Reinforcing Steel Bars Research Articles

Study of the quality materials used to produce reinforced concrete in Benghazi

Reinforced concrete is the basic material in construction and consists of a mixture of cement, water, aggregate (gravel, sand, or crushed rocks), and reinforcing steel. When concrete hardens, it becomes a strong and durable material mainly used to construct buildings, bridges, highways, and other structures. Therefore, the quality of the materials used in concrete manufacture significantly impacts the structures' behavior and durability. This research aims to study and compare the quality of the materials that make up reinforced concrete found in Benghazi from different sources, including local and imported ones. Local cement (El-Salaba from Benghazi factory and El-Borj from Zliten factory) and imported cement from Egypt (Beni Suef and Helwan) were studied, as well as aggregate (Al-Abyar and Ajdabiya quarries), sand (Shatt Al-Badin and Zueitina), locally manufactured steel bars (Misurata for Iron and Steel Factory and That Al-Imad Factory, Tripoli) and imported steel bars (Ezz from Egypt). Laboratory tests were conducted on all samples to match the quality of these materials with the British and American standard specifications to ensure the construction of stronger and durability concrete. The results indicated that the locally manufactured Al-Burj, Beni Suef, and Helwan cement imported from Egypt conformed to the specifications and obtained similar compressive strength and 27% higher than El-Salaba cement. The Ajdabiya aggregate also met the standard specifications, while the imported Ezz Steel bars from Egypt outperformed the rest of the locally manufactured types by obtaining a yield strength 38% higher than the rest of the locally manufactured samples. An economic feasibility study should be conducted to compare the cost of importing and producing cement and reinforcing steel bars. The quality control centers affiliated with the Libyan state should conduct periodic tests on locally produced cement and reinforcing steel bars and evaluate the imported ones to ensure that they conform to the specifications in the labor market. Keywords: Cement quality, aggregate, reinforcing steel bars, concrete, laboratory tests, Benghazi.

Comparative Study Between Geopolymer and Ordinary Concrete Regarding Compressive and Flexural Strength in RC Beam and their Environmental Sustainability Assessment for Construction

In this study, the compressive strength, flexural strength, and bond behavior of geopolymer and regular Portland cement (OPC) concrete are compared in reinforced concrete (RC) beams. The principal binder of geopolymer concrete is industrial by-product such as fly ash, and it provides an ecologically benign and sustainable substitute for regular OPC concrete. According to the research, geopolymer concrete is a potential material for structural applications because of its better qualities, which include increased compressive strength, improved durability, and enhanced resistance to sulfate, acid, and high temperatures. In contrast to OPC concrete, geopolymer concrete has better mechanical qualities, a reduced carbon footprint, and increased durability when combined with reinforcing steel bars to form strong and long-lasting structural elements in RC beams. The study emphasizes how crucial it is to comprehend the characteristics and behavior of geopolymer concrete in RC beams in order to help build ecologically responsible and sustainable infrastructure. This research offers important insights into the possible applications of geopolymer concrete in the construction industry, which may help lessen the environmental effect of concrete manufacturing and promote sustainable growth, by comparing the performance of geopolymer concrete with OPC concrete.

Intelligent Sensor Software for Robust and Energy-Sustainable Decision-Making in Welding of Steel Reinforcement for Concrete.

In today's industrial landscape, optimizing energy consumption, reducing production times, and maintaining quality standards are critical challenges, particularly in energy-intensive processes like resistance spot welding (RSW). This study introduces an intelligent decision support system designed to optimize the RSW process for steel reinforcement bars. By creating robust machine learning models trained on limited datasets, the system generates interactive heat maps that provide real-time guidance to production engineers or intelligent systems, enabling dynamic adaptation to changing conditions and external factors such as fluctuating energy costs. These heat maps serve as a flexible and intuitive tool for identifying robust operational points that balance quality, energy efficiency, and productivity. The proposed methodology advances decision-making in welding processes by combining robust predictive modeling with innovative visualization techniques, offering a versatile solution for multiobjective optimization in real-world industrial applications.

