Strength Of Reinforced Concrete Research Articles

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Hybrid Fiber Reinforced Polymer Systems using ANSYS

Background: Existing reinforced concrete (RC) structures can deteriorate over time due to aging, poor construction design, natural disasters, etc. In recent years, fiber-reinforced polymer (FRP) composite materials are becoming a preferred choice for concrete construction repair due to their durability, high strength, and corrosion resistance. This study aimed to study and analyze the properties of the constituent materials to identify any weaknesses and potential improvements. Methods: The present study investigated the effectiveness of flexural strengthening of RC beams using a hybrid grouping of glass-FRP (GFRP) and carbon-FRP (CFRP) unidirectional laminates. ANSYS finite element analysis (FE) software was used to investigate the failure modes of the beams and the stress-strain parameters. The impact of adopting two different grades of reinforcing bars in RC beam modeling was also contrasted in the study. Results: Comparisons between the finite element analysis and experimental literature results were made. Based on the test findings, it could be concluded that retrofitted beams perform better than non-retrofitted beams. According to experimental results, the HY14 sheet enhanced beam had a 188.46% higher ultimate load than the unenhanced beams. Conclusion: Comparing experimental findings to the conclusions of the numerical analysis, a maximum difference of ultimate load and deflection at mid-span of 3.40% and 4.91%, respectively, were used to assess the accuracy of the results.

Near-surface Mounted Technology in Strengthening Reinforced Concrete Beam

Structural strengthening is essential in civil engineering to ensure the integrity, safety, and longevity of various types of structures. Effective strengthening is required to solve these issues and lengthen the service life of structures as they naturally deteriorate with time. Hence, the use of various strengthening techniques to enhance the structural integrity of existing structures and infrastructure has gained prominence in recent years. This study demonstrates how Reinforced Concrete (RC) structures may benefit from Near-Surface Mounted (NSM) technology. The demonstration involves the experimental study on the performance of three different types of RC beams; unstrengthened RC beam, RC beam strengthened with NSM procedure using a conventional steel ribbed bar, and RC beam strengthened with NSM procedure using an iron-based smart memory alloy (Fe-SMA) ribbed bar. Consequently, three RC beams were evaluated at room temperature throughout the experimental testing, while the remaining three RC beams were examined after being exposed to a 200°C temperature exposure. The load-deflection, strain deformation and crack propagation were demonstrated to determine the behaviour of the RC beam. The experimental findings suggested that the performance of RC beams strengthened using NSM techniques was superior to that of RC beams that had not been strengthened. Although the results generally indicated a decrease in ultimate load obtained in the RC beams exposed to elevated temperature compared to RC beams tested at room temperature. It is shown that Fe-SMA RC beams performance better compared to steel strengthened RC beams. The RC beams strengthened with an Iron-based smart memory alloy ribbed bar recorded an increase in load-carrying capacity. These results demonstrate the substantial variations in load-bearing capacities among the beams and emphasise the efficiency of the strengthening application for RC beams in the constructions industry, particularly the use of iron-based smart memory alloy ribbed bars as strengthening materials.

Shear strengthening of reinforced concrete T-beams with anchored fiber-reinforced polymer composites

T-shaped beams are widely used in reinforced concrete (RC) structures, both buildings and bridges. Under-designed shear reinforcement and long-term aging make these structural elements susceptible to shear failure during earthquakes. The currenlty availalbe experimental work investigating the retrofit of these beams against shear failure is very limited. In this work, the external strengthening of RC T-beams with splay anchored strips of fiber reinforced polymer (FRP) composites under cyclic shear loading for the cases of normal and high strength concrete was studied. Six beams with 3.05 m length and 0.46 m that were conservatively reinforced against flexural failure were designed. The shear reinforcement of the beams was sufficiently high to ensure the dominance of shear failure. Three of the beams were built using a normal strength concrete and the other three were built using a high strength concrete with 28-day strengths of 30.5 MPa and 44.0 MPa, respectively. From each group of normal and high strength RC beams, one beam served as the reference. The other two beams were retrofitted with external strips of FRP composites that were bonded on the web and anchored under the flange of the beams. The beams were tested under cyclic four-point loading to evaluate the performance of the FRP retrofitting system against shear failure under simulated seismic loading. The deflection and the strain in the FRP composites were recorded while monitoring the strain of the longitudinal reinforcement to ensure an elastic response in flexure. The reference beams failed by shear cracking and the retrofitted beams failed by shear cracking and FRP delamination. The retrofitting technique increased the shear capacity of the beams by up to 37% and 20% for the normal and high strength beams, respectively, and promoted the beam ductility prior to failure.

