Reinforcement Bars Research Articles

Experimental study of corrosion effects on pulling force of hook bars in external beam-column connections

The external beam-column connection in concrete structures is particularly important because it is necessary to secure the reinforcement bars of the beam that are embedded within the column, which are often formed as a 90° hook. The attack of chloride ions is also one of the most dangerous damages that affect constructions and reduce their service life. Hence, it was necessary to study the effect of corrosion resulting from chloride ion attack on the strength of hook bars. To achieve this purpose, 26 specimens were designed with various variables, including the corrosion level of the reinforcement bars, compressive strength of the concrete, specimen loading, and the spacing between the stirrups relative to their diameter (S/D). The specimens were subjected to accelerated corrosion in the laboratory using the current density method by applying 0.35 mA/cm2 for 21 and 58 days. The experimental results showed that corrosion of the reinforcing bar in the joint weakens the mechanical behavior of rebars by reducing their strength and the bond between them and the concrete. The effect of the compressive strength of the concrete, specimen loading, and S\\D on the hook pulling force for corroded and non-corroded specimens has been observed, and they also affected the determination of the level of corrosion. Equations have been proposed to develop Faraday's law and determine the pulling force of a hook bar. The proposed equations yielded results that closely matched those from the experimental test.

Reusing Egyptian in-situ construction &demolition waste(CDW)to produce sustainable concrete.Investigation of compressive &bond strengths using steel & glass fiber reinforced polymer(GFRP)rebars

ABSTRACT This research paper presents the effect of using recycled concrete aggregate (RCA), from the Egyptian construction waste, in different proportions on the bond performance between concrete and its internal reinforcement, where two types of reinforcement were used: a- steel reinforcing bars, and b- glass fiber reinforced polymer (GFRP) bars. 72 samples of concrete were prepared and tested with replacement ratios for natural aggregate (NA) with RCA: 0, 20, 40, 60, 80, and 100 %. The samples were divided into 150 mm cubes to conduct axial compression tests, and pull-out samples to investigate the effect of replacement ratios on the bond between concrete with steel and GFRP rebars. Results showed that concrete loses 26% of its compressive strength after replacing NA with 100% RCA. The results of the pull-out test for steel samples showed 30% higher bonding than GFRP samples. A slight decrease in bond was observed between the control and the tested samples, where the steel and GFRP samples showed a decrease of 5% and 9%, respectively, over the control samples for each, at a replacement percentage of 100%. It was also clear that the steel reinforcement bars had a stronger bond with the concrete, and this can be attributed to the stronger mechanical interlocking of the steel ribs than their counterparts in the GFRP. Failure patterns showed the crushing of concrete with steel bars, in contrast to the GFRP bars, which showed slipping from within the concrete with failure of the ribs in many samples.

Effect of silica fume on Pullout capacity and corrosion resistance of hook bars in the external beam-column concrete joint

Purpose This study aims to determine the effect of replacing a portion of the cement in the concrete mixture with silica fume (SF) on the corrosion resistance of reinforcing bars, the compressive strength of concrete and the tensile strength of hook bars in both corroded and non-corroded external joints of structures. The external beam-column connection was studied because of its critical role in maintaining structural continuity in all three directions and providing resistance to rotation. Design/methodology/approach In external concrete joints, the bars at the end of the beams are often bent at 90° to form hooks that embed in columns. Owing to the importance of embedding distance and the need to understand its susceptibility to corrosion damage from chloride attack, a series of experiments were conducted on 12 specimens that accurately simulate real-site conditions in terms of dimensions, reinforcement and hook bars. SF was replaced with 10% and 15% of the weight of cement in the concrete mixture. To simulate corrosion, the specimens were subjected to accelerated corrosion in the laboratory by applying a low continuous current of 0.35 mA for 58 days. Findings The results revealed the effect of SF in improving the compressive strength of concrete, the pullout resistance of the hook bars and the corrosion resistance. In addition, it showed an apparent effect of the corrosion of reinforcing bars in reducing the bonding strength of hook bars with concrete and the effect of SF in improving this strength. Originality/value It was noted that the improvement of the results, achieved by replacing 10% of the weight of cement with SF, was significantly close to the results obtained by replacing 15% of the SF. It is recommended that an SF ratio of 10% be adopted to achieve the greatest economic savings.

