Steel Reinforced Concrete Beams Research Articles

Shear strength model of FRP-reinforced concrete beams without shear reinforcement

The current design codes for evaluating the shear strength of concrete beams reinforced with fiber-reinforced polymer (FRP) bars predominantly rely on a semi-empirical approach through test data calibration without a robust theoretical background. This approach may lead to either overestimation or underestimation, resulting in significant scattering in strength predictions. This study proposed a modified approach to enhance the existing unified shear-strength model developed for steel-reinforced concrete (RC) beams based on the compression zone failure mechanism, for predicting the shear strength of FRP-RC beams without shear reinforcement. The proposed model integrates strain and stress approaches, accounting for the distinctive characteristics associated with FRP reinforcement. Additionally, the overall shear resistance capacity of the FRP-RC beam is considered as the sum of contributions from the intact concrete of the compression zone and the aggregate interlock mechanism. The reliability of the proposed model is verified by comparing its predictions with a comprehensive database comprising 264 FRP-RC beam specimens without shear reinforcement reported by 41 research groups. Furthermore, the accuracy of the proposed model was assessed through a comparative analysis with existing evaluation methods, encompassing machine learning-based models, empirical models, theoretical models, and design codes. The results indicate that the proposed model satisfactorily predicts the shear strength of FRP-RC beams within a wide range of design parameters. In comparison with machine learning-based models, the proposed theoretical model exhibits a similar level of accuracy in terms of the mean shear strength ratio and coefficient of determination (R2) values but with less scattering, indicated by lower coefficient of variation (COV) and root mean square error (RMSE) values. In addition, the proposed model outperforms existing empirical and theoretical models, as well as current design codes, by significantly enhancing prediction accuracy, demonstrated by lower COV, RMSE, and higher R2 values. Finally, a parametric study was conducted to investigate the effects of the key parameters on the shear strength of FRP-RC beams using both the proposed model and representative existing evaluation methods.

Experimental and numerical analysis on shear capacity of steel-reinforced geopolymer concrete beams with different shear span ratios

PurposeThe purpose of this study is to use the corrected stress field theory to derive the shear capacity of geopolymer concrete beams (GPC) and consider the shear-span ratio as a major factor affecting the shear capacity. This research aims to provide guidance for studying the shear capacity of GPC and to observe how the failure modes of beams change with the variation of the shear-span ratio, thereby discovering underlying patterns.Design/methodology/approachThree test beams with shear span ratios of 1.5, 2.0 and 2.5 are investigated in this paper. For GPC beams with shear-span ratios of 1.5, 2.0 and 2.5, ultimate capacities are 337kN, 235kN and 195kN, respectively. Transitioning from 1.5 to 2.0 results in a 30% decrease in capacity, a reduction of 102kN. Moving from 2.0 to 2.5 sees a 17% decrease, with a loss of 40KN in capacity. A shear capacity formula, derived from modified compression field theory and considering concrete shear strength, stirrups and aggregate interlocking force, was validated through finite element modeling. Additionally, models with shear ratios of 1 and 3 were created to observe crack propagation patterns.FindingsFor GPC beams with shear-span ratios of 1.5, 2.0 and 2.5, ultimate capacities of 337KN, 235KN and 195KN are achieved, respectively. A reduction in capacity of 102KN occurs when transitioning from 1.5 to 2.0 and a decrease of 40KN is observed when moving from 2.0 to 2.5. The average test-to-theory ratio, at 1.015 with a variance of 0.001, demonstrates strong agreement. ABAQUS models beams with ratios ranging from 1.0 to 3.0, revealing crack trends indicative of reduced crack angles with higher ratios. The failure mode observed in the models aligns with experimental results.Originality/valueThis article provides a reference for the shear bearing capacity formula of geopolymer reinforced concrete (GRC) beams, addressing the limited research in this area. Additionally, an exponential model incorporating the shear-span ratio as a variable was employed to calculate the shear capacity, based on previous studies. Moreover, the analysis of shear capacity results integrated literature from prior research. By fitting previous experimental data to the proposed formula, the accuracy of this study's derived formula was further validated, with theoretical values aligning well with experimental results. Additionally, guidance is offered for utilizing ABAQUS in simulating the failure process of GRC beams.

