Reinforcement Bars Research Articles

Seismic performance analysis of coastal reinforced concrete frames considering the pitting corrosion in the longitudinal reinforcement bars

Reinforcement corrosion is a major factor that influences the durability of reinforced concrete (RC) structures. In this study, the detrimental effects of pitting corrosion of longitudinal reinforcement and the dominant wind direction on the seismic performance of RC frame structures were investigated on the basis of a reliable numerical simulation method, which considers the degraded mechanical properties of the longitudinal reinforcement, confined concrete and bond-slip under a chloride ion attack. Two typical collapse failure modes, namely, column and beam failure modes, are observed in the corroded frames with increasing service time. The column failure mode is caused by the failure of compressive reinforcement for the bottom column. Meanwhile, the beam failure mode is caused by the failure of tensile reinforcement for the frame beam. The collapse failure mode of the structure changes from the column failure mode to the beam failure mode with increasing service time. Moreover, this transition is more likely to occur, and the ultimate deformation capacity of the structure is further reduced when the effects of pitting corrosion and wind direction are simultaneously considered.

Laboratory modelling of stiffened deep mixing columns with variable diameter under vertical load in loose sand

ABSTRACT The T-shaped deep mixing column (TDM) is a new proposed technique used to increase the ultimate load of the deep mixing column in loose sand. Enlarging the column diameter at a certain depth provides additional bearing area beneath the column under the enlarged part, which leads to an increase in the ultimate load. In this study, a series of laboratory tests were conducted to study and analyse the behaviour of stiffened deep cement mixing columns in loose sand under compression loading. The impact of different parameters such as stiffening methods, embedment ratio, TDM cap length ratio, TDM cap diameter ratio, and the position of the T-shape were studied. It is found that all stiffening methods significantly enhance the load-settlement response of the deep cement mixing (DCM) columns. The stiffening technique of reinforcement bars with a T-shape gives the greatest improvement, increasing the ultimate load by 191.1% compared with the conventional column.

Modelling of flexural fatigue behaviours of hybrid engineered cementitious composite link slabs using cycle-driven analysis

Link slabs are designed and expected to be serviced under high-cycle traffic loadings. Although their high-cycle fatigue performance is critical in their practical applications, very few experimental and numerical studies have been conducted to study high-cycle fatigue failure of link slabs due to the huge amount of time and resources needed for fatigue tests and the lack of efficient modelling method for high-cycle fatigue failure. Recently, as a newly developed material with superior mechanical properties, the hybrid fibre reinforced engineered cementitious composite (hybrid ECC) has been recommended for link slab application. In this study, a novel and efficient cycle-driven analysis (CDA) procedure was developed to model the structural behaviour of ECC link slabs made of the hybrid ECC under high-cycle fatigue loadings, which is the first attempt for CDA to be applied in high-cycle fatigue structural modelling of a hybrid ECC link slab with reinforcement bars. In the proposed CDA, fatigue damages of both hybrid ECC and reinforcement bars were taken into account. The accuracy and reliability of the new CDA procedure were validated by comparing the modelling predictions with the experimental results on two quarter-scaled hybrid ECC link slabs. It was found that the proposed CDA procedure could predict the overall fatigue behaviours including the deflection histories, crack patterns, fatigue life, fatigue failure mode and the residual static strength of the hybrid ECC link slabs after fatigue damage with good accuracy.

The development and performance evaluation of diagonal tension cracks control devices

ABSTRACT The cause of diagonal tension cracks is the drying shrinkage of the initial concrete, which causes them to appear at the corners of square openings, which are the most vulnerable areas to stress. Looking specifically at the cause from a structural aspect, the concentrated stress exceeds the tensile strength of the concrete, causing cracks to occur at the corners. Typically, diagonal tension reinforcement bars are arranged to prevent diagonal tension cracks, however, they have often failed to be practical solutions because they do not entirely prevent the continued occurrence of cracks. Consequently, the present study developed diagonal tension cracks control devices that are capable of preventing diagonal tension cracks. Next, comparative experiments on existing diagonal tension reinforcement bars with respect to drying shrinkage were conducted to verify the utility of the diagonal tension crack reinforcement materials through performance evaluation. According to the results, the maximum elastic strain at the top and bottom opening edges was 29.2% and 35.8%, respectively, which was a large reduction compared to the 6.7% and 4.9% of the existing diagonal tension reinforcement. Considering the above points, it is expected that the developed control device will be very practical in terms of industry.