Assessing the Seismic Performance of Exterior Precast Concrete Joints with Ultra-High-Performance Fiber-Reinforced Concrete

This study was conducted to evaluate the seismic performance of an exterior precast concrete (PC) beam–column joint with ultra-high-performance fiber-reinforced concrete (UHPFRC). Currently, 45 MPa non-shrinkage mortar is used as grouting for the connection between PC beams and columns. In this study, PC joint specimens were designed using 45 MPa non-shrinkage mortar and 120 MPa UHPFRC as a grouting agent for connecting PC members. The shear reinforcement effect of UHPFRC was confirmed to reduce shear cracks in the joint core; this trend was similar in the specimens with reduced shear rebars. The maximum moment of the test specimen with the corbel was slightly increased, but there was no significant difference, and the failure pattern also showed similar results to the specimen without the corbel. In the test specimen to which the U-shaped beam was applied, the attachment surface of ultra-high-performance concrete and normal concrete were separated, and a large decrease in strength was observed. Considering workability, U-shaped beam do not seem to have any major merits in general, such as increased strength and difficulty in manufacturing, and it was judged that it was effective to separate the PC beams from the column face through corbels. Shear reinforcement through UHPFRC is effective in relieving congestion by reducing shear reinforcement bars at the joint, and it is judged that it can be used as PC joint grouting due to its excellent fluidity.

Ballistic impact resistance of ultra-high-performance concrete (UHPC): A comprehensive experimental investigation and parametric analysis

This study explores the ballistic impact resistance of Ultra-High Performance Concrete (UHPC) through an extensive and detailed experimental investigation. This study will address various gaps related to the impact performance of UHPC. This investigation focused on understanding the ballistic resistance performance of UHPC based on (a) the influence of projectile/bullet parameters (hardness, velocity/energy, diameter, and nose shape), (b) the effect of hybrid fibers, (c) comparative analysis of the use of steel mesh and reinforcement bars and (d) effect of sub-zero temperature. In this parametric investigation, different types and shapes (flat, conical, and ogive) of hardened steel projectiles (diameter 12 and 18 mm) with impact velocities ranging from 103 to 182 m/s or impact energy ranging from 674 to 2103 J and UHPC slabs with thickness ranging from 36 to 100 mm was considered. Steel mesh and reinforcement bars at different spacing (with and without fiber UHPC) were also assessed, along with the effect of sub-zero temperature of −30 °C. The impact energy of the projectile and thickness of UHPC targets were statistically significant parameters affecting penetration depth in UHPC compared to other parameters with a p-value much less than 0.001. The Artificial Neural Network (ANN) model developed in the study could predict the penetration depth with reasonable accuracy (MAPE and RMSE were observed to be 7.69 and 12.12, respectively). The experimental results of this study will provide insights into the development of guidelines for using UHPC as a protective material, which can help ensure the safety and resilience of infrastructures in the face of potential threats.

The effect on punching shear failure in centrally loaded ground-supported concrete slabs for different aspects like slab thickness, size and the position of reinforcement bar, and the strength of concrete using a validated FE model

The effect of slab thickness, presence of reinforcement and concrete strength on punching shear capacity of the ground-supported concrete slabs (GSCS) is an important issue in Industrial Ground-supported slab construction. In this study, a three-dimensional nonlinear finite element (FE) model for GSCS was validated with three experimental results from literature and used to assess those effects. A Concrete damaged plasticity model in ABAQUS2020 software with a suitable simulation technique and the theory-based material property was adopted. The results of FE models and predictions of the Technical Report34 (TR34) of the Concrete Society were compared with the experimental results. The average FE predicted/Experimental punching shear capacity ratio was 0.93 with a 0.06 standard deviation and the average TR34 predicted/Experimental punching shear capacity ratio was 1.01 with 0.06 standard deviation. However, the average TR34 predicted/FE predicted punching shear capacity ratio was 1.08 with a 0.13 standard deviation. TR34 prediction was little bit liberal. The results of 72 FE models were compared with the TR34 prediction. The average TR34 predicted/FE predicted punching shear capacity ratio is 1.17 with a 0.21 standard deviation. TR34 prediction was liberal compared to FE prediction. The study showed that the effects of an increase of Slab thickness, Concrete strength, and reinforcement were positive in both FE and TR34 predictions, whereas TR34 predictions were conservative up to a certain slab thickness around 115–130mm for concrete grade 20–40 MPa. As concrete strength and thickness increase, TR34 predictions become more liberal. The bottom layer reinforcement provides greater strength, however, TR34 was unable to predict that.