Flexural behaviour of one-part fibre-reinforced geopolymer beams

This research focuses on the structural application of one-part fibre-reinforced geopolymer composite (OP-FRGC), a pioneering low-carbon, high-performance construction material. While extensive studies have been conducted on the basic mechanical properties and mix proportions of OP-FRGC, structural applications remain underexplored. This investigation of the flexural performance of steel-reinforced OP-FRGC beams employed four-point bending tests and digital image correlation (DIC) to elucidate bending failure mechanisms. The results were then compared with those of conventional steel-reinforced concrete (RC) beams. Findings indicate that the integration of fibres in OP-FRGC effectively distributes cracks and enhances flexural toughness. Additionally, the research evaluates the predictive accuracy of existing structural codes from China, the United States, and Europe for steel-reinforced OP-FRGC beams. A comparative analysis of the carbon emissions from these structural systems underscores the environmental advantages of steel-reinforced OP-FRGC beams, highlighting their potential to reduce the carbon footprint in the construction sector.

A statistical-experimental study to investigate the optimal parameters of fibres made from waste PET bottles for strengthening concrete

This research investigated using waste polyethylene terephthalate (PET) bottle fibres in concrete. Experimental tests were conducted to evaluate the mechanical properties of PET fibre-strengthened concrete. The effects of the fibre volume fraction and fibre length were studied to obtain optimal values. Moreover, a thorough statistical analysis was performed to identify the parameter that impacts the inclusion of PET fibres in concrete. Furthermore, the study explored the effect of PET fibres on reinforced concrete beams of shear failure mode. The results showed that incorporating PET fibres significantly enhances the ductility of the concrete material and reduces shrinkage. It also promotes the initial stiffness, the inelastic absorbed energy and the ductility of steel-reinforced concrete beams.

Prediction of fatigue lives for steel beams and steel reinforced concrete beams

With the wide application of steel reinforced concrete (SRC) beams, the problem of fatigue has become increasingly prominent. To deeply understand the fatigue performance of SRC beams, a finite element analysis (FEA) about fatigue failure process of SRC beams was performed. The internal H-steel inside SRC beam (SRCH-steel) was shown to possess similar fatigue failure characteristics to steel beam and exert a deciding influence on the fatigue resistance of SRC beam in previous experiments. Therefore, FEA of fatigue crack growth (FCG) was conducted using a fully-automated remeshing technique for steel beam first. Comparisons were made and a good agreement was found between predicted and experimental fatigue lives. The average value of ratio between predicted and experimental fatigue lives for the five steel beams is 1.149, which verifies the accuracy of FEA model. Then, based on the FEA model of steel beam, rebars and external concrete were included to simulate fatigue failure process of SRC beams. The results suggest that the average value of ratio between predicted and experimental fatigue lives for SRCH-steels inside the thirty-nine SRC beams is 1.191, and the average value for tensile rebars is 1.212, which indicates that the numerical model is accurate and reliable. At last, further analysis about influences of critical parameters on fatigue performance of SRC beams was conducted, such as nominal stress range, steel ratio of SRCH-steel, steel ratio of tensile rebars, fatigue strength of tensile rebars, shear span-to-depth ratio, concrete strength grade and stirrup ratio.

