Development of Analytical Model for Bonding of CFRP Rod in Concrete Subjected to Cyclic Loads

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Authors have presented a well written manuscript but still many corrections are required before its final publication.
- Authors must present reason of improvement in the performance of the CFRP-UHP-FRP bond under cyclic loading in one line in the abstract section. 
- Keywords should be very specific and unique, by which you can define the manuscript....as per my understanding contact surface, cyclic loads are common words...revised these keywords section.
- Very less literature were presented related to UHPC, HPC and FRP...Add some quality recently published literature. Also add recently published literature related to sustainability.
- Add proper codal specifications for various testing methodology throughout the manuscript.
- Add error bar in compressive strength graphs for various cubes of G40, UHPFRC.
- Add some supportive literature for compressive strength as well as all testing methodology.
- Improve technical writing throughout the manuscript.

Author Response

Reviewer #1:

 

Reviewer Comment (1):

Authors must present reason of improvement in the performance of the CFRP-UHP-FRP bond under cyclic loading in one line in the abstract section.

Author’s Reply:

Thank you for your valuable feedback. I have incorporated the suggested statement into the last line of the abstract to provide context for the observed improvement in the CFRP-UHPFRC bond under cyclic loading:

“The improved performance of the CFRP-UHPFRC bond under cyclic loading is attributed to the optimized interface model that enhances the bond integrity between CFRP rods and concrete.”

 

Reviewer Comment (2):

Keywords should be very specific and unique, by which you can define the manuscript....as per my understanding contact surface, cyclic loads are common words...revised these keywords section.

Author’s Reply:

T The suggested comment has been incorporated, and the accompanying descriptions have been integrated into the manuscript:

“Revised Keywords: CFRP-UHPFRC Interface; FEA of CFRP Embedded in Concrete; Cyclic bond strength enhancement; Cyclic load Response Modelling; Interface Element Development for bond simulation; Durability characteristics under cyclic loading”

 

Reviewer Comment (3):

Very less literature was presented related to UHPC, HPC and FRP...Add some quality recently published literature. Also add recently published literature related to sustainability.

Author’s Reply:

Additional Literature has been added as below:

“Scott Muzenski and Benjamin Graybeal, examined the efficacy of ultra-high-performance concrete (UHPC) overlays in bridge deck rehabilitation. The research considered the application of UHPC on bridge decks showing incipient surface deterioration but still structurally competent. The findings highlighted UHPC's low permeability which curbs the ingress of damaging agents, thereby prolonging the deck's service life. Structural tests, including both cyclic and monotonic loading, were conducted on conventional concrete slabs treated with UHPC overlays. Various factors like moment bending, joint detailing, and overlay depth were investigated. The results showed that UHPC overlays can indeed bolster the structural capacity of bridge decks. Particularly, correct detailing at cold joints was found to be crucial in preserving the enhanced performance of the treated decks. The study provides empirical support for utilizing UHPC overlays in bridge maintenance, emphasizing the need for careful detailing to fully exploit the material's benefits [3].”

“X.M. You, L.B. Lin, Bing Fu, and Yu Xiang, examined the concept of reinforcing ultra-high-performance concrete (UHPC) with recycled macro fibres from waste glass-fibre-reinforced polymer (GFRP) composites. This novel approach aims to overcome the cost barriers associated with UHPC while also providing a sustainability solution for waste GFRP. The experimental results show that while workability decreases and compressive strength can be reduced by up to 21.8%, enhancements in flexural strength and toughness by 27.9% and 46.9 times respectively were observed. This research suggests a promising direction for producing more affordable and durable UHPC structures, with the added benefit of addressing environmental waste management challenges [4].”

“Ali A. Semendary and Dagmar Svecova’s study delves into the numerical simulation of load transfer at UHPC interfaces, particularly focusing on the finite element modelling (FEM) to understand bond strength. Their research is pivotal in addressing the generally weak links found in precast UHPC systems, thereby enhancing interface bonding through strategically exposed fibres on surfaces. They utilized parameters derived from an array of stress tests including tensile, shear, and compression-shear. The resulting FEM yielded results that correlated closely with experimental data, validating the model’s ability to accurately simulate interface behaviour. This work contributes significantly to the predictive modelling techniques within UHPC applications and can inform the design and assessment of UHPC structural interfaces [5].”

“The study by Kee-Yen Ong et al. focused on developing a finite element model for high-strength concrete columns reinforced with FRP, subjected to cyclic lateral loads. Their model, verified against experimental data, accurately captures the improved ductility and moment resistance of the columns correlating with the FRP confinement ratio. These results confirm the model’s potential as a predictive tool for the seismic performance of FRP-confined concrete columns[6].”

