Steel Reinforcement Ratio Research Articles

Flexural improvement of reinforced concrete beams strengthened with self-prestressing shape memory alloys

The study reported here aims to investigate the application of shape memory alloys (SMAs) in the form of strips for strengthening cracked reinforced concrete (RC) beams. The study proposes an innovative technique for prestressing RC beams by utilizing the shape recovery property of the alloy. Nine full-scale RC beams with a length of 3.75 m and a cross-section of 200 mm × 300 mm were categorized into three groups based on the steel reinforcement ratio, and tested under static loading. Three RC beams were used as control specimens and the other six were retrofitted with either one layer or two layers of SMA strips. The beams to be strengthened were exposed to an initial applied load before the installation of the SMA strip to simulate the deterioration scenario. SMA strips were retrofitted on the soffits of the deteriorated beams and activated by applying temperature from an external heat source while the temperature-deflection-strain measurements were monitored. Specimens were tested again up to failure to evaluate the strength improvement of the retrofitted specimens. Beams retrofitted with one layer of SMA experienced a deflection recovery up to 2.3 mm upon activation and an additional service load of up to 62%, whereas beams retrofitted with two layers experienced a deflection recovery up to 2.8 mm and an additional service load of up to 95%. In general, the deflection recovery was proportional to the ratio of the total reinforcement ratio after strengthening to the initial reinforcement ratio before strengthening. Therefore, tested specimens with two SMA layers experienced less improvement than specimens with one SMA layer. Finally, the experimental results were evaluated with two analytical methods: ACI method and the non-linear sectional analysis proposed by Oukaili.

Evaluation of shear behavior of short-span reinforced concrete deep beams strengthened with fiber reinforced polymer strips

The application of externally bonded fiber-reinforced polymers (EB-FRP) is known to improve the shear behavior of reinforced concrete beams. Nevertheless, the studies available in the literature are not sufficient to explain the shear behavior of the beams that have low shear span to effective depth ratios (av/d) and are strengthened with FRP and the interaction between the horizontal steel shear reinforcement and FRP strips. To fill these gaps in the literature, an experimental study involving twenty-two tests of deep beams with a low av/d and with different amounts of vertical and horizontal steel shear reinforcement was carried out. Both unstrengthened and strengthened with fully wrapped FRP strips beams were tested where the number of FRP layers, the spacing between them and the type of FRP material were varied. The experimental results showed that the FRP strips improved the shear and ductility capacities of beams with low av/d. In addition, as the vertical shear steel reinforcement ratio in the beams strengthened with FRP strips increased, the percentage increases in the shear and deflection capacities decreased. Also, as the horizontal shear steel reinforcement ratio in the strengthened beams increased, the percentage increase in the shear capacity increased. Finally, a new equation was proposed to estimate the FRP contribution to the shear capacity. To prove the reliability of the proposed equation, a comparative study was conducted using twenty existing equations.

The Experimental and Theoretical Effect of Fire on the Structural Behavior of Laced Reinforced Concrete Deep Beams

A Laced Reinforced Concrete (LRC) structural element comprises continuously inclined shear reinforcement in the form of lacing that connects the longitudinal reinforcements on both faces of the structural element. This study conducted a theoretical investigation of LRC deep beams to predict their behavior after exposure to fire and high temperatures. Four simply supported reinforced concrete beams of 1500 mm, 200 mm, and 240 mm length, width, and depth, respectively, were considered. The specimens were identical in terms of compressive strength ( 40 MPa) and steel reinforcement details. The same laced steel reinforcement ratio of 0.0035 was used. Three specimens were burned at variable durations and steady-state temperatures (one hour at 500 °C and 600 °C, and two hours at 500 °C). The flexural behavior of the simply supported deep beams, subjected to the two concentric loads in the middle third of the beam, was investigated with ABAQUS software. The results showed that the laced reinforcement with an inclination of 45˚ improved the structural behavior of the deep beams, and the lacing resisted failure and extended the life of the model. The optimal structural response was observed for the specimens. The laced reinforcement improved the failure mode and converted it from shear to flexure-shear failure. The parametric study showed that the lacing bars remarkably improved the strength of the deep beams and they were not affected more by the steady-state temperature and duration. Furthermore, a greater increase in load-carrying capacity was associated with an increase in the flexural diameter of approximately 12 and 16 mm by approximately 24.77% and 87.61%, respectively, compared to the reference LRC deep beams.