Cementitious Resins for Strengthening Reinforced Concrete Beams with Near-Surface-Mounted Carbon Fiber-Reinforced Polymer

Cementitious Resins for Strengthening Reinforced Concrete Beams with Near-Surface-Mounted Carbon Fiber-Reinforced Polymer

The Effect of Binder Types of Strengthening Panel for Shear Strengthening Reinforced Concrete Beams

This paper presents the shear behavior, crack patterns, and failure modes of reinforced concrete beams strengthened with geopolymer and Portland cement mortar panels. The specimens were prepared in the form of geopolymer and Portland cement mortar panels with a size of 300 mm x 700 mm, each consisting of 4 pieces. The reinforced concrete beams specimen were produced with dimension of 150 mm x 300 mm x 2300 mm and static monotonic loading test was carried out. To ensure the strength of the geopolymer and concrete used is in based on the target, a compressive strength test is carried out at the age of 28 days, with 3 samples each. According to the results of the loading test of reinforced concrete beams, the maximum load on the beam strengthed with geopolymer and Portland cement mortar panels increased by 34.98% and 29.54%, respectively, compared to the control beam. The addition of panels to reinforced concrete beams causes it’s behavior to change, becoming more ductile. This also has an impact on the crack patterns and failure modes. CB beams experience shear failure, which is indicated by the appearance of diagonal cracks along the shear area to the point of loading, whereas mortar panel reinforced beams experience flexural failure.

Prediction of Deflection Behavior of NSM Strengthened Reinforced Concrete Beam Using Fuzzy Logic

Abstract This paper aims to present a deflection prediction model of Near Surface Mounted (NSM) Reinforce Concrete (RC) beams using the Fuzzy Logic Expert System (FLES) with different types of membership functions (MF). The absence of a complete theoretical deflection prediction model of NSM-strengthened RC beams persuades this research to develop an Artificial Intelligence (AI) based prediction model using FLES. The proposed model uses triangular and trapezoidal MF to predict the deflection behavior of six NSM-strengthened RC beams. The research variables are strengthening materials and NSM bar length. In this study, two inputs (applied load and variable length) were used to predict two outputs (deflection of two types of strengthened RC beams). The relative error of predicted values was within 5% and the suitability of fit was close to 1.0 which affirms the efficacy of the FLES. Besides, a tiny difference was detected using triangular and trapezoidal MF for the prediction model.

Fatigue response of RC beam strengthened by BFRP laminate

Strengthening RC structures become more essential due to its deterioration, updating in new design codes, lack of quality control, and changes in the use of the structure. The technique of external bonding fiber reinforced polymer is recognized as a convenient method for repairing existing reinforced concrete structures and provides immediate shelter rather than replacement of the whole existing structure. Basalt Fiber Reinforced Polymer gaining more demand in recent research due to its eco-friendly properties. In this regard, this research investigates the efficaciousness of externally bonded Basalt Fiber Reinforced Polymer (BFRP) laminates in the reinforced concrete beam under repeated load. BFRP is externally bonded at the soffit of reinforced concrete (RC) beams to enhance its fatigue resistance. The load-deflection relationship, stiffness, crack pattern, and energy dissipation capacity of the BFRP-reinforced concrete beams are experimentally investigated and validated with the ANSYS simulated results. The experimental results exhibits that the BFRP reinforced concrete beams enhances the fatigue response, load carrying capacity and prevention of premature failure. The numerical results are validated with the experimental results which are found to be correlated with negligible deviation. Also, both investigations reveal the failure mode of RC beams, which helps fatigue life prediction in its application.

Flexural strengthening of RC columns with EB-CFRP sheets and NSM-CFRP rods and ropes

Externally bonded (EB) and near-surface-mounted (NSM) systems have been investigated in the literature to be used in flexural strengthening of reinforced concrete (RC) columns. Research has shown that NSM-FRP systems are preferred in most cases over the use of EB-FRP systems especially in flexural strengthening RC columns against lateral loads. However, limited studies have been conducted to accurately compare the behavior of columns strengthened with EB-FRP or NSM-FRP systems. In this study, six specimens were fabricated and tested. To add to the novelty of this investigation, CFRP ropes were used for the first time in flexural strengthening of RC columns against cyclic lateral loads. Two of the columns were strengthened with NSM-CFRP ropes, one with NSM-CFRP rods, one with EB-CFRP sheet, and one with CFRP lateral confinement only. The results showed that both EB-CFRP and NSM-CFRP techniques can improve the flexural resistance of RC columns. The percentage of enhancement in lateral resistance ranged from 35% to 60%. Limited slippage of NSM-CFRP rods was an advantage and led to a more ductile response. Finally, theoretical analyses were performed to predict the lateral response of strengthened RC columns. The predicted load–displacement relationships had good agreement with the experimental results.