“Jun Zhao, Xiaopeng Li, and Xiangcheng Zhang conducted experimental and theoretical studies on the bond performance between carbon fiber-reinforced polymer (CFRP) bars and concrete through a series of bond stress-slip tests under monotonic and reversed cyclic loading conditions. The findings indicate a direct correlation between increased concrete compressive strength and higher maximum bond stress, while a smaller diameter of CFRP bar or reduced embedment length leads to a decrease in this maximum stress. Remarkably, under reversed cyclic loading, the study observes lower maximum bond stresses compared to monotonic loading for specimens with identical concrete compressive strength, CFRP bar diameter, and embedment length. The research introduces analytical bond stress-slip models that accurately predict bond stress-slip curves under both loading conditions, offering a theoretical foundation for precise calculations of bond-slip performance. The mathematical definition of the descending branch C'D' and the descending stages of skeleton curves (CD and GH segments) contributes significantly to enhancing our understanding of the intricate bond behavior between CFRP bars and concrete. This review consolidates key insights from the research, laying the groundwork for advancements in the design and evaluation of CFRP-reinforced concrete structures [10].”

“The research paper by Hao Zhou, Dilum Fernando, Van Thuan Nguyen, and Jian-Guo Dai explores the bond behaviour of Carbon Fiber Reinforced Polymer (CFRP) to concrete bonded joints when subjected to fatigue cyclic loading, a phenomenon not widely understood despite its importance in the durability of reinforced concrete (RC) structures. Through experimental studies utilizing a bespoke data acquisition system, various failure modes of CFRP-to-concrete bonded joints under fatigue loading were identified – namely, cohesion failures within concrete, within adhesive, and interlaminar failures in CFRP itself. These failures depended on factors such as concrete strength, CFRP laminate type, and loading amplitude. It was discovered that damage begins to initiate when the interfacial shear stress exceeds 80% of the interface’s shear strength. The paper’s findings help inform the understanding of the progressive damage and failure mechanisms in CFRP strengthened structures under real-world loading conditions [13].”

 

List of New Added References:

[3] S. Muzenski and B. Graybeal, “Structural Performance of UHPC Overlays.”

[4] X. M. You, L. B. Lin, B. Fu, and Y. Xiang, “Ultra-high performance concrete reinforced with macro fibres recycled from waste GFRP composites,” Case Studies in Construction Materials, vol. 18, Jul. 2023, doi: 10.1016/j.cscm.2023.e02120.

[5] A. A. Semendary and D. Svecova, “Numerical Simulation of the Load Transfer Mechanism at UHPC-UHPC Interface.”

[6] K. Y. Ong, C. K. Ma, N. M. Apandi, A. Z. Awang, and W. Omar, “Modeling of high-strength concrete-filled FRP tube columns under cyclic load,” in AIP Conference Proceedings, American Institute of Physics Inc., May 2018. doi: 10.1063/1.5034563.

[10] J. Zhao, X. Li, and X. Zhang, “Experimental and theoretical research on bond performance between CFRP bar and concrete under monotonic and reversed cyclic loading,” Eng Struct, vol. 246, Nov. 2021, doi: 10.1016/j.engstruct.2021.112994.

[13] H. Zhou, D. Fernando, V. Thuan Nguyen, and J. G. Dai, “The bond behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading: An experimental study,” Constr Build Mater, vol. 273, p. 121674, Mar. 2021, doi: 10.1016/J.CONBUILDMAT.2020.121674.

 

 

Reviewer Comment (4):

Add proper codal specifications for various testing methodology throughout the manuscript.

Author’s Response:

“The experimental uses RILEM/CEB/FIP (1978) arrangements with two testing specimens which produced by embedding CFRP rod in double lap joint under cyclic loading.”

 

Reviewer Comment (5):

Add error bar in compressive strength graphs for various cubes of G40, UHPFRC.

Author’s Response:

The graph in “Figure 14. Test Result Comparison of Concrete G-40 and UHPFRC” has been updated.

 

Reviewer Comment (6):

Add some supportive literature for compressive strength as well as all testing methodology.

Author’s Response:

“The assessment of concrete compressive strength is pivotal for ensuring the structural reliability of construction materials. Global standard BS EN 12390-3:2002, underscore the meticulous methodologies employed in this evaluation. Adherence to precise specimen dimensions, calibration of pressure testing machines with specified failure load parameters (20% to 80% of full scale), and a stringent ±1% relative error tolerance are crucial aspects of the compressive strength testing process [21]. The com-pressive mechanical test conducted using a MATEST (MTS) machine.”

List of New Added References:

[21]       “BS EN 12390 Part 3 (British Standards Institute, 2009 c).

 

 

Reviewer Comment (7):

Improve technical writing throughout the manuscript.

Author’s Response:

The manuscript has undergone a review to improve technical writing.

