CFRP Strengthened RC Beams Research Articles

An interpretable machine learning-based model for shear resistance prediction of CFRP-strengthened RC beams using experimental and synthetic dataset

Existing analytical models for predicting the shear resistance of RC beams strengthened with externally bonded CFRP reinforcements exhibit deficient performance due to their inability to accurately capture the complex resisting mechanisms. Combined with significant statistical uncertainties in shear failure, driven by its brittle nature, this further undermines the reliability of these models. To address these limitations, this study leverages Machine Learning (ML) to develop more robust and reliable predictive tool. A rigorous feature-selection process identified eight predictors as the most influential. Subsequently, nine ML-algorithms were trained on a refined experimental dataset comprising 239 beams, with XGBoost emerging as the top performer. This model also outperformed established models likefib Bulletin-90 and ACI 2023 models. However, the limited scope of the experimental dataset constrained the model’s predictive performance especially when separately evaluated on beams strengthened with U-wraps, full wraps or side-bonded FRP configurations. Therefore, to achieve a more reliable model a synthetic dataset was generated using Tabular Variational Auto-Encoder. The XGBoost model trained with the synthetic dataset significantly improved the performance of the former model and exhibited better predictions for all strengthening configurations. Finally, to ensure the physical consistency of predictions, values obtained from the SHapley Additive exPlanations method were analysed.

The effect of concrete compressive strength to the strengthening efficiency of RC beams using CFRP in slits

The near-surface mounted technique (NSM) is one of the most effective techniques to strengthen concrete structures, mainly in bending and shear. ABAQUS software has been used to establish a numerical model for the mechanical behavior of a RC beams strengthened by CFRP NSM. In this paper, three rectangular CFRP strengthened RC beams were simulated using ABAQUS and tested in four-point bending scheme in order to investigate the impact of concrete compressive strength to the strengthening efficiency. The results showed that increasing the Concrete compressive strength induced a positive impact to the peak load. further changing the compressive strength influence the failure criteria of the tested specimens.

Shear strength prediction of CFRP-strengthened deep RC beams without shear reinforcement

Shear strength prediction of CFRP-strengthened deep RC beams without shear reinforcement

Suitability of DIC in capturing flexural behaviour of as-built and CFRP-strengthened RC beams

In this paper, the suitability of digital image correlation (DIC) technology in evaluating the flexural behaviour of as-built and carbon-fiber-reinforced polymer (CFRP) strengthened reinforced concrete beams was verified by conducting a four-point bending test on four large-size beams. The DIC data obtained during the tests were compared to the results measured using traditional techniques such as displacement sensors and electrical strain gauges, as well as the findings derived from finite element (FE) numerical simulations. A good agreement was achieved between the local displacement and strain measurements and the data from DIC as a function of the applied load. Moreover, the crack patterns generated by the FE modelling were validated by the corresponding patterns derived from DIC. This suitability study is expected to contribute to the future field implementation of DIC technology to monitor the CFRP-strengthened members of critical structures such as bridges.

Cracking behavior of prestressed CFRP strengthened RC beams subjected to wetting/drying cycling under flexural load

The cracking pattern and spacing are essential for the structural durability of RC structures strengthened by prestressed CFRP plates. In this study, the effects of prestressing levels and wetting/drying cycling (WDC) on the cracking behavior of RC beams strengthened by prestressed CFRP plates were investigated. A modified model for calculating the average crack spacing was developed by incorporating the interfacial stress between adjacent cracks, the prestressing levels, and the WDCs. The effects of interfacial properties and prestressing levels on the average crack spacing were analytically studied. Besides, four-point bending tests were conducted on seventeen strengthened beams subjected to WDC. The results show that cracking propagation was restrained by prestressing forces but facilitated by WDCs. Moreover, WDC and prestressing force lead to an increase in the average cracking spacing of the strengthened beams. The average cracking spacings calculated by different equations were compared to the experimental results, and it can be found that the modified modelprovides the closer prediction of the average crack spacing for CFRP-strengthened beams under WDC and prestressing.

