Plastic Hinge Length Mechanism of Steel-Fiber-Reinforced Concrete Slab under Repeated Loading

Round 1

Reviewer 1 Report

The submitted article “jcs-1725080” entitled: “Plastic Hinge Length Mechanism of Steel Fiber Reinforced Concrete Slab under Cyclic Loading” investigates the influence of steel fibers at the plastic hinge length of Steel Fiber Reinforced Concrete (SFRC) slab specimens tested under repeated loading. Compressive and splitting tensile strength of SFRC is also experimentally evaluated. The experimental efforts of the authors are acknowledged. The following comments, questions and suggestions are raised for authors’ reference:

1. The state-of the-art reported in section “Introduction” does not adequately highlight the gaps in the existing literature that the current study is trying to fill. This introductory part is recommended to be improved providing more convincing motivations of this research. Further, research significance and subsequent impact of this study on the state of the practice should be highlighted.

2. The novelty of the study should be highlighted in the end of introduction section. How this study is different from the published study in literature? How the outcome of this study will benefit researchers and end users? This need to be highlighted in introduction or end of conclusion.

3. The background study on the influence of steel fibers in large-scale SFRC structural members with or without conventional steel reinforcement (longitudinal reinforcing bars and stirrups) is insufficient.

4. It is known that short steel fibers added in concrete as mass reinforcement mainly provide crack control due to the tensile stress transfer capability of the steel fibers across crack surfaces known as crack-bridging, after cracking. This way, fibers provide significant resistance to shear across developing cracks, and therefore, SFRC demonstrate a pseudo-ductile response, increased residual strength (especially in tension) and enhanced energy dissipations capacities, relative to the brittle behavior of plain concrete mixtures. Cracking diagnosis in fiber-reinforced concrete specimens could also be examined. Further, “flexural analysis of SFRC members” can be combined in the slab specimens tested in this experimental research.

5. The advantageous characteristics of SFRC under tension are also very important for the shear response of concrete structural members which is governing by the tensile response of the fibrous material. Thus, fibers have been proved as a promising non-conventional reinforcement in concrete elements under shear stresses due to the beneficial cracking performance of SFRC and, under specific circumstances, could alter the brittle shear failures to ductile flexural ones. It would be beneficial for the paper to extend these findings in an enlarged frame of shear-critical SFRC structural members with or without conventional steel reinforcement. The “effect of steel fibers on the hysteretic performance of concrete beams with or without steel reinforcement” should be examined and commented. This way, test results derived of this study would be more useful on the state of the practice and for real-scale constructions.

6. Ductility of SFRC is an important parameter of SFRC performance that could be discussed further. Further, “analysis of the residual flexural stiffness of SFRC beams with conventional steel reinforcement” could be discussed properly.

7. Cyclic loading usually refers to reversal deformation sequence that includes hysteretic response caused by loading - unloading - loading to the opposite direction - unloading, etc. The performed fatigue compression tests include loading - unloading - reloading (to the same direction) - unloading, etc. Thus, the term “…repeated loading” seems to fit better than “…cyclic loading” through the entire manuscript.

8. The relationship between the text and the figures is weak; the text leads the readers to believe that the figures will provide the desired information and/or clarification of the work done but the figures do not provide this. Discussion and further commentary of the figures should be provided.

9. The English language, terms and style needs substantial polishing. Presentation and the quality of the figures can be further refined.

Author Response

Responses to Reviewer comments

The authors sincerely thank the editor and the two reviewers for their constructive comments. All of their comments have been carefully considered and, wherever appropriate, revisions have been made to the manuscript. Responses to these comments and revisions implemented in the paper are detailed below. The Reviewers’ comments are in italic black fonts while our replies are in blue. Text changed in the manuscript is highlighted in green.

