Reinforcement Bars Research Articles

Validation of reinforced concrete bond stress–slip models through an analytical strain distribution comparison

The bond and slip between concrete and the reinforcement bars, cover a key role in the inter-material force transfer of Reinforced Concrete (RC) structures. In light of the lack of tools able to thoroughly inspect the inner workings of RC structures and to extract reliable bond stress values, modern bond stress–slip (Bond–slip) models are often inaccurate and in contradiction with each other. Considering the recent surge of novel hyper-performant strain sampling tools (Distributed Sensing for example), their application for the creation of novel and physically accurate Bond–slip models is just a matter of time. This being said, one of the main reasons behind the modern coexistence of multiple inaccurate and at times contradictory Bond–slip models is the absence of a tool that has allowed researchers to rapidly corroborate and calibrate their newly created models. To this end, the present article proposes such a Bond–slip validation tool for RC elements. This one is designed to extract reinforcement strain profiles at any given load level on the grounds of a specific bond–slip law and geometrical inputs. Said profile is then compared against an experimentally extracted one based on specimens with identical geometrical features. The performance of the validation tool is demonstrated through an application to six existing bond–slip models. Granted the proposal of validation tools is paramount for the future of the discussion on bond–slip modelling, stress-transfer analyses and serviceability of RC structures, the here proposed validation tool is a first significant step in that direction.

Evaluation of carbonation coefficient of reinforced concrete structures

ABSTRACT With the advancement of modern construction technology, reinforced concrete (RC) has become the most widely used composite construction material. Corrosion of embedded reinforcement bars in RC structures, which is essentially the result of carbonation and chloride attack, is regarded as one of the weaknesses. Hence, many research studies have been conducted to evaluate the effect of corrosion on the service life of RC structures. However, so far no proper equation has been derived to predict the extent of carbonation-induced corrosion. Identifying this research gap, the present study intends to derive an equation for the coefficient of carbonation (K), which is the governing measure of the rate of carbonation. This paper identifies concrete grade, exposed CO2 gas concentration, and exposed Relative Humidity (RH) level as the major parameters affecting the carbonation process. The behaviour of each factor along with K was identified by conducting a modified accelerated carbonation test (ACT). These experimentally derived K values were statistically analysed under the principle of multiple linear regression, to derive an equation for predicting K values for RC structures. Based on the results, this paper proposes two user-friendly mathematical models covering the entire environmental RH range to predict the K values of RC structures.

Parametric investigation and economic design of slender steel fibre reinforced concrete beams using shear resisting mechanisms approach

The shear resisting mechanisms (SRM) in slender steel fibre reinforced concrete (SFRC) beam (without stirrups) comprised of four shear resisting mechanisms (uncracked concrete in the compression zone, the dowel action of the longitudinal reinforcement bars, the aggregate interlocking through the aggregates protruding at the critical diagonal shear crack, and the steel fibres bridging the diagonal crack). These shear resisting mechanisms are interrelated to each other and very complex to quantify. However, parametric analysis is one of the methods which can easily be applied and quantify their interconnection. As a result, the parametric analysis has been carried out in this research with the main focus on the effect of influential parameters on shear strength, shear resisting mechanisms, and the interrelationship between them. Thus, the SRM model has been again verified and validated through the results of parametric investigation. Furthermore, the SRM based model has been further modified, and a cost analysis for economic beam design was performed. Finally, design recommendations from the standpoint of practical application have been proposed.

