Flexural Behavior of a New Precast Insulation Mortar Sandwich Panel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the Reviewer opinion the research paper entitled “Flexural behavior of a new precast insulation mortar sandwich panel” is good.

This article introduces the experimental and analytical research results of four precast insulation mortar sandwich panels (PIMSP) under bending load as one-way slabs. The experimental results were discussed in terms of ultimate flexural strength capacity, moment-vertical deflection profile, load–strain relationship, strain varia-tion across the slab depth, cracking patterns, and ultimate flexural load at failure. Then, finite element analysis was used to analyze and study the unidirectional flat plate model. Experiments and finite element models have demonstrated that PIMSP panels can serve as a structural substi-tute for regular concrete floors in buildings.

Some comments which greatly enhance the understanding of the paper and its value are presented below. Specific issues that require further consideration are:

1. The title of the manuscript is matched to its content.
2. The Introduction generally covers the cases.
3. The methodology was clearly presented.
4. In the Reviewer’s opinion, the current state of knowledge relating to the manuscript topic has been presented, but the author's contribution and novelty are not enough emphasized.
5. Experimental program and results looks interesting and was clearly presented.
6. Fig. 7 should be better described.
7. In the Reviewer’s opinion, the bibliography, comprising 31 references, is more less representative.
8. An analysis of the manuscript content and the References shows that the manuscript under review constitutes a summary of the Author(s) achievements in the field.
9. In the Reviewer’s opinion the manuscript is well written, and it should be published in the journal after minor revision.

Comments on the Quality of English Language

No comments

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article that I have reviewed is of special interest for structural engineering, since it presents the study of insulated sandwich-type panels of reinforced concrete, with three-dimensional trusses. Below I propose a series of improvements that the authors should carry out in order to adapt the current version of the paper to a version of greater scientific solidity.

1. The introduction is quite illuminating, but I consider that there is the possibility of expanding and improving the bibliographic references that give context to the paper.

2. In section 2 a solid description of the applied research methodology is expected. However, the authors from the beginning with the experimental phase, leaving the reader without an overview, very necessary to understand all the relationships existing in the research. I recommend redoing this section, including a complete description of the methodology.

3. Table 3. Why not to put E in MPa?

4. In section 3 (results and discussion) it is necessary for the authors to compare their results with the expected values for a slab. Are these values acceptable from the point of view of service loads? Are these values acceptable from the point of view of ultimate loads? I believe that the discussion should be given a more concrete nature, since if there is no comparison with real-life cases, it is up to the reader's interpretation whether the recommendations are adoptable in common construction projects. Give more context

5. In figure 12, separate the four figures into sub-figures, indicating the value of the load applied in each of these.

6. The results focus on the effects of bending. Although the experiment has been designed with the aim of generating pure bending, the authors should include additional comments on the effects of shear on the panels, which should not be lost sight of to ensure proper structural behavior.

7. In the footer of Figure 17, the meanings of the sub-figures must be indicated.

8. In section 4.2, the authors should reflect on how the simplifying hypotheses of the behavior of the adhesion of steel bars against concrete could have influenced the results obtained during the numerical simulations. This aspect is not trivial and should be considered not only in the discussion of the results, but also in the conclusions.

9. Given the large difference shown in Figure 21 between the deformations of the laboratory test and the finite element simulation, the authors should provide further indications on the reasons that have caused such a difference.

10. In the conclusions, the authors should indicate the advantages of the lightweight panel over ordinary reinforced concrete slabs, so that it can be seen if it is truly worth adopting this new solution. Extend beyond the particular results obtained.

11. The statement in the conclusions of: "The results of FEM are significantly consistent with the experimental results." seems to me to be contradictory with what was observed in Figure 21. I consider that this statement should be redrafted in light of the results.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Summary of the research and overall impression:

 

The authors present an article exploring the flexural behavior of a precast panel that uses mortar as an insulation layer. The goal of the variation of this system, which incorporates a new insulation, is to be used as a one-way floor slab. Although there is limited information for comparison, the researchers tracked strains at several parts of the panel, which is useful for analytical and numerical model validations. However, I think some methods and background sections need improvement in order to support the results, discussion, and conclusions.

 

When elaborating on the following comments, I have considered the authors' paper's positive and negative aspects and strongly think that addressing them will increase the overall quality of the manuscript.

Comments

 

Abstract:

·       The abstract needs to be revised entirely; it has a lot of text overlap with another publication in the Journal of Building Engineering:

Amran, Y. M., Rashid, R. S., Hejazi, F., Safiee, N. A., & Ali, A. A. (2016). Response of precast foamed concrete sandwich panels to flexural loading. Journal of Building Engineering, 7, 143-158.

·       When writing the abstract, please address the introduction to the problem you are dealing with and the article's overarching goal, methods, main results, and conclusions of your study.

·       In lines 18-19, the authors claim that this system can serve as a structural substitute for regular concrete slabs. However, the reviewer thinks that making such a claim with only 4 panels tested is too premature.

 

Introduction: The introduction misses very important articles in the literature that explain many concepts that the authors miss throughout the manuscript.

·       In lines 40-41, the authors mention the heat transfer coefficient of the insulation used in the manuscript. Could the authors elaborate more on other coefficients for the typical insulations used in the concrete sandwich wall panel industry, such as EPS, XPS, and PolyIso?