Reviewer 1

The submitted article “JCS-1725080” entitled: “Plastic Hinge Length Mechanism of Steel Fiber Reinforced Concrete Slab under Cyclic Loading” investigates the influence of steel fibers at the plastic hinge length of Steel Fiber Reinforced Concrete(SFRC) slab specimens tested under repeated loading. Compressive and splitting tensile strength of SFRC is also experimentally evaluated. The experimental efforts of the authors are acknowledged. The following comments, questions and suggestions are raised for the authors’ reference:

(Q1)    The state-of-the-art reported in section “Introduction” does not adequately highlight the gaps in the existing literature that the current study is trying to fill. This introductory part is recommended to be improved providing more convincing motivations for this research. Further, the research significance and subsequent impact of this study on the state of the practice should be highlighted.

(A1)                 We thank the reviewer for this valuable comment. The gap in the existing literature is updated in the introduction part and the impact of this study is highlighted in green.

            Experimental and numerical analyses were used to investigate the impact of fibre clustering on the fatigue behaviour of steel-fiber-reinforced concrete (SFRC) beams with reinforcements. Furthermore, to better understand the underlying mechanism, the fibre distribution in the cross-section of concrete was experimentally investigated. The results showed that when the fibre volume percentage grew, the fatigue life of the beam increased [22]. To forecast the shear strength of steel fibre reinforced concrete beams, a mechanics-based mathematical model that considers the effect to resist shear was suggested (without transverse reinforcement). The suggested model's efficacy was tested using a wide number of datasets, and it was discovered that it had good correlations with experimental results, with mean, standard deviation, and coefficient of variation of 0.94, 0.22, and 22.99 %, respectively. In addition, each effect to resist shear contribution was recommended [23].

          Although the importance of fibre distribution to the characteristics of SFRC members was highlighted in the literature listed above, the underlying mechanism of fibre distribution to the fatigue performance of SFRC, as well as the behaviour of beam and slab under static and repetitive loading, was not. Even though there have been some studies on identifying plastic hinges, the contribution of steel fibres at plastic hinge length has little attention. There has been no research on the impacts of fibre distribution at the slab's plastic hinge length under repeated stress.

(Q2)    The novelty of the study should be highlighted in the end of introduction section. How this study is different from the published study in literature? How the outcome of this study will benefit researchers and end users? This need to be highlighted in introduction or end of conclusion.

(A2)      We thank the reviewer for this suggestion. The novelty of the study is discussed at the end of the introduction section and the difference with reference to previous work is highlighted in green. Outcome benefits to researchers are also discussed and highlighted in green.

In this paper, the concrete was tested experimentally with various SFRC parameters at various plastic hinge lengths. Using five different slabs of varying parameters, the behaviour of steel fibre at the plastic hinge length under repetitive loads was investigated. The mechanical properties of the RCC slab were determined for standard concrete and SFRC. The properties of the steel fibre slab at plastic hinge length were determined under repeated loading becomes the novelty of this work. In the future, the plastic hinge length concept along with different strengthening techniques may be applied to beams and slabs under different types of loading.

(Q3)    The background study on the influence of steel fibers in large-scale SFRC structural members with or without conventional steel reinforcement (longitudinal reinforcing bars and stirrups) is insufficient.

(A3)     We thank the reviewer for this comment.  The study on influence of steel fibers in large-scale SFRC structural members with or without conventional steel reinforcement has now been included in the introduction section of this paper by adding the following two references.

22. D. Gao, Z. Gu, C. Wei, C. Wu, and Y. Pang, “Effects of fiber clustering on fatigue behavior of steel fiber reinforced concrete beams,” Constr. Build. Mater., vol. 301, no. May, 2021, doi: 10.1016/j.conbuildmat.2021.124070.

23     B. Singh Negi and K. Jain, “Shear resistant mechanisms in steel fiber reinforced concrete beams: An analytical investigation,” Structures, vol. 39, no. September 2021, pp. 607–619, 2022, doi: 10.1016/j.istruc.2022.03.061.

(Q4)    Cracking diagnosis in fiber-reinforced concrete specimens could also be examined. Further, “flexural analysis of SFRC members” can be combined in the slab specimens tested in this experimental research.

(A4)    We thank the reviewer for this comment. Flexural analysis of conventional concrete and SFRC members with their corresponding results are included in the experimental procedure and results in this revised manuscript.

