Seismic Behavior of RC Beam Column Joints with 600 MPa High Strength Steel Bars

Round 1

Reviewer 1 Report

1. Please clarify the meaning of “shear-compression” in the abstract.
2. Please revise the entire manuscript to correct minor misprints (e.g., “in reinforcement in reinforcement”, line 71) and English use mistakes.
3. Line 88. The authors state that for the joint region, the spacing is reduced. The actual spacing adopted is reasonable, however it is not clear if the Authors adopted some code or literature formulations to assess the maximum possible shear demand in the joint and, consequently, the amount of transverse reinforcement needed to avoid a premature shear failure and/or minimum code requirements.
4. Line 161. The authors state that “In the regions of the joints, most of the specimens had no damage”. Actually, diagonal cracks in the joint panel are clearly visible. Please, provide a more detailed description of the damage state of the joint panel (whose response is the core issue of the paper).
5. Section 3.5. Please compare the methodology adopted for energy dissipation assessment with that proposed by:

Melo, J., Varum, H., & Rossetto, T. (2015). Cyclic behaviour of interior beam-column joints reinforced with plain bars. Earthquake Engineering & Structural Dynamics, 44(9), 1351-1371.

 

Verderame, G. M., De Risi, M. T., & Ricci, P. (2018). Experimental investigation of exterior unreinforced beam-column joints with plain and deformed bars. Journal of Earthquake Engineering, 22(3), 404-434.

 

 

6. I have a general question to the Authors of this interesting paper. I understand that the use of high strength steel for longitudinal rebars reduces the consumption of steel bars and may fix issues related to steel congestion and concrete placement. However, during design, the use of high strength rebars may yield to a higher value of the shear demand acting on the beam-column joints. Of course, this yields to a higher amount of transverse reinforcement in the beam-column joint, which may yield, in tune, to steel congestion and difficulties in concrete placement. The Authors are invited to comment on this topic.

 

Author Response

Dear Editor and Reviewer,

 

Thanks for your letter and for the reviewer’s comments concerning our manuscript originally entitled “Seismic Behavior of RC Beam Column Joints With 600 MPa High Strength Steel Bars” (ID: applsci-820692). The comments are valuable and helpful for the improvement of the manuscript, and of significant importance to our research work. The responses are given in the appendix.

 

We have substantially revised our manuscript after reading the comments. The revisions include content revisions and language improvement. Besides, we extend part of our work, discussing the subsequent research directions. The revised portions are highlighted clearly in the revised manuscript.

 

Best regard

 

Jianguo Cai

Department of Structural Engineering

School of Civil Engineering

Southeast University

Nanjing, Jiangsu, P.R.China

Author Response File: Author Response.pdf

Reviewer 2 Report

Interesting and ordered list of test results. 

The systematic presentation of the test campaign is the most positive part of the paper.

Indeed some statement from the Introduction remained without answer (lines 28-39). I do not believe, according to personal experience, that the use of HRB600 steel bars will lead to a tangible reduction of the amount of reinforcement ratio, mostly adopting almost regular C30  concrete.

 Even without laboratory example, it will be interesting to evaluate the equivalente required bar area when design  beam/columns. Probaly a table could show  the ultimate resistance (resistance domain, M-N) of the HRB600 and corresponding bar area along with the similar resistance domain) of standard 450MPa steel. That could support more the initial statement.

Author Response

Dear Editor and Reviewer,

 

Thanks for your letter and for the reviewer’s comments concerning our manuscript originally entitled “Seismic Behavior of RC Beam Column Joints With 600 MPa High Strength Steel Bars” (ID: applsci-820692). The comments are valuable and helpful for the improvement of the manuscript, and of significant importance to our research work. The responses are given in the appendix.

 

We have substantially revised our manuscript after reading the comments. The revisions include content revisions and language improvement. Besides, we extend part of our work, discussing the subsequent research directions. The revised portions are highlighted clearly in the revised manuscript.

