Failure Modes of Reinforced Concrete Beams Strengthened in Flexure with Externally Bonded Aramid Fiber-Reinforced Polymer Sheets under Impact Loading

Round 1

Reviewer 1 Report

The work is a significant contribution to the field of the effectiveness of reinforcement with FRP fiber sheets in exploited or designed reinforced concrete structures. A novelty in relation to the research carried out so far is the assessment of the effectiveness of sheet reinforcements under the influence of dynamic loads of different values. The article is the result of a wide cycle of research, the results of which have become the basis for formulating conclusions regarding reinforcements of different intensity.

The article is correctly written and follows the breakdown structure specified in the Journal's Guide for Authors. The text is legible; minor linguistic correction is suggested, although the article can be published in the present form. It is recommended to supplement its content according to the comments below.

General comments:

1. It is recommended to separate discussion on the analyzed issue and the obtained results from chapter 3.
2. The presented conclusions are rather a summary of the research carried out and the results obtained. It would be interesting to indicate some examples of practical implementation of the test results in terms of the presented reinforcement of the exploited structure subjected to dynamic load, at risk of losing load capacity.
3. The Authors made a detailed analysis of the issue in question on the basis of the published results of previous research. The reviewer points out that many of the cited items in the References were published many years ago. Please make sure that the items cited are up-to-date and complete this overview.

Detailed comments:

4. The Authors do not provide criteria for the use of a beam with a span of 3.0 m and a cross-section of 0.25x0.20 m, with a given cross-section of reinforcement bars. Please justify the selection of the beam parameters adopted for the tests, and in the discussion chapter please indicate what potential differences will occur in the case of larger spans of the beams, greater degree of reinforcement of the cross-section, other (lower) concrete class.
5. The method of joining successive FRP sheets to the reinforced structure is unclear. Please describe how the perfect adhesion of the sheets to the concrete was achieved, how were the surfaces of the concrete beams prepared? Will the poor condition of the concrete surface in exploitation be a problem and prevent the use of the analyzed type of reinforcement?
6. The authors do not specify the period in which the entire research cycle was performed.
7. The Authors conclude that “To accurately determine the relationship between the curvature and bending moment for each strain level, a cross-section of the beam was divided into horizontal layers within 5-mm thicknesses corresponding to the concrete and reinforcements, as shown in Figure 6. " (185 - 187). Please explain why the structure was divided into 5mm thick layers.
8. There is no information as to whether the depth of penetration of cracks and their width were measured during the tests. Alternatively, what measurement method was used?

 

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

 

This article investigated the strengthening of reinforced concrete beams in flexure using externally bonded aramid FRP sheets under Impact Loading. The article provides an insight into the strengthening of existing structures using the FRP laminate and their performance under impact loading. The article needs to be improved by addressing the comments as listed below.

1. Line 13; mention the height of drop in the abstract.
2. Keywords: remove the static loading from the keywords since the impact testing only was conducted in this investigation.
3. The introduction section has written well and sufficiently described the current problem and discussed relevant literatures. Add a few lines about the significance of the research.
4. Please use the IMRAD format. What are the raw materials used to prepare the beams? It should be discussed in the manuscript.
5. Provide some pictures related to the casting of beams and explain the mixing and casting procedure of concrete beams.
6. Add mix proportion table and results from Table 1 should be discussed in the results and discussion chapter.
7. How are the flexural and shear capacity determined? Introduce the equations in the manuscript.
8. Explain how the dimension of the beam is decided.
9. Explain the procedure of FRP laminate in beams with pictures.
10. Why is the AFRP adopted in this study since GFRP and CFRP are primarily employed in practice?
11. Figures 2 and 3 can be improved. Mention the accessories used for the testing.
12. On what basis the weight of the hammer and height of the drop is selected?
13. Section 3.1.3, the crack pattern of the beams under the static load, can be discussed more in detail. What is the most important failure observed in the beams under static loading?
14. How is the input energy calculated?
15. The discussion of impact test results is presented well. However, the influence of loading (Static and impact) in the failure pattern of the beams can be compared and discussed.
16. Conclusions can be strengthened by adding more impact test findings.
17. Lines 497-498 “the RC beams strengthened with externally bonded AFRP sheets can be reduced the maximum and/or residual displacement by 497 up to 35% and 85%, respectively”. This sentence should be revised.

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled "Failure Modes of Reinforced Concrete Beams Strengthened in Flexure with Externally Bonded Aramid Fiber-Reinforced Polymer Sheets under Impact Loading” conducted impact loading tests on RC beams strengthened with AFRP sheets. Un-strengthened beams were also tested as reference beams.