The conventional RCC slab developed a 2mm diagonal crack running almost the whole length of the specimen and the SFRC Slab at 70 mm plastic hinge length shows the wider brittle cracks of 4mm at the middle of the slab where the maximum deflection took place. Meanwhile, the SFRC Slab with minimum reinforcement and the SFRC Slab with 150 mm plastic hinge length shows a 1mm crack width and that crack moved away from the maximum deflection zone to another area.

(Q5)    The “effect of steel fibers on the hysteretic performance of concrete beams with or without steel reinforcement” should be examined and commented.

 (A5)   We thank the reviewer for this comment. The hysteretic performance of members with or without steel reinforcement was examined and commented on as shown in Table 7 (Specimens 1 and 2, respectively). Meanwhile, the hysteretic curve is shown in Figures 8 (a & b) with or without steel reinforcement.              

(Q6)    Ductility of SFRC is an important parameter of SFRC performance that could be discussed further.

(A6)       We thank the reviewer for this comment. Ductility of SFRC is discussed in the result part and the same has been highlighted in green.

Split tensile strength of steel fiber reinforced concrete seems to be 1.5 times higher than that of conventional concrete due to the distribution of steel fibers in concrete which influence the bonding and improves the ductility. The modulus of elasticity was calculated by applying uniaxial compression to the cylinder specimen showing that SFRC specimen with 1.5% steel fiber performs 1.14 times better than the conventional concrete specimen. Hence the same was adopted for slab specimen casting. The behavior under bending is evident from the flexural strength test, where the flexure beam with steel fibers shows 1.39 times performance improvement than that of a conventional concrete beam.

(Q7)    Cyclic loading usually refers to reversal deformation sequence that includes hysteretic response caused by loading - unloading - loading to the opposite direction -unloading, etc. The performed fatigue compression tests include loading - unloading - reloading (to the same direction)- unloading, etc. Thus, the term “…repeated loading” seems to fit better than “…cyclic loading” through the entire manuscript.

(A7)     We thank the reviewer for this comment. The repeated loading has now been used to replace cyclic loading all along the manuscript with half-cycle in some places and this change has been highlighted in green.

(Q8)    The relationship between the text and the figures is weak; the text leads the readers to believe that the figures will provide the desired information and/or clarification of the work done but the figures do not provide this. Discussion and further commentary of the figures should be provided.

.

(A8)     We thank the reviewer for this valuable comment. New figures have been added and the sentences have also been revised to give a proper relationship between Figures 7(a, c-f) and text and these changes have been highlighted in green.

(Q9)    The English language, terms and style needs substantial polishing. Presentation and the quality of the figures can be further refined.

(A9) We thank the reviewer for this valuable comment. English terms and style were polished, and the figure quality has now been improved along with new figures being added in the revised script. New figures were added and the sentences were revised to give a proper relationship between Figures 7(a, c-f) and the text which are highlighted in green.

Author Response File: Author Response.pdf

Reviewer 2 Report

Paper title:    Plastic Hinge Length Mechanism of Steel Fiber Reinforced Concrete Slab under Cyclic Loading.

 Authors:   

 Pradeep Sivanantham, G. Beulah Gnana Ananthi, Krishanu Roy, Karthikeyan.R, Deepak P

The paper is interesting and useful for the practicing engineers. The influence of the use of steel fibers on the plastic hinge formation of reinforced concrete slabs is experimentally studied.

The use of steel fibers for the production of concrete with increased flexural and compressive strength can be considered as a relatively new and promising direction for demanding constructions.

The literature background reported in Introduction is rather informative. However, the state-of-the-art related to the flexural and cracking response and the analysis of beams with steel fibers is not adequately highlighted. The manuscript partially fails to build on the existing works and to establish the relevance of the work reported in the paper; recent experimental papers dealing with the use of steel fibers as reinforcement of reinforced concrete beams are not traced in the introduction.

The results are interesting, nevertheless, some comments and amendments could be suggested as follows:

- A table of the tested specimens with their characteristics has to be included in the revised manuscript.

- In paragraph '2. Materials'. It is stated that steel fibers accounts for 1.5 percent of the volume of concrete whereas in paragraph 3.1 in the 4th line it is stated that ‘cubes are casted with steel fiber reinforced concrete of 1.5 % dosage by weight of concrete’. There must be a contradiction, please re-check it.