Load-Bearing Performance of Non-Prismatic RC Beams Wrapped with Carbon FRP Composites

This study investigated the influence of CFRP composite wrapping techniques on the load–deflection and strain relationships of non-prismatic RC beams. A total of twelve non-prismatic beams with and without openings were tested in the present study. The length of the non-prismatic section was also varied to assess the effect on the behavior and load capacity of non-prismatic beams. The strengthening of beams was performed by using carbon fiber-reinforced polymer (CFRP) composites in the form of individual strips or full wraps. The linear variable differential transducers and strain gauges were installed at the steel bars to observe the load–deflection and strain responses of non-prismatic RC beams, respectively. The cracking behavior of unstrengthened beams was accompanied by excessive flexural and shear cracks. The influence of CFRP strips and full wraps was primarily observed in solid section beams without shear cracks, resulting in enhanced performance. In contrast, hollow section strengthened beams exhibited minor shear cracks alongside the primary flexural cracks within the constant moment region. The absence of shear cracks was reflected in the load–deflection curves of strengthened beams, which demonstrated a ductile behavior. The strengthened beams demonstrated 40% to 70% higher peak loads than control beams, whereas the ultimate deflection was increased up to 524.87% compared to that of the control beams. The improvement in the peak load was more prominent as the length of the non-prismatic section increased. A better improvement in ductility was achieved for the case of CFRP strips in the case of short non-prismatic lengths, whereas the efficiency of CFRP strips was reduced as the length of the non-prismatic section increased. Moreover, the load–strain capacity of CFRP-strengthened non-prismatic RC beams was higher than the control beams.

Experimental study on shear performance of CFRP-strengthened RC beams with geopolymer adhesive

PurposeThe effects of carbon fiber reinforced polymer (CFRP) reinforcement form, adhesive type and pre-crack width on failure mode, shear capacity, deflection response, CFRP strain response and crack patterns of strengthened specimens were investigated.Design/methodology/approachThis paper presents a geopolymer adhesive that matches the performance requirements of CFRP adhesive, which is applied to pre-cracked beams reinforced with CFRP strips. FindingsFor specimens with varying structural properties, two failure modes, the CFRP-concrete interface substrate failure and the fracture failure of CFRP, are observed. Moreover, the shear capacity, ultimate deflection and bending stiffness of the U-shaped CFRP-strengthened beams are enhanced in comparison to the complete-wrapping CFRP-strengthened beams. With an increase in pre-crack width, the increase in shear capacity of RC beams shear-strengthened with CFRP strips is less than that of non-cracked beams, resulting in a limited influence on the stiffness of CFRP-strengthened beams. The comparison of experimental results showed that the proposed finite element model (FEM) effectively evaluated the mechanical characteristics of CFRP-strengthened RC beams.Originality/valueTaking into consideration the reinforcement effect and the concept of environmental protection, the geopolymer adhesive reinforcement scheme is preferable to applying epoxy resin to the CFRP-strengthened RC beams.

Development of a local bond shear stress-slip model of RC beams externally strengthened with FRP materials

This paper presents an analysis of the numerical investigation of RC beams, strengthened with CFRP and tested in flexure, using the ANSYS© numerical analysis code. In the first part of this paper, finite-element models of RC beams (control and CFRP-strengthened), subjected to four-point bending, are developed based on experimental tests as reported in the literature. Then, a 3D nonlinear finite-element analysis (NLFEAs) with perfect bonding, along with 12 cohesive zone material (CZM) models proposed by researchers in literature, are explored to simulate the behaviour of CFRP-strengthened RC beams. In the second part of this work, the compressive strength of the concrete and the elastic modulus of the epoxy resin are examined to study their effect on the same CFRP-strengthened RC beam. On the basis of those two studies, a bilinear CZM model is modified to predict the behaviour of RC beams strengthened with FRP materials, and interfacial shear debonding phenomena. The modified CZM model is verified against a database of experimental results that includes 23 RC beams, strengthened with FRP tested in flexure, with different concrete compressive strength, FRP modulus of elasticity and resin elastic modulus. The experimental and predicted ultimate loads are compared to verify the accuracy of the modified CZM model. The level of fitness between the modified CZM model and experimental results is elaborated with statistical metrics such as integral of the absolute error (IAE), root mean square error (RMSE) and coefficient of determination (R2). The results show good agreement between the experimental and predicted ultimate loads.

A new flexural strength model of CFRP-strengthened RC beams with intermediate crack induced debonding failure

A new flexural strength model of CFRP-strengthened RC beams with intermediate crack induced debonding failure

Multi-impact performance of prestressed CFRP-strengthened RC beams using H-typed end anchors