Experimental and theoretical investigations on the static behavior of low aspect ratio shear stud connectors in ultra high performance concrete

In reinforcement project for early-built orthotropic steel bridge decks (OSDs) using ultra high performance concrete (UHPC), low aspect ratio shear stud connectors in UHPC are required. In present study, push-out tests of six static UHPC specimens with and without reinforcement bars were first conducted. The failure modes, load-slip curves and shear capacity of shear stud connectors embedded in UHPC with an aspect ratio of 1.84 were investigated. Subsequently, the experimental results of shear capacity and load-slip curves were compared with the theoretical calculation results. Finally, a new theoretical model of shear stiffness was proposed for low aspect ratio shear studs based on the energy equivalence theory. The experimental results indicated that the failure mode of all specimens was stud shank failure, while the UHPC slabs without reinforcement bars showed extensive cracks. The effect of reinforcement bars on the behavior of shear studs embedded in UHPC slabs can be negligible. The reinforcement bars mainly affected the internal force flow in the UHPC, thus limiting crack initiation and extension. The compressive strength of the UHPC and the weld collar had significant impact on the shear capacity of short studs in the UHPC. In calculating the load-slip curves of short shear stud connectors in UHPC, the theoretical results calculated using the fractional form equations were in better agreement with the experimental results. The proposed theoretical model neglecting the deformation of shear stud in elastic stage can accurately predict the shear stiffness of low aspect ratio shear stud connectors in UHPC.

Static Bending Mechanical Properties of Prestressed Concrete Composite Slab with Removable Rectangular Steel-Tube Lattice Girders

In recent years, with the development of building technology, the Chinese construction industry has begun to gradually promote the prefabricated buildings to save on construction costs. Among them, composite slabs, as essential components of prefabricated buildings, have been widely used by designers mainly in favor of their low cost. However, is it possible to further reduce the cost without affecting the quality? Researchers think so if the operation cycle of support from the bottom of composite slabs can accelerate and the mechanical properties of their bottom plate can be optimized. To prove this hypothesis, researchers proposed a new type of prestressed concrete composite slab with removable rectangular steel-tube lattice girders (referred to as CDB composite slabs), whose bottom plate consists of a temporary structure composed of a prestressed concrete prefabricated plate and removable rectangular steel-tube lattice girders. Through static bending performance tests on three prefabricated bottom plates and one composite slab, researchers measured corresponding load-displacement curves, load-strain curves, crack development, and distribution, etc. The test results show that the top chord rectangular steel tubes connected to the bottom plate concrete through web reinforcement bars significantly improve the rigidity, crack resistance, and load-bearing capacity of the bottom plate and possess better ductility and out-of-plane stability. The number of supports at the bottom of the bottom plate is effectively reduced, with the maximum unsupported span reaching 4.8 m. Beyond 4.8 m, only one additional support is needed, and the maximum support span can be up to 9.0 m, which provides space for cost reduction. The cooperative load-bearing performance of the prefabricated bottom plate and the post-cast composite layer concrete is good. The top chord rectangular steel tubes are easy to dismantle and can be reused, which reduces the steel consumption by about 24% compared to that used for the same size of ordinary steel-tube lattice-girder concrete composite slabs. It can greatly decrease the cost. In conclusion, the results have shown that the new method researchers proposed here is practically applicable and also provides great space to save on financial costs.

Damage detection of lightweight concrete dual systems reinforced with GFRP bars considering various building heights and earthquake intensities

