Reinforcing Steel Bars Research Articles

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.

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 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.

Bond behavior of reinforcing steel bars in metakaolin – calcium carbide residue-based geopolymer concrete

The bond property of concrete is a key characteristic of concrete that affect the structural activity of reinforced concrete beams. Concrete produced from geopolymer has the prospect to replace concrete produced from ordinary Portland cement (OPC) for structural applications. Therefore, this research evaluates the bond behavior of metakaolin-calcium carbide residue (CCR)-based geopolymer concrete for use in in situ structural applications. Comparative studies were carried out on concrete made of geopolymer and OPC. The embedment lengths (5ϕ and 7ϕ) and reinforcing bar diameters (14 and 16 mm) were varied and the bonding activity of the different concrete types was studied. Additionally, the qualities of the concrete produced were assessed, including density, ultrasonic pulse velocity, and compressive and flexural strengths. Generally, the metakaolin-CCR-based geopolymer concrete samples had the best mechanical properties, followed by metakaolin-based geopolymer and OPC concrete, respectively. Bond activity enhanced when embedment length and diameter of reinforcement were reduced in all types of concrete. Thus, with a reinforcing bar diameter of 14 mm and an embedment length of 5ϕ, the average bond strength of the metakaolin-CCR-based geopolymer concrete was 14.3MPa, which was 18.87% and 105.46% higher than that of the metakaolin-based geopolymer and OPC concrete, respectively. Influenced by experimental conclusions, it can be established that the metakaolin-CCR-based geopolymer concrete has the capacity to be used in place of OPC concrete in bond applications where steel reinforcing bars are employed.

Shear strength and ductility of novel steel fibre-reinforced concrete dowel connections for composite beams

In this paper, a novel steel fibre-reinforced concrete (SFRC) dowel connection without traditional steel bar reinforcement is proposed for steel-concrete composite beams. Push-out tests on thirty-six specimens were conducted to investigate the shear strength and ductility of SFRC dowel connections with varying dowel sizes, concrete densities, fibre content and type. Even without the presence of reinforcing bars, the SFRC dowels were able to resist substantial loads and maintained a ductile load-slip behaviour. The shear strength of SFRC dowels increased with an increase in the fibre content, dowel size, and concrete density. Further, dowels with higher steel fibres content exhibited enhanced ductility, displaying a near elastic-plastic load-slip behaviour, with an ability to resist up to 80 % of the ultimate load even at 6 mm slip. A unique analytical model to predict the ultimate load and the load-slip curve is proposed in this study. The model was able to predict the ultimate load to within 6 % of test results, on average, while the mean load at 6 mm slip was predicted to within 3 % of the test results, with standard deviation of 17 % and 13 % respectively. The general shape of the load-slip curve was also well predicted. The study also proposes simplified equations, which predicted the shear strength of SFRC dowels to within 2 % of the test results with a standard deviation of 13 %.

Meta-arch structure: Designed reinforcement cage to enhance vibration isolation performance

In this study, inspired by the mechanical metamaterials with bandgap properties, a new type of meta-arch structure (MAS) for the attenuation of elastic waves is proposed. In this metastructure, the reinforcement cage, typically employed to enhance the tensile properties of building materials, has been redesigned and transformed into a new structure containing circular tubes with embedded resonant microstructures. The vibration reduction performance of the MAS was illustrated by the frequency response analysis in the simulation calculation, and the generation mechanism of the vibration attenuation band was revealed. The specimens of the complex MAS consisting of gypsum, reinforced steel bars, and tubes were fabricated, and the vibration response experiments were carried out to determine the dynamic properties of the novel MAS. The results show that the designed arch structure exhibits a broad vibration attenuation band without sacrificing its structural bearing capacity. Additionally, the robustness of the band gap is demonstrated by analyzing how changes in the positions of excitation and response points influence the band gap. Moreover, the MAS can be customized for specific application scenarios of vibration reduction according to the parameter analysis. Finally, the experimental results closely align with the numerical estimations, confirming the feasibility of the design method for reducing vibrations. This work provides a new method for the development of building structures for vibration and noise control.