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.

Compressive behaviour of circular steel tube confined reinforced concrete (STCRC) columns considering shrinkage and creep

Thin-walled steel tube confined reinforced concrete (STCRC) columns are increasingly used in high-rise and heavily loaded structures. One concern is whether concrete shrinkage affects the load resistance of STCRC columns, as the confinement to the concrete may become less effective when the concrete shrinks. This paper presents ultimate tests on STCRC columns after subjected to 490-day-sustained-loading or 490-day-shrinkage. The compression tests are conducted on specimens with different steel ratios, reinforcement ratios, concrete strengths and steel-concrete interfacial bonding conditions, or with long-term load first applied at different concrete ages. The sustained load history and the shrinkage effects on the short-term axial stiffness, ultimate strength, and peak strain of STCRC columns are investigated. The development of confinement effects and the tube's axial stiffness contribution after shrinkage and creep history are compared against those test results without experiencing shrinkage or long-term load history. A non-linear finite element model is finally developed for the ultimate response prediction of STCRC columns with the consideration of the creep and shrinkage history, and its accuracy is compared against the test data. The results show that concrete shrinkage and creep significantly affect the occurrence and development of the confinement effects, but not the confining pressure at the peak load. The axial stiffness and peak strain of STCRC columns are sensitive to time effects, while the ultimate strength is not. Under service loading, the tube's contribution to the axial stiffness of STCRC columns is negligible due to concrete shrinkage, while at the ultimate strength limit state condition, the column compression resistance is barely influenced by shrinkage and creep effects. The proposed FE model achieves reasonable accuracy in evaluating the ultimate responses of STCRC columns considering the shrinkage and creep effects.

Torsional behavior of FRP-strengthened reinforced concrete members considering various wrapping configurations: Theoretical analysis and modeling

Reinforced concrete (RC) structural members such as spandrel, flanged and curved beams, slab beams, and bridge girders may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, very little is known about the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, very limited guidelines apply to the design of externally bonded FRP systems for torsional strengthening, and no design provisions exist for the U-wrapped and 2-sided strengthening systems in torsion. This study aims to contribute to this growing area of research by developing a new analytical model to predict the full torsional response of strengthened RC members with many conventional configurations such as spiral, transverse and longitudinal FRP, continuous and intermittent strips along the beam length, side bonded, and full-wrapped systems. Moreover, this study provided an analytical model accurately predicting the contribution, efficiency, and failure mode of side-bonded strengthening systems. Additionally, the influence of various parameters such as FRP stiffness and transverse steel reinforcement ratio is taken into account in the constitutive law of concrete and internal reinforcement for the first time. The good agreement between the test results of 32 collected FRP-strengthened RC beams from the literature and the theoretical ones, which were predicted through programming proves the validity and accuracy of the presented theory.

Experimental investigation on alternate load path mechanisms in double-span beams with unsymmetrical span lengths and reinforcement ratios

In the design and assessment of reinforced concrete (RC) structures against progressive collapse via single column removal scenarios, also known as the “alternate load path (ALP) method”, the development of secondary mechanisms in double-span beams, i.e. compressive arch action (CAA) and catenary action (CA), has been thoroughly investigated and identified in many previous studies. The majority of the experimental tests were conducted on symmetrical double-span beams (identical span length and steel reinforcement ratio for both beams). However, variations in span length and reinforcement details of beams adjacent to one another are common in RC buildings due to architectural requirements. Hence, an experimental study with a total of 6 tests was conducted to investigate the development of ALP mechanisms (CAA and CA) in double-span RC frames with unsymmetrical 1) span length and/or 2) longitudinal reinforcement ratio. The 6 tests included 3 symmetrically-designed specimens that served as the baseline to facilitate comparison and quantification of the ALP development for the other 3 unsymmetrical continuous beams. The behaviour and development of ALP mechanisms in all the 6 specimens were analysed at structural level including general observations and measurements of the external forces, displacements, and strains. Last but not least, a simplified method that was initially developed based on symmetrical test data was employed to validate unsymmetrical test results, with the aim to provide a robust and simple tool for preliminary design considerations of the ALP mechanisms.