Because of their distinct mechanical, rheological, and physical features, lightweight concrete and glass fiber reinforced polymers (GFRP) bars have a significant growth in the modern building sectors over the past decade. Minimizing subsequent quake damages, particularly in multistory residential or administrative RC structures, is a key concern for governments in earthquake zones. The dual frame-wall system is among the most appropriate structural systems for resisting seismic loads in multistory concrete structures. Therefore, this research aims to quantify the seismic damage of multistory dual frame-wall systems with varying heights of 12, 20, and 25 stories under mild, medium, and severe earthquake intensities. The inelastic damage analysis of RC buildings program is utilized to nonlinearly analyze 54 cases containing various materials such as normal concrete, lightweight concrete, steel reinforcement bars, and GFRP bars. Using lightweight concrete with half the density of normal concrete and pure linear-elastic GFRP bars in floor construction will significantly decrease the geometric nonlinearity effect created by the load-displacement (P-Δ) effect and dissipate a large amount of the kinetic energy generated by seismic excitation, resulting in a significant reduction in post-earthquake damage. When compared to the normal concrete, using lightweight concrete in floor construction reduced the mean story damage index by 14–20% as the building's height increased, while reinforcing these floors with GFRP bars resulted in substantial decreases in the overall damage index, reaching about 57–68% when both building's heights and seismic excitation intensities were considered.

Experimental Investigation into Strength Properties of Ribbed Mild Steel Reinforcing Bars (RMSRBs) Produced by Local Companies in Ghana

The construction of high-rise buildings has increased the production and demand of ribbed mild steel reinforcing bars (RMSRBs) in Ghana. This study aimed at investigating the strength properties of RMSRBs manufactured in Ghana from scrap metals. Three steel-producing companies were considered for this study. A total of 90 samples of 12, 16, and 20mm diameters with lengths of 500, 50, and 20mm were used for the study. The prepared specimens were subjected to tensile strength test, chemical composition analysis, micro-hardness test, and microstructure analysis. The results indicate that the average tensile strength of between 576.00 and 768.40N/mm2 were above the minimum tensile strength of 250N/mm2 recommended by ASTM E8/E8M-16a. The carbon equivalent values (CEVs) of between 0.287 and 0.333% obtained were almost within the range of 0.3 to 0.55% recommended by ASTM A706/A706M-09b. It was also identified that the average Vickers hardness values of between 255.76 and 295.38HV were acceptable. The microstructural images showed good distribution of the pearlite and ferrite of the core. One Way ANOVA results indicated that the differences in the tensile strength values for 12mm (p-value ˂0.000) and 16mm (p-value =0.001) were statistically significant, however, the 20mm (p-value =0.138) was not statistically significant. The study, therefore, concludes that the strength properties of the 12, 16, and 20mm diameters of the RMSRBs produced by the three different companies in Ghana meet the standard requirements, and are recommended for use by contractors for the production of reinforced concrete.

Lateral load response and collapse probability of reinforced concrete shear walls retrofitted for repairability

AbstractThis paper demonstrates the efficacy of a new reinforced concrete shear wall seismic retrofit method through a series of nonlinear static and incremental dynamic analyses. Unlike traditional retrofit methods, the method investigated aims to convert conventional walls into self‐centering walls whose behavior is governed by rocking and flexure. The retrofit involves creating a cold joint at the foundation–wall interface, cutting some reinforcing bars to allow rocking, adding external post‐tensioning to enable self‐centering, and externally confining wall toes to prevent concrete crushing. The retrofit was applied to two building archetypes, each with two different shear wall designs. The four walls were retrofitted by varying retrofit parameters (portion of the vertical reinforcement bars cut, and external post‐tensioning amount). Nonlinear static and nonlinear response history analyses were performed using experimentally validated, computationally efficient models that simulate walls with fiber‐based beam–column elements. Incremental dynamic analysis was used to create collapse fragility functions for pre‐ and post‐retrofit walls. The results show that the retrofit is effective when some vertical reinforcement bars are left uncut across the foundation–wall interface. The retrofit is more effective for walls with vertical reinforcement distributed across cross‐section as compared to walls with reinforcement concentrated near boundary elements and for walls with structurally efficient amounts of reinforcement as compared to walls with higher amounts of reinforcement. This is attributed to the larger amount of reinforcement bars cut in walls with concentrated reinforcement layouts or heavy reinforcement amounts, leading to a larger loss of strength, recovery of which requires larger amounts of post‐tensioning.