Statistical insight into the quality of reinforcing steel bars used in construction projects

Steel bars are part and parcel of reinforced concrete used in the construction projects, ranging from single family houses to super tall buildings and long span bridges. Maintaining the quality of the steel bars has always been challenging especially in developing countries. Low quality steel bars result in serviceability issues and reduce useful life of structures. This research work is focused on examining and investigating some basic facts about the quality of the steel bars produced in Pakistan. Pakistan being 5th most populous country in the world has huge consumption of steel. Laboratory testing data of steel bars are statistically analysed to have an insight in to the quality of bars. These steel bars were tested over a period of two years, which belong to several real-life projects. Properties like weight per unit length, yield strength, ultimate strength and percentage elongation were mainly analysed. Findings show that out of the stock of 4782 bars, 17.4 % failed to meet the minimum requirements provided by American Society of Testing and Materials (ASTM A615). Quality of grade 60 bars was found better than those of grade 40.

Effect of shear span-to-depth ratio on flexural and fracture behaviors of reinforced UHPMC beams based on four-point bending test and acoustic emission monitoring

Ultra-high performance manufactured sand concrete (UHPMC), using manufactured sand (MS) as aggregate, belongs to a brand-new ultra-high performance concrete (UHPC). Better understanding the failure behavior of UHPMC beams reinforced with steel reinforcement bars is crucial in structural design. This study investigates the effects of different shear span-to-depth ratios (λ = 1.2, 1.6 and 2.0) on the failure modes, mid-span deflection, concrete and rebar strain, flexural toughness, initial cracking load, ultimate load, energy dissipation capacity, and crack propagation patterns based on four-point bending tests for totally twelve reinforced UHPMC beams. Meanwhile, acoustic emission (AE) monitoring is used to evaluate corresponding fracture characteristics. Results reveal that an increase in shear span-to-depth ratio leads to a significant increase in mid-span strain and better ductility but lower equivalent stiffness. The maximum strain of specimen with λ = 1.2 is 24.8 % lower than that with λ = 2.0, and specimen with λ = 1.6 exhibits 22.3 % greater equivalent stiffness than that with λ = 2.0. Beams with larger shear span-to-depth ratios demonstrate superior ductility and energy absorption capacity, specimen with λ = 2.0 showing a ductility factor 2.85 times higher than that with λ = 1.2. The presence of MS significantly improves initial cracking load by 26.9 %, ultimate load by 4.5 %, and energy dissipation capacity by 37 %. MS also enhances toughness and delays crack propagation in the early stages. This effect can make the fracture transform into more rapid energy release in the later stages, indicating that MS could alter crack propagation patterns, forcing cracks to propagate along paths with greater resistance to crack propagation. These conclusions can offer insights for the safer and economical design and application of UHPMC beams, especially the balance among shear span-to-depth ratio, MS and mechanical performance in the environmentally friendly structures design and failure prevention process.

Shear strength of hybrid GFRP-steel reinforced concrete corbels without vertical stirrups: Experimental research and prediction models

This paper investigates the behavior and predicts the shear strength of concrete corbels reinforced with hybrid glass fiber reinforced polymer (GFRP)/steel reinforcement bars. For this purpose, the study consists of two main parts: the first part was an experimental study carried out on eight hybrid reinforced concrete corbels and four GFRP reinforced concrete corbels with a shear span to depth ratio (a/d) of 0.7 and 1.0; in the second part, a nonlinear finite element model (NFEM) was developed and validated against experimental results. Comprehensive parametric studies based on the validated NFEM were conducted to assess the impact of main parameters on the shear capacity. As a result, an empirical formula predicting the shear capacity of hybrid RC corbels was proposed. Furthermore, a softened strut-and-tie model (SSTM) was further developed to predict the shear capacity of hybrid RC corbels. The test results indicate that increasing the steel reinforcement ratio significantly enhances the shear strength. The width of the inclined crack band narrows as a portion of GFRP reinforcement is replaced with steel reinforcement. The NFEM shows good agreement with test results in terms of load-deflection curve, strain of rebar and failure modes. The proposed empirical formula and extended SSTM accurately predict the shear capacity of hybrid RC corbels compared to test results and numerical simulations.