DEFORMABILITY AND CRACK RESISTANCE OF REINFORCED CONCRETE AND FIBER CONCRETE BEAMS

The work presents the results of the study of deformability and crack resistance of reinforced concrete beams with additional steel fiber reinforcement. Beam samples of three series were produced (three in each series): series I ― beams made of ordinary concrete; II series ― steel-reinforced concrete beams; III series ― beams of combined section, in which the lower zone (0.5 from the height of the beam) is made of steel fiber concrete, and the upper zone is made of ordinary concrete. One sample of each series was made from one batch. At the same time, material samples were made from the same batch. Fiber, the total volume of which was 1% of the volume, was uniformly added to the composition of the concrete mass for the II and III series of samples during mixing. The load was applied in increments of 1 ton. Deformations were determined using strain gauges, watch-type indicators with a division value of 0.01 mm in the middle of the beam span. At each stage, a certain amount of time was required to read the instruments, find and fix the cracks, as well as to measure the length and width of their opening using a Brinell tube. The tests showed that the deformability of the beams of the three series and the character of the crack formation are significantly different from each other. Moreover, the series III beam with combined reinforcement occupies an intermediate position in terms of these characteristics. Thus, by the end of the tests, the reinforced concrete beam (series I) had 19 cracks, the fiber concrete beam (series II) ― 28, the beams with combined reinforcement (series III) ― 23. At the same time, the maximum final crack opening width for beams I, II, III series was 0.8 mm, 0.1 mm (one crack) and 0.1 mm (two cracks), respectively. Cracks in a fiber concrete beam are much smaller in width. And the maximum length of the cracks here turned out to be the largest ― 31.3 cm, while in the beams of the I and III series this value was 25.5 cm and 20.4 cm, respectively.
 The analysis of the given results shows that the best indicators of crack resistance are revealed by beams with full dispersion reinforcement. The use of fiber allows you to change the nature of the destruction process. Unlike ordinary concrete, in which this process occurs almost instantaneously, in fiber concrete there is no brittle failure, and the beam continues to resist the load, and the nature of the failure changes from brittle to viscous.

Probabilistic code-based shear capacity model for I-shaped steel reinforced concrete (SRC) beams

A code-based probabilistic prediction model is developed for structural design and reliability analysis of the shear capacity of shear-critical steel reinforced concrete (SRC) beams. First, an experimental database of 83 shear tests was compiled from the literature, including steel-reinforced normal-strength concrete, steel-reinforced high-strength concrete, and steel reinforced lightweight aggregate concrete. Then, three deterministic formulations from the most commonly-used specifications JGJ, AIJ, and ACI-AISC were presented and compared against the database. Based on the different shear mechanism and formula considerations in the code-based deterministic models, this study developed 12 probabilistic models that account for both epistemic and aleatory uncertainty to examine the impact of concrete strength, shear span ratio, number of parameters, and their interactions. The Bayesian theory and Markov Chain Monte Carlo (MCMC) simulation method were utilized to calibrate the models by generating posterior distributions of the model parameters and the standard deviation (SD) of the model error. Optimal model selection hinges upon balancing precision and intricacy. An analysis was then conducted to evaluate the accuracy of the selected model, and the probabilistic model was applied to estimate the shear reliability of a SRC beam. Results demonstrate that the model objectively represents the probabilistic properties of the shear capacity of SRC beams and has the capability to conduct reliability analysis.

Quantitative reliability measures determination of a steel-reinforced concrete beam taking into account fatigue damage accumulation in flexible pin stops

