Effects of Large-Diameter Rebar Replacement on Seismic Behavior of Precast Concrete Columns with Grouted Sleeve Connections
Round 1
Reviewer 1 Report
In this study, a series of large-scale reinforced concrete (RC) columns adopting similar concrete strength, longitudinal rebar ratio, and transverse rebar ratio were fabricated and tested. Six of the columns were prefabricated with grouted sleeve connections and remaining two were cast-in-place (CIP) for reference. The longitudinal rebar diameter varies from 18 mm to 32 mm. Low-cycle reversed horizontal load was applied to study their seismic performance, including failure modes, load bearing capacity, hysteresis behavior, stiffness degeneration, and energy dissipation capacity. The test results showed that the PC column with large diameter longitudinal rebar replacement performed similarly in general. In general, the contents are interesting and well written, the reviewer recommends publication, but a few questions are required to be well handled.
1. The authors performed the experimental study of precast columns, which is a great work. The reviewer suggests to focus more on the short comings of the existing references. The following papers related to the precast structures can be included into the Intro and contents. 10.1016/j.jobe.2022.103988;
2. From the hysteresis curves of precast columns, it seems the pinching effect occurs. How do the authors consider this aspect as it commonly affects the energy dissipation capacity of precast structures.
3. In the study, the grouting sleeves are used as the connection of reinforcement, and the structural performance is compared with the CIP. Thus, maybe some explanations of the design procedure of grouting sleeves are needed (e.g., dimensions, positions, grouting mortar), as the variations of grouting sleeves can obviously affect the hysteresis performance (e.g., unqualified grouting sleeves adoption will reduce the peak capacity of structures).
4. In the conclusion, the novelty and findings of this paper can be further enhanced, and maybe the words can be further refined.
Author Response
- The authors performed the experimental study of precast columns, which is a great work. The reviewer suggests to focus more on the short comings of the existing references. The following papers related to the precast structures can be included into the Intro and contents. 10.1016/j.jobe.2022.103988; 10.1016/j.jobe.2022.104904; 10.1016/j.engstruct.2022.113982.
Reply：As suggested by the reviewer, the introduction of this part had been added to the introduction and highlighted.
- From the hysteresis curves of precast columns, it seems the pinching effect occurs. How do the authors consider this aspect as it commonly affects the energy dissipation capacity of precast structures.
Reply：Thanks for the reviewer’s suggestion. The main purpose of this paper is to elaborate the influence of large diameter longitudinal reinforcement on the seismic performance of precast columns and reveal its mechanism. Poor energy dissipation capacity is one of its effects. How to improve or enhance the seismic performance of precast columns will be my next important research topic.
- In the study, the grouting sleeves are used as the connection of reinforcement, and the structural performance is compared with the CIP. Thus, maybe some explanations of the design procedure of grouting sleeves are needed (e.g., dimensions, positions, grouting mortar), as the variations of grouting sleeves can obviously affect the hysteresis performance (e.g., unqualified grouting sleeves adoption will reduce the peak capacity of structures).
Reply：Thanks for the reviewer’s suggestion. The grouting operation (refer to Figure 5) was carried out according to the requirements specified in the industry standard Technical Specification for Grout Sleeve Splicing of Rebars (JGJ 355-2015) [1]. The design procedure of grouting sleeve (including size, position, performance of grouting mortar and pull-out test of reinforcement with sleeve) is strictly in accordance with this technical specification(refer to Figure 2-4).
[1] MOHURD (Ministry of Housing and Urban-Rural Development Republic of China). JGJ 355-2015: Technical specification for grout sleeve splicing of rebars. Beijing, China: China
- In the conclusion, the novelty and findings of this paper can be further enhanced, and maybe the words can be further refined.
Reply：Thanks for the reviewer’s suggestion. Conclusion 5 was added and highlighted in line 402 to 405.