Experimental and Analytical Investigation of Moment-Carrying Capacities of Reinforced Concrete Frame Systems Corroded by Accelerated Corrosion Method

Technical investigations carried out after the devastating earthquakes in Turkey in the last 25 years show that one of the main causes of damage to reinforced concrete structures is reinforcement bar corrosion. The deterioration caused by reinforcement corrosion in reinforced concrete elements reduces the parameters that define the performance level of the structure, such as ductility, stiffness, bond-slip relationship, load carrying capacity, and energy absorption capacity. Therefore, determining the specified performance levels of reinforced concrete structures exposed to corrosion before any seismic activity occurs is of great importance in preventing loss of life and property. Cross-section behavior in reinforced concrete structures represents the load-bearing element behavior In order to accurately determine the section behavior, the Moment-Curvature relationship must be defined. In this study, the structural behavior of reinforced concrete frames exposed to corrosion was examined experimentally and analytically. For this purpose, 4 of the 5 reinforced concrete frame specimens constructed were corroded at different ratios using the accelerated corrosion method. After the corrosion process was completed, in the experimental part of the study, all specimens were tested under the effect of a 20% constant axial load and reversal-cyclic loading. In the analytical study, as a result of the cross-sectional analyzes carried out by taking into account the material-mechanical properties changing with the effect of corrosion, it was determined that the calculated moment values were in high predicted with the experimentally measured moment values.

Behaviour of Concrete-Filled Plastic Tube (CFPT) Embedded with Reinforcement Bar under Axial Compressive Load

Behaviour of Concrete-Filled Plastic Tube (CFPT) Embedded with Reinforcement Bar under Axial Compressive Load

Corrosion at the Steel–Medium Interface

Corrosion on the interface between a metal alloy, such as steel, and a wet, permeable non-metallic medium is of considerable practical interest. Examples include the interface between steel and water, the atmosphere or concrete, as for steel reinforcement bars; between metal and soil, as for buried cast iron or steel pipes; deposits of some type, as in under-deposit corrosion; and the interface with insulation, protective coatings, or macro- or micro-biological agents. In all cases, corrosion initiation depends on the characteristics of the interfacial zone, both of the metal and the medium, and the spatial variability. For (near-)homogeneous semi-infinite media with good interfacial contact, the pitting, crevices and general corrosion of the metal will be largely controlled by the metal (micro-)characteristics, including its inclusions, imperfections and surface roughness. In other cases, these may be overshadowed by the macro-characteristics of the medium and the degree of interfacial contact, possibly with severe resulting corrosion. Where the build-up of corrosion products can occur at the interface, they will dominate longer-term corrosion and govern the long-term corrosion rate. For media of finite thickness, diffusion issues and material deterioration may also be involved. The practical implications are outlined. It is argued that with the presence of a suitable medium, it is possible to achieve negligible long-term corrosion but only if certain practical actions are taken.

Comparative Analysis of Precast and In situ Concrete and Their Effectiveness on Koga Irrigation Structures

Most construction projects in Ethiopia are built by using conventional cast in situ concrete. However, the latest technology reveals various priorities of the precast construction method over the cast in situ concrete. The main aim of this study is to analyze better irrigation lining concrete among two types of casting by conducting visual inspection methods and non-destructive tests to characterize defects. Koga irrigation main canal, which is found in Northwest Ethiopia, was used as a study area because it is made of both in situ and precast concrete linings. The study reveals that the lower strength, severe defects, and lower uniformity due to the high level of difficulty in pouring and vibrating the concrete on the side slopes of the canal were observed in the in situ lined canal. However, the growth of grass in the joints, and sealing of closely spaced and less water-tight joints are observed at the precast part of the canal lining. Providing reinforcement bars on the in situ canals and providing water-tight joints for the precast concrete part are viable solutions.