Bending strength characteristics of sawdust- crete laminated composite slab

This paper presents the bending characteristics of sawdust-crete laminated composite slab. The materials used in the laboratory experiments include: Ordinary Portland Cement, river sand, gravel, sawdust, plywood, nails, reinforcement bars, stirrups and water. Manual mixing method was adopted and all sawdust-crete ingredients were batched by weight. A total of 48 slabs of size 1200mm x 1000mm x 100mm, 1200mm x 1000mm x 125mm, 1200mm x 1000mm x 150mm and 1200mm x 100mm x 175mm were cast for flexural strength from the mix ratios 0.75:1:2:2 and 0.75:1:3:3. Out of the 48 slabs cast, 32 were produced from sawdust-crete laminated composite (with 12.5mm and 20mm as the thickness of plywood for the laminate), 8 were produced from normal concrete ingredients (coarse aggregates, fine aggregates, cement and water) with 10mm rebar and mix ratio of 0.45:1:2:4. The remaining 8 slabs were made from plain sawdust-crete with mix ratio of 0.75:1:3:3. During the experiment, the maximum deflection for the slab was observed to occur at the slab with size 1200mm x 1000mm x 100mm no matter the core content used to produce the slab while the minimum deflection occurs at the size 1200mm x 1000mm x 175mm. The deflection of slab decreases with increase in slab thickness while flexural strength increases with increase in slab thickness. The flexural strength results of slab were compared by percentage difference and the results shows that there is significant difference between the two sets of slabs. Also, by comparing the results of plain sawdust-crete slab to that of sawdust-crete laminated composite slab, the result show that laminates with plywood increases flexural strength up to 68.4%. Conclusively, laminated sawdust-crete can be used for slabs that is not carrying too much load like residential houses.

The finite element model of chloride diffusion in pre-stressed corroded reinforcement bars of reinforced concrete structures

Introduction. The general corrosion model, made for reinforced concrete structures, must include the initiation of environmental influences such as carbonation, cracking and chloride ion penetration. It depends on the rate and degree of corrosion, corrosive effects in reduced areas, as well as the lower strength of bond between pre-stressed and unstressed reinforcement bars and concrete. The majority of earlier studies were focused on one-dimensional diffusion problems with an assumed constant corrosion rate.
 
 Materials and methods. In the aftermath of general corrosion, localized corrosion is accompanied by a release of hydrogen and alkaline water, chlorine ions. Crack propagation in reinforcement wires is calculated using the transient finite element software for chloride diffusion, which is time-dependent.
 
 Results. In most cases, the diffusion equation does not have a closed form solution, and therefore, the finite difference method can be used. The authors have shown that the corrosion rate decreases with time if current density has different water-cement ratios. If the water-cement ratio increases, the corrosion rate increases, as well.
 
 Conclusions. In a pre-stressed reinforced concrete beam, the corrosion of one bar affects the total corrosion of all bars and the reduction in the cross-sectional area of bars that does not exceed 15 %.

Solution of a paradox related to the rigid bar pull-out problem in standard elasticity

This paper aims at modeling pull-out tests of a reinforcement bar from a concrete matrix. The considered system is an elastic cylinder, within which is embedded a rigid bar placed along the central axis. The pull-out test consists in extracting the bar while fixing the outer lateral boundary of the cylinder. Typically, the concrete matrix would be modeled as a Cauchy continuum (i.e. first gradient elastic continuum), while the slender reinforcement bar would be modeled either as an inner elastic cylinder, or – when its radius tends to zero – as a one-dimensional beam. However, we show that such a model yields a null total deformation energy for the concrete cylinder if the bar is modeled as a beam. This result is physically paradoxical, as the extraction of even the slenderest bar requires an energy input, which is transferred to the concrete matrix as deformation energy.In the present work, this paradox is solved by considering a strain-gradient deformation energy for the concrete matrix. It is shown that such a modeling approach allows deformation to occur even when the radius of the inner bar tends to zero. This result is found to be parametrized by a characteristic length which is physically justified through granular micromechanics. Numerical results are also obtained and hint at a possible way to identify the characteristic length experimentally in future works.

Flexural Performance Evaluation of Single Reinforced Concrete Beams with FRP Reinforcing Bars Compared to RC

Flexural Performance Evaluation of Single Reinforced Concrete Beams with FRP Reinforcing Bars Compared to RC

A Study on Flexural Performance of Double Reinforced Concrete Beams with FRP Reinforcing Bars

A Study on Flexural Performance of Double Reinforced Concrete Beams with FRP Reinforcing Bars