Experimental and numerical investigations on RC beams flexurally strengthened utilizing hybrid FRP sheets

During structural evaluations and inspections of existing buildings to determine their soundness, a number of structural defects are usually identified, especially in older buildings whose functional lifespan and safety could be increased by timely retrofitting or rehabilitation operations. Due to their superior performance as reinforcing material for restoration projects, fiber reinforced polymer (FRP) composites are widely used in various civil engineering applications. This research study focuses on the execution of, reinforced concrete (RC) beams whose flexural strength is significantly improved with the usage of hybrid-FRP (HFRP) composites, a combination of aramid-FRP (AFRP) and glass-FRP (GFRP) laminates/sheets. Five RC beams are cast and tested using a four-point bending configuration as sample for experimental and numerical studies. The steel reinforcement ratio used for designing RC beams is 0.47%. The thickness of HFRP laminates is the main varied test factor used in this investigation. One of the five beams is designated as the control beam, while the other four were strengthened using HFRP laminates. The findings of the present study demonstrate that using HFRP laminates effectively improves the load-bearing capability of the RC beams. However, using thicker HFRP sheets to increase strength is not advised because flexural strength is controlled by epoxy properties and surface quality of the concrete. According to the experimental findings, the increase in the ultimate load of the HFRP3-strengthened beam (SH3) is noted to be 202.63%, as compared to the control beam. Furthermore, the experimental outcomes are compared with that of the finite element (FE) analysis using a finite element software and it is observed that there is good agreement between these results.

Effect of Fire Flame (High Temperature) on the Behaviour of Axially loaded Reinforced SCC Short Columns

Experimental research was carried out to investigate the effect of fire flame (high temperature) on specimens of short columns manufactured using SCC (Self compacted concrete). To simulate the real practical fire disasters, the specimens were exposed to high temperature flame, using furnace manufactured for this purpose. The column specimens were cooled in two ways. In the first the specimens were left in the air and suddenly cooled using water, after that the specimens were loaded to study the effect of degree of temperature, steel reinforcement ratio and cooling rate, on the load carrying capacity of the reinforced concrete column specimens. The results will be compared with behaviour of columns without burning (control specimens). The results showed that, the ultimate load capacity of columns exposed to fire decreases with increasing the fire flame temperature. At burning temperature 300 Co , 500 Co and 700 Co , the average residual ultimate load capacity for gradually cooled specimens were 91%, 81% and 71% respectively. By increasing the ratio of longitudinal reinforcement 44% , the maximum improvement in the ultimate load capacity was 24% and 17% for the gradually and sudden cooling respectively at Co 500 . For the same longitudinal reinforcement ratio and fire burning temperature, the ultimate capacity for the sudden cooling specimens was less than that of gradually cooled specimens by about 10%.

Numerical Investigation on the Performance of Exterior Beam–Column Joints Reinforced with Shape Memory Alloys

Upgraded design standards coupled with the damage caused by natural disasters have led to the development of smart materials with the potential to modernize current construction practices. This investigation proposes a nonlinear finite element (FE) model for evaluating the performance of beam–column joints (RC-BCJ) reinforced with shape memory alloys (SMA) and steel rebars. The model was validated based on accredited experimental data, followed by parametric analysis in ABAQUS to optimize the use of SMA bars for enhancing the seismic resistance of RC-BCJ without compromising their energy dissipation capacity. Parameters investigated include the (a) SMA–steel reinforcement ratio, (b) lengths of SMA bars, (c) elastic modulus of SMA, (d) compressive strength of concrete, and (e) axial load applied on the column. The finite element simulation results indicated that the model was capable of predicting the optimum length of SMA bars sufficient for relocating the plastic hinge away from the face of the column along the beam. Further, simulation results proved that the use of SMA bars in conjunction with steel reinforcement could be considered as an effective tool for enhancing the seismic performance of RC-BCJ joints. Among the parameters investigated, high-strength concrete was the most effective in improving joint resistance.