COMPARATIVE REVIEW OF PROPERTIES OF STEELS USED IN NIGERIA TO FORESTALL BUILDING COLLAPSES

This research analyzed the mechanical properties of reinforcing steel bars used in Nigeria and compared them to four different standards (AISI 1018, ASTM A706, BS4449, and NST-65-Mn). This was done as a result of frequent building collapses in Nigeria, which has revealed the knowledge gap between what the designers expect and the true mechanical properties of the products they typically receive from manufacturers. Related literature from published articles was collected and analyzed based on the mechanical properties of locally produced and imported steels. Results showed that the tensile strength, yield strength, hardness, percentage elongation, and percentage carbon composition of most products met and exceeded the requirements of AISI 1018, ASTM A706, BS4449, and Nst-65-Mn when compared, while some fell below what these standards required. Federated Steel Mills Limited, Ogun State, has the highest tensile stress value at 799.49 MPa, followed by Real Steel Reinforcing Pty Limited, Auckland, New Zealand, at 726.34 MPa, and Landcraft Industries Limited, Ikorudu, Lagos, at 708.3 MPa, according to a yield and tensile strengths analysis of 16 mm steel bars produced locally and imported. The lowest tensile strengths ever reported are 410 MPa for African Steel Nig. Limited, Ikorodu, Lagos, and 538.51 MPa for steel imported from Brazil. It is hoped that the data from this study will bridge the knowledge gap between the team players in this field, thus preventing catastrophe.

Methodology for Reliability Analysis of Reinforced Concrete Structures over time Considering Combined Corrosion

One of the main causes of deterioration in reinforced concrete structures (RC) is the corrosion of steel bars. Many factors, including materials, environments, and loading conditions, which often have uncertain characteristics, affect the performance of RC structures. Some uncertainties may depend on time and location, and associated reliability issues become more difficult to address. This study presents a comprehensive method for assessing the temporal reliability of reinforced concrete structures, taking into account combined effects of carbonation (general corrosion) and chloride penetration (pitting corrosion). Probabilistic models are used to capture uncertainties related to the beginning, propagation, and combined effects of corrosion on structural performance over time. The time-dependent reliability of bridge structures is evaluated using sophisticated numerical simulations in conjunction with the FORM method for reliability analysis. Both time and space variables are treated as uniformly distributed random variables within specific intervals when generating sample points. Engineers and decision-makers can assess the reliability of reinforced concrete bridges using a systematic framework that considers the complex interactions of corrosion mechanisms. This aids an informed maintenance planning and effective resource allocation to ensure long-term structural safety and durability. Finally, the suggested method is tested on a reinforced concrete bridge with corroded steel reinforcement bars. The original work is validated, and the results are compared with the crude Monte Carlo simulation (MCS) method.

Predicting bond strength of corroded reinforced concrete after high-temperature exposure: A stacking model and feature selection

The bond strength between concrete and steel reinforcement bars is crucial for determining the ultimate load-carrying capacity and serviceability of reinforced concrete (RC) structures. However, rebar corrosion and exposure to high temperatures significantly affect this bond strength. Regrettably, research on the combined effect of these two factors on bond strength is scarce, and there is a lack of a unified, precise, and efficient predictive model. This research developed a stacking model to forecast bond strength under the combined impact of high temperature and corrosion. The initial layer of the model comprises SVR, KNN, MLP, RF, GBDT, and XGBoost as base learners, with the second layer being the linear regression model. The analysis led to the following conclusions: In a comparative study, the stacked model demonstrated superior performance compared to the six base learner models (SVR, KNN, MLP, RF, GBDT, and XGBoost). Among all combinations, Stacking Model Three showed the most robust predictive performance, achieving an R² value of 0.9439, an MAE of 0.8553, an MSE of 2.2721, and an RMSE of 1.5073. Stacking Model Three surpassed XGBoost, the most effective base learner, showing improvements of 1.78 % in R², 20.69 % in MAE, 22.66 % in MSE, and 12.05 % in RMSE. The machine learning model’s enhanced reliability was further confirmed by comparison with existing models. Stacking Model Three outshone the Australian Standard model with improvements of 639.04 % in MAE, 2568.77 % in MSE, and 416.61 % in RMSE. Similarly, XGBoost, the top base learner, exceeded the Australian Standard model with gains of 486.09 % in MAE, 1964.39 % in MSE, and 354.36 % in RMSE. The outcomes of the SHapley Additive exPlanations (SHAP) affirm the interpretability and physical validity of the stacking model employed. The SHAP analysis indicates that the corrosion level of steel bars (CL) and temperature (T) are the critical factors influencing bond strength. This research underscores the practical value of SHAP feature importance in feature selection by comparing the predictive performance of stacked models with various input feature combinations, thus confirming that feature selection significantly impacts the model’s predictive accuracy. In optimizing traditional civil engineering standards and empirical formulas, the feature selection results of machine learning can be referenced.