The amount of steel fibers in concrete has to be defined in the text of the revised manuscript (and not only in Table). Define whether the contents of steel fibers is in w/v or v/v. In any case simply write the weight of the fibers per m3 of concrete.

- A justification (comments) for the steel fiber content has to be included in the revised paper. What would be the results for lower amount of fibers per m3? Add comments.

- The inclusion of stress-strain diagrams obtained from typical compression tests would really enhance the presented work significantly. In case it is possible, add in the revised manuscript stress-strain diagrams.

- Cross-section analysis of the critical section of the tested specimens is required. Calculation of curvature ductility and displacement ductility and comparisons to the observed values could enhance the validity of the results in the revised manuscript.

- Design of specimens. Design loads and design targets. Design code. Comparison to the test results.

- The addition of steel fibers into concrete mixture increases its tensional strength and probably the post-peak ductility of the compression behavior. How these observations resulted to the failure of the compression zone of the beams (in some cases)? Add comments.

- The behavior of steel fiber concrete beams under various loadings (flexural, shear and torsion) is investigated experimentally in many research papers - Materials 2020 Vol. 13, 2698. 

- Measurement and comparison of the evolution of the crack width during the loading would be interesting for the extraction of conclusions,

- The conclusions of the submitted paper are interesting. The authors could include both qualitative and quantitative data in the conclusions.

Final conclusions

The submitted paper is an interesting work. Amendments and improvements based on the aforementioned suggestions may help the authors to improve their work.

Acceptance after a careful revision is recommended.

Author Response

Reviewer 2

The suggestions for this manuscript are listed below:

(Q1)    The literature background reported in Introduction is rather informative. However, the state-of-the-art related to the flexural and cracking response and the analysis of beams with steel fibres is not adequately highlighted. The manuscript partially fails to build on the existing works and to establish the relevance of the work reported in the paper; recent experimental papers dealing with the use of steel fibres as reinforcement of reinforced concrete beams are not traced in the introduction.

(A1)     We thank the reviewer for this valuable comment. The recent work dealing with the use of steel fibres as reinforcement of reinforced concrete beams has been incorporated in the introduction section of the revised paper and highlighted in green for your kind reference.

Experimental and numerical analyses were used to investigate the impact of fibre clustering on the fatigue behaviour of steel-fiber-reinforced concrete (SFRC) beams with reinforcements. Furthermore, to better understand the underlying mechanism, the fibre distribution in the cross-section of concrete was experimentally investigated. The results showed that when the fibre volume percentage grew, the fatigue life of the beam increased [22]. To forecast the shear strength of steel fibre reinforced concrete beams, a mechanics-based mathematical model that considers the effect to resist shear was suggested (without transverse reinforcement). The suggested model's efficacy was tested using a wide number of datasets, and it was discovered that it had good correlations with experimental results, with mean, standard deviation, and coefficient of variation of 0.94, 0.22, and 22.99 %, respectively. In addition, each effect to resist shear contribution was recommended [23].

(Q2)    A table of the tested specimens with their characteristics has to be included in the revised manuscript

(A2)     We thank the reviewer for this valuable comment. The tables of the tested specimen along with their dimensions and mechanical properties have now been included in the revised manuscript and the same has been highlighted in green.

Table 4. Dimensions and Specifications of Slabs

Table 5. Mechanical Properties of Concrete

Table.6 Modulus of Elasticity of Specimens

(Q3)    In paragraph '2. Materials'. It is stated that steel fibers accounts for 1.5 percent of the volume of concrete whereas in paragraph 3.1 in the 4th line it is stated that ‘cubes are casted with steel fiber reinforced concrete of 1.5 % dosage by weight of concrete’. There must be a contradiction, please re-check it.

The amount of steel fibers in concrete has to be defined in the text of the revised manuscript (and not only in Table). Define whether the contents of steel fibers is in w/v or v/v. In any case simply write the weight of the fibers per m3 of concrete.