Dynamic beam-end tests: Investigation using split Hopkinson bar

The bond between concrete and steel reinforcement is a highly investigated topic under both quasi-static and dynamic loading conditions. Strain rate sensitivity and dynamic increase factor are the key aspects affecting the resulting response of the structure and represent crucial parameters for modelling the impact-related events. Measuring the bond properties under dynamic conditions, however, is a complex task requiring advanced experimental techniques and methodology. In this paper, the bond stress-slip relationships during dynamic pull-out was measured using an innovative technique based on a tensile split Hopkinson bar and a near-to-full-scale beam-end specimen representing an end-part of a reinforced concrete beam.A tensile split Hopkinson bar was used to generate a tensile stress wave with a long duration that pulls a reinforcement bar with a short bond length out of the concrete block. As a very complex wave propagation behavior was observed during the impact, the forward and backward propagating waves have to be separated and subsequently used to properly calculate the bond stress-slip relationship. Two redundant methods utilizing strain gauge signals and digital image correlation for separation of the longitudinal stress waves were employed to solve the problem. The proof-of-concept and applicability of the method which are the main focus of the contribution were demonstrated with a numerical simulation performed in LS-DYNA. An exemplary evaluation of the results of the real tests performed at medium impact velocity with full pull-out of the rebar was performed. The presented method is considered suitable for the evaluation of the dynamic bond stress-slip relationship and produced high-quality results during the initial impact phase and reasonable quality results up to the full pull-out.

Hysteretic Performance of Hybrid GFRP-Steel Reinforced Concrete Shear Walls: An Experimental Investigation

The vulnerability of steel reinforcement to corrosion is a severe problem affecting the overall performance and durability of concrete structures in aggressive environments. The interest in using alternative Glass fibre-reinforced polymer (GFRP) bars lies in their corrosion resistance and higher tensile strength-to-weight ratio. Nevertheless, experimental results on the seismic behaviour of GFRP-reinforced walls are scarce. This paper investigates the hysteretic performance of hybrid steel-GFRP reinforced concrete shear walls to provide valuable experimental evidence for such walls under seismic loading. Six RC shear walls with steel and GFRP reinforcement were tested under pseudo-static reversed-cyclic lateral load. Three shear walls were reinforced by GFRP bars as longitudinal and transversal reinforcement, and two walls were reinforced with hybrid GFRP-steel bars with different ratios of web reinforcement. A reference specimen, ordinary steel-RC shear walls, was also introduced to certify the capability of GFRP as reinforcement bars. The results indicated that the GFRP-reinforced concrete slender walls had a stable hysteretic response and slight residual drift up to failure. Lower residual deformations, higher displacement capacity, and increased lateral strength could be observed with the GFRP web reinforcement ratio increase. Moreover, the fundamental period of GFRP and hybrid GFRP-steel reinforced walls can reach more than twice its original value prior to failure.

An interactive and collaborative augmented reality environment for civil engineering education: steel reinforcement bars teaching as an example

PurposeAt present, teaching methods based on 2D drawings are still commonly used for educating students on the location of steel reinforcement bars in concrete. However, traditional teaching methods have limitations as students can find it difficult to understand 2D drawings. This study aims to develop an interactive and collaborative augmented reality environment (ICARE) using augmented reality (AR) technology to improve students' engagement in learning.Design/methodology/approachThis study develops an ICARE prototype, which is organized into two stages: (1) The augmented teaching environment comprising of models and interactive components; (2) The AR collaborative application which uses Photon Unity Networking (PUN) plugin and Azure spatial anchors cloud service. The AR-based teaching environment runs with Universal Windows Platform (UWP) to enable development in the HoloLens 2 through Microsoft Visual Studio.FindingsAn experimental study was conducted, where 60 students were divided into three groups employing Drawings-based, building information modeling (BIM)-based and AR-based methods for teaching. After the test, the three groups of students were requested to complete a questionnaire. According to the analysis of the experimental results, the ICARE can improve students' comprehension, memory of learned materials and their ability to read and understand steel reinforcement drawings improving the quality of teaching, especially interactivity and engagement.Originality/valueAs illustrated in the experiments, the developed ICARE has outstanding performance over conventional approaches in civil engineering courses that can improve students' comprehension and memory of knowledge and their ability to read and understand steel bar drawings. This study provides empirical evidence that AR is a promising technology that can be integrated with traditional classroom instruction and can improve students' comprehension and memory of knowledge and their ability to read and understand steel bar drawings.