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this paper, a finite element model was built and two specimens were designed and conducted to investigated the bond behavior of CFRP rods with both standard grade 40 concrete and UHPFRC under cyclic stresses. Based on the experimental results, a new finite element model with an interface element was developed, resulting in an improvement in predicting the performance of the CFRP-UHPFRC bond under cyclic loading. However, the current manuscript contains a large number of grammatical errors and typos in text and figures. It is recommended to check throughout the whole manuscript, and the authors should make substantial modifications regarding the manuscript by carefully considering the following aspects.

(1) In Introduction, the reference format of References [2]- [6] is not standardized and there is a lack of symbols. This issue persists in the following chapters, please thoroughly examine it and make the necessary corrections one by one.

(2) In the fourth paragraph of section 2.1, line 8, the manuscript 'denoted as '25d' 9,21] ' should probably be 'denoted as '25d' [9]. '

(3) In the column of 'Embedment Length (mm)' in Table 1, '21]' after '300' need to be deleted.

(4) In Figure 1, the color format of dimensioning is not uniform.

(5) In the first paragraph of section 2.2.1, the manuscript 'The Concrete G-40 specimen consist of 3 main components of concrete, reinforcement The Grade 40 concrete (G-40) specimen is composed of three primary elements: concrete, reinforcement, and CFRP rod.' is repeated and the first sentence should be deleted.

(6) In Table 2, the symbol representation of density 'Kg/M3' is not standardized and should be changed to 'kg/m³'.

(7) Table 3 does not indicate the units of different values.

(8) The picture in Table 4 is blurred and please replace a more appropriate picture.

(9) In the first paragraph of section 3.1.2, the manuscript 'we assume isotropy' seems informal and does not align with the standards of thesis writing. In line 4, the comma ', ' after 'torque' should be deleted.

(11) In the first paragraph of section 3.1.3, the manuscript 'As shown in Table 7, the magnitude of strain increases, steel reinforcement bars have inelastic and nonlinear behavior which is called plasticity.' does not align with the information shown in Table 7.

(12) In Table 7, the number in the unit symbol should be in the superscript format and the row height of Table 7 is obviously inconsistent with other tables.

(13) In section 3.2, the author defines the global mesh size of concrete as 20 mm. However, based on relevant research on traditional reinforced concrete bond slip numerical simulation, more accurate results are obtained when the mesh size of concrete in the core anchorage zone is 3-5 mm. Is there any analysis of grid sensitivity?

(14) The name of Figure 3. (a) 'illustrates the meshing mechanism' is not standardized.

(15) The figure 4 is blurry, making it difficult to identify the relevant information in the image. Please select a clearer and more standardized image.

(16) In line 7 of page 8, the manuscript 'The Amplitude Shows in Figure 6 is…' should be a description of Figure 5. (b). There is no figure 6 in the paper.

(17) In page 9, this paragraph provides a detailed analysis of the load-displacement curve in Figure 9. However, the author's expression is unclear, and there are logical errors. Moreover, the load-displacement curve in Figure 9 is too chaotic to extract meaningful information. It is recommended that the author should carefully revise and reprocess the load-displacement curve to present relevant information more effectively.

(18) In page 10, line 18, the manuscript 'The experimental test consists of two testing specimens were produced by embedding CFRP rod in double lap joint under cyclic loading.' is difficult to understand and misleading, please check and revise the similar parts.

(19) In section 4.1, the author only introduces 3 strain gauges of the CFRP rod in the unanchored area, are there additional strain gauges arranged in the anchorage zone at both ends to obtain the bond slip behavior of the interface.

(20) In page 12, line 5, the manuscript '1515,16]' should be changed to '[15, 16]', the sentence 'UHPFRC has a considerably greater strength than regular concrete. UHPFRC has a quick mechanical property evolution in time,' seems colloquial and does not meet the writing requirements of the thesis.

(21) In page 13, line 11, the author mentioned ' [Figure 15. (d)]', but there is no Figure 15. (d) in the article and the reference format to the picture in the text is no standardized.

(22) In page 17, the author mentioned ' Obtained displacement from numerical and experimental are consider very minor difference which shows the proof of accuracy of conducted experiment and obtained numerical result.’. However, results listed in Table 12 shown that the numerical and experimental errors are not small, which seems cannot explain the correctness of the finite element model.

(23) In page 25-27, in reference to the description of Fig.26 and Fig.27 in the text, the names of Fig.26 and Fig.27 are reversed. Referring to Fig.28 and Fig.29, the data of columns 'Without interface' and 'With interface' are inverted, please check and modify.

(24) As this paper focuses on behavior and design of composite structures and interfacial performance, some state-of-the-art research on novel composite structures are recommended to be referred for improving the literature review part, including:

[1] Wu et al. Elastic buckling formulas of multi-stiffened corrugated steel plate shear walls. ENG STRUCT. 300 (2024), 117218.

