its fracture behavior for small deformations could be ...enhanced with a small amount of steel-hooked fibers, obtaining a hybrid fiber-reinforced concrete well suited for structural use. Four types of conventional fiber-reinforced concrete with steel and polyolefin fibers were produced on the basis of the same self-compacting concrete also manufactured as reference. These concrete mixtures were manufactured separately with the same fiber contents being subsequently used for two more hybrid mixtures. Fracture properties, in addition to fresh and mechanical properties, were assessed. The research showed both synergies (with the two types of fibers working together in the fracture processes) and an improvement of the orientation and distribution of the fibers on the fracture surface.
•TRC and F/TRC materials are viable strengthening solutions for RC beams in shear.•Low matrix performance in tension might induce premature interlaminar TRC failure.•F/TRC materials outperform ...traditional TRC preventing interlaminar shearing.•Existing models provide good estimations of the shear contribution of TRC and F/TRC.
Textile Reinforced Concrete (TRC) materials have proven to be not only a viable solution, but also an effective one when used to strengthen Reinforced Concrete (RC) structures. The main drawbacks associated with this type of composites is mainly related to the low tensile strength of the cementitious matrix. To overcome such limitation, an improved class of such materials, named Fibre/Textile Reinforced Concrete (F/TRC) and consisting in the addition of short dispersed fibres to the cementitious matrix, was recently developed. An experimental campaign aimed at assessing and comparing of both TRC and F/TRC strengthening solutions upon the shear strength of real-scale RC beams was performed. Different parameters were investigated, including shape and number of textile layers, presence of short dispersed steel fibres, and presence of mechanical anchorages. The results show how the different parameters influence the overall behaviour of the tested specimens and highlight the strong increase in performance achievable using F/TRC materials compared to normal TRC.
•The seismic performance of retrofitted columns was investigated.•Two different retrofit strategies were applied to the concrete columns.•The effect of various retrofit methods on seismic performance ...of concrete columns was analyzed.•Nonlinear modeling parameters for concrete columns specified in ASCE 41–13 were modified.•The nonlinear load-deformation curves of retrofitted columns were established and verified.
In this study, various retrofit methods for concrete columns with non-seismic reinforcement details were developed and investigated: steel jacketing, carbon fiber reinforced polymer (CFRP) wrapping, concrete jacketing with non-shrinkage mortar, and new concrete jacketing with amorphous metallic fiber (AMF) reinforced concrete. Eleven half-scale reinforced concrete columns including two different control specimens, which were designed to fail in shear or flexure-shear, and nine retrofitted specimens were fabricated and tested under cyclic loading, simulating earthquake loading combined with axial loading. Two different retrofit strategies were applied to the control specimens: partial retrofit in the plastic hinge zone, mainly aiming at increasing deformability, and full retrofit in the entire range of columns, aiming at increasing both shear strength and deformability. The seismic capacity of the test specimens was analyzed in terms of various factors: load–drift relationship, dissipated energy, damping ratio, effective stiffness, and ductility. The test results showed that the retrofitted specimens presented ductile failure mode and enhancement in the dissipated energy and the damping ratio, but the effect differed for each retrofit method. Furthermore, based on the test results, the variables (or conditions) used to define the modeling parameters of the nonlinear analysis specified in ASCE 41-13 were modified in order to use the parameters of nonlinear analysis after retrofitting the columns. In addition, the nonlinear load-deformation curves established based on the modified conditions were compared with the test results.
•UHPFRC-strengthened columns were proposed to improve vehicle-impact resistance.•High-resolution FE models were developed and validated by existing test data.•A damping-based method was proposed to ...efficiently exert initial permanent loads.•The influences of design parameters were clarified using response surface methodology.•The response surface model was demonstrated as capable of accurately predicting impact-induced responses.