Confinement effect of two‐way beam‐and‐slab system on the effective compressive strength of interior concrete columns

AbstractMultistory concrete buildings may resort to the strategy to cast columns and slabs with high and normal compressive concrete strength, respectively. Current design codes propose expressions to specify the effective compressive strength of interior columns confined only by flat slabs or beams with the same width as the column. However, when thin slabs and narrower beams are used, the confinement may not be enough to increase the lateral stress. The structural behavior of these interior columns is investigated in this paper using numerical nonlinear models. The influence of concrete strength column‐slab ratio, the steel reinforcement ratio of the column and the beam, beam height and the column width ratio and the biggest dimension of the column's cross section were tested with and without vertical load on the beam. The results were compared with expressions found in the literature.

Effectiveness of Strengthening RC Beams Using Composite Materials—An Accelerated Strengthening Method

The article analyses the results obtained from tests of preloaded reinforced concrete beams strengthened with carbon fibre strips bonded into the concrete reinforcement cover (NSMR method). Adhesive (thixotropic epoxy resin) bonding takes 7 days at 23 °C. The strengthening process was accelerated by heating the strip using a prototype heating device. Tests on the reinforced concrete members confirmed that accelerating the strengthening process is feasible and allowed the selection of the optimal heating temperature to provide the greatest strengthening level. The study primarily aimed to analyse the effectiveness of strengthening applied to the bottom of reinforced concrete beams under sustained loading throughout the adhesive curing process, simulating real conditions on site. Significantly higher strengthening efficiency was achieved with the use of strip heating, which accelerated adhesive cure time and reduced the strengthening execution time from 7 days to 1.5 h. The analysis included the evaluation of the effect of the steel and composite reinforcement ratios on strengthening effectiveness.

An Experimental and Numerical Analysis of the Flexural Performance of Lightweight Concrete Beams reinforced with GFRP Bars

Occasionally it is more crucial to lower the mass of a building component than to improve its rigidity, specifically in massive buildings like long-span structures where the self-weight of the floors is one of the significant challenges that engineers confront. Therefore, the main objective of this work is to explore the flexural performance of Lightweight Concrete Beams (LWCBs) reinforced with Glass Fiber Reinforced Polymer (GFRP) bars in terms of curvature, cracks and failure modes, deflection, material stress-strain relationship, and joint end rotation. The flexural performance of LWCBs reinforced with varied GFRP bars and Steel Reinforcement (SR) ratios is assessed and compared to that of Normal Concrete Beams (NCBs) reinforced with SR. Numerical analytical models for the tested beams were created utilizing the iDiana software. Both analytical and experimental test results were compared. The study revealed a high correlation between the findings of Finite Element Models (FEMs) and those acquired from beam testing. The performance of LWCBs that utilized SR was equivalent to that of NCBs. The GFRP-reinforced LWCBs performed mostly as elastic deformed elements, with just little deflection post-load release. The study emphasized the significant potential for employing LWC and GFRP bars in the construction field's growth.

Assessment of seismic retrofitting interventions in reinforced concrete structures

Destruction of reinforced concrete (RC) structures, particularly non-ductile RC structures, in recent earthquakes demonstrate their vulnerability under lateral forces generated in an earthquake. Despite the extensive literature on the subject and the wide variety of strengthening techniques available, there is no consensus on the efficiency of these techniques in improving the seismic performance of RC structures. In this study, a five-storeyed RC-framed building is considered to evaluate its seismic performance through static non-linear pushover analysis. To examine the effect of various cases encountered in practice, the pushover analysis is carried out on the RC frame for various cases, i.e. a bare RC frame, an RC frame with masonry infills but with an open ground storey, and RC frames with shear walls with a variety of thicknesses and steel reinforcement ratios. Further, to investigate the effect of retrofitting, the RC frame is strengthened using local jacketing and bracings. From the results, it is observed that the initial stiffness and base shear of masonry infilled RC frame with an open ground storey exhibit an increase of 2.6%, and 19%, respectively, as compared to the bare frame. The use of shear walls increases the initial stiffness and base shears, and they increase by 6–14% and 8–20%, respectively, with an increase in the reinforcement ratio in the shear wall. Retrofitting with the use of both diagonal bracings causes the base shear to increase by a factor of 7.7 as compared to that of the open ground storey. Finally, the probability of damage to the RC frame in all cases was compared using seismic fragility curves.