Development and mechanical performance evaluation of a GFRP-reinforced concrete boat-approach slab

The use of glass fiber-reinforced polymer (GFRP) composite bars as internal reinforcement in concrete structures exposed to marine and aggressive environments has gained popularity in recent years. The fact that designers and workers are unfamiliar with the design and handling of GFRP bars contributes to GFRP bars being used less often than traditional steel reinforcement bars. This case study presents the construction and loading test for GFRP-reinforced concrete boat-approach slab. Two types of reinforcement mesh stemmed from a similar design requirement were implemented: 16 mm diameter bars spaced 150 mm apart in both directions and 24 mm diameter bars spaced 300 mm apart in both directions to evaluate the fabrication and installation efficiency with GFRP bars. Loading tests and monitoring were employed to evaluate the field performance of the GFRP-reinforced slab. The results show that a slab reinforced with 16 mm diameter GFRP bars can be durable and reliable, and can increase worker productivity during handing and installation. Moreover, considering the appropriate subgrade modulus for the supporting ground in the design and analysis can lead to a more cost-effective design of GFRP-reinforced concrete approach slabs. Lastly, this case study demonstrates the durability and resilience of GFRP-reinforced concrete as boating infrastructure.

Evaluation of common defects of grouted sleeve connectors

Grouted sleeve connectors have been widely used in vertical connections of prefabricated reinforced concrete structures. However, the quality of grouted sleeve connections are likely affected by adverse factors during winter construction such as grouting operation error, adverse environmental change, and management negligence. Some defects in winter construction are difficult to check including insufficient strength of grouting material, insufficient anchorage length of connecting reinforcement bars and adverse impact of low-temperature grouting. Although research has been carried out on the connection performance of grouted sleeves with defects, few are on the comprehensive evaluation of the connection performance of grouted sleeves with different defects caused in winter construction. In this paper, 25 groups (75 sleeves) of semi-grouted sleeve connectors with various defects are designed and manufactured. The effects of insufficient anchorage (i.e. insufficient length of reinforcement bar extending into the sleeve), insufficient strength of grouting materials and low-temperature grouting on the tensile properties of semi-grouted sleeve connectors are experimentally studied. On the basis of the test, finite element analysis is performed on extended defect conditions to comprehensively evaluate the safety control indicators. This research provides reference for the safety evaluation of grouted sleeve connections for prefabricated structures.

FRP Stay-in-Place Formworks for High Performance of Concrete Slabs

Stay-in-Place (SiP) formworks obviate the transportation, placement, removal and storage requirements of conventional formworks. Fibre Reinforced Polymer SiPs (FRP-SiP) have additional advantages, such as corrosion resistance, high specific strength and durability. This paper discusses an experimental instigation consisting of two sets of slabs having varying span-to-depth ratios cast on an FRP-SiP. Control specimens with conventional steel bar reinforcements were also cast. Several treatments for improving interfacial bonds at the interface between concrete and FRP-SiP have been investigated. Cyclic flexural tests were performed to evaluate their structural performance. Load-displacement relationship and load capacity are presented. Failure envelopes and energy absorption capacity were evaluated. It was found that the load capacity of FRP-SiP was around 107% greater than the conventional steel rebar specimens. Bond treatment on the FRP-SiP specimens increased the load capacity by around 215% over the untreated specimens. The load-deflection behaviour and the failure modes of the FRP-SiP specimens were distinctly different from those of the conventional specimens. The flexure and shear provisions in American Concrete Institute Standards (ACI 440) were found to be conservative in comparison to the present results. This study demonstrates that FRP-SiPs improve both the structural performance and construction efficiency of concrete slabs, however, new standards would be necessary to be able to utilize their improved capacity.

