Dynamic Behavior of RC Columns Confined with Micro-Expansive Concrete-Filled Steel Tubes Subjected to Lateral Low-Velocity Impact: Experimental and Numerical Study

Round 1

Reviewer 1 Report

The research presented in the article entitled “Dynamic behavior of RC columns confined with micro-expansive concrete filled steel tubes subjected to lateral low-velocity impact: Experimental and numerical study” presents an experimental study on the anti-collision performance of RC columns strengthened with micro-expansive concrete filled steel tube using a combination of experiment and finite element calculation.

The Abstract summarizes properly the research presented in the article, it is well structured and it includes on short the aim of the paper, the study highlights and the results.

Introduction presents the necessary notions in order to make a general view on the subject and to understand its importance, it ensures adequate motivation for the purpose of the study. The aim of the paper is clearly stated.

The Experimental design is in detail described.

The Results, Numerical calculation and Validation sections are extensively discussed.

The Conclusions highlights the results obtained and what they mean.

The article is well belabored and engaging, rigorous and clearly structured.

Author Response

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Reviewer 2 Report

The authors investigated the dynamic response of a RC column confined by micro-expansive concrete filled steel tube under an impact. The experiment and analysis were conducted in this study. The reviewer has the following major comments:

1. The introduction should be more extensive to cover concrete filled steel tubes in strengthening columns. The behavior of micro-expansive concrete should also be reviewed. So that readers will understand the background and the highlight of this article clearly.
2. In Figure 2, the location of the load cell is missing in the sketch.
3. In Section 2.3, what was the sampling rate used? And discuss the response frequency of devices, particularly displacement sensors and load cell to ensure the accuracy of measured results.
4. In Figure 8, why did the load for the SM-RC column become negative beyond 0.03s?
5. In Section 3, it would be interesting to present the result in terms of energy absorption. The impact energy can also be derived since the mass and velocity are known.
6. In Section 4.2, avoid using uncommon terms for example CSCM, MAT_****, CONTACT**. Clearly define and explain the terms in details.
7. How was the strain rate effect of materials taken into account in the model?
8. Free oscillation is observed in the analytical results (Figures 13-17). Discuss why this oscillation occurred. How was damping incorporated in the model?

Author Response

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Please see the attachment.

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Author Response File: Author Response.pdf

Reviewer 3 Report

This research aims to investigate the dynamic behaviour of RC columns confined with micro-expansive concrete-filled steel tubes subjected to lateral low-velocity impact. This study is useful for the design of structures subjected to impact loading. However, the article should be improved by addressing the comments as follows.

 

1. Abstract: more clear information should be included regarding the influence of steel tube strength, micro expansive concrete strength and steel tube wall thickness. The description of the work is shallow and should be enhanced.

2. Abstract: key findings from the research are very general, quantify the results and include in the abstract.

3. Section 1, Add more literatures regarding the expansive concrete-filled steel tubes. The current literature only focused on the RC columns.

4. Section 2.1, many sentences are too long and hard to follow. It would be great to break the sentences.

5. Figure 1, how the column dimensions are selected?

6. Figure 1, mention the thickness of the expansive agent.

7. What type of cement used?, mention the basic properties.

8. Mention the properties of fine and coarse aggregate in section 2.2.

9. The expansive micro concrete is made with Portland cement, fly ash, silica fume, mineral powder. Mention the properties of these materials.

10. Figure 2, include an experimental test setup picture rather than a schematic.

11. Figure 3 (b) should be an RC column inserted into the steel tube.

12. Figure 3(c), no details are mentioned in the picture. It simply shows the image of the bottom steel tube.

13. Figure 4, experimental setup can be included.

14. What is the magnitude of impact force applied? The velocity of impact?

15. Experimental impact test setup needs more explanations and improvements.

16. Where is the contact point of impact with the column? Mention?

17. Why is the impact load applied on the column's bottom portion? What are the support conditions used for the column? Justify this.

18. Explain more in detail the failure pattern of the column.

19. Correlate results with the earlier literature.

20. The discussion section is adequate and well organized.

21. Conclusions are general and weak. Quantify the results and add key findings.

Author Response

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Please see the attachment!

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Some parts of the manuscript were updated to incorporate the comments. There are outstanding points as follows:

1. Explain the reason for negative values of the measure load in the manuscript. Otherwise readers may doubt credibility of the results.
2. Explain why there is oscillation in the analytical results in the manuscript.
3. Explain the parameters used in considering the strain rate effect in the model. Discuss how it affects the result. 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

All comments are addressed sufficiently. Please check Figure 2 presented twice.

Author Response

Thank the reviewers for their recognition of our work！

 

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