[2] Yu et al. Experimental and numerical study on seismic performance of L-shaped multi-cellular CFST frames. J CONSTR STEEL RES. 213 (2024), 108360.

[3] Tong et al. Experimental and numerical investigations on seismic behavior of stiffened corrugated steel plate shear walls. EARTHQ ENG STRUCT D. 52 (2023), 3551-3574.

[4] Chen et al. Flexural behavior of novel profiled steel-UHTCC assembled composite bridge decks. J CONSTR STEEL RES. 212 (2024), 108258.

Comments on the Quality of English Language

It should be checked throughout the whole manuscript to avoid grammatical errors and typos.

Author Response

Reviewer #2:

Reviewer Comment (1):

In Introduction, the reference format of References [2]- [6] is not standardized and there is a lack of symbols. This issue persists in the following chapters, please thoroughly examine it and make the necessary corrections one by one.

Author’s Reply:

Thank you for your feedback. I appreciate your observation regarding the missing brackets in the reference numbers. I have revised the references to ensure the correct formatting, and the brackets are now in place.

 

Reviewer Comment (2):

In the fourth paragraph of section 2.1, line 8, the manuscript 'denoted as '25d' 9,21] ' should probably be 'denoted as '25d' [9]. '

Author’s Reply:

Apologies for the typo. In reference to the previous comment, the brackets were missing; the accurate version should be ‘[9,21],’ referring to reference numbers 9 and 21. Given the updated reference list, the correct numbering, now implemented in the manuscript, is “[15,22]”.

 

Reviewer Comment (3):

In the column of 'Embedment Length (mm)' in Table 1, '21]' after '300' need to be deleted.

Author’s Reply:

The ‘21]’ was missing a bracket at the beginning which the correct version is “[21]”, denoting the reference number 21 in the bibliography which is showing the paper that the 300 mm embedment length is referred to.

 

Reviewer Comment (4):

In Figure 1, the color format of dimensioning is not uniform.

Author’s Reply:

The “⌀12mm” have been change from purple to cyan to be in uniform colour.

 

Reviewer Comment (5):

In the first paragraph of section 2.2.1, the manuscript 'The Concrete G-40 specimen consist of 3 main components of concrete, reinforcement The Grade 40 concrete (G-40) specimen is composed of three primary elements: concrete, reinforcement, and CFRP rod.' is repeated and the first sentence should be deleted.

Author’s Reply:

Thank You for your attention and the comment. The first sentence was redundant which has been deleted.

 

Reviewer Comment (6):

In Table 2, the symbol representation of density 'Kg/M3' is not standardized and should be changed to 'kg/m3'.

Author’s Reply:

Thank you for your comment, the unit for Density and Mass/Unit Volume are both standardized.

 

Reviewer Comment (7):

Table 3 does not indicate the units of different values.

Author’s Reply:

The units for l_f, d_f and stress are indicated as mm, mm and N/m², respectively.

 

Reviewer Comment (8):

The picture in Table 4 is blurred and please replace a more appropriate picture.

Author’s Reply:

The picture has been changed to more appropriate picture to demonstrate the smoothness of CFRP Rod that has been used in this experiment.

 

Reviewer Comment (9):

In the first paragraph of section 3.1.2, the manuscript 'we assume isotropy' seems informal and does not align with the standards of thesis writing. In line 4, the comma ', ' after 'torque' should be deleted.

Author’s Reply:

Sorry for the grammatical issue. The whole paragraph has been restructured as below:
“Composite materials like CFRP, comprised of fibres and a matrix, are typically treated as orthotropic, characterized by directional young’s modulus. Accurate analysis necessitates data predicting stress, forces, torque, and damage in CFRP. In this modelling, the elastic properties of CFRP have been assumed to be isotropic, exhibiting uniform behaviour in all directions. For the 3D modelling of the CFRP rod in this study, 'Engineering Constants' were utilized to represent these properties, and the corresponding data are presented in Table 5.”.

 

Reviewer Comment (10):

In the first paragraph of section 3.1.3, the manuscript 'As shown in Table 7, the magnitude of strain increases, steel reinforcement bars have inelastic and nonlinear behaviour which is called plasticity.' does not align with the information shown in Table 7.

Author’s Reply:

The who sentence has been restructured as below:

At low strain magnitudes, steel reinforcement bars exhibit nearly linear elastic behaviour, and the elastic modulus remains constant, as detailed in Table 7. As the stress magnitude increases, steel reinforcement bars demonstrate inelastic and nonlinear behaviour, commonly referred to as plasticity. It is noteworthy that for the purposes of this research, the plastic behaviour of steel is presumed to be linear, given that the study does not address the behaviour of steel reinforcement embedded in concrete. Table 8 provides an overview of the plastic criteria governing the stress-strain relationship of steel.