A new uniaxial material model for the simulation of lateral buckling of steel rebars

Lateral buckling of longitudinal rebars is a crucial phenomenon in the response of reinforced concrete structures since it often anticipates crushing of the core concrete and triggers failure of the member. Owing to this, lateral buckling has been simulated in some uniaxial steel models available in the literature. However, most of these models concentrate their novelties on the compression backbone curve of rebars characterised by low-to-medium slenderness ratios and inaccurately simulate the response of bars characterised by high slenderness ratio or the transition from the compression backbone curve to tension. Moreover, all these models neglect the effects of the concrete cover on the lateral buckling of the rebar. This paper presents a new uniaxial material model of reinforcing steel bars with the aim of achieving a more accurate evaluation of the response of rebars including the effects of lateral buckling. The proposed model is calibrated on the results of numerical analyses conducted on refined models of steel rebars characterised by low-to-high slenderness ratios. The proposed model incorporates the possibility to simulate the behaviour of bare and embedded rebars. The response is path-dependent and described by means of smooth curves so as to guarantee numerical stability in nonlinear finite element simulations. The accuracy of the model has been validated by comparison with the response of laboratory tests performed by other researchers on steel rebars. Finally, applications are shown on six reinforced concrete columns in order to highlight the effects of the simulation of buckling of the steel rebars on the global and local responses.

Assessment of Oil Paints for Corrosion Protection of Reinforcing Steel Bars in Concrete

Corrosion becomes a threat to reinforced concrete structural integrity during the service life of the structural member. This situation has become a global concern because of the economic and safety implications. Hence, many corrosion inhibition techniques including coating with materials (organic and inorganic) were used to prevent its devastating effects. The present study used three oil paint brands (mat, red-oxide and gloss Leyland oil paints in Ghana) to variedly coat reinforcing steel bars to ascertain their corrosion protection capacity in concrete. There were zero, one, two and three paint coats of average film thickness, 72 µm, 129 µm and 220 µm respectively explored. An Electrochemical process involved simulated concrete pore solution made of 10% sodium chloride (NaCl) in distilled water with three electrode systems to represent a corrosion medium was used to determine corrosion protection capacity of the paints. The results indicate over 90% corrosion resistance of the paints used. Comparing the corrosion rates of the coated and uncoated reinforcing steel bars, while it would take a one coat steel bar 342.5 years and 237 years respectively for spraying and manual brushing modes to reduce in diameter by 0.616mm, it would take only one year for an uncoated steel bar to reduce by this same 0.616mm. The protection capacity proved better with increasing coats on all corrosion variables for the selected paints used. The implication is that the selected oil paint brands are capable of protecting reinforcing steel bars in concrete against corrosion and therefore recommended for application to reduce maintenance cost. Statistically, no significant difference existed between coating mode, number of coatings, paint type and steel type on the corrosion variables for the coated steel bars. However, a further study about the durability of the coating in the concrete during its service time is recommended.

A Case Study on Using the Concrete Cover Block in Steel Reinforcement Bar: Ghorahi Dang, Nepal

Cover block is one of the basic component on building structure like slab, column, beam, foundation. It is a multi- functionary engineering material. In maximum construction sites, bricks, stones, steel bars are used instead of cover block. This brings a lots of depraved consequences on building structures like lack of well spacing between surface and reinforcement bars, unbalance position of steel bars, reduce the lifespan of building and corrosion. Here, the main function of cover block is to reinforce the building structure by avoiding the corrosion on steel bar or avoiding the moisture with the steel bar, providing the resistive property, distributing an uniform load and managing space. In this way, the cover block is attached in a reinforcement bar in order to reinforce a building structure. When cover block was applied in a building structure, it made a building more durable as well as more attractive by maintaining the shape. This observation suggests that the use of cover block can contribute in strengthening a building structure and maintaining a position and space of a reinforcement bars as well as a structure. Key Words: Concrete cover block, Reinforcement bar, Potential failure of structure, Space maintaining, Corrosion activity.