Author Response File: 
Author Response.doc
Reviewer 2 Report
In table 4 the ultimate displacement is called "â–³u". In Notes for the table the ductility ratio, and ultimate drift ratio "μΔ= ductility ratio（μΔ=Δm/Δy）, θm= ultimate drift ratiot（θm=Δm/l，l is column height"
please use the same abbreviation letter for the entire article.
I strongly reccomand changing the bars graphs of figures 13, 14. 15 to line graphs
In chapter 5 it states: "Seismic tests were carried out on eight full-size columns with identical concrete 365 strength, longitudinal rebar ratio, and transverse reinforcement ratio but subjected to the 366 axial compressive ratios of 0.3 and 0.6.".
I would rephrase first line to: "cyclic monotonic loading in order to evaluate seismic behavior." - The tests were performed as "static" loading with large time develop prescribed displacements, and not acceleration controlled.
Conclusion 4 contradicts chapter 4.3&4.4 "4. PC columns reinforced with 32 mm diameter rebar have comparable seismic performance as the columns reinforced with 22 mm or 18 mm diameter rebar but with 100% and 200% increased assembly efficiency, respectively."
There is a strong ductility reduction and energy reduction (see table 4)
Please rephrase conclusion 4. It is not acceptable to conclude "Therefore, the design of PC column with relatively large diameter of longitudinal rebar is acceptable"
Author Response
- In table 4 the ultimate displacement is called "â–³u". In Notes for the table the ductility ratio, and ultimate drift ratio "μΔ= ductility ratio（μΔ=Δm/Δy）, θm= ultimate drift ratiot（θm=Δm/l，l is column height"
please use the same abbreviation letter for the entire article.
Response: As suggested by the reviewer, the same abbreviated letter has been used throughout the entire article.
- I strongly reccomand changing the bars graphs of figures 13, 14. 15 to line graphs
Response: As suggested by the reviewer, figures 13, 14 and 15 have been changed to line graphs.
- In chapter 5 it states: "Seismic tests were carried out on eight full-size columns with identical concrete 365 strength, longitudinal rebar ratio, and transverse reinforcement ratio but subjected to the 366 axial compressive ratios of 0.3 and 0.6.".
I would rephrase first line to: "cyclic monotonic loading in order to evaluate seismic behavior." - The tests were performed as "static" loading with large time develop prescribed displacements, and not acceleration controlled.
Response: As suggested by the reviewer, the first line of the chapter 5 has been replaced and highlighted.
- Conclusion 4 contradicts chapter 4.3&4.4 "4. PC columns reinforced with 32 mm diameter rebar have comparable seismic performance as the columns reinforced with 22 mm or 18 mm diameter rebar but with 100% and 200% increased assembly efficiency, respectively."
There is a strong ductility reduction and energy reduction (see table 4)
Please rephrase conclusion 4. It is not acceptable to conclude "Therefore, the design of PC column with relatively large diameter of longitudinal rebar is acceptable"
Response: Thanks for the reviewer’s suggestion. Conclusion 4 was rephrased and highlighted in line 393 to 396.
Author Response File: Author Response.doc
Reviewer 3 Report
The article is well written and the results were well presented in the article
Author Response
The authors appreciate the reviewer’s satisfaction on this study.
Reviewer 4 Report
The research idea is interesting, but the execution leaves a lot to be desired.
1) First of all, it should be noted that each tested column is different or was tested under different loading conditions. Therefore, the authors of the work tested each type of load and each type of reinforcement only once.
The authors of the work did not present any reproducibility of the results, any statistics of the results.
In the case of testing brittle elements such as concrete, drawing conclusions based on individual tests is very debatable.
In my opinion, on the basis of such a small number of tests, it is impossible to draw substantive, valuable conclusions.
2) The proportion of the length of the column to its cross-section is small. Therefore, the proportion of stiffness of this element in relation to its length is strongly disturbed and clearly differs from real building structures.
3) This article lacks a photo showing the entire measurement station.
4) In my opinion, there is a lack of more detailed information regarding the measuring sensors used. For example, what exactly LVDT sensors were used (model, range, etc.) what strain gauges were used (measuring base, measuring bridge system, thermal compensation, etc.)