 

Reviewer Comment (11):

In Table 7, the number in the unit symbol should be in the superscript format and the row height of Table 7 is obviously inconsistent with other tables.

Author’s Reply:

Thank you for you comment, the necessary modification has been implemented.

 

Reviewer Comment (13):

In section 3.2, the author defines the global mesh size of concrete as 20 mm. However, based on relevant research on traditional reinforced concrete bond slip numerical simulation, more accurate results are obtained when the mesh size of concrete in the core anchorage zone is 3-5 mm. Is there any analysis of grid sensitivity?

Author’s Reply:

We have conducted sensitivity analysis on meshing size. Although by using fine mesh, more accurate results have been expected but through sensitivity analysis it is revealed that mesh size in range of 5mm to 20mm is resulting same outputs. Therefore, in order to reduce roundoff error and computation time, 20mm mesh size have been used. It is worthy to highlight that sensitivity analysis of meshing size is highly depend on the considered model and it may result different size for different models. These descriptions have been added to the manuscript

 

Reviewer Comment (14):

The name of Figure 3. (a) 'illustrates the meshing mechanism' is not standardized.

 

Author’s Reply:

Figure 3 (a) has been changed to Mesh of Concrete.

 

Reviewer Comment (15):

The figure 4 is blurry, making it difficult to identify the relevant information in the image. Please select a clearer and more standardized image.

Author’s Reply:

The image enhanced to be readable.

 

Reviewer Comment (16):

In line 7 of page 8, the manuscript 'The Amplitude Shows in Figure 6 is…' should be a description of Figure 5. (b). There is no figure 6 in the paper.

Author’s Reply:

Sorry for the typo, the figure is related to figure 5. (b) and it had been modified.

 

Reviewer Comment (17):

In page 9, this paragraph provides a detailed analysis of the load-displacement curve in Figure 9. However, the author's expression is unclear, and there are logical errors. Moreover, the load-displacement curve in Figure 9 is too chaotic to extract meaningful information. It is recommended that the author should carefully revise and reprocess the load-displacement curve to present relevant information more effectively.

Author’s Reply:

The paragraph rephrased to be more logical with additional explanation, as well as the graph changed to different colouring and weight line to be clearer.

The examination of the load-displacement curve in Figure 9 provides valuable insights into the behaviour of Concrete G40 under cyclic loading. Notably, the force peaks at 33.66 kN when the displacement reaches 6 mm. In contrast, the load-displacement curve for UHPFRC specimens reveals more promising outcomes. The force-displacement relationship indicates a robust cyclic loading response with noticeable energy dissipation. Although the maximum force reaches around 70 kN at 8 mm displacement, the bonding persists, and debonding occurs, averaging at 9.39 mm. This underscores the ductility of UHPFRC, as despite the force decreasing due to debonding at the tip of the CFRP in the bottom concrete, the surface of the CFRP rod in contact with UHPFRC continues to endure the cyclic loading.   

 

Reviewer Comment (18):

In page 10, line 18, the manuscript 'The experimental test consists of two testing specimens were produced by embedding CFRP rod in double lap joint under cyclic loading.' is difficult to understand and misleading, please check and revise the similar parts.

Author’s Reply:

The sentence restructured to simpler wording and clearer version as below:
“The experimental uses RILEM/CEB/FIP (1978) arrangements fabrication of two cube specimens, where the top cube measured 400*400*430 mm and the bottom sample measured 700*700*430 mm. Both specimens were prepared by embedding a CFRP rod in the top and bottom concrete, facilitating the execution of a cyclic pull-out test.”

 

Reviewer Comment (19):

In section 4.1, the author only introduces 3 strain gauges of the CFRP rod in the unanchored area, are there additional strain gauges arranged in the anchorage zone at both ends to obtain the bond slip behaviour of the interface.

Author’s Reply:

we didn't add any strain gauge at both ends.

 

 

Reviewer Comment (20):

In page 12, line 5, the manuscript '1515,16]' should be changed to '[15, 16]', the sentence 'UHPFRC has a considerably greater strength than regular concrete. UHPFRC has a quick mechanical property evolution in time,' seems colloquial and does not meet the writing requirements of the thesis.

Author’s Reply:

The passage has been changed to more academic writing scheme as below:

“The ultra-high-performance fibre-reinforced concrete (UHPFRC) exhibits significantly greater strength than regular concrete. It undergoes a rapid evolution of mechanical properties over time, achieving high early-age strength and stiffness, with a short-term hydration regime that is nearly complete within 90 daysError! Reference source not found.]”

 

Reviewer Comment (21):

In page 13, line 11, the author mentioned ' [Figure 15. (d)]', but there is no Figure 15. (d) in the article and the reference format to the picture in the text is no standardized.