Effect of Wire-Mesh Type on Strengthening Reinforced Concrete Beams

Structural strengthening is a method of application to raise the load-ability capacity of building structures to meet the building's need to carry additional and unexpected loads that were not accounted for in the main design. In this study, Ferro-cement was used for strengthening concrete beams. Three locally available wire mesh types were used with an ordinary cement mortar to strengthen reinforced concrete beams under flexural loading. The results show that using a Ferro-cement layer with wire mesh of 15 mm size square opening has the best effect on increasing reinforced concrete beams' bearing capacity and deflection more than when using the other two types of meshes. The first crack and failure load increases were 72 and 79%, respectively. In contrast, the deflection increased 70 and 51% at the first crack and failure load.

Investigating Fibre Reinforced Concrete's Strength, Flexibility, and Longevity

There have been several difficulties with mesh-reinforced lining constructions because to the complex tunnelling circumstances and varying technical requirements. Thereafter, steel fiber reinforced concrete (SFRC) is promoted as a trustworthy replacement for mesh-reinforced linings. In this study, we take a look at the components and typical characteristics of SFRC. Cracks or structural failures in mesh-reinforced linings are summarized, and contemporary difficulties in this field are discussed. Tunnel linings made from SFRC are discussed, along with the benefits of doing so. In addition, the performance of SFRC in tunnel lining applications is reviewed, along with various design considerations and practical instances. The evaluation found that SFRC lining had a favourable impact on limiting rock movement, decreasing lining pressure, and ensuring both global and local support structure integrity. The study provides useful information for advancing the use of SFRC

Explainable machine learning using real, synthetic and augmented fire tests to predict fire resistance and spalling of RC columns

This paper presents the development of systematic machine learning (ML) approach to enable explainable and rapid assessment of fire resistance and fire-induced spalling of reinforced concrete (RC) columns. The developed approach comprises an ensemble of three novel ML algorithms namely; random forest (RF), extreme gradient boosted trees (ExGBT), and deep learning (DL). These algorithms are trained to account for a wide collection of geometric characteristics and material properties, as well as loading conditions to examine fire performance of normal and high strength RC columns by analyzing a comprehensive database of fire tests comprising of over 494 observations. The developed ensemble is also capable of presenting quantifiable insights to ML predictions; thus, breaking free from the notion of “black-box” ML and establishing a solid step towards transparent and explainable ML. Most importantly, this work tackles the scarcity of available fire tests by proposing new techniques to leverage the use of real, synthetic, and augmented fire test observations. The developed ML ensemble has been calibrated and validated for standard and design fire exposures and one-, two-, three- and four-sided fire exposures thus; covering a wide range of practical scenarios present during fire incidents. When fully deployed, the developed ensemble can analyze over 5,000 RC columns in under 60 s; thus, providing an attractive solution for researchers and practitioners. The presented approach can also be easily extended for evaluating fire resistance and spalling of other structural members under varying fire scenarios and loading conditions and hence paves the way to modernize the state of this research area and practice.

Width Effect of Composite Material on its Tensile Behavior at Strengthening Reinforced Concrete Structures

Width Effect of Composite Material on its Tensile Behavior at Strengthening Reinforced Concrete Structures

Experimental and theoretical analyses of the progressive collapse resistance of NSM strengthening RC frames after the failure of a corner column

When exposed to accidental loads, reinforced concrete (RC) frames are vulnerable to progressive collapse after the failure of a corner column, so necessary strengthening schemes should be employed for the frame. By strengthening the slab with near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) layer, this study experimentally revealed the effect of the strengthening method on the progressive collapse behavior of beam-slab systems after the removal of a corner column. Then, on the basis of experimental results, a theoretical analysis method of the peak capacity for the beam-slab system is proposed according to the principle of virtual work and the yield-line theory. The derived formula can accurately predict the progressive collapse resistance of the RC beam-slab system after the failure of a corner column and quantitatively evaluate the contribution of floor slabs to the structural capacity. The validity of the method is also proven by the application to the structural capacity of a flat-slab system and a beam-column system. Finally, according to the theoretical formula, the influence of several parameters on the structural capacity is investigated, such as the earthquake fortification intensity of the frame, the over-strength factors, the column spacing, and the depth-to-span ratio of the beam. The research results demonstrate that after considering the L-beam action, the capacities of the test specimens can be improved by 52%–65%. The capacity of the flat-slab system is the lowest among the above three structural systems. The structural progressive collapse resistance can be effectively improved through enhancing the constraint stiffness of the corner beam-column joint and utilizing building materials with high plastic development ability.