A new prediction model for residual deformation capacity of corroded steel bars

Corrosion of reinforcing steel bars (rebar) is one of the primary factors leading to the performance degradation of reinforced concrete (RC) structures. It is essential to take into consideration the deteriorating effects of corrosion when it comes to assessing the performance of existing RC structures. However, due to the uncertainties and randomness associated with the degree and distribution of corrosion, accurately assessing the residual deformation capacity of corroded rebar is a significant challenge. This paper presents a comprehensive theoretical model for the prediction of the residual deformation capacity of corroded rebar. Taking into account the mechanical characteristics of the steel material, three classes of non-uniform corrosion in rebar are firstly defined on a quantitative basis to characterize the deformation distribution patterns under tension. Based on the concept of deformation accumulation, a simplified theoretical model is proposed for evaluating the residual deformation capacity of corroded rebar, incorporating both the non-uniformity of corrosion and the sample (or gauge) length; thus, a length scale is built into the nominal strain measure to accommodate the use of different sample or gauge lengths. Numerical tensile tests on 500 randomly generated samples of rebar with varying corrosion levels are conducted, and the parameters of the theoretical model for the three corrosion classes are determined based on a regression analysis of the tensile test results. Comparisons with actual experimental results and existing degradation models demonstrate that the proposed theoretical model provides a more accurate estimation for the deformation capacity of corroded rebar. The model offers a reliable reference for accurately assessing the tensile performance of corroded rebar in subsequent engineering applications.

Hierarchical Bayesian modeling for calibration and uncertainty quantification of constitutive material models: Application to a uniaxial steel material model

Constitutive material models play an integral role in finite element (FE) modeling of structural components and systems and are governed by a set of parameters. The values of the material model parameters are important for the FE model to be able to predict the real structural behavior as closely as possible. Realistic cyclic material constitutive models well calibrated to experimental data are critical when predicting the nonlinear dynamic response of structural systems to extreme loads (e.g., earthquakes, high winds, blast). Hence, this study focuses on the inference and uncertainty quantification of material model parameters from an experimental dataset consisting of data from experiments on multiple specimens of the same kind, which is a topic of great interest to the structural modeling and simulation community. Traditionally, Bayesian inference is performed by pooling the data from all the specimens, or by considering the data from a single specimen, disregarding the inherent variability (aleatory uncertainty) among specimens of the same kind. Consequently, traditional approaches fail to capture the population distribution of material model parameters, which represents the aleatory specimen-to-specimen variability that is essential for conducting reliability analysis and uncertainty propagation studies. Moreover, these approaches cannot accurately simulate the response of new specimens. To overcome these limitations, this study introduces a novel application of hierarchical Bayesian inference for calibrating material model parameters. By simultaneously considering experimental data from multiple specimens of the same kind, hierarchical Bayesian modeling quantifies both epistemic uncertainty and aleatory specimen-to-specimen variability. In this study, the parameters of the well-known Giuffré-Menegotto-Pinto (GMP) uniaxial material model for reinforcing steel are calibrated and validated based on a dataset of experimental cyclic tests conducted on thirty-six steel specimens, or coupons, originating from three different manufacturing mills, complying to two different manufacturing standards, and subjected to different strain histories. These strain histories are similar to those experienced during seismic events by reinforcing steel bars within reinforced concrete structures. The material model parameters are calibrated using both the traditional and the hierarchical Bayesian approach and the results are compared. Based on the experimental dataset employed in this study, a joint probability distribution of the GMP material model parameters that quantifies both epistemic (due to finite sample size) and aleatory (coupon-to-coupon) variability or uncertainty is provided which can be used for uncertainty propagation in reliability and risk analyses of nonlinear dynamic systems.