Compressive and Bonding Performance of GFRP-Reinforced Concrete Columns

The use of glass-fiber-reinforced polymer (GFRP) bars as an alternative to steel bars for reinforcing concrete (RC) structures has gained increasing attention in recent years. GFRP bars offer several advantages over steel bars, such as corrosion resistance, lightweight, high tensile strength, and non-magnetic properties. However, there are also some challenges and uncertainties associated with the behavior and performance of GFRP-reinforced concrete (GFRP-RC) structures, especially under compression and bonding behavior. Therefore, there is a need for comprehensive experimental investigations to validate the effectiveness of GFRP bars in concrete columns. This paper presents a study that aims to address these issues by conducting experimental tests on GFRP-RC columns. The experimental tests examine the mechanical properties of GFRP bars and their bond behavior with concrete, as well as the axial compressive behavior of GFRP-RC columns with different reinforcement configurations, tie spacing, and bar sizes. The findings reveal that GFRP bars demonstrate a comparable, if not superior, compressive capacity to traditional steel bars, significantly contributing to the load-bearing capacity of concrete columns. The study concludes with a set of recommendations for further exploration, underscoring the potential of GFRP bars in revolutionizing the construction industry.

The effect of depth-dependent carbonation on the interfacial strength between GFRP reinforcement bar and reactive magnesia cementitious composites

Reactive magnesia cement (RMC) is an emerging class of low-alkaline and CO2-sequestering binder, which can mitigate the deterioration of GFRP reinforcements induced by a high-alkaline environment, e.g., in Portland cement. This study investigated the slip behavior of GFRP rebar embedded in RMC composite, which varies with carbonation depth significantly. The variation of the interfacial bond was determined by a specially designed push-out test of the GFRP core; the variation of the carbonation degree and microstructure was examined by SEM-EDX, MIP, XRD, TGA, FTIR, and acid digestion tests. Both properties demonstrated a similar trend, decreasing rapidly with increasing depth. A new finite element model that considers the depth-dependency of the matrix compositions and the rebar-to-matrix interfacial bond is established. It can predict the constitutive bond-slip behavior of a long GFRP rebar embedded in an RMC composite with non-uniform carbonation.

Effect of high-energy shot peening on the corrosion behavior and chloride threshold concentration of AISI 316L stainless steel rebar in simulated concrete pore solution

The corrosion behavior and chloride threshold concentration of AISI 316L stainless steel reinforcement bar (rebar), subjected to high-energy shot peening (HESPed), are compared with its solution-annealed (SAed) counterpart in simulated concrete pore solution (CPS). X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that HESP significantly reduces the surface grain size to the ultrafine/nanometric range and increases the density of various dislocation structures, including dislocation walls and cells. This augmented presence of grain boundaries and dislocations, acting as high diffusivity paths, contributed to the formation of a thicker surface film with higher Cr content and lower donor/acceptor density in the HESPed sample compared to the SAed. Moreover, corrosion behavior analyses in CPSs with NaCl concentrations ranging from 0.0 to 2.0 M demonstrated that HESPed samples exhibit broader passivation ranges, more positive corrosion potentials, and higher polarization resistance under equivalent chloride concentrations. Additionally, threshold chloride concentrations obtained from the potentiodynamic polarization tests show values between 0.5 and 1.0 M for the SAed and between 1.0 and 1.5 M for the HESPed samples. Based on diffusion equations, a physical model is proposed to elucidate the improved behavior resulting from the HESP treatment.

Synergistic protection of borate and silicate salts composite for controlling the chloride-induced pitting and uniform corrosion of steel reinforcement bars embedded in mortars

In this study, the efficacy of the combined effect of borate and silicate alkali metal salts added to mortars for controlling the chloride-induced uniform and localized corrosion of embedded steel rebars is examined. The individually added salts in mortars are found to have insignificant effects in terms of reducing the uniform corrosion rate and localized damage. However, their combination (0.50% sodium tetra borate + 0.10% sodium silicate added with respect to the weight of the binder) provides complete protection to reinforcements tested for long durations under wet/dry treatments with mortars in saline water and laboratory atmospheres. Electrochemical impedance spectroscopy, direct current cyclic polarization, polarization resistance, and visual observations are used for quantitative and qualitative evaluations of the protective effects of the tested additives. X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis of the corrosion products formed on the embedded steel surfaces help explain the possible mechanisms behind the considerable improvement in the inhibitive effects of a mixed composition of borate and silicate. This combination also improves the compressive strength and workability of the mixed concrete. The results reveal that the synergistic protection provided by a mixture of borate and silicate can be attributed to the co-deposition of an iron-boron + ferrosilicate + cortensitite (an iron-silicon phase) film on the rebar surface.