Author’s Reply:

It is related to Figure 15. (b) which mistakenly typed ‘(d’). Additionally, the caption of the picture standardized to the format of the journal.

 

Reviewer Comment (22):

In page 17, the author mentioned ' Obtained displacement from numerical and experimental are consider very minor difference which shows the proof of accuracy of conducted experiment and obtained numerical result.’. However, results listed in Table 12 shown that the numerical and experimental errors are not small, which seems cannot explain the correctness of the finite element model.

Author’s Reply:

The table 12 had not demonstrated the correct comparison. Although the numbers were correct but it confused the reader. Table 12 has totally restructured to be clearer for the reader. The revised table (below) is presented to provide a more accurate and comprehensible depiction of the comparison. It shows that the discrepancy is significant when the modelling performed without interface element with “Tie” contact surface. Understanding the necessity of interface element in the numerical modelling has led to finding the suitable interface element, in order to reduce such significant discrepancies.

“The analysis of the revised table underscores notable differences between experimental and numerical results for UHPFRC and Concrete G40. In the case of UHPFRC, the experimental force of 41.5 kN is considerably lower than the numerical force of 75 kN, resulting in a significant 57.51% difference. The accompanying displacement data shows a more substantial 21.45% difference, indicating a noteworthy disparity in pre-dictions. For Concrete G40, the experimental force of 11.5 kN is substantially lower than the numerical force of 33.6 kN, yielding a considerable 96% difference. The associated displacement values indicate a 44.15% difference, emphasizing a noticeable disparity. While the discrepancies in force measurements are substantial, the numerical model appears to provide relatively accurate predictions for displacement. The analysis reinforces the critical need to refine the numerical model, particularly in ad-dressing sources of error impacting force calculations. Recognizing these significant discrepancies highlights the urgency for implementing an interface element in the numerical model to minimize such substantial differences. This research aims to fulfil this objective by providing an interface element to enhance the accuracy of predictions and mitigate discrepancies between experimental and numerical results.”

Table 12. Force-Displacement Comparison Between Experimental and Numerical Results for Concrete G40 and UHPFRC Testing Specimens

	Type	Force (kN)	Error (kN)	Difference (%)	Displacement(mm)	Error (mm)	Difference (%)
UHPFRC	Experimental	41.5	28.5	57.51	10.4	1.26	21.45
	Numerical w/o interface	75			12.9
Concrete G40	Experimental	11.5	22.1	96	9.4	3.4	44.15
	Numerical w/o interface	33.6			6

 

 

Reviewer Comment (23):

In page 25-27, in reference to the description of Fig.26 and Fig.27 in the text, the names of Fig.26 and Fig.27 are reversed. Referring to Fig.28 and Fig.29, the data of columns 'Without interface' and 'With interface' are inverted, please check and modify.

Author’s Reply:

Thank you for your comment. As a matter of fact, there figure 26 and 27 reversed as their title. Figure 26 refers to Force displacement of CFRP-UHPFRC without interface element and Figure 27 refers to CFRP-UHPFRC with interface element. The text has been modified:

“The Force-Displacement curve that has been shown in Figure 26 shows the data obtained from the sample without interface element under cyclic loading. The maxi-mum force obtained has reached up to 75 kN at the displacement of 12.9 mm. On the contrary, the similar sample with interface element, has shown the force up to 44.5 kN with corresponding 10.7 mm displacement. (Figure 27)”
However, Referring to Figure 28 and 29, the demonstrations are correct.

 

Reviewer Comment (23):

As this paper focuses on behaviour and design of composite structures and interfacial performance, some state-of-the-art research on novel composite structures are recommended to be referred for improving the literature review part, including:

[1] Wu et al. Elastic buckling formulas of multi-stiffened corrugated steel plate shear walls. ENG STRUCT. 300 (2024), 117218.

[2] Yu et al. Experimental and numerical study on seismic performance of L-shaped multi-cellular CFST frames. J CONSTR STEEL RES. 213 (2024), 108360.

[3] Tong et al. Experimental and numerical investigations on seismic behaviour of stiffened corrugated steel plate shear walls. EARTHQ ENG STRUCT D. 52 (2023), 3551-3574.

[4] Chen et al. Flexural behaviour of novel profiled steel-UHTCC assembled composite bridge decks. J CONSTR STEEL RES. 212 (2024), 108258.

 

Author’s Reply:

New References added to enhance the literature of the study:

List of New Added References:

[3] S. Muzenski and B. Graybeal, “Structural Performance of UHPC Overlays.”

[4] X. M. You, L. B. Lin, B. Fu, and Y. Xiang, “Ultra-high performance concrete reinforced with macro fibres recycled from waste GFRP composites,” Case Studies in Construction Materials, vol. 18, Jul. 2023, doi: 10.1016/j.cscm.2023.e02120.