Effects of Different Inhibitors on the Corrosion Mitigation of Steel Rebar Immersed in NaCl-Contaminated Concrete Pore Solution

The corrosion of steel rebar embedded in concrete under marine conditions is a major global concern. Therefore, it needs a proper corrosion mitigation method. Various types of corrosion inhibitors are used to mitigate the corrosion of steel rebar in chloride-contaminated concrete; however, selecting the appropriate inhibitor and determining its optimal concentration remains a concern. Therefore, in the present study, three types of inhibitors—calcium nitrite (CN: Ca(NO2)2), N,N′-dimethyl ethanol amine (DMEA: (CH3)2NCH2CH2OH), and L-arginine (LA: C6H14N4O2) in three different concentrations, i.e., 0.3, 0.6 and 1.2 M—were compared with a control (without inhibitor, i.e., blank) sample to determine the optimum concentration of the inhibitor for corrosion resistance performance evaluation of reinforcement bars immersed in 0.3 M NaCl-contaminated concrete pore (NCCP) solution for various durations. The corrosion resistance properties were assessed using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) with immersion duration, and potentiodynamic polarization (PDP) after 168 h of exposure. The results showed that the CN inhibitor performed exceptionally well (corrosion inhibition efficiency greater than 97%) in terms of corrosion resistance. However, due to its hazardous nature and its ban in the U.S. and European Union, CN cannot be used in construction. In comparison, while DMEA showed some effectiveness, LA performed better and is also eco-friendly. The corrosion resistance efficiency of samples containing 0.6 M LA remains above 97% even after 168 h of immersion in the NCCP solution. This efficiency is consistent throughout the entire immersion period, from 1 h to 168 h. Therefore, it is recommended that LA be used as a corrosion inhibitor for steel reinforcement bars instead of CN, particularly in chloride-contaminated concrete, as it is both effective and safer than CN.

Early age bond-slip behavior of reinforcing steel bars in concrete subjected to uniaxial lateral pressure: An experimental study

The bond between reinforcing bars and concrete is a crucial factor concerning the serviceability of reinforced concrete structures, particularly for those during construction in some developing areas where plain bars were still used as reinforcements. Despite numerous studies on early age bond behavior between steel bars and concrete, little research has been conducted to quantify the effect of uniaxial lateral pressures on this bond. This study involved testing a total of 378 pullout specimens to evaluate the early age bond-slip behavior of plain bars in concrete under uniaxial lateral pressure. The main test parameters included the concrete ages (1, 3, 7, 14 and 28 days), lateral pressures (0, 0.1, 0.2, 0.4 and 0.6 times the compressive strengths of concrete), concrete strength grades (C20, C35 and C45), and bar diameters (12, 16 and 20 mm). Based on the experimental results, a series of analytical expressions were developed for bond strength, maximum bond slip and residual bond stress predictions considering the effects of early age and lateral pressure. The results demonstrate that degradation of bond strength at early ages can be effectively mitigated by uniaxial lateral pressures. As the age decreases from 28 to 1 days, the bond strength exhibits a significant decrease of up to 51.59 %, while this adverse effect can be reduced by around 10 % in the presence of lateral pressures. Increasing the pressure level from 0 to 0.4 results in a significant increased early age bond strength by 112.6 % to 199.0 % for different bar diameters. However, the residual-to-maximum bond stress ratio remains nearly constant at 0.49 regardless of age and lateral pressure, as the pressure primarily contributes to frictional forces at the bar-concrete interface. An age-dependent bond-slip constitutive model considering the effect of uniaxial lateral pressures was finally proposed and verified with the test results. The paper concludes that given the concrete compressive strength at 28 days, the proposed bond strength and bond stress-slip models can predict the early age bond responses of plain bars in concrete under uniaxial lateral pressures with reasonable accuracy.