To address the problem of insufficient ductility of traditional Carbon Fibre-reinforced polymer (CFRP) strengthened marine structures and to enhance the application of CFRP in marine engineering, the present study develops novel prestressed CFRP-strengthened RC beams using H-type end anchors with ductility controllable devices. In this device, part of the reinforcement bars are replaced by CFRP, which is prestressed as the structural enhancement material. The CFRP sheet is connected with a tensioned screw, which is used to realize the function of early warning based on a large plastic deformation when the structure is overloaded. Thus, the ductility of the composite structure could be improved based on yielding of the screw rod rather than the fracture failure of the CFRP sheet compared to that with CFRP bonded. This study investigates the flexural static and impact performance of the representative large-scale RC beams strengthened by prestressed CFRP through four-point bending and drop-weight impact. The results show that the H-typed end anchor and raising the prestress level of CFRP not only improve the ultimate resistance and ductility, but also realize the overload warning function under static load. Accordingly, the design still shows advantages in energy consumption and impact resistance through drop-weight impact. An advanced 3D nonlinear finite element model is built to simulate well the multiple impact performance in terms of the failure modes, impact force and displacement history. This study provides a new approach to address design deficiencies with insufficient ductility behaviour while using CFRP as a strengthening material. This prestressing technology is able to utilize the material efficiency of high-strength CFRP and open a new path for CFRP applications in marine civil engineering.

Behavior of CFRP-strengthened RC beams with circular web openings in shear zones: Numerical study

In practice, especially the basement floor beams are drilled and damaged by the users. In some cases, this damage to the beams can be significant for the load-bearing element and the whole structure. In this study, the behavior of reinforced concrete beams with circular openings and the failure types resulting from strengthening these beams with CFRP are parametrically investigated. The diameter of the opening/beam height ratio (D/H), concrete compressive strength, stirrup spacing, the position of the opening to the beam support, the type of CFRP application, CFRP ply orientation, and the number of CFRP layers were selected as parameters. Numerical models were verified using 9 specimens having different circular openings with/without CFRP strengthening and the analyses of 95 numerical models with the selected parameters were carried out utilizing the finite element program, ABAQUS. The ultimate load capacity, ductility, stiffness, energy dissipation capacity and failure modes of the beams were determined. As a result of the study, it was observed that there was no significant loss in ductility for the beams with D/H ≤ 0.3 and the number of CFRP layer and type of application did not have a significant effect on D/H ≤ 0.44. However, for the beams with D/H > 0.64, the CFRP application that completely surrounds openings should be preferred instead of partial CFRP strengthening. In addition, the concrete strength is an effective parameter for the beams with D/H ≤ 0.44. The effect of the stirrup spacings in the beam on the ductile behavior was also limited with the increase in the hole diameter. The number of CFRP layers should theoretically be 4 for an effective strengthening in beams with D/H > 0.44. Finally, U wrapping is recommended instead of using full wrapping. It has been seen that the location and diameter of the hole are very important parameters in the failure type of the beam.

Numerical Assessment of the Impact Behavior of CFRP strengthened RC beams using different concrete models

Numerical Assessment of the Impact Behavior of CFRP strengthened RC beams using different concrete models

The shear behavior of Anchored CFRP Strengthened RC beams

The shear behavior of Anchored CFRP Strengthened RC beams

Influence of FRP on the shear behaviour of RC rectangular beam elements

This article presents the outcomes of an experimental study on the shear behaviour of FRP strengthened RC beams. Shear deficient RC beams may exhibit brittle shear failure when the applied stress exceeds the designed level. Many strengthening measures, such as steel plate bonding, RC-jacketing etc., are efficient but laborious and not time effective solutions compared to the externally bonded FRP wrapping technique. External FRP wrapping is one of the efficient strengthening schemes in terms of its strength to weight ratio. This technique does not increase the structural member's cross-sectional size and dead load. The cost of FRP materials and mechanical properties also varies with respect to the type of fibre, thickness, and profile. In this study, RC beams of a/d ratio 1.25 have been used with CFRP and BFRP composites. The test results show a 17.98% increase in strength and improves ductility by 77%. The strengthening scheme increases the shear strength by controlling the early formation of diagonal cracks in the strengthened shear zone and exhibiting ductile failure. Triantafillou’s model has been validated with the test results of CFRP strengthened beams, and the proposed model has been verified using the experimental data and literature data collected. The proposed methodology works well in estimating the shear capacity of CFRP strengthened RC beams.