Near-surface mounted-FRP flexural retrofitting of concrete members using nanomaterial-modified epoxy adhesives

This study, serving as the first of its kind in this scope, investigates the effectiveness of nanomaterial-modified epoxy adhesives (NMEAs) for Near-Surface Mounted (NSM)-FRP flexural retrofitting of concrete. A total of 48 concrete prisms were retrofitted using three different types of FRP reinforcement bars (CFRP, GFRP and BFRP) inserted in grooves sized 8 × 8, 10 × 10 or 12 × 12 mm and bonded to the concrete substrate using either neat epoxy (NE) or NMEAs. NMEAs were developed by incorporating either carbon-based (i.e. CNF, cellulose and graphite) or silicon-based (i.e. silica and MMT clay) nanoparticles into epoxy at 0.1 wt. %, whereas the graphite NMEAs were prepared with more wt.% (i.e. 0.2 and 0.3). SEM and XRD techniques were used to assess the dispersion quality of nanoparticles within the matrix along with the porosity and crystallinity percentages of the NMEAs. Results showed that using silica, clay and graphite NMEAs rather than NE enhanced the retrofitted concrete capacities, whereas a decrease in strength was observed when using CNF- and cellulose-modified epoxies. Moreover, it was found that the specimens bonded with silicon-based NMEAs had, on average, higher capacities than those bonded with carbon-based NMEAs, which, on the other hand, showed more ductile behaviour. Results also suggested that the specimens’ capacities decreased as the wt. % concentration of the nanoparticles (i.e. graphite) increased. Increasing the groove size from 8 × 8 mm to 10 × 10 mm decreased the capacities but enhanced the ductility, whereas increases in both the capacities and ductility were achieved when moving from 8 × 8 mm to 12 × 12 mm.

Study on the influence law of cavities behind the shotcrete lining on the lattice girders

The field monitoring data showed that a small amount of main reinforcement bars of lattice girder at the arch of a tunnel were pulled, and the calculation showed that the initial support structure should be compressed. To find out the reason for the tension of the main reinforcement, the geological radar was used to detect the cavity in the sprayed concrete layer at the tension position. In order to clarify the tension mechanism of the main reinforcement and the influence of factors such as the position and size of the cavity on the main reinforcement, numerical simulations were carried out. The results show that the cavity causes the eccentric compression of the shotcrete layer, resulting in moment of the lattice girder and the change of the stress distribution of the main reinforcement. The main reinforcement experiences tensile stress when the cavity size surpasses 3 m × 0.2 m, reaching a tensile stress of 81 MPa at a cavity size of 6 m × 0.2 m. Notably, the cavity located at the foot of the arch is more likely to produce substantial tensile stress on the primary reinforcement compared to those at the arch crown and waist. The research results provide a theoretical basis for the interpretation and analysis of tunnel lattice girder monitoring data.

Experimental and statistical investigations of the material properties of FRP reinforcement in compression

Internationally leading standards currently do not permit to consider the contribution of reinforcement made of fibre reinforced polymers (FRP) to a concrete member’s compressive load-bearing capacity due to a lack of reliable knowledge regarding FRP’s material properties in compression. Thus, there is a very high demand for carefully specifying an optimised test setup for FRP bar reinforcement that accounts for both theoretical considerations and established standards from other industry branches. This paper presents an extensive literature review on mechanical approaches to describe FRP material properties in compression, existing test setups from various industry branches as well as experimental studies that have been conducted in order to research the compressive material properties of FRP reinforcement. Based on experimental results from literature a database was compiled. Following a reasonable choice of a test setup based on the literature study, an experimental campaign was setup, in order to investigate the influence of different fibre materials (carbon, glass, basalt), polymer matrices and bar diameters on the compressive material properties of FRP reinforcement bars. In addition to the experimental determination of the material properties, the joint evaluation of the total sample size of n = 95 own experimental test results and the results from the database generated from literature allows for statistical investigations. Thus, the determination of material scatter and the estimation of the distribution type by means of a statistical analysis applying the Kolmogorov-Smirnov test provides the basis for further research towards the reliability of concrete structures reinforced with FRP bars in compression.

Finite element modelling of reinforced concrete beam strengthening using ultra-high performance fiber-reinforced shotcrete combined with reinforcing bars

Ultra-high performance fiber-reinforced shotcrete (UHPFRS) is advanced concrete material for strengthening and repairing concrete structures, especially in narrow and difficult-to-access places. However, there has been little quantitative analysis of its strengthening capacity for concrete structures. Therefore, this paper develops a Finite Element (FE) model to simulate the structural behavior of reinforced concrete (RC) beams strengthened by a UHPFRS layer. The traction-separation model combined with the concrete damaged plasticity (CDP) model can accurately simulate the structural behavior of the NSC-UHPFRS composite beam by calibrating and validating with experimental results. Based on this FE model, a parametric study is conducted to asset the effect of the height, reinforcement ratio, and fiber orientation of the UHPFRS layer on the strengthening capacity of UHPFRS for the RC beam. The findings show that those parameters significantly impact the composite beam's load-displacement characteristics. It also contributes to a better understanding of applying UHPFRS in strengthening RC beams as well as structures to extend the service life effectively.