 

Best regard

 

Jianguo Cai

Department of Structural Engineering

School of Civil Engineering

Southeast University

Nanjing, Jiangsu, P.R.China

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors should address the following comments:

1. Why the beams were reinforced with 600MPa bar not the columns? How the strong column weak beam condition was satisfied?
2. Why LVDTs were used only at beam ends? How did the authors measure the rotation at the beam-column joint?
3. Why unsymmetric hysteresis behavior was observed for BD3?

Author Response

Dear Editor and Reviewer,

 

Thanks for your letter and for the reviewer’s comments concerning our manuscript originally entitled “Seismic Behavior of RC Beam Column Joints With 600 MPa High Strength Steel Bars” (ID: applsci-820692). The comments are valuable and helpful for the improvement of the manuscript, and of significant importance to our research work. The responses are given in the appendix.

 

We have substantially revised our manuscript after reading the comments. The revisions include content revisions and language improvement. Besides, we extend part of our work, discussing the subsequent research directions. The revised portions are highlighted clearly in the revised manuscript.

 

Best regard

 

Jianguo Cai

Department of Structural Engineering

School of Civil Engineering

Southeast University

Nanjing, Jiangsu, P.R.China

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors present an experimental investigation of the seismic performance of interior beam-column joints with beams reinforced with grade 600 longitudinal steel bars. Six full-scale reinforced concrete (RC) interior joints are designed with different axial compression ratios, shear compression, and longitudinal reinforcement ratios, which are tested under reversed cyclic loading. Failure modes, skeleton, skeleton hysteretic curves, energy dissipation capacity and ductility of joints are investigated systematically. Moreover, the effect of the different axial compression ratios, shear-compression, and longitudinal reinforcement ratios on the seismic behavior of the joints are deeply studied. The manuscript has an important critical message. However, the manuscript needs to be revised.

 

• Section of Introduction, the review of the present work is insufficient, which in turn makes the research weak. Other literature on numerical and experimental models for the same purpose (or similar) can be added, addressing the assumptions, main challenges and advancements. The authors only mention a few research articles without discussing and clearly stating what is missing in the literature as well as what is the novelty of this research. For example, you can take a look at these articles:

https://doi.org/10.1016/j.engstruct.2020.110766
https://doi.org/10.1016/j.jobe.2020.101333

• The authors need to explain about “stress-strain behavior of reinforcements bars”, “stress-strain relationship for concrete”, and show these behaviors with figures.
• In the section “Experimental investigation”, the sentence “The dimensions of beams and columns are 250 mm× 500 mm× 1500 mm and 450 mm× 450 mm× 2500 mm, respectively”. What are the criteria for selection such dimensions for beam and column?
• The parameters and values in Table 1 should be clearer. The authors should clarify whether the parameters "II", "III" and “0.1g”, “0.2g” are selected based on a specific code? If yes, this table needs a reference.
• The authors stated in the section “Test setup and loading system” following sentence: “Two full cycles were applied until the specimens failed ….”. However, two pages after in the section: “failure mode”, they stated that “During the third cycle, the concrete at the end of the….”, OR “During the fourth cycle, the concrete on the column surface above the beam ….”. The authors need to clarify whether these tests were performed by 2 cycles or more.
• Equations (1), (2) and (3) need a reference.
• Table 2, the parameters “yielding strength”, “maximum strength” and “ failure load”, have to be written in the table.
• The conclusions of the article should be explained more comprehensively.

Comments for author File: Comments.docx

Author Response

Dear Editor and Reviewer,

 

Thanks for your letter and for the reviewer’s comments concerning our manuscript originally entitled “Seismic Behavior of RC Beam Column Joints With 600 MPa High Strength Steel Bars” (ID: applsci-820692). The comments are valuable and helpful for the improvement of the manuscript, and of significant importance to our research work. The responses are given in the appendix.

 

We have substantially revised our manuscript after reading the comments. The revisions include content revisions and language improvement. Besides, we extend part of our work, discussing the subsequent research directions. The revised portions are highlighted clearly in the revised manuscript.

 

Best regard

 

Jianguo Cai

Department of Structural Engineering

School of Civil Engineering

Southeast University

Nanjing, Jiangsu, P.R.China

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

I believe the manuscript has been significantly improved and it is ready for publication in Applied Sciences Journal