Reliability of Steel-Fiber Reinforced Polymer Strengthened Reinforced Concrete Bridge Columns

AbstractThe reliability of reinforced concrete (RC) bridge columns strengthened with externally bonded, steel-fiber reinforced polymer (SFRP) fabric subjected to blast loads was investigated. Colum...

ASSESSMENT OF NOMINAL SHEAR STRENGTH OF REINFORCED CONCRETE COLUMN

: SNI 2847-2019 and ACI 318-19 have regulated the use of materials in the design for shear strength. This study presents an evaluation of nominal shear strength in Reinforced Concrete (RC) column from SNI 2847-2019 and ACI 318-19 by variants of the RC columns experimental database. RC column variants consist of normal strength and high strength RC column with a total of 162 specimens. Furthermore, the database also provides a variety of shear span to depth ratio and axial-load ratio. In this study, the calculation was carried out the mean and the coefficient of variation of measured to calculated strength ratio which is according to SNI, ACI, and other experimental models. Both SNI 2847-2019 and ACI 318-19 have 2 different (concrete nominal shear strength) equations. The calculation results show that the equation is more conservative in both SNI and ACI compared to other nominal shear strength equations. Overall, the combination of both normal strength and high strength RC columns, the calculation using ACI 318-19 with the first nominal shear strength equation can be said to be more conservative than any other calculations models. This study also shows that by using the ACI 318-19 model in the second equation which is used the size effect modification factor , the results do not have a significant effect because the value is close to 1.

The Effectiveness of the DIC as a Measurement System in SRG Shear Strengthened Reinforced Concrete Beams

Steel Reinforced Grout (SRG) materials are generating considerable interest as strengthening system of reinforced concrete (RC) structures. They are finding increasing use in several civil engineering applications mainly due to the advantages they offer over traditional material such as high strength to weight ratio, ease of application, durability and low price. This paper describes the results of an experimental investigation carried out on SRG shear strengthened RC beams and gives evidence of the Digital Image Correlation (DIC) effectiveness as a measurement system. The tests performed had two main objectives: (i) assess the effectiveness of continuous and discontinuous U-wrapped jackets comprising a different number of layers and strips; (ii) assess the shear crack distribution during the tests by means of the DIC measurements. The results confirmed that reinforcing RC beams with SRG jackets can increase the load-bearing capacity; when the beam was reinforced with a continuous two-layered SRG strip, an increase of 84% was observed (compared to the unreinforced beam). The Linear Variable Differential Transformers (LVDT) measurements validated the results obtained by means of the DIC.

Review on Strengthening Reinforced Concrete Columns Using Reinforced Concrete Jackets

This paper highlights the review of the effects of concrete surface treatment and loading on the structural behavior of reinforced concrete (RC) columns retrofitted with RC jackets. The concrete surface treatment aspect is assessed based on the surface roughness, use of dowel bars, use of shear connectors, and applying bonding agent between the column core and the jacket. However, the loading aspect is evaluated based on preloading history and the applied loading pattern. The latest researches and recommendations for concrete jacketing are presented. It is found that sand-blasting with the use of dowel bars or shear connectors helps the retrofitted column to behave monolithically. Preloading does not have a significant effect on the retrofitted column. However, it is recommended to apply the load on the full retrofitted cross-section.