Reliability is one of the most important properties of road bridges due to their degree of responsibility and strategic importance for the transport system. For steel-reinforced concrete bridges, which are widespread nowadays, the question of their overall structure reliability dependence on the element’s condition of steel beam and reinforced concrete slab connection remains not fully studied. The authors have performed fatigue damage accumulation numerical modelling in the conjunction elements of steel-reinforced concrete beam from the cyclic temporary loads influence and analysed this process influence on the overall structure reliability. Based on the previous studies data, a relationship model between the conjunction element shear rigidity and the amount of damage accumulated by it is proposed. The nonlinear finite element calculation algorithm with regard to the conjunction element’s rigidity reduction is proposed and tested on the model of the steel-reinforced concrete superstructure. The selection method of the equivalent time load for modelling the accumulation of fatigue damage process from traffic flow is proposed. In order to optimise the computational resources used it is proposed to use loading process clusterization into enlarged cycles groups and the rational group size is determined. A numerical experiment on the simply supported steel reinforced concrete beam model with different loading cycles number (from 1 loading to 100 million loading cycles) to determine the reliability index β under the assumption of variability of two parameters — design steel resistance and the value of temporary load. FORM (First Order Reliability Method) was used for probabilistic analysis. The study results have shown that the accumulation of fatigue damage in the elements of steel-reinforced concrete superstructures has a significant effect both on the load-bearing capacity of the superstructure beams and on the quantitative indicators of structural reliability (increase in the probability of structural failure, decrease in the reliability index β).

Experimental and Numerical Study on the Flexural Behaviors of Unbonded Prestressed I-Shaped Steel Encased in Ultra-High-Performance Concrete Beams

A novel type of traditional composite member-unbonded prestressed I-shaped steel encased in a UHPC (PSRUHPC) beam is proposed to reduce the brittleness of UHPC beams and improve their bearing capacity. A PSRUHPC beam, an unbonded prestressed UHPC (PRUHPC) beam, and an I-shape steel UHPC (SRUHPC) beam were manufactured, and their flexural static performances were assessed using a flexural comparison test. The test results reveal that the flexural process of the PSRUHPC beam is similar to that of ordinary reinforced concrete beams, and UHPC crushing in the compression zone is a sign of failure. Due to the bridge coupling effect of steel fiber, the crushed concrete still maintains good integrity without bursting, the UHPC in the tension zone remains functional after cracking, and the cracking inflection point of the load–deflection curve was not obvious. The PSRUHPC beam showed a significantly improved bearing capacity and flexural stiffness, its load–deflection curve exhibited significantly more energy consumption, and its bending ductility performance was improved, with better deformation properties. Compared with PRUHPC beams, PSRUHPC beams show a bearing capacity increase of 55.3%, a cracking load increase of 11.9%, and a displacement ductility coefficient increase of 76.2%. Compared with SRUHPC beams, PSRUHPC beams show a 15.4% increase in bearing capacity, a 50.2% increase in cracking load, and a 12.1% increase in displacement ductility coefficient. The application of prestress can significantly improve the stiffness of the beam prior to cracking. The cracking loads of prestressed ordinary concrete beams and steel-reinforced concrete beams account for 20–30% of their ultimate loads, which value was 40–50% for the tested beams. The change trend of strain in the section steel and UHPC is roughly the same at the same height, and the strains of the two deviated after most of the section steel yielded under tension, but they can generally work together. When the tested beams were cracked, multiple cracks appeared, which were fine and dense. The magnetic flux sensor cable force-monitoring system can better monitor the strand stress increment of unbonded prestressed steel UHPC beams, where the prestressed strand did not yield tension under the final state; the load–strand stress increment curve was basically the same as the load–deflection curve, and the stress increment of the unbonded steel strand positively correlated with the midspan deflection. Finite element simulation was used to verify the test results, and we determined the reinforcement ratios for non-prestressed and prestressed reinforcement, as well as the ratio of a steel-containing section, the effective prestress, the height of prestressed reinforcement, the position and strength of I-shaped steel, and whether or not the prestressed reinforcement was bonded. The effects of these parameters on the bearing capacity and displacement ductility coefficient of PSRUHPC beams were studied. The results can provide a reference for subsequent theoretical design calculations.