Flexural performance of rapid-hardening concrete (RHC) beams with tension lap splice

BackgroundRapid-hardening concrete (RHC) is a specialized type of concrete that gains strength at an accelerated rate, allowing for faster construction and reduced project timelines. The use of RHC in structural applications, such as in beams subjected to flexural loads, has gained significant attention due to its potential for improving construction efficiency. This study focuses on the flexural performance of RHC beams with tension lap splice, which is considered a common method for joining reinforcement bars in concrete structures.ResultsSeveral parameters were taken into consideration, such as concrete type, concrete cover, and reinforcement bar diameter. The loading test was performed on sixteen beams to show results of load capacities, moment–displacement response, energy absorption, and ductility. As a result, the flexural performance of RHC beams is compared to that of NC beams.ConclusionsResults indicate that RHC beams require 30 Φ splice length after 3 days of casting, while NC beams require 40 Φ splice length after 28 days. The RHC beam had higher load capacities, ductility, resilience, and toughness than NC beams, by 73%, 41%, 82%, and 88%, respectively. The bar diameter and concrete cover had a significant effect on increasing loads and resilience, while toughness decreased.

Degradation of RC Columns under Combined Exposure to Axial Loading, Stray Currents, and Chloride Ingress.

Coastal regions, home to a significant portion of the world's population, confront a formidable challenge: the corrosive impact of chloride-rich environments on vital infrastructure. These areas often host essential transportation systems, such as trains and metros, reliant on pre-existing electrical infrastructure. Unfortunately, complete isolation of this infrastructure is rarely feasible, resulting in the emergence of stray currents and electrical potentials that expedite corrosion processes. When coupled with conducive mediums facilitating chemical electrocell formation, the corrosion of reinforced concrete elements accelerates significantly. To combat this issue, international standards have been established, primarily focusing on augmenting the thickness of reinforcement bar covers and restricting stray voltage between rails and the ground. Nevertheless, these measures only provide partial solutions. When subjected to service loads, these elements develop cracks, especially when exposed to stray currents and chlorides, dramatically increasing corrosion rates. Corrosion products, which expand in volume compared to steel, exert internal forces that widen cracks, hastening the deterioration of structural elements. The study deals with the degradation of reinforced concrete columns under the combined action of loads, chloride-rich environments, and electrical voltage-simulating stray currents. In these conditions, degradation and reduction of load-bearing capacity accelerate compared to unloaded conditions, significantly amplifying the corrosion rate. Astonishingly, even in the absence of mechanical loads, stray currents alone induce tensile stresses in elements due to corrosion product formation, leading to longitudinal cracks parallel to the reinforcement bars.

Post-damage recovery of substandard RC columns by CFRPs

Cyclic response of substandard reinforced concrete (RC) columns and structural repair of pre-damaged columns by carbon-fiber-reinforced polymers (CFRPs) were investigated through combination of experimental and advanced numerical modeling methods. The specimens, representing typical RC columns in substandard buildings, were constructed from low-strength concrete, plain round bars, and nonconforming reinforcement details. The key parameters under investigation included the lap-splice, hook detail in the longitudinal reinforcement, and axial load ratio. First, the RC columns were subjected to cyclic loading until the attainment of their heavy damage state. The failure mode was dominated by the flexural response alongside significant reinforcement slip and axial damage, involving concrete crushing and reinforcement buckling. Subsequently, the severe cracks and concrete damage were repaired by the externally wrapped CFRP sheets. The former load-carrying capacities of the repaired RC columns were recovered. The damage formation in the concrete and reinforcement was transferred to CFRP sheets. The final failure mode was characterized by local deformations in the CFRP, with minimal damage observed in the concrete and reinforcement bars. Furthermore, the numerical solution effectively reproduced the nonlinear behavior of the as-built specimens. The crack patterns and capacities observed in the numerical solutions align with the responses observed in the experimental tests.