Numerical modeling of the transfer length of 17.8 mm (0.7 in) diameter prestressing strands in pretensioned members

The bond between concrete and reinforcing steel bars in reinforced concrete structures is crucial. Prestressing strands with a diameter of 17.8 mm (0.7 in) transfer higher compression per unit area than smaller strands, improving moment capacity and shear strength and extending the girder span. However, limited research on the bond performance of these 17.8 mm diameter prestressing strands has restricted their widespread use despite their advantages. This study presents a methodology to determine the transfer length of pretensioned members numerically. The influence of pretension force and bond strength on a 17.8 mm diameter strand was assessed through the validation of a finite element model using experimental results from a standardized pretensioned pull-out test. Analytical calculations using different code formulas were also conducted, encompassing strands of varying diameters. Our finite element analysis suggests that a 50.8 mm spacing between adjacent 17.8 mm diameter strands is applicable, ensuring there is no stress overlap in the transfer zones, which can lead to concrete cracking and reduced structural integrity. Existing code formulas, such as ACI 318–19 and AASHTO LRFD 9th edition, require longer transfer lengths when compared with the numerical results. The fib MC 2010 and EC2 formulas offer closer results to numerical results of smaller diameter strands but underestimate the transfer length for the 17.8 mm diameter strand. Therefore, improvements to code formulations may be necessary for more accurate transfer length predictions for this specific strand size.

Influence of the basalt fibre and fly ash on the structural properties of sustainable high-strength concrete

Abstract The present article describes the experimental research carried out to investigate the properties of concrete containing basalt fibre reinforcement and concrete containing basalt fibres and fly ash additives. Each test was done as per Indian standards (IS-516). The experiments sought to establish both fresh and hardened concrete properties. In respect of new concrete, slump, setting time, bleeding, temperature, and density were estimated to check its quality. Compressive, flexural and split tensile strength are the three main parameters for assessing those qualities in a solidified state. It was determined that the utilization of fly ash with 20%, 30% or 40% proportions of cement involved resulted in a stronger concrete mixture. To these samples, different contents of basalt fibres 0.25%, 0.5%, and 0.75% by volume were added respectively. Standard samples were cast, cured and tested accordingly. Thus, the studies show that it is possible to mix concrete with basalt fibres without any segregation or balling effect on it or even sticking together during the mixing processes. Modestly increased splitting tensile and bending strengths have been obtained due to the introduction of basalt fibres on this composite material using which improved workability can be achieved more rapidly than conventional hydration reactions based solely upon Portland Cement chemistry, moreover, thermal stability has also been considerably enhanced, besides that even basic physical-chemical properties should be very much similar to those of ordinary Portland cement. Based materials thus ensuring better compatibility during processing from raw constituents towards final composites up-to-date with known technological aspects related specifically towards production practices carried out in developing countries like India. Such situations usually result primarily due to poor engineering control exercised over construction activities. Resulting problems areas namely joint locations limited access space between steel reinforcement bars inside walls. So often appearing weak points in overall design yield inadequate structural performance compared to intended specifications. Another reason why sustainable building methods cannot be fully adopted has been found that they lack proper skilled manpower despite having all necessary resources that are easily renewable. By compared with traditional ones made up of non-renewable sources such as fossil fuels. However, fly ash used in place of concrete only makes it harder without improving workability and strength at the optimum percentage.

Finite Element Analysis of Fiber Reinforced Concrete Slabs under Torsion

Introduction This study has investigated the behavior and strength of steel fiber-reinforced concrete slabs under torsion using Finite Element Analysis (FEA). The research has focused on the effects of steel fiber volume ratio and reinforcement bar size on the torsional properties of concrete slabs. Methods A 3D solid element model with non-linear analysis has been employed using ABAQUS software to simulate the behavior of fifteen square slabs with varying fiber volume ratios and reinforcement bar sizes. The analysis has assessed the torsional properties, including cracking moment, yielding moment, ultimate moment, and stiffness. Results The results have indicated that using steel fibers could enhance the torsional cracking, yielding, and ultimate moments. The torsional ultimate moment has increased between 3% to 4% by using fibers with a volume ratio of 0.5%, but it has increased between 106% to 148% by using fibers with a volume ratio of 2%. The study has concluded the proper volume ratio of fibers to improve the torsional ultimate moment to be between 1% to 2%. Moreover, an increase in reinforcement bar size has led to a higher torsional ultimate moment. Conclusion The torsional stiffness of slabs in uncracked phases has been found to be about 14.4-30.9 times the stiffness in the cracked phase. Fiber reinforcement has been found to lead to an increase in the stiffness of the cracked phase.