(A3)     We thank the reviewer for this valuable comment. In paragraphs 2 and 3.1, the amount of steel fiber was converted as 1.5% by the weight of concrete. The content of steel fiber has now been explained as highlighted in green.

Steel fiber accounts for 1.5% of the weight of concrete in the specimen. -Paragraph 2

Meanwhile remaining 5 same-sized cubes were cast with steel fiber reinforced concrete of 1.5 % by weight of concrete-Paragraph 3.1.

(Q4)    Justification (comments) for the steel fiber content has to be included in the revised paper. What would be the results for lower amount of fibers per m3? Add comments

(A3)     We thank the reviewer for this valuable comment. The justification of steel fiber content used as 1.5% by weight of concrete was taken from the previous study [7] of the authors which has been cited in this paper as given below:

256. Pradeep, V. U. E. Vengai, and D. Florence, “Experimental Investigation on the Usage of Steel Fibres and Carbon Fibre Mesh at Plastic Hinge Length of Slab,” 2019, Materials Today Proceedings, 14(2), pp 248-256. doi.org/10.1016/j.matpr.2019.04.144

(Q5)    The inclusion of stress-strain diagrams obtained from typical compression tests would really enhance the presented work significantly. In case it is possible, add in the revised manuscript stress-strain diagrams.

(A5)     We thank the reviewer for this valuable comment. Stress-strain diagrams along with young’s modulus obtained from the compression test have been included in the revised manuscript as highlighted in green.

          Table.6 Modulus of Elasticity of Specimens

(Q6)    Cross-section analysis of the critical section of the tested specimens is required. Calculation of curvature ductility and displacement ductility and comparisons to the observed values could enhance the validity of the results in the revised manuscript.

(A6)                 We thank the reviewer for this valuable comment. Cross-section analysis of the critical section was not carried out in this present study. The same will however be implemented in future studies by the same authors. Thanks for your understanding.

(Q7)    Design of specimens. Design loads and design targets. Design code. Comparison to the test results.

(A7)                 We thank the reviewer for this valuable comment. The design of specimens as per the codal provisions were used as shown in the figure.

The slabs cast for the experimentation had the dimensions of 850mm × 300mm × 80mm as per the Indian standard IS456-2000.

The tests was carried out using a compressometer in accordance with the IS 516-1959.

(Q8)    The addition of steel fibers into concrete mixture increases its tensional strength and probably the post-peak ductility of the compression behavior. How these observations resulted to the failure of the compression zone of the beams (in some cases)? Add comments.

(A8)                 We thank the reviewer for this valuable comment. The main reason was that the strengthening effects of fibers on the stiffness of the beam under fatigue loading could be attributed to the increased bonding force between the steel bar and concrete, the decreased fatigue damage of concrete in the compression zone and increased tensile strength of concrete in the tension zone [22-23].

(Q9)    Measurement and comparison of the evolution of the crack width during the loading would be interesting for the extraction of conclusions; the conclusions of the submitted paper are interesting. The authors could include both qualitative and quantitative data in the conclusions.

(A9)  We thank the reviewer for this positive comment. The evolution of crack width was considered and discussed in the revised manuscript. The quantitative and qualitative data were included in the conclusions and the changes made are highlighted in green.

Cracks formation in the steel fiber reinforced slab at plastic hinge length of 150 mm shows 1mm crack width, which moved away from the maximum stress zone. The crack pattern was similar to that of a fully steel fiber reinforced concrete slab.

Split tensile strength of steel fiber reinforced concrete seems to be 1.5 times higher than that of conventional concrete due to the distribution of steel fibers in concrete which influence the bonding and improves the ductility. The modulus of elasticity was calculated by applying uniaxial compression to the cylinder specimen showing that SFRC specimen with 1.5% steel fiber performs 1.14 times better than the conventional concrete specimen. Hence the same was adopted for slab specimen casting. The behavior under bending is evident from the flexural strength test, where the flexure beam with steel fibers shows 1.39 times performance improvement than that of a conventional concrete beam.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript with number “jcs-1725080-v2” and the new title: “Plastic Hinge Length Mechanism of Steel Fiber Reinforced Concrete Slab under repeated Loading” has been improved extensively. The efforts performed by the Authors to consider all the recommendations and to respond to all the criticisms of the previous review, as presented below, are greatly appreciated. Hence, it is suggested the revised version of this paper to be accepted for publication, more or less, as it is. Some minor revisions based on the comments of the previous review report (round 1) are raised for authors’ reference to the final amelioration of their good paper.