Impact of developed hybrid polypropylene fiber inclusion on the flexural performance of concrete beams reinforced with innovative hybrid bars

This paper investigates the impact of incorporating a hybrid combination of structural polypropylene fibers on the flexural behavior of concrete beams reinforced with steel, GFRP, and innovative hybrid bars. A new ductile hybrid bar with equivalent bilinear stress-strain characteristics has been developed to address steel corrosion and FRP ductility issues. Fourteen half-scale RC beams were fabricated and tested under four-point loading configuration to study the flexural response. The tensile reinforcement types (steel, GFRP, and hybrid), hybrid reinforcement ratios (0.85 %, 1.26 %, and 1.70 %), reinforcement hybridization schemes (hybrid-hybrid, hybrid-GFRP, and GFRP-steel), and hybrid fiber ratio (0.0 %, 1.0 %, and 2.0 %) are the major parameters studied. The test results were recorded and analyzed in terms of mid-span deflection, cracking load, flexural capacity, and failure mechanism. The results demonstrated that the addition of hybrid fibers and using hybrid bars significantly improved the peak strength, ductility index, and bending stiffness. Moreover, the hybrid-reinforced concrete beams exhibit large inelastic deformations similar to steel-reinforced concrete beams. The inclusion of hybrid fibers improves the post-peak response of the tested beam due to fiber bridging capabilities. For design purposes, a simplified formula proposed by ACI 544 for predicting the nominal flexural capacity of hybrid fiber concrete beams reinforced with hybrid bars was presented, compared with experimental results and validated with 44 specimens from other studies. The predicted and test results were in good agreement with a standard deviation of 0.12. Additionally, 3D nonlinear finite element analysis was developed to validate the test results, demonstrating reasonable accuracy in predicting the flexural behavior of the beams.

Performance of 3D-Printed Beams and Slabs Using Self-Sensing Cementitious Composites and DIC Method.

This paper aims to explore the structural performance of 3D-printed and casted cement-based steel-reinforced concrete beams and one-way slabs incorporating short carbon fibre and activated carbon powder, which have been shown to enhance concrete's flexural strength and reduce its electrical resistivity. The samples are cast and printed in 250 × 325 × 3500 mm beams and 150 × 400 × 3500 mm one-way slabs and mechanical, electrical, and piezoresistivity properties were measured. This length of beams and one-way slabs with rebars have been considered as they can magnify the flexural and cracking behaviour and make them easier to be monitored and analysed. The samples were loaded up to 80% of maximum stress. Crack propagation and strain was assessed using the 2D digital image correlation (DIC) method. The results compared samples under continuously increasing loads between 3D-printed and cast samples. The 3D-printed composites had a better piezoresistive response due to the enhanced anisotropic behaviour. DIC analysis illustrated similar results among different samples, while 3D-printed blocks had lower cracking performance due to the horizontal case fracture in lower stress.

Flexural performance tests and machine learning analysis of prestressed high strength steel reinforced concrete beams

ABSTRACT This paper reports a study on the flexural performance of prestressed high strength steel reinforced concrete (PHSSRC) beams and proposes machine learning (ML) models for predicting the flexural bearing capacity of steel reinforced concrete (SRC) beams. Seven prestressed steel reinforced concrete (PSRC) beams were tested under a four-point bending load to investigate the effect of steel strength grade, steel ratio, and longitudinal reinforcement ratio on the flexural load capacity of beams. The test results indicated that increasing the steel strength grade and steel ratio significantly enhanced the bearing capacity of PSRC beams. A database consisting of 112 sets of experimental data on the flexural performance of SRC beams, including the test data in this study, was established for training and validating the ML models. Artificial Neural Network (ANN) model and eXtreme Gradient Boosting (XGBoost) model were respectively developed to predict the flexural load capacity of SRC beams, and the accuracy of the flexural load capacity values predicted by the design specification, the ANN model and the XGBoost model were compared. The results show that the XGBoost model has the best prediction performance. Finally, the sensitivity analysis of the parameters was performed using the Shapley Additivity (SHAP) interpretation method.