Ginger powder as sustainable and eco-friendly corrosion inhibitor for the protection of steel reinforcement bars

In the present studies, ginger powder has been used as an eco-friendly admixture for the cement mortar. Different amounts i.e. 0 wt% (M1), 0.10 wt% (M2), 0.25 wt% (M3) and 0.50 wt% (M4) ginger powder was mixed in the cement mortar (M1) and assessed the durability. The ginger powder with 0.50 wt% (M4) improves the compressive strength by 17 % owing to the water reducing capability, which enhance the hydration reaction and fill the pore matrix of the cement mortar. The active ingredient of ginger powder i.e. shogaol adsorbs on the steel rebar surface through leaching mechanism by interaction of oxygen (O) and п-electrons with iron (Fe) and provide corrosion protection at longer duration of continuous immersion in 3.5 wt% NaCl solution. Following 173 d in a 3.5 wt% NaCl solution, the M4 sample exhibits 82.10 % corrosion inhibition efficiency. Therefore, it is suggested that ginger powder could be a potential eco-friendly admixture to be used in construction industries to get high durability performance in the coastal areas.

Flexural Behaviour and Environmental Impact of African Fan Palm Reinforced Concrete Beams under Symmetrical Loading Conditions

The paper presents the results of investigation on reinforced beams adopting eco-friendly materials for sustainable concrete. The use of African fan palm is explored to mitigate the environmental impact aimed at reducing carbon emissions associated with the production and use of steel reinforcement. The beams were tested under a four -point loading system with the ends simply supported. The test comprised twenty-three beams that were reinforced with African fan palm bars whilst two beams were reinforced with mild steel bars to serve as control beams. The study investigated the flexural strength and deformation characteristics of the beams under monotonic loading. Two concrete strengths of 15.34N/mm2 or 22.37N/mm2 were adopted and proposed optimal tensile ratios for an under reinforced fan palm section. The parameters considered included the tension bars ratio (ρ), concrete compressive strength, span-to-effective-depth ratio and loading conditions. A linear elastic behaviour of both fan palm and steel reinforced concrete beams was observed to the point of first crack load beyond which the beam stiffness continued to reduce until failure. A comparison of the experimental results with results of theoretical analysis of the beams revealed that a 1.22% increase in the tensile ratio of steel in the control beams increased the cracking moment (Mcr) to 36%, while the fan palm beam of the same size and same concrete strength with a higher tensile ratio of 9.69% exhibited a lower Mcr of 11.86%. This shows a significant effect of reinforcing steel bars on concrete cracking compared to the fan palm. The averages of experimental to theoretical failure loads of fan palm to steel were compared with failure loads of 36.52kN to 20.19kN and 32kN to 19.78kN respectively. These results of the study based on the failure mode, and failure loads, highlights the suitability of using African fan palm as substitute reinforcing material for low rise buildings. Furthermore, the study also proposed minimum and maximum tensile ratio of 0.76% and 5.60% respectively for fan palm reinforced concrete beams based on the Indian Standard and modulus of elasticity of steel.

Thermal Degradation of Mechanical Properties in Super Ductile Reinforcing Steel Bars: A Comparative Study with Conventional Bars

Thermal Degradation of Mechanical Properties in Super Ductile Reinforcing Steel Bars: A Comparative Study with Conventional Bars

Flexural Behaviour of Concrete Beams Reinforced With Major Steel Bars under Normal and Corrosive Operational Conditions

Quality assurance of construction materials is very fundamental for structural safety, reliability, serviceability, and durability of constructed civil infrastructure. Inflow of defective or substandard building and construction materials into the industry, particularly reinforcing steel bars, is responsible for many structurally deficient constructed facilities which often lead to failure or ultimate collapse of reinforced concrete (RC) structures. Characterization of steel rebars from two major manufacturers into Botswana construction industry, designated herein as M1 and M2, were conducted as a basis for the evaluation of the quality assurance and control of the products. The flexural behaviour of their respective RC beams, designated herein as B-M1 and B-M2, of dimension 150 × 200 × 3000 mm and subject to four-point loading tests were determined under normal and artificially induced corrosion conditions to assess the influence of steel rebars M1 and M2 on the stiffness and load-carrying capacity. The average yield strengths of steel reinforcing bars were 427 N/mm2 for M1 and 459 N/mm2 for M2. The moduli of elasticity for M1 and M2 were 203 GPa and 205 GPa, respectively. The percentage elongation was found to be 7.93% for M1 and 7.24% for M2. The flexural strength of beams reinforced with M1 was 7% and 16.5% lower than RC beam with M2 under normal and accelerated corrosion of 5% of NaCl solution for 60 hours condition, respectively. The flexural behaviour of RC beams reinforced with B-M1 had a lower flexural strength under both normal and corrosive environmental conditions as compared to B-M2. The flexural strength of B-M1 had reduced from 48.5 N/mm2 to 41.0 N/mm2, while B-M2 reduced from 52.2 N/mm2 to 49.2 N/mm2. This represented loss of load-carrying capacity of 15.4% and 5.8% for B-M1 and B-M2 respectively due to exposure to corrosive environment. The findings revealed disparity in bending capacity due to the low interfacial bonding due to reduced relative rib areas. A more intensive quality control of imported steel should be ensured at the ports of entry by relevant regulatory agencies.