Torsional behavior of solid and hollow concrete beams reinforced with inclined spirals

Enhancing the torsional capacity of reinforced concrete (RC) beams while maintaining reasonably economic and efficient cross-sections poses a practical challenge in the design of such elements. Thus, developing and testing economically viable reinforcing techniques for enhancing the torsional capacity of RC beams is a significant aspect. Among these techniques is the continuous spiral reinforcement system that has shown promising results in enhancing the torsional capacity of rectangular RC elements.In this study, the role of continuous rectangular spiral stirrups, as a transverse reinforcement with a controllable pitch (P) and inclination angle (θ), in enhancing the torsional behavior of rectangular solid and hollow RC beams has been investigated experimentally. The applied torque was directed to lock the spirals for all specimens. The experimental program of this investigation included testing of ten specimens of normal strength RC beams; two of which were solid with closed and spiral rectangular stirrups. While the rest of specimens were hollow specimens included one beam reinforced by closed stirrups and seven beams reinforced by rectangular spiral stirrups with different reinforcing ratios. Different variables were considered to develop a wide range of the beams’ reinforcing scenarios. This includes stirrups type (conventional closed stirrups and rectangular spiral stirrups), inclined stirrups ratio, pitch, inclination angle and finally the longitudinal reinforcement ratio. In addition, a three-dimensional finite element model using ANSYS-15.0 was developed to examine the capability of the model to capture the observed torsional behavior of the experimentally tested beams.The obtained results showed that using inclined spiral rectangular stirrups in reinforcing RC solid and hollow beams greatly enhanced the torsional capacity by about 16% and 18%, respectively compared to using the conventional closed stirrups. Moreover, the results showed that using that technique leads to higher twist- angles, more ductile failure and increased strain energy by about 27% and 16% for solid and hollow beams, respectively. Lastly, the comparison between the results obtained from numerical model and experimental results showed good agreement and thus the numerical model can be used to extend the experimental work for investigating different reinforcing schemes.

Experimental Research of Technology for Strengthening Reinforced Concrete Columns with Carbon Fibers

Reinforcement of columns (piers) is usually accomplished by increasing cross-section through building-up, injecting reinforcing solutions and external reinforcement. The most and progressive method for strengthening is currently external reinforcement, its essence is to glue high-strength sheets, plates or strips (lamellas) onto structure surface with the help of special adhesives. Scientists pay special attention to theoretical and experimental studies of design solutions for external reinforcement of vertical load-bearing structures. Unfortunately, the results of such studies, for example, influence of technology for execution of works on strengthening efficiency are virtually absent. Therefore, the objective of this paper is to carry out experiments with the purpose to study influence of technological factors on efficiency in strengthening of reinforced concrete structures, which absorb compressive forces. The experimental studies have been made in six series that changed the technology of executed works while using various technological factors. Among the main factors are the following: presence/absence of acute angles; preparation of a base (surface coating); method for gluing reinforcing materials to a structure. A criterion for evaluation of technology efficiency has been breaking strength for axial compression of reinforced samples. Analysis on the results of experimental studies has shown that the highest load-bearing capacity is achieved while using samples of columns with rounded edges, provided that an adhesive is applied to sample base and carbon fiber (40.6 tons). The compressive strength of such samples is by 82.2 % higher than the strength of control samples. The strength of reinforced specimens with non-rounded edges has appeared to be the lowest one, namely 34.0 tons. Strengthening of the samples with fiber impregnated with an adhesive has increased the indicator by 74.3 % compared to the control samples. The compressive strength of samples reinforced with carbon fiber adhered to the adhesive which is preliminary spread on the basis is equal to 38.6 tons, which is by 73.4 % higher than the strength of the control samples.

Efficiency of flexural strengthening RC beams using fiber reinforced polymer materials

The purpose of this study is to evaluate the efficiency of the flexural strengthening of reinforced concrete (RC) beams using the fiber reinforced polymer (FRP). The calculation procedures according to design standards including ACI 440.2R-17 and FIB-2019 are employed to assess the flexural capacity of strengthened RC beams. Three types of FRP materials, which are glass FRP (GFRP), aramid FRP (AFRP), and carbon FRP (CFRP), are used. For CFRP, three kinds of tensile strengths consisting of low (CFRP-L), medium (CFRP-M), and high (CFRP-H) levels are also utilized in calculations and assessments. A numerical model of FRP strengthening beam is developed in ANSYS and then verified with the results of design standards. Comparative studies on the efficiency of flexural capacity and cost benefit between the use of FRP sheets and a conventional retrofitting method are conducted considering a specific area of FRP sheets and 50% flexural strengthening target. The results reveal that flexural strength after strengthening based on ACI and FIB is very similar. The optimal options considering the strength and cost effects are CFRP-L and CFRP-M when using a constant area of FRP. Additionally, we suggest using CFRP-H or CFRP-M for strengthening the RC beams with satisfying a target strength improvement of 50%. Comparing with the conventional method such as section increment, using FRP is more beneficial for both required strength and costs as well.