[5] A. A. Semendary and D. Svecova, “Numerical Simulation of the Load Transfer Mechanism at UHPC-UHPC Interface.”

[6] K. Y. Ong, C. K. Ma, N. M. Apandi, A. Z. Awang, and W. Omar, “Modeling of high-strength concrete-filled FRP tube columns under cyclic load,” in AIP Conference Proceedings, American Institute of Physics Inc., May 2018. doi: 10.1063/1.5034563.

[10] J. Zhao, X. Li, and X. Zhang, “Experimental and theoretical research on bond performance between CFRP bar and concrete under monotonic and reversed cyclic loading,” Eng Struct, vol. 246, Nov. 2021, doi: 10.1016/j.engstruct.2021.112994.

[13] H. Zhou, D. Fernando, V. Thuan Nguyen, and J. G. Dai, “The bond behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading: An experimental study,” Constr Build Mater, vol. 273, p. 121674, Mar. 2021, doi: 10.1016/J.CONBUILDMAT.2020.121674.

[21]       “BS EN 12390 Part 3 (British Standards Institute, 2009 c).

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Authors have addressed all the comments satisfactorily. So my final decision is ACCEPT on the manuscript. 

Author Response

Thanks for your compliment and kind support. 

Reviewer 2 Report

Comments and Suggestions for Authors

In response to the previous comments, the author has made some revisions. However, there are still several issues need to be addressed, as described below:

(1) In Table 2, the number "3" in the unit should be in superscript format.

(2) The figure numbers in the article are not continuous, and Figure 6 is still missing.

(3) In page 15, line 7, the author mentioned ' [Figure 15. (d)]', but there is no Figure 15. (d) in the article. This issue was highlighted in the previous review, but it has not been addressed in the revision.

(4) Tables 17 and 18 share the same name, and it is recommended to revise them for clarity.

(5) The logic of Section 9 in the article has been significantly improved compared to the previous version. However, there is only a pair of data comparisons in Table 18, along with load-displacement curve comparison information presented in Figure 28, which makes the finite element method with interface element proposed by the author less convincing.

Comments on the Quality of English Language

A large number of grammatical errors and typos are noticed in the manuscript.

Author Response

Reviewer #2:

 

Reviewer Comment (1):

In Table 2, the number "3" in the unit should be in superscript format.

Author’s Reply:

Thank you for pointing out this typo in Table 2. I have corrected it in all tables to ensure consistency.

 

Reviewer Comment (2):

The figure numbers in the article are not continuous, and Figure 6 is still missing.

Author’s Reply:

Thank you for bringing to our attention the inconsistency in figure numbering and the omission of Figure 6. The entire manuscript has been reviewed and ensured that all figure numbers are now consecutive.

 

Reviewer Comment (3):

In page 15, line 7, the author mentioned ' [Figure 15. (d)]', but there is no Figure 15. (d) in the article. This issue was highlighted in the previous review, but it has not been addressed in the revision.

Author’s Reply:

I deeply regret the persistence of this error. I have carefully reviewed the manuscript and corrected the figure reference in page 15, line 7. The erroneous reference to Figure 15. (d) has been replaced with the correct reference to Figures 14. (a) and 14. (b).

 

Reviewer Comment (4):

Tables 17 and 18 share the same name, and it is recommended to revise them for clarity.

Author’s Reply:

Instead, I have created a more comprehensive comparison table based on Table 15, which effectively summarizes the key findings and comparisons.

 

Reviewer Comment (5):

The logic of Section 9 in the article has been significantly improved compared to the previous version. However, there is only a pair of data comparisons in Table 18, along with load-displacement curve comparison information presented in Figure 28, which makes the finite element method with interface element proposed by the author less convincing.

Author’s Reply:

Thank you for your insightful observation regarding the need for more extensive data comparisons to fully demonstrate the effectiveness of the proposed finite element method with interface element. I agree that a broader range of data comparisons would strengthen the manuscript's argument and provide a more comprehensive picture of the model's capabilities.

To address this concern, I have expanded upon the data comparisons provided in Table 17 and incorporated additional comparisons throughout the manuscript. I have also included a new section that delves into the development and validation of the interface element, providing a more detailed explanation of its underlying principles and the rationale behind its formulation.

I believe that these modifications will significantly enhance the manuscript's clarity and persuasiveness, effectively showcasing the strength and accuracy of the proposed finite element method. The revised version of Section “9. Discussion”, is as below:

“The study aimed to enhance our understanding of the relationship between Carbon Fibre Reinforced Polymer (CFRP) rods and both conventional concrete Grade 40 and Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) under the demanding conditions of cyclic loading. Experimental and analytical findings revealed that the CFRP-UHPFRC bond exhibits significantly higher strength and displacement than the CFRP-concrete bond. This remarkable performance stems from several factors: the superior tensile strength and stiffness of UHPFRC compared to concrete; the enhanced interfacial bonding between the CFRP rod and UHPFRC, attributable to the denser microstructure of UHPFRC; and the reduced cracking tendency of UHPFRC, resulting in more ductile bond behaviour.