Refinement in the understanding of confinement of concrete

The compressive axial load-deformation curve of a reinforced concrete (RC) member reflects the contributions of the concrete in compression and tension, the longitudinal and transverse reinforcement bars in compression and bending, and the aggregate interlocking in concrete in its dilated state. Together these factors enhance the axial response of RC compared to its plain counterpart. Even though expressions proposed in the past capture the composite response of this confining effect in an empirical sense, none of them separate the said individual contributions. This study provides a mechanics-based method to obtain the axial-load deformation response of a RC member, and thereby the stress-strain curve of confined concrete, by assembling the combined effect from each contributing parameter. The governing contributions are fundamental and physically intuitive; they include contributions of unconfined concrete, transverse reinforcement, longitudinal reinforcement (including buckling), and aggregate interlocking. The stress-strain curves from the proposed method compare well with those obtained from many tests on confined concrete available in the literature, and seem to better estimate the response than two popularly used confinement expressions. Similar comparisons are made with the axial load-deformation curves. A parametric study is undertaken to capture the effects of section geometry, high-strength materials, and area ratio on the confinement of concrete. Finally, a refined understanding is presented of the estimation of strength of confined of concrete.

The Application of Mathematical Modelling to Optimize Steel Reinforcement Shipping Cost for Construction Projects by Julius Berger

The problem of transporting steel reinforcement for construction purposes has always been eminent in construction projects. In this study, the transportation model was applied while shipping steel reinforcement from three supply locations to three construction sites owned by Julius Berger construction limited, in the city of Port Harcourt. The study was done for 100-ton truck load of steel reinforcement bars with standard 12m lengths and diameters 8mm to 40mm. This was from the three selected steel depots in Port Harcourt. The costs of transporting the steel reinforcement bars were analyzed using the basic steps of simplex algorithm for solving transportation problems. The initial and optimum feasible solutions were obtained. The Stepping Stone method was used for the optimum solution after three consecutive iterations, which amounted to $3,813 or (₦2,897,880 as of March 2023). The result was compared with that obtained from Microsoft Excel solver. There was no difference between the two results.

Finite element method for sustainable and resilient structures made with bar and fiber -reinforced EAFS concrete

Structural engineers have to address the climate change challenge by designing sustainable and resilient structures. At this juncture, Electric Arc Furnace Slags (EAFS), a steel-industry waste, are used in replacement of natural aggregates to enhance concrete properties. Moreover, steel and synthetic fibers are added to improve the postcracking behavior while the traditional bar reinforcement enhances the tensile performance. This makes EAFS concrete substantially ductile compared to normal concrete, which contributes to a higher structural resiliency, and hence minimizes functionality disruptions. However the use of fiber and bar -reinforced EAFS concrete in structures is still limited due to the uncertainties introduced by EAFS and fibers. This justify the development of advanced modeling techniques (ie. Finite element Analysis, FEA), which can be used to predict the behavior of EAFS concrete structures at the designing stage. This work build up from the extensive work of the coauthors in the testing of EAFS concrete and, more recently, in the developed FEA of fiber-reinforced EAFS concrete. In this paper the modeling of bar reinforcement is added to the FEA to study the behavior of structural elements made with fiber-reinforced EAFS concrete. The presented FEA is validated through full-scale experiments (four-point flexural test), which shows that the presented FEA is appropriate. The presented numerical model enables to study phenomena difficult to study from experiments or in-situ such as the cracking. It is worth noting that the addition of steel fibers reduced the crack mouth opening displacement in 29.3% and the depth of the cracks in 12.7% in the presented EAFS concrete.

Description of the constitutive behaviour of stainless steel reinforcement

This paper presents a comprehensive analysis of the constitutive relationship of stainless steel reinforcement and proposes new material models for both austenitic and duplex stainless steel bars. These are an advancement on existing models which have largely been developed for structural stainless steel plate, rather than for reinforcement bars. Current design guidance for material modelling of reinforcing bars does not include representative stress-strain relationships which capture the unique mechanical properties of stainless steel reinforcement. Codes include idealised elastic-plastic material models which are inappropriate and inefficient for the highly nonlinear and ductile material response of stainless steel. The present study aims to address this issue by first conducting a series of tensile tests to ascertain the stress-strain material responses and then employing this data to examine the validity of existing approaches and propose new material models where required. It is shown that new material models are required and those that are developed are able to accurately capture the stress-strain response of stainless steel reinforcement, and provide a better, more accurate, representation than existing methods.