Bridge columns made of normal concrete are evidenced to be susceptible to vehicle collisions. Particularly in the United States, vehicle collision has become one of the primary causes of bridge failures. This is largely due to the low crashworthiness of a conventional reinforced concrete (RC) column. Ultra-high-performance fiber-reinforced concrete (UHPFRC) as one of advanced concrete materials has been experimentally demonstrated to possess excellent strength, durability, impact resistance and energy-absorbing capacity. Accordingly, one type of UHPFRC-strengthened columns was proposed in this study as an alternative to RC columns that may be at risk for vehicle collision incidents. High-resolution finite element (FE) models were developed to investigate the performance of UHPFRC-strengthened columns subjected to vehicle collisions. In the high-resolution FE model, a three-span simply-supported girder bridge (including girder, pier column, column cap, bearing, etc.) was adopted and modelled. Material models regarding normal concrete and UHPFRC as well as the vehicle model were carefully calibrated by experimental data. The influence of initial gravity loads on impact responses was found to be pronounced, and a damping-based method was proposed to efficiently exert permanent loads on pier columns prior to a collision. Three different simplified models, as published in current studies, were investigated to replace the whole bridge model. Two single-column models with different boundaries were shown to have low accuracy. The pier-bent model considering the superstructure gravity was demonstrated as capable of predicting collision-induced responses that are in good agreement with the high-resolution FE model. The impact resistances of both RC and UHPFRC-strengthened columns were extensively investigated using the appropriate simplified model. The crashworthiness of UHPFRC-strengthened column was found to be considerably superior to that of RC column. An extensive parametric study was performed using response surface methodology to explore the influences of reinforcement ratios, thickness of UHPFRC jacket, UHPFRC strength and initial impact speed. The impact-resistant performance is mostly sensitive to changes in the thickness of UHPFRC jacket when the impact speed is not very high. On the contrary, the residual capacity of the bridge column is hardly increased by thickening UHPFRC jacket. In addition, the developed response surface models provided easy estimation of impact-induced responses of an UHPFRC-strengthened column, which have potential use as the surrogates of time-consuming FE simulations to efficiently examine the reliability and optimization of bridge columns under impact loadings.
To study the brittle/ductile behavior of concrete beams reinforced with low amounts of rebar and fibers, a new multi-scale model is presented. It is used to predict the flexural response of an ideal ...Hybrid Reinforced Concrete (HRC) beam in bending, and it is validated with the results of a specific experimental campaign, and some tests available in the technical literature. Both the numerical and the experimental measurements define a linear relationship between the amount of reinforcement and the Ductility Index (DI). The latter is a non-dimensional function depending on the difference between the ultimate load and the effective cracking load of a concrete beam. As a result, a new design-by-testing procedure can be established to determine the minimum reinforcement of HRC elements. It corresponds to DI = 0, and can be considered as a linear combination of the minimum area of rebar (of the same reinforced concrete beam) and the minimum fiber volume fraction (of the same fiber-reinforced concrete beam), respectively.
This paper presents an experimental investigation of how varying the volume fraction of chopped basalt fibers affects the mechanical properties of fiber‐reinforced concrete (FRC). The fiber content ...is varied in the range of 0–2%. The main parameters investigated are workability, compressive strength, splitting tensile strength, flexural strength, and flexural toughness. Test results showed that the compression strength of concrete decreased marginally with the addition of basalt fibers in comparison with plain concrete. However, the mode of failure of FRC under compression is changed from the brittle to ductile. The splitting tensile strength of concrete is improved by 15% when basalt fibers with 2% volume fraction are added to the concrete mix. A significant increase of up to 75% is noticed in the flexural tensile strength of basalt FRC, with better post‐peak residual strength compared with the plain concrete. Furthermore, the flexural toughness of basalt FRC is increased by nearly three times that of the plain concrete based on the round panel tests.