Finite element modeling and design equations of partially steel-reinforced concrete beam-to-steel tube column joint

Steel reinforced concrete beams are increasingly used as novel transfer structures in high-rise buildings. In this paper, numerical and theoretical studies were carried out on a novel joint of steel-reinforced concrete beam and steel tube column, in which the beam was reinforced by a short steel beam with partial length. Based on the previous experimental studies, finite element modeling was performed to consider the evolution of the concrete damage and to investigate the effects of the main design parameters on the seismic performance of the new joint. It was found that the length of the steel shape, the thickness of the concrete cover, and the concrete compressive strength have significant effects on the initial stiffness and peak capacity of the new joint, while changing those parameters may not change the failure mode of the joint. A theoretical analysis was performed to establish an analytical model for the shear capacity of the new connection that takes into account the contributions of the steel web, stirrups, and concrete. The model was verified against the database of experimental and numerical analysis results. Design equations and recommendations for checking the flexural and shear strength of the embedded steel shape, the composite beam and the RC part of the beam were also provided.

Seismic behavior of steel-reinforced high-strength concrete composite beams with bonded tendons

To study the seismic behavior of steel-reinforced high-strength concrete composite beams with bonded tendons (PSRHSCBs) under low cyclic loading, 13 PSRHSCBs were designed with the main parameters of the span-to-height ratio of beams (L/H), the cubic strength of concrete (fcu), the eccentricity of H-shaped steel (eH), the volume stirrup ratio (pv), the longitudinal reinforcement ratio (p), and the tension control stress of tendons(σcon). Using the simplified bilinear constitutive model of steel and the nonlinear constitutive model of high-strength concrete, and introducing plastic damage of concrete, fine finite element models were established with ABAQUS software. 11 similar test specimens were conducted by above modeling method, by comparing existing test curves and numerical simulation curves, both of them match well, which verified the validity of the modeling method. Subsequently, parameter analysis for 13 PSRHSCB specimens was performed, and the influence regularity of different parameters on the seismic behavior of this kind of composite beams was obtained. The results show that hysteretic curves of this kind of composite beams are full, and the failure mode is manifested as bending failure. The ultimate load, the energy dissipation capacity and the ductility coefficient of specimens can be improved significantly by increasing pv, on the contrary, the energy dissipation capacity and the ductility coefficient decrease gradually by increasing fcu. The stiffness degradation of specimens significantly slows down with the increasing of L/H and σcon, and the decreasing of eH. Finally, the trilinear skeleton curve model and the restoring force model are established by statistical regression, and the corresponding seismic design suggestions are given, and these can provide theoretical support for the seismic design of such composite beams in actual engineering.

Piezoresistive behavior in cement-based sensors: Nonlinear modeling and preliminary application

Self-sensing cement sensors detect stress/strain by measuring the fractional change in electrical resistivity. However, neglecting the nonlinear portion of the FCR-stress/strain curves may limit monitoring range. Existing functional models lack versatility and physical meanings of parameters. A new model based on Ramberg-Osgood relation, incorporating the gauge factor, fractional change in resistance, and strain was proposed to cover linear and nonlinear regions. To validate the model, compression and tension cement sensors made of ultra-high toughness cementitious composite and multi-walled carbon nanotubes were tested. Results from various types of cement-based sensors validated the model's versatility. A four-point bending test on a C70 steel-reinforced concrete beam with an embedded cement sensor confirmed the feasibility of the proposed functional model.