Deliberate development and integration of an analytical interface element into a finite element model addressed the previously recognized gap in these models' ability to accurately replicate empirical data. The introduction of this interface element proved crucial, aligning computational predictions more closely with experimental results, thereby laying a foundation for the construction or rehabilitation of more reliable and robust infrastructure. The FEM model developed in this study demonstrated accurate predictions of load-bearing capacity, displacement at peak force, bond strength, and average shear stress along the CFRP rod for CFRP-UHPFRC bond. Discrepancies between experimental and analytical results were within 10% for all parameters.

The utilization of the interface element stands at the core of our enhanced finite element method (FEM). Data presented in Table 17 highlights that initial simulations without the interface element exhibited significant deviations from experimental data. Notably, the maximum pull-out force was overestimated by a substantial 57.51%. The incorporation of the newly developed interface element effectively mitigated this difference, bringing the force prediction to a much-improved accuracy level of 8.62%. Additionally, the disparity in the critical parameter of displacement at peak forces was dramatically reduced from 21.45% without the interface element to an impressive 2.84% once the element was introduced into the model.

The efficacy of implementing the interface element is further emphasized by the improvement in bond strength predictions – a parameter of paramount importance for structural integrity where inaccuracies can lead to catastrophic miscalculations. The initial model projected bond strength at an overestimated figure that was 50.97% higher than the experimental observation. With the inclusion of the interface element, this figure was corrected, with only 7.07% of error present, corresponding to a 43.9% improvement. This aspect of the model’s improvement is particularly noteworthy, as bond strength directly influences the structural endurance and safety margins of built infrastructure.

The average shear stress along the CFRP rod is of utmost importance, and yet, the original FEM significantly overestimated the stress by an astonishing 100.141%. With the incorporation of the interface element, the error was remarkably reduced to a negligible 6.76%, representing a significant advancement in precision.

The findings of this research underscore that interface elements are not mere computational artifacts but rather pivotal components, particularly for cyclic loading conditions. They hold the potential to transform finite element modelling from estimative guesswork into accurate, results-oriented predictive tools. Computational models equipped with these interface elements will provide critical insights into the future design, optimization, and risk assessment protocols for concrete structures reinforced with CFRP rods.

Table 17. Comparison of data

	Parameters	UHPFRC	Discrepancy	Improvement
Maximum Pull out Force (kN)	Numerical w/o Interface	75	57.51%	48.89
	Experimental Data	41.5
			8.62%
	Numerical with Interface	45.13
Displacement at Peak Force (mm)	Numerical w/o Interface	12.9	21.45%	19%
	Experimental Data	10.4
			2.84%
	Numerical with Interface	10.7
Bond Strength (MPa)	Numerical w/o Interface	13.54	50.97%	43.9%
	Experimental Data	8.04
			7.07%
	Numerical with Interface	8.63
Average Shear Stress along CFRP Rod (MPa)	Numerical w/o Interface	26.6	100.141%	93.38%
	Experimental Data	8.85
			6.76%
	Numerical with Interface	9.47

 

The results of the study indicate that the combination of CFRP rods with UHPFRC offers superior performance compared to conventional concrete Grade 40. This is attributed to the enhanced bonding strength and the ductile behaviour of UHPFRC, which can better accommodate the cyclic loading conditions (Figure 27).

Figure 27. Force Comparison of All Obtained Data

Figure 28. Force-Displacement Comparison of All Obtained Data

The obtained results and comparisons of the interface elements demonstrate their efficacy, as they have been analytically formulated and validated based on experimental results. These results confirm that smooth CFRP has sufficient bonding properties to effectively reinforce concrete. However, when combined with high-performance concretes like UHPFRC, brittle CFRP exhibits exceptional performance due to the ductility of UHPFRC, which prevents abrupt damage to the CFRP composite. This is supported by the comparison presented in Table 19, which shows the data obtained by T Tibet Akbas et al. and the results of the current research [‎28].”

 

Reviewer Comment (6):

A large number of grammatical errors and typos are noticed in the manuscript.

Author’s Reply:

I sincerely apologize for the grammatical errors and typos that were present in the previous version of the manuscript. I have thoroughly reviewed the entire text and have implemented extensive editing and proofreading. The manuscript has undergone significant revisions to ensure accuracy, clarity, and adherence to proper English grammar and language usage.

Author Response File: Author Response.pdf