Fiber-reinforced concrete (FRC) is increasingly used in structural applications owing to its benefits in terms of toughness, durability, ductility, construction cost and time. However, research on ...the creep behavior of FRC has not kept pace with other areas such as short-term properties. Therefore, this study aims to present a comprehensive and critical review of literature on the creep properties and behavior of FRC with recommendations for future research. A transparent literature search and filtering methodology were used to identify studies regarding creep on the single fiber level, FRC material level, and level of structural behavior of FRC members. Both experimental and theoretical research are analyzed. The results of the review show that, at the single fiber level, pull-out creep should be considered for steel fiber-reinforced concrete, whereas fiber creep can be a governing design parameter in the case of polymeric fiber reinforced concrete subjected to permanent tensile stresses incompatible with the mechanical time-dependent performance of the fiber. On the material level of FRC, a wide variety of test parameters still hinders the formulation of comprehensive constitutive models that allow proper consideration of the creep in the design of FRC elements. Although significant research remains to be carried out, the experience gained so far confirms that both steel and polymeric fibers can be used as concrete reinforcement provided certain limitations in terms of structural applications are imposed. Finally, by providing recommendations for future research, this study aims to contribute to code development and industry uptake of structural FRC applications.
•The addition of the BMF to concrete mixes improved their flexural tensile strength and ductility.•The ductility of BFRP-BFRC beams was improved by increasing the Vf of BMF.•The moment redistribution ...of BFRP-BFRC beams was investigated experimentally.•Increasing Sagging-to-hogging reinforcement improved moment redistribution of the beams.•A proposed equation incorporating ACI 440.1R-15 guide and a model suggested by Rjoub is proposed.
This study investigated the structural performance and moment redistribution of basalt fiber reinforced concrete (BFRC) continuous beams reinforced with basalt fiber reinforced polymers (BFRP) bars. A total of 10 reinforced concrete (RC) continuous beams over two equal spans of 1800 mm were tested under five-point loading until failure. The test variables were the type of main bars, sagging-to-hogging reinforcement ratio, volume fractions (Vf) of basalt macro fibers (BMF), and stirrups spacing. Seven beams were longitudinally reinforced with BFRP bars, while the remaining three beams were reinforced with conventional steel bars and served as a control. Test results showed that BFRC-RC beams had higher crack widths, mid-span deflections, and strains than steel-RC beams. Furthermore, the ductility index, load-carrying capacities and moment redistribution of the tested beams considerably improved by increasing the Vf of BMF and sagging-to-hogging reinforcement ratio, and decreasing stirrups spacing. However, increasing the reinforcement ratio and Vf of BMF was more effective in improving the moment redistribution than reducing the stirrups spacing. Analytically, the experimental sagging and hogging moments were compared to the available existing models and codes equations. A modified equation incorporating ACI 440.1R-15 provisions and a model suggested by Rjoub provided the most accurate predictions of the tested beams' moment capacities.
•Carbon textile reinforced concrete (CTRC) with short fibers was used to strengthen the square concrete columns.•The CTRC jackets significantly improved the compressive behavior of concrete ...columns.•The compound confinement contributions from CTRC composites and stirrups for strengthened RC columns are analyzed.•An analytical model was established to predict the stress–strain response of concrete columns confined by CTRC.
In this study, with the aim of investigating the confinement behavior and stress–strain response of concrete columns strengthened with carbon textile reinforced concrete (CTRC) under a uniaxial load, a total of 20 column specimens with square cross-sections were cast and subjected to monotonic axial compression. Next, the effects of the number of textile layers, stirrup reinforcement ratio, concrete strength and short fibers on the efficiency of CTRC confining system were evaluated. The experimental results indicated that the CTRC-confined columns obtained a maximum improvement of up to 67.3% in bearing capacity and 65.2% in displacement ductility compared to the un-strengthened reference columns, and exhibited a more significant ductile failure characteristic. Moreover, the bearing capacity and displacement ductility of the confined columns were characterized by increasing with an increase in the number of textile layers and stirrup ratio, and a decrease in the concrete strength. The short fibers mixed in the strengthening layers also made a beneficial contribution to the bearing capacity and displacement ductility, particularly to the cracking load of the confined columns. Finally, a semi-empirical model was proposed to predict the axial stress and strain of concrete column specimens strengthened with CTRC based on the experimental results and theoretical analysis. The results calculated by the proposed model were evidenced to be fundamentally consistent with the experimental results. Therefore, the proposed model in this study could effectively predict the stress–strain response of square RC columns confined with CTRC composites.
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