EXPERIMENTAL FLEXURAL STRENGTH OF GLASS FIBER REINFORCED POLYMER (GFRP) HYBRID REINFORCED CONCRETE BEAMS

Materials technology is an excellent opportunity to be developed industrially and on a needs scale according to the demands of society, namely supporting the environment, low maintenance, and long-term use. Using composite materials with reinforced polymers is a hot topic of discussion in civil engineering as new materials, strength/stiffness enhancers, or applications in building rehabilitation or renovation. Fiber Reinforced Polymer (FRP) is excellent as a new material because, in addition to being lightweight, corrosion resistant, and easy to work with, it also has high flexural strength, so it is a consideration to replace and or strengthen steel materials that are high in cost value. However, until now there has not been found the correct pattern or variant and volume of fibre so that it can be an alternative to the use of steel. The purpose of the study was to experimentally determine the flexural strength of Glass Fiber Reinforced Polymer (GFRP) hybrid beams either with steel reinforcement, with GFRP reinforcement, or with steel and GFRP combination reinforcement and different GFRP ratios (variants) through two-point load bending tests.The designed model is a development of a previous study that used one layer of 4 mm and produced a flexural strength smaller than the targeted flexural strength, so in this study, two layers of 8 mm were used. In addition, other experimental data that has been carried out from the literature is also used where the results of parametric studies provide evidence of the positive effect of hybrid steel and GFRP reinforcement ratios when obtaining GFRP models and volumes.The materials used to manufacture concrete beam test specimens 53x15x15 cm3 with quality of fc'35MPa have been tested according to SNI standards and meet both the minimum and maximum requirements specified. Based on the results of the material test, it is planned that the characteristic concrete quality fcr'=40.31 MPa, and based on the compressive strength test, the quality fcr'=41.68MPa is produced.The hybrid designed material with concrete or concrete and steel has been tensile tested with a maximum arcing load for the two layers = 8 mm variant; the tensile strength of the GFRP woven roving type with two layers 2 x 4 mm is 92.66 MPa. While plain steel reinforcement Diameter 8mm quality 280 MPa has a minimum tensile strength of 350 MPa (3.8 times the tensile strength of GFRP 8 mm).The results of testing and calculating the effect of GFRP as a substitute for steel reinforcement contributed to the flexural strength of concrete beams on average by 47.52%. In comparison, the contribution of flexural strength produced by concrete with steel reinforcement was 107.09%. The concrete variant of hybrid steel reinforcement and GFRP contributes to an increase in the average flexural strength of 117.02% > 4.8% compared to steel-reinforced concrete beams alone.

Atmospheric chloride-induced corrosion of steel-reinforced concrete beam exposed to real marine-environment for 7 years

Steel-reinforced concrete structure easily suffers from chloride corrosion when exposed to a marine atmosphere environment. In this work, OPC/slag concrete beams combined with loading were naturally exposed to My Island (Qingdao, China) for 7-years and their chloride distributions were investigated as well as carbonation and corrosion-products. The results show that a concentration (Cs,%)-time (t,month) relationship was obtained as Cs=0.022t for concrete surface-chloride. With the increasing corrosion-depth, twice chloride accumulations occurred and were located near the carbonation depth and frontier, respectively. Slag increased the depth and height of the first accumulation peak-value while exacerbating its faster decrease of chloride concentration compared to the control. The chloride increment in the tensile zone was greater than its reduction in the compressive zone. The chloride corrosion mainly occurred in the stirrup bends, where the inner corrosion products mainly contained α-FeOOH and γ-FeOOH while further transforming into Fe3O4 in its outer layer.

Experimental and numerical investigation of flexural behaviour of concrete beams reinforced with GFRP bars