Comment 1:  Well-addressed. No further revision is required.

Comment 1:  The state-of the-art reported in section “Introduction” has been improved substantially. A few additional articles are suggested to be considered based on the following comments.

Comment 2:  Well-addressed. No further revision is required.

Comment 3: The findings of the following articles would help to establish the influence of steel fibers in large-scale SFRC structural members with or without conventional steel reinforcement (longitudinal reinforcing bars and stirrups):

- “Response of steel fiber-reinforced concrete beams with and without stirrups”, ACI Structural Journal 2012.

- “Cyclic response of steel fiber reinforced concrete slender beams: An experimental study”, Materials 2019.

4. The following articles are suggested to be considered to justify further the results of this study and to highlight the contribution of short steel fibers as concrete mass reinforcement to provide crack control and resistance to shear across developing cracks:

- “Flexural analysis of steel fibre-reinforced concrete members”, Computers and Concrete 2018.

- “Flexural capacity prediction model for steel fibre-reinforced concrete beams”, International Journal of Concrete Structures and Materials 2021.

Comment 5:  Well-addressed. No further revision is required.

Comment 6:  Well-addressed. No further revision is required.

Comment 7:  Well-addressed. No further revision is required.

Comment 8:  Well-addressed. No further revision is required.

Comment 9:  Well-addressed. No further revision is required.

Reviewer 2 Report

Revised Paper title:    Plastic Hinge Length Mechanism of Steel Fiber Reinforced Concrete Slab under Cyclic Loading.

 Authors:   

 Pradeep Sivanantham, G. Beulah Gnana Ananthi, Krishanu Roy,

Karthikeyan.R, Deepak P

As stated in the first review the paper is interesting and useful for the practicing engineers. The use of steel fibers for the production of concrete with increased flexural and compressive strength can be considered as a relatively new and promising direction for demanding constructions.

The literature background reported in Introduction is rather informative. However, the state-of-the-art related to the flexural and cracking response and the analysis of beams with steel fibers is not adequately highlighted. The manuscript partially fails to build on the existing works and to establish the relevance of the work reported in the paper; recent experimental papers dealing with the use of steel fibers as reinforcement of reinforced concrete bars are not traced in the introduction.

Following the reviewer’s comments a new table of the tested specimens with their characteristics has been included in the revised manuscript.

Clarification about the steel fibers has been added.

- Cross-section analysis of the critical section of the tested specimens has not been carried out in the revised manuscript.

Final conclusions

The submitted paper is an interesting work.

Some of the reviewer’s comments have been successfully responded, some have not.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The whole manuscript needs revision. The abstract is not clear. The main sections are also not clear whether the steel fibres were placed at the plastic hinge location of the tested slabs, and if so, how they were kept in place.  Section 3.1 refers to Figures 6(a) to 6(e) as slab specimens, but Figure 6 is the experimental setup. The methodology of applying the cyclic load is not clear. Many terminologies are referred to inappropriately, not as expected in a standard writing format.  Some paragraphs are repeating (Section 4.1). Some sentences are not complete.

Reviewer 2 Report

The Authors of the paper presents the study on the influence off steel fiber on the load-displacement behavior of RC slabs. Although the idea of optimizing the use of steel fibers in only critical sections may be interesting, the performed study is weak. Several critical aspects may be mentioned:

1. After reading the introduction it is quite difficult to understand the object of the present study: punching shear, glass fibers, steel fibers, FRP strengthening, acoustic emission, plastic hinges, high strength concrete are discussed in a random manner.
2. The description of the study is poor – it is difficult to understand the differences between the specimens, results are presented unreasonably.
3. There are a lot of mistakes, repetitions, wrong captions etc. in the text
4. The results of the study hardly brings any new substantiated insights.