Analysis of concrete beams reinforced by GFRP bars with varying parameters

Abstract Structural buildings consist of concrete and steel, and these buildings have confronted many challenges from various aggressive environments against the materials manufactured from them. It contains high water levels and buildings whose concrete cover may be damaged and thus lead to the deterioration and corrosion of steel. It was important to have an alternative to steel, such as the glass fiber reinforced polymer (GFRP), which is distinguished by its great effectiveness in resisting corrosion, as well as its strong tensile resistance. Still, one of its drawbacks is that it has a low modulus of elasticity. This research article aims to conduct a numerical study using the nonlinear finite element ABAQUS program on eight beam models with various parameters such as stirrup spacing, compressive strength, reinforcement layer, and type of bar reinforcement under four-point bending. The result shows that the ultimate load capacity of the GFRP beam is higher than that of a beam reinforced with steel and the number and width of cracks are greater in the GFRP-reinforced beam than in the steel-reinforced beam. In general, the serviceability reflected by cracks and deflection is lower in GFRP-reinforced beams than in steel-reinforced beams with higher serviceability. The results, on either hand, showed the expected behavior of GFRP, which is linear elastic to the failure stage. These beams are divided into four groups of beams with different variables studied to understand GFRP bars’ behavior under static loading. The variables taken in this study are the spacing between the stirrups, the compressive strength of concrete, the effect of the number of layers of reinforcement, and the type of reinforcement bar.

Shear behavior of RC pile cap beams strengthened using ultra-high performance concrete reinforced with steel mesh fabric

Although pile cap bases of structures are the most significant element in the construction and one of the most difficult parts in strengthening applications, previous studies on this element, particularly strengthening, are quite limited. The most extensively utilized, highly efficient, and simple to implement solution is ultra-high performance concrete (UHPC). In this study, six-half scaled pile cap beams were prepared and experimentally tested. Three of them were strengthened with UHPC (one in shear with connectors only, one in shear with connectors and steel mesh fabric (SMF), and one in shear and punching with connectors and SMF), while the other three were not strengthened to explore the influence of side bars. The bottom bars of the all six beams were identical, consisting of main longitudinal tensile and secondary lateral reinforcement. The load-displacement response, ultimate carrying load, failure mechanisms, energy dissipation capacity, and shear ductility of pile cap beams were all thoroughly investigated. The results revealed that using side bar reinforcement and UHPC with various techniques significantly enhanced the shear strength and ductility of pile cap beams. Except for the specimen including additional internal side bars, there were no appreciable differences in the peak load of un-strengthened reinforced concrete (RC) pile cap beams. The gain in peak load was 59% due to use of side bars. The RC pile cap beam strengthened in shear and punching with connectors and SMF exhibited the highest peak load and the highest energy dissipation capacity among all tested specimens.

Current condition of recovery method of disaster embankments using geo-cell and soil reinforcement bar

Recently, many embankment disasters have occurred. The main causes of these disasters are natural hazards, such as earthquakes, rainfalls and the combination of these. We are proposing a sustainable seismic and rainfall countermeasures for railway and road embankments by means of geo-cells (made of HDPE) and soil reinforcement bars (Gc-Rb embankment). The soil reinforcement bar is inserted into an embankment, and the geo-cell is laid on the slope of the embankment. The characteristics of this method are the convenience of construction and the economy, in addition to the reinforcement against the natural hazards. The embankment of the Sanriku Railway Riasu Line was seriously damaged by the Tohoku Region Pacific Offshore Earthquake occurred on March 11, 2011 in Japan. Many civil structures were damaged not only in the Sanriku railway but also in Pacific ocean side of Tohoku area. In the restoration works of these structures, the shortage of the construction machine, the machine operator and related materials was the problem. Therefore easiness of construction and usual materials were demanded (such materials other than concrete and so on). The proposed method satisfies these required conditions. The operation of this railway line was restarted on April 3, 2013, two years after the earthquake. In this paper we report the current state of the embankment using this recovery method, including the maintenance, after 6 years from the restart of the service.