Machine learning-based models for predicting the shear strength of synthetic fiber reinforced concrete beams without stirrups

Stirrups can be added to reinforced concrete (RC) beams made of plain concrete to increase the shear strength providing better performance against embrittlement. If the need for shear stress is less than the strength of RC beams, reinforced with the minimum number of stirrups, then this choice might not be the most cost-effective. Synthetic Fiber Reinforced Concrete (SyFRC) in Reinforced Concrete (RC) structures is limited due to the lack of predicting models for this emerging material in current literature. However, recent advances in concrete technology have revealed more significant benefits of SyFRC, including high deformation capacity and less corrosive concrete. This study predicts shear strength of SyFRC beams without stirrups using the ACI 318-19 equation in addition to Machine Learning (ML) methods such as LightGBM, XGBoost, and Gene Expression (GEP). A database of 102 tested SyFRC specimens were compiled, processed, and evaluated. With R2 values of 98.91% and 97.22%, respectively, the LightGBM and XGBoost outperformed the other examined algorithms by having the least predictions discrepancy and highest accuracy values. As the ACI 318-19 equation does not account for the fibers volume ratio and shear span-to-depth ratio effects on the shear strength contribution, it projected shear strength with the lowest degree of accuracy, with R2 = 75.5%. The feature importance analysis revealed that these two factors, in addition to the effective beam depth, beam width, longitudinal steel reinforcement ratio, and concrete compressive strength should not be negligible in shear strength prediction. For forecasting the shear strength, a closed-form GEP-based model was suggested. The proposed GEP model has a little lower prediction accuracy with R2 = 88.4%. The performance of the four examined models was evaluated from various perspectives. The analysis shows that, apart from the ACI equation, all considered models effectively predict the effects of shear span-to-depth ratio. This is critical for investigating deep and slender beams, and size effect, which are critical for beams with high effective depths. The current study's findings should give practitioners a solid platform for making precise and straightforward assessments of shear strength.

Mechanical performance of spun-cast full-scale precast pipes incorporating hybrid conventional rebar cage and steel fibers

Precast reinforced concrete (RC) pipes are an important component of urban infrastructure for conveyance of stormwater and sewage disposal. This study investigates the mechanical performance of spun-cast precast full-scale pipes under three-edge bearing test (TEBT) and patch or point load tests for replicating the field loading scenarios. Six types of precast pipes incorporating various amount of conventional rebar reinforcement and local steel fibers were tested. Straight steel fibers of 25 mm length were cut from locally manufactured long steel wires. Two steel fiber dosages (i.e., 20 kg/m3 and 40 kg/m3) in concrete mixture were examined for mechanical behavior of pipes along with conventional rebar cage. It was observed that full-scale precast pipes without steel fibers and conventional rebar cage failed in an abrupt manner into various pieces. However, pipe made with concrete mixture incorporating steel fibers only without conventional rebar cage also failed into pieces but showed post-peak behavior and fiber crack bridging phenomena. Pipes having double conventional steel reinforcement ratio showed 60% higher ultimate load. Pipes incorporating 20 kg/m3 and 40 kg/m3 along with conventional rebar cage showed 10% and 30% higher ultimate load compared to that of identical pipe without steel fibers. Improved deflection softening and hardening behaviour were observed for pipes with fibers. Furthermore, multiple secondary cracks were observed during TEBT for pipe specimens incorporating fibers. Similarly, higher ultimate load and improved cracking behavior was observed under patch load for pipe specimens incorporating steel fibers. All the tested pipes incorporating steel fibers and conventional rebar cage satisfied the Class III and Class IV requirements of ASTM C76. It can be envisioned that the implementation of hybrid spun-cast pipes incorporating conventional rebar cage and local steel fibers lead towards the development of economical pipes for controlling the premature cracking and improved structural behaviour.