This reviewer recommends major editing and resubmitted for re-review because of the following comments.

Technical comments:

• The plagiarism percentage is 38%, and it should be reduced.
• The authors provided more information in lines 100-110 that should be highlighted in the abstract like static loading until failure.
• Lines 9-10: The authors highlighted the main purpose of this study, which was how the volume affects the failure mechanism of the FRP sheet. However, the authors did not address the conclusion related to this purpose. Therefore, the answer for the purpose in lines 9 and 10 should be highlighted in the abstract.
• Lines 21-22: These keywords should be modified to be more reliable. So what is the difference between "fiber-reinforced polymer sheet" and "AFRP sheet".
• Table 1: The 8^th This reviewer is feeling that "flexural capacity" is the moment of resistance of the beam. However, the provided values are the "load capacities" or "ultimate capacities".
• Table 1: The 10th column title should be "Shear-ultimate capacity" or "Shear-Load capacity".
• Line 120: The cited version to calculate the shear and load capacities of the tested beams is very old (2007). Why? I think there should be a new version. The same notice for reference 34.
• Figure 1: The first figure should be "Elevation", not "Side view". Also, the AFRP sheet should be illustrated in the first figure.
• Lines 130-131: Is it the real case in reinforced concrete beams?
• Section 2: More information about the used epoxy to bond the AFRP sheets to the concrete surfaces should be provided.
• Line 139: What do you mean by "after the three-point loading test"?! It is an unclear sentence. I think you mean "static loading was conducted after impact loading".
• Line 144: How did the authors recognize the yielding of steel rebars?
• Figure 3: I am not sure if this is correct or not. However, this reviewer is feeling that the specimen in Figure 2 has a rectangular cross-section and that one in Figure 3 has a square cross-section.
• Section 3.1: This reviewer is confused about this section, which is related to static loading tests. I am not sure why did the authors conduct this type of test.
• First of all, this section should be included in the Results and Discussions section. Second, the authors highlighted the novelty of the manuscript in the abstract by saying "However, how volume affects the failure mechanism of the FRP sheet of strengthened RC members has not been studied". So what is the main purpose to provide this analytical model?
• Table 3: How the authors did determine the yield load? The authors did not use strain gauges on the steel rebars.
• Figure 8: The mode of failure should be highlighted if it is debonding, peeling, rupture, or concrete crushing.
• Line 284: What do you mean by "residual deflection". Do you mean the deflection after static loading or the permanent deflection after impact loading?
• Table 4: More information about how did the authors determine the measured input energy should be provided.

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors. Congratulations on your interesting research. I have only a few suggestions for editorial changes:

1. I could not find any information about the adhesive used (epoxy?). In the acknowledgements there is only a mention of the manufacturer.

2. On what basis was the experimental rebar yield load given in Table 3 determined? I found no information about direct measurement of rebar strains. Was it determined from the graphs in Figure 4? What was the criterion? The inflection point of the curve for Beam A1660S may be debatable.

3. I understand that nonstrengthened beams were not tested for drop heights of 2.0, 3.0 and 3.5m due to insufficient bearing capacity. This information is missing from the manuscript, and the content of the paragraphs on lines 281 and 348 might suggest that all beams were tested over the entire drop height range.

4. In Figure 11f, for beam A1660, the information is missing that the entire sheet has completely debonded.

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have addressed most of the reviewer's comments. However, this reviewer still has concerns about three points:

1- The plagiarism percentage is 38%, and it should be reduced. The authors responded as "According to the "iThenticate Report," our manuscript has a plagiarism rate of 38%. However, in our article, the report indicated that the most duplicate words and phrases were from sources 1 and 2. These are our published articles. We confirm that there are no conflicts of copyright". I think the authors need to think more about their response.

2- Lines 130-131: Is it the real case in reinforced concrete beams? The authors responded as "Yes, it has described the reinforced concrete beams used in this experiment". The reviewer means is it a real case in a structure to weld the steel rebars to a steel beam. I am not asking about your specimens.

3- How did the authors recognize the yielding of steel rebars? The authors responded as "In this situation, we had found that the yield of the reinforcement bars when the load was increasing steadily then decreased suddenly. After that, the load increased again due to the hardening effect of the reinforcement". I think the yielding of steel rebars should be confirmed by measuring the strains in these rebars. The concrete cracking and crushing can affect the non-linearity of the load-deflection relationships.

Author Response

"Please see the attachment."

Author Response File: Author Response.docx