Adapting Overlap Per Two Floors for Vertical Structural Members:Column and Shear Wall

The main aim of this study is adapting overlap per two floors for vertical structural members for column and shear wall. Since this concept is new and not applied widely in Ethiopia, the challenges, technical solution for challenges and economic differences were assessed and drawn. This study was used qualitative and quantitative research methodologies. The amounts of reinforcement bars were determined. In depth interviews, site observation, theoretical concepts, previous practical experience and secondary data were used. Purposive sampling technique was applied for selection of respondents and their working companies. In depth interviews were interpreted with respect to structural, architectural and cost perspectives. The results obtained from the purposively selected interviews, observations, theoretical concepts, practical experience and referring secondary materials for providing overlap per two floors on all columns and shear walls has no any effect on the architectural aspects of the column and shear wall. Because, overlapping per two floors for columns and shear wall does not affect the shape and cross section of the vertical elements and covered completely by concrete. Typically, the analysis of cost of reinforcement bars was done for G + 10 building. The total percentage of wastage of bars per two floors is reduced by 13.51% and 11.11% for 2.7m and 3.5m story height compared to per one floor respectively. Key word s: Overlap, Shear wall, Column, Challenge, Solution, Cost DOI: 10.7176/CER/14-6-01 Publication date: October 31 st 2022

Artificial neural network algorithms to predict the bond strength of reinforced concrete: Coupled effect of corrosion, concrete cover, and compressive strength

• The bond strength between steel and concrete was predicted using artificial neural network (ANN) models. • Softplus activation function provided an accurate prediction in comparison to Sigmoid and ReLU functions. • Bond strength is predominantly influenced by the level of steel corrosion. Degradation of the bond between reinforcement steel bars and concrete poses a huge challenge to the design of sustainable infrastructure. In this study, an initial effort was made to develop and apply Artificial Neural Network (ANN) models to predict the bond strength between steel reinforcement and concrete. To assess the efficiency of ANN under a case of limited experimental data, the ANN models were activated through Softplus, Rectified Linear unit (ReLU), or Sigmoid functions and their results were compared. The experimental/test data used in the modeling study only covered corrosion levels from 0 to 20 % of the reinforcement bars' weight, concrete compressive strengths of 23 and 51 MPa, and concrete covers ranging between 15 and 45 mm. A comparison was made between the bond strength values predicted by the ANN models, linear/non-linear statistical regression equations, and other analytical equations available in the literature. The model results indicated that the bond strength was predominantly affected by the level of corrosion (in comparison to the other parameters). Moreover, the ANN(Softplus) model with a mean squared error (J) of 2.89 and a coefficient of determination (R 2 ) of 96 % demonstrated a more accurate prediction of the bond strength in comparison to the ANN(Sigmoid), ANN(ReLu), and statistical regression models.

Experimental study of dynamic bond behaviour between corroded steel reinforcement and concrete

Corrosion damage of steel reinforcement is detrimental to the load-carrying capacity of reinforced concrete structures because it not only reduces the cross sectional area and strength of reinforcement bars, but also weakens the bond between reinforcement and concrete. Many studies have investigated the effects of corrosion on reinforcement loss and static bond strength between reinforcement and concrete, but no study of the influence of corrosion damage on dynamic bond strength has been reported yet. In this study, laboratory tests were conducted to investigate the effect of corrosion on the bond behaviour between steel reinforcement and concrete subjected to high rate dynamic load. Accelerated corrosion damage was induced to steel bars embedded in concrete specimens under laboratory condition. The bond parameters of steel reinforcement and concrete including the ultimate bonding load and bond-slip relationship corresponding to the various strain rates and corrosion degrees were obtained through dynamic pull-out tests. The empirical formulae of dynamic increase factors (DIFs) of the ultimate bonding strength corresponding to different corrosion levels and strain rates were proposed. The experimental results show that the strain rate effect on bonding behaviour is prominent irrespective of the corrosion level. The increase in the ultimate bonding strength with strain rate for the heavily corroded reinforcement (η = 5 %-10 %) is more prominent than that for the slightly corroded reinforcement (η = 0 %-5%). The decrease in the ultimate pull-out force caused by the corrosion damage at high strain rate is more pronounced than that at low strain rate. Corrosion-induced crack and the tensile strength of concrete have significant effect on both the static and dynamic bond behaviours. The results presented in the paper can be used for better modelling and prediction of the responses of corroded reinforced concrete structures subjected to dynamic loads.