Flexural strengthening of reinforced concrete cantilever beams having insufficient splice length

Structural systems often undergo changes due to variations in the usage, the loading conditions, or the presence of defects in their elements. The problem can be exacerbated when there is insufficient overlap between reinforcing bars in critical moment zones. This article investigates the behavior of reinforced concrete cantilever beams exhibiting insufficient overlap between bars that used as main reinforcing steel bars in the negative moment zone. Various strengthening techniques were employed in order to improve these defected cantilever beams. Eleven beams underwent flexural testing until reaching failure. The experimental parameters encompassed the strengthening scenarios and the bonded length. Three strategies were used: the application of stainless-steel plates (SSPs) as externally bonded reinforcement, near surface mounted (NSM) reinforcement in which additional deformed steel bars were bonded utilizing engineering cementitious composites, and externally pre-stressing technique. The anchorage length was examined at 40, 50, and 60 times the internal bar diameter. It was noted that the most substantial improvement achieved with the NSM method, followed by the externally pre-stressing method. It is worth mentioning that most of the beams failed in a flexural manner, with partial debonding occurring in beams strengthened using external strengthening. Moreover, this article includes the development of a numerical model employing the finite element method to replicate the response observed from the experimentally tested beams. The accuracy of the model was confirmed through the comparison of its outcomes with the experimental data, demonstrating an acceptable level of accuracy with deviations of less than 4.4 %. This successful numerical investigation was also used to conduct a parametric study. From this study it is evident that the effect of debonding on SSPs can be reduced by adding steel anchors at the ends of these plates. Finally, an analytical method was proposed to calculate the ultimate load capacity of strengthened reinforced concrete beams.

Structural performance of hybrid reinforced concrete beams containing polyvinyl alcohol fibers under thermal loads

This study focused on the efficiency of concrete beams containing polyvinyl alcohol fibers (PVA) under thermal loads. The eighteen concrete beams were reinforced with hybrid bars or a combination of GFRP bars and steel reinforcement bars (hybrid scheme). The main experimental variables were the level of temperature (25o, 300o, and 600o C), PVA fiber volume (0 %, 0.50 %, and 1.0 %), and the flexural reinforcement bars. The experimental test results are discussed in terms of the first crack load, flexural capacity, and load-deflection curves. Moreover, the initial and post-crack stiffness, ductility factor, and failure modes are discussed. The test results demonstrated a significant increase in the capacity of PVA concrete beams reinforced with hybrid reinforcement bars. At a temperature of 300o C, the inclusion of 0.50 % and 1.0 % PVA ratios improved the flexural capacities by 11 % and 24 %, respectively. Furthermore, the addition of PVA fibers enhanced the toughness by 34 % and 67 %, respectively, when compared to normal concrete beams. The results also demonstrate that using PVA fibers prevents the spalling of concrete beams after exposure to elevated temperatures. At 600 °C, beams containing 0.50 % and 1.0 % PVA fibers exhibited flexural capacities that were 9 % and 6 % higher, respectively, compared to normal concrete beams. Additionally, the inclusion of PVA fibers increased the toughness by 27 % and 21 % for the respective fiber ratios. Finally, a nonlinear finite element analysis (NLFEA) simulation was performed to verify the experimental test results and supplement experiments by predicting the results that are difficult to accomplish through experiments. With an average ratio of 1.02 between experimental and NLFEA ultimate capacity, the numerical results were an exact match of the patterns observed in the experimental results.