Experimental investigation on ultra high-performance concrete beams without shear reinforcement

Seven ultra high-performance concrete (UHPC) beams without shear reinforcement are tested in this work to examine their structural behavior as shear failure is a major concern in such members. Coarse aggregate was not used in two of the beams while the other five are made with coarse aggregate as 50% replacement of fine sand. Three longitudinal steel reinforcement ratios (1.14%, 1.64% and 2.46%) and three steel fiber ratios (0, 1% and 2%) are used. Results show that UHPC beams with coarse aggregate show higher ultimate loads (4.7% − 11.5%) than UHPC beams without coarse aggregate and incorporating 1% and 2% steel fiber raises ultimate loads by 60% and 131%, respectively for beams with coarse aggregate. Also, using 2% steel fiber changes failure mode from brittle shear failure by diagonal crack in beams of 0 or 1% steel fiber to ductile flexural failure by yielding of longitudinal reinforcement. Higher stiffness and toughness and lower deflections are observed with the increase of longitudinal reinforcement, steel fiber or coarse aggregate. Using 2% steel fiber highly improved toughness by more than 17 times. Lower rates of improvement are recorded for longitudinal reinforcement and coarse aggregate. However, it is recommended to perform more research to examine more parameters such as fiber types.

Shear transfer strength estimation of concrete elements using generalized artificial neural network models

Abstract Based on published test findings, this article outlines the use of artificial neural networks (ANNs) to forecast the efficiency factor of shear transfer strength in concrete. Backpropagation neural networks with feed-forward have been employed. The ANN model was created by incorporating a huge experimental database and carefully selecting the architecture and training procedure. The presented ANN model offered a more accurate tool to compute R (where R is a measure of the closeness of association of the points in a scatterplot to a linear regression line based on those points) and capture the impacts of five primary parameters: concrete compressive strength, steel reinforcement ratio, steel yield strength, fiber volumetric ration, and steel fiber aspect ratio are given from experimental data. The obtained results reveal that the first important parameter is concrete compressive strength. In addition, ρ y f y parameter represents the normalized tensile force in steel reinforcements of section, whereas the smallest importance parameter L/D is aspect ratio of steel fibers. Also, the current study illustrated the facilities of using generalized artificial neural networks on predicting the shear transfer strength across the concrete sections, whether they are fibrous or not. From the results, the correlation factor (R 2) is estimated to be about 83%, which means it had a good correlation within the input parameters. In addition, the mean absolute percentage error was 2.06.

Flexural Performance and End Debonding Prediction of NSM Carbon FRP-Strengthened Reinforced Concrete Beams under Different Service Temperatures

This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (Tg) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy Tg), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.

Effect of ECC layer thickness and reinforcement ratio on the load carrying capacity of steel‐reinforced composite beams

AbstractThe present study investigates the effect of Engineered Cementitious Composites (ECC) layer thickness against various reinforcement ratios on the flexural performance of reinforced ECC–concrete composite beams. In total, 20 reinforced composite beams are selected from the literature to predict their flexural response using Finite Element (FE) analysis. In addition to the FE analyses, a detailed analytical study is performed using the strain compatibility procedure to predict the flexural strength of ECC–concrete composite beams. The results from the FE analyses are compared against the experimental results and are found to show a close agreement. Using the validated FE models, detailed parametric studies are conducted to determine the effectiveness of different design parameters such as (a) ECC height replacement for a reinforcement ratio, (b) reinforcement ratio for an ECC height replacement, and (c) adequate reinforcement ratio for effective strengthening. The results of the parametric study show that the use of 0.4 ECC height replacement ratio and 1.70% steel reinforcement ratio exhibit better load‐carrying capacity in ECC–concrete composite beams. The effective tensile reinforcement ratio for the ECC–concrete composite beams from minimum to maximum varies in the range of 0.92%–1.85%, respectively. The moment capacities predicted from the section analysis is in good agreement with the experimental and numerical moment capacities.