Shielding Effect for γ-rays with Reinforcing Bars in Reinforced Concrete (Plane Source)

Shielding Effect for γ-rays with Reinforcing Bars in Reinforced Concrete (Plane Source)

Theoretical effects of corrosion on lateral stress along reinforcement bars in concrete

Literature review of latest research findings on the bond behavior of corroded reinforcing steel bars suggests that the bond mechanism is minimally affected by corrosion. However, discrepancies exist among research concerning the influence of corrosion on the critical parameters that govern bond behavior of bars.Former studies have primarily focused on the diminishing bond strength caused by corrosion. Several key factors influencing bond strength have been identified, including corrosion of the main bar, concrete cover thickness, concrete type, stirrups, stirrup corrosion, and corrosion rate. However, existing bond strength models are largely based on specific test results and lack generalizability.This work is a part of a wider study aiming to evaluate main concrete and steel parameters effect on corroded reinforced concrete structures. The scope of present paper is to evaluate the effect of several parameters on bond behavior. Some concrete exposure classes are considered, and corrosion process is simulated using a non-linear analytical model. Three bond theories are considered to have comparative results. Corrosion simulation has been done using different concrete and steel parameters to evaluate their effects on RC corroded elements’ bond capacity.

ИССЛЕДОВАНИЕ ПОЛЗУЧЕСТИ СТАЛЕЖЕЛЕЗОБЕТОННЫХ ОБРАЗЦОВ

The paper presents the results of investigation of creep and shrinkage of steel-reinforced concrete specimens. For this purpose, parallel tests of specimens made of the same class of concrete but with different reinforcement were carried out. Concrete specimens, specimens reinforced with bar reinforcement frames and steel reinforced concrete specimens with external sheet reinforcement were investigated. The tests were carried out in climatic rooms using spring setups to maintain a constant load acting on the specimens over time. The load on the specimens was selected based on the equality of stresses in the concrete in all series of specimens. The specimens were tested both waterproofed and non-waterproofed, and the effect of waterproofing coating on shrinkage and creep strains was evaluated for different series of specimens. A system was developed to capture information. which allows, in addition to longitudinal shrinkage and creep deformations, to determine transverse deformations, longitudinal deformations along the faces of the specimen to determine the influence of reinforcement and steel of the outer plate, to evaluate the change in longitudinal deformations from the center of the specimen to its edges, to evaluate separately the deformations of concrete and steel plate in steel-reinforced concrete specimens. The analysis of the results allowed a comparative assessment of the influence of conventional bar reinforcement as well as steel sheet of steel-reinforced concrete specimens on creep and shrinkage deformations; the influence of waterproofing coating on the test results in different series was also assessed. Based on the results of this work, extended requirements for experimental and theoretical studies of steel-reinforced concrete specimens with external sheet reinforcement to determine their design stiffnesses were formulated.

A Comparison of Nondestructive Methods for Detecting Reinforcing Bar Placement

A Comparison of Nondestructive Methods for Detecting Reinforcing Bar Placement

Performance of Polyester Grouted Connector for Splicing of Reinforcement Bars

Performance of Polyester Grouted Connector for Splicing of Reinforcement Bars

Analysis of the Behaviour of Composite Connections in Multi-Storey Buildings Under Earthquake Loading

In the past years, number of beams and slabs in steel structures that are executed as composite steel – concrete elements has significantly increased. In moment-resisting frames with composite steel – concrete slabs, slab reinforcement in tensile zone needs to be considered in design of composite steel – concrete beam – to – column connections with steel plates and bolts in tensile zone. However, the number of reinforcement bars that should be taken into account in connection design significantly depends on the effective width of the concrete slab. Moreover, directions for calculation of the effective width of the concrete slab are still not unambiguous as they can be calculated either according to recommendations from Eurocode 4 or Eurocode 8. In this paper, composite connections are briefly explained and main differences between composite steel – concrete beam – to – column connections and corresponding steel connections are summarized. Furthermore, behaviour of a composite steel – concrete beam – to – column connection under bending moment and shear force induced by earthquake loading is investigated using finite element analysis in software package Abaqus. Finally, a parametric study is carried out in order to examine the suitability of two code recommendations for determination of the effective width of concrete slab in case of seismic loading.