5) Figure 7 lacks description and scale for the horizontal axis.
6) Figures 16 and 17 do not show the strain measurement results for the RC columns. Figure 1 shows that these columns also have strain gauges.
7) The conclusions presented in the work are quite obvious. In my opinion, they do not bring much new to engineering knowledge.
Author Response
- First of all, it should be noted that each tested column is different or was tested under different loading conditions. Therefore, the authors of the work tested each type of load and each type of reinforcement only once.
The authors of the work did not present any reproducibility of the results, any statistics of the results.
In the case of testing brittle elements such as concrete, drawing conclusions based on individual tests is very debatable.
In my opinion, on the basis of such a small number of tests, it is impossible to draw substantive, valuable conclusions.
Response: Thanks for the reviewer’s suggestion. It can be seen from Table 1 that the 8 test pieces designed for this test have certain rules to follow, that is, there are many identical test conditions. Eight full-size RC columns adopting identical concrete strength, longitudinal rebar ratio, and transverse rebar ratio were designed and fabricated. Six are PC and remaining two are CIP for comparison. In general, in this large-scale full-scale seismic test, 8 specimens can discover some scientific laws and reveal some mechanisms. Compared with the test results in the relevant literature [1] and the prediction results in the prediction model (Fig. 10), it can be seen that the results in this paper are reliable.
[1]Zhao Y, Li R, Wang XF, Han C. Experimental research on seismic behaviors of precast concrete columns with large-diameter and high-yield strength reinforcements splicing by grout-filled coupling sleeves. China Civil. Eng. J. 2017, 50(5), 31-39+75(in Chinese). https://doi:10.15951/j.tmgcxb.
- The proportion of the length of the column to its cross-section is small. Therefore, the proportion of stiffness of this element in relation to its length is strongly disturbed and clearly differs from real building structures.
Response: As pointed out by the reviewer，a concentrated load was applied at the top of the cantilever column in this study. The height from the load to the column base is 1.5 m. However, it should be pointed out that in reality, the column was deformed in double-curvature. Thus, actually, in this study, the lateral load was applied at the contra-flexural point and the column and only half height of the column was simulated. Thus, actually, the column height is 3.0 m, which is very close to the column height in reality.
- This article lacks a photo showing the entire measurement station.
Response: As suggested by the reviewer, Photo of the measurement station has been added in Figure 6 and highlighted.
- In my opinion, there is a lack of more detailed information regarding the measuring sensors used. For example, what exactly LVDT sensors were used (model, range, etc.) what strain gauges were used (measuring base, measuring bridge system, thermal compensation, etc.)
Response: As suggested by the reviewer, Information about LVDTs and strain gauges has been added in section 2.3 and highlighted.
- Figure 7 lacks description and scale for the horizontal axis.
Response: As suggested by the reviewer, The description and ratio of the horizontal axis in Figure 7 has been added.
- Figures 16 and 17 do not show the strain measurement results for the RC columns. Figure 1 shows that these columns also have strain gauges.
Response: As suggested by the reviewer, The strains of the longitudinal and hoop bars of the RC column have been added in Figures 16 and 17
- The conclusions presented in the work are quite obvious. In my opinion, they do not bring much new to engineering knowledge.
Response: Thanks for the reviewer’s suggestion. It is a national strategy to develop prefabricated structures. But at present, the practice of prefabricated structure mostly follows the tradition and habit of cast-in-place structure. The diameter of longitudinal bars of building structural members is rarely 32mm. It is rarely reported in the literature that it is used in the reinforcement replacement of the precast column to discover the difference of its seismic performance and reveal its mechanism. Next, the authors will focus on how to improve the seismic performance of large-diameter longitudinal reinforcement precast columns. Compared with the potential improvement of assembly efficiency and construction quality, the precast column with large diameter rebar is worthy of promotion. Therefore, this study is very meaningful.
Author Response File: Author Response.doc