The behavior of CFRP strengthened RC beams subjected to blast loading

The behavior of CFRP strengthened RC beams subjected to blast loading

Shear behavior of flexural CFRP-strengthened RC beams with crack-induced delamination: Experimental investigation and strength model

This study investigates the shear behavior and debonding characteristics of initially ductile RC beams (failing in flexure when unstrengthened) at the verge of transitioning to a more brittle shear failure upon strengthening using external flexural carbon fiber reinforced polymer (CFRP). Despite the absence of shear CFRP strengthening, various degrees of improvement in the shear capacity were achieved depending on the flexural CFRP amount. However, steeper shear cracks that bypass the stirrups in addition to the nonyielding stirrups results in shear capacities that cannot be reliably predicted using the ACI and other similar codes’ provisions. Instead of adopting capacity models that focus on the shear failure alone or the crack-induced debonding as oneway cause-effect (shear crack-debonding) relationship, a more holistic capacity prediction approach (calibrated with finite element anlaysis) that considers the synergistic effect between the shear failure and the CFRP debonding is provided. Since any enhancement in flexure must be checked against shear, the presented capacity prediction approach could be a more handy means to assess the shear strengthening level needed in such cases where the flexural strengthening is insufficient to achieve the overall structural upgrade sought. The designed beams – i.e. at the verge of changing failure mode with flexural FRP strengthening – and the test program could serve as a bond assessment philosophy in the sense that this upper bound brittle failure mechanism provides more realistic behavior of the crack-induced debonding performance of FRP-strengthened beams. Analytical load–deflection assessment of the tested specimens is also provided.

Modeling of CFRP strengthened RC beams using the SNSM technique, proposed as an alternative to NSM and EBR techniques

In this paper, an analytical and numerical study in FEM finite element by the ABAQUS software was conducted. Which aims to study the behaviour of RC beams bending strengthened with SNSM side near surface mounted technique, proposed as a solution to avoid the failure mode by debonding of the strengthening, the disadvantage of the EBR externally bonded reinforced technique, and the failure mode by separation of the concrete cover relative to the NSM near surface mounted technique, by comparing the behaviour of the three techniques, the effect of the quantity of strengthening and confirm the results with the literature. The results of this study show that the numerical and analytical model can predict the behaviour of strengthened RC beams according to the three techniques, a clear improvement of the bending capacity of beams strengthened is noticed. A good preservation of the ductility of SNSM beams with a better failure mode.

Experimental assessment of the performance of reinforced concrete beams strengthened with carbon fiber reinforced polymer laminates

In this study, experimental research is carried out to assess the flexural performance of RC beams strengthened with different amount of CFRP laminates at the tension face. Twelve rectangular RC beams were fabricated and three are un-strengthened and used as reference beams and the remaining nine are strengthened with different amount of CFRP varying from single to triple layers and all are tested to failure under three points bending test. The increase of ultimate strength provided by the bonded CFRP laminates is assessed and failure modes is identified and compared to the un-strengthened RC beams. The results indicated that the flexural capacity of the beams was significantly improved as the amount of the laminates increases that ranged from 20% to 52% increased for single to triple layers laminates. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened RC beams. Based on the observed results, recommendations are made that externally application of CFRP laminates can be used for a significant enhancement of the strength deficient RC beams in increasing the ultimate load carrying capacity.
 Keywords: CPRP laminate, Reinforced concrete, ductility, index, epoxy resin, flexural strengthening

Experimental and analytical study on the flexural performance of CFRP-strengthened RC beams at various pre-stressing levels

This work aimed to evaluate the flexural performanceof RC beams strengthened by carbon fibre-reinforced polymer (CFRP) plates, which were applied at the soffit of beams and pre-stressed at various levels. Six RC beams were prepared that were pre-stressed at 0, 20 and 40% of the ultimate strength of the CFRP plate, and they were subjected to four-point bending tests to evaluate the cracking load, yield load, and ultimate load of the beams. The variation in strain of the CFRP plate and deflection were monitored under applied load. With the pre-stressing level, it was observed that all types of the aforementioned loads were increased, whereas the deflection and ductility were decreased. Cracking moment was evaluated analytically by proposing one modification factor into existing equation that was obtained by regressing the data of 41 analogous RC beams. Modified equation was also verified by the calculated deflection, which have close resemblance with the experimental observations.

Simplified Temperature Prediction Method for Insulated CFRP-Strengthened RC Beams Exposed to Standard Fire

This paper presented the finite element (FE) models for thermal analysis of insulated CFRP-strengthened reinforcement concrete beams under standard fire condition. Based on these models, the influences of some parameters (e.g. thermal conductivity, thickness of fireproof coating, time of exposure to fire, and steel bar location) on thermal response were analyzed. The numerical results showed that the temperature at the surface of coating could be calculated by combining standard fire curve and time of fire exposure. The temperature at the surface of concrete beam decreased with the increase of coating thickness and increased linearly with the increase of thermal conductivity. The temperatures at internal concrete were only influenced by the temperature at the surface, the location from the surface and the time of fire exposure. After numerical analysis, a simplified calculating method was presented to predict the temperature value at any points of insulated CFRP-strengthened RC beam section, under standard fire condition. By comparing with the experimental results, the simplified method was well verified.