To solve the issue of corrosion, the use of glass fibre reinforced polymer (GFRP) bars in reinforced concrete (RC) has emerged as a feasible option for conventional steel bar RC. Given that GFRP RC beams have different mechanical properties and behaviours than steel counterparts, a thorough investigation of the load–deflection behaviour, failure modes, and overall performance of GFRP RC beams via experimental, analytical, and numerical studies is required. Therefore, this study encompasses the experimental, analytical, and numerical investigation of GFRP RC beams. Total of 9 beams are experimentally investigated, three (3) reinforced with steel bars (10 mm dia) while six (6) reinforced with GFRP bars (10 mm and 16 mm dia). Experimental results reveal that GFRP RC beams exhibit lower load carrying capacity and more deflection than their steel equivalents, respectively. GFRP RC beams have a 32.4 % lower ultimate load and a 16 % higher ultimate deflection than steel RC beams for the same reinforcing ratio. Steel RC beams failed under tension control, whereas GFRP RC beams failed under compression control. Analytical models, primarily based on effective flexural stiffness, are used to predict the load–deflection behaviour of GFRP RC beams. Nonlinear numerical modelling of GFRP RC beams is carried out using ATENA 2D. The load–deflection responses obtained from analytical and numerical studies are compared with experimental results and found to be in good agreement. After the validation of numerical models, the behaviour of GFRP RC beams has been investigated using a thorough parametric research, which looked at the impact of concrete compressive strength, longitudinal reinforcement ratio, GFRP bar elasticity modulus, and shear span to depth ratio.

Effect of the NSM material and area on the flexural response of normal strength concrete beams internally reinforced with GFRP and steel bars

Strengthening the steel-reinforced concrete (RC) beams by fiber-reinforced polymer (FRP) elements have become common several years ago. Recently, the RC beams internally reinforced with FRP reinforcement, especially Glass FRP (GFRP) bars, became popular worldwide. The carbon FRP (CFRP) elements (strips and bars) were recently used to strengthen the internally GFRP RC beams. In contrast, using the GFRP elements to upgrade the RC beams, especially those with GFRP bars as the main tensile reinforcement, was rarely studied. In this paper, the GFRP bars were implemented as near-surface mounted (NSM) elements to upgrade the beams reinforced in their tension side with GFRP or steel bars. All beams were experimentally loaded in flexure using a four-point loading scheme. The experimentally studied parameters were the main tensile reinforcement area, NSM area, and main reinforcement properties. Moreover, a numerical model was established and validated using the available experimental data to investigate the impact of main and NSM materials properties and areas on RC beam response. The experimental results highlighted that increasing the internal and NSM GFRP area by 96% and 100 % increased the beam capacity by 61.6% and 59.7%, respectively, which underlined a slightly higher efficiency of the main reinforcement than NSM bars on the beam load capacity. In addition, substituting the main steel with GFRP bars for the beams upgraded with NSM GFRP reinforcement enhanced their capacities by 11.33–15.1%. This emphasized the great effect of the linear response of the FRP materials and their higher tensile strengths than steel on the interaction between the main and NSM reinforcement, especially after the steel yielding. The FE results showed the highest load capacity using CFRP and GFRP bars as main and NSM reinforcement for the simulated beams. Conversely, using CFRP bars as NSM strengthening was more efficient than GFRP bars for the RC beams with steel or GFRP bars.

Experimental and numerical study on seismic behavior of partially steel-reinforced concrete beam-to-steel tube column joint

Steel-reinforced concrete (SRC) beams are commonly used in the transfer structures of high- and super-high-rise buildings since concrete-encased steel elements have good resistance to buckling and seismic performance. However, the full-length steel shapes utilized in SRC beams are ineffective and pose many construction challenges. This study proposes a new steel-reinforced concrete beam-square steel tube (SST) column joint in which the SRC beam is embedded with a partial-length steel shape. Experimental tests are conducted on three joint specimens with varying cross-sectional dimensions of the SRC beam and lengths of the steel shape. The experimental results show that all the specimens exhibit good deformation, load-carrying capacity, and stable hysteresis responses. The three specimens demonstrate a considerable strength drop at drifts exceeding 5%. Besides, significant plastic deformation occurred at the column base region and in a limited region of the steel beam flange near the beam-column joint. Finite element models are developed to study the effects of single-side steel length, shear stud spacing, and thickness of beam concrete cover on the seismic performance of the proposed joint. The elastic deformations that caused the total column drift were theoretically analyzed. The predicted joint initial rotational stiffness using the proposed equation agrees well with the test and numerical results. The study’s limitations are also discussed.