·       Lines 52-54 state, "the quantity and quality of shear connectors affect composite action," but do not provide any references. Could the authors provide supporting evidence on how the quantity and layout affect this parameter? Perhaps these articles may help strengthen the case:

1.     Gombeda, M. J., Naito, C. J., & Quiel, S. E. (2021). Flexural performance of precast concrete insulated wall panels with various configurations of ductile shear ties. Journal of Building Engineering, 33, 101574. https://doi.org/10.1016/j.jobe.2020.101574

2.     Bai, F., Sun, Y., Liu, X., & Li, X. (2021). A theoretical perspective on the effective distribution of shear connectors in sandwich structures. Composite Structures, 272, 114139.

3.     Cox, B., Syndergaard, P., Al-Rubaye, S., Pozo-Lora, F. F., Tawadrous, R., & Maguire, M. (2019). Lumped gfrp star connector system for partial composite action in insulated precast concrete sandwich panels. Composite Structures, 229, 111465. https://doi.org/10.1016/j.compstruct.2019.111465

·       In lines 65-66, the authors claim that the fully composite behavior means no damage to the connector. Could the authors explain what would happen to the composite action if the panel layers slipped (relative displacement between the concrete layers) but the connector did not sustain damage?

·       The body of information presented in the literature review misses very important papers published in the last 30 years related to sandwich wall panels, such as:

For gravity loads:

1.     Luebke, J., Pozo-Lora, F. F., Al-Rubaye, S., & Maguire, M. (2023). Out-of-plane flexural behavior of insulated wall panels constructed with large insulation thicknesses. Materials, 16, 4160. https://doi.org/10.3 390/ma16114160

2.     Teixeira, N., & Fam, A. (2017). Fatigue behavior of partially composite insulated concrete sandwich walls. ACI Structural Journal, 114, 125–136. https://doi.org/10.14359/51689153

3.     Choi, I., Kim, J., & Kim, H.-R. (2015). Composite behavior of insulated concrete sandwich wall panels subjected to wind pressure and suction. Materials, 8, 1264–1282. https://doi.org/10.3390/ma8031264

4.     Pantelides, C. P., Surapaneni, R., & Reaveley, L. D. (2008). Structural performance of hybrid gfrp/steel concrete sandwich panels. Journal of Composites for Construction, 12, 570–576. https://doi.org/10. 1061/(ASCE)1090-0268(2008)12:5(570).

For thermal loads:

1.     Bai, F., Sun, Y., Liu, X., & Li, X. (2021). A theoretical perspective on the effective distribution of shear connectors in sandwich structures. Composite Structures, 272, 114139.

2.     Arevalo, S., & Tomlinson, D. (2020). Experimental thermal bowing response of precast concrete insulated wall panels with stiff shear connectors and simple supports. Journal of Building Engineering, 30, 101319. https://doi.org/10.1016/j.jobe.2020.101319

3.     Pozo-Lora, F., & Maguire, M. (2020). Thermal bowing of concrete sandwich panels with flexible shear connectors. Journal of Building Engineering, 29, 101124. https://doi.org/10.1016/j.jobe.2019.101124

·       It is unclear which point the authors try to make in lines 93-94 about the connectors. It seems that a part of the sentences is missing. What must the researchers rely on experimental research analysis to do?

·       Lines 98-100: Is the practice of putting insulation layers on the slab typical in the authors’ area (country)? Could the authors elaborate more on the subject?  As a part-time practitioner in the construction industry, I have rarely needed to add insulation to a floor.

·       Lines 101-102 mention that steel connectors were not used as shear members in sandwich panels. However, this is incorrect. Primitive sandwich panels used both solid sections and steel rebar. There’s even a system that uses stainless steel bars as connectors. The steel is no longer popular due to thermal bridging, as pointed out in:

1.     Sorensen, T. J., Dorafshan, S., Thomas, R. J., & Maguire, M. (2018). Thermal bridging in concrete sandwich walls. Concrete International, 40, 45–49. https://www.concrete.org/publications/internationalconcreteabstractsportal.aspx?m=details&ID=51711173

·       Lines 102-106 claim some savings in weight and construction ease. Could the authors back that claim up with a quick analysis? The reviewer is having trouble visualizing the system's savings and construction ease.

·       In general, the scientific and practical significance of the manuscript needs to be framed better. See the lines 98-106.

 

 

Methods:

·       Could the authors explain the possible behavior change introduced by the lifting devices pictured in Figure 7? Since the steel connects the concrete layers, it also provides restraint against slips and unintentionally enhances the composite behavior.

·       Experimental design: In lines 115-122, the experimental design of the article needs to be revised to explain why these panel sizes were chosen for testing. It also needs to include the design method followed and its underlying assumptions.

·       In the same order, which testing standards were followed to conduct the testing of the materials? Which standards do their fabrication conform to?

·       Lines 147-148: The steel mesh was placed, not poured.

·       Lines 163-164: Could the authors please point out to which figure these sensors belong?

·       Lines 167-170: Could the authors specify what is the nomenclature followed by the LVDTs in Figure 9? Is it W or other?

·       A color-blind person couldn’t clearly see the text in Figure 10 without someone else help. Please revise it.

·        

 

 

Results and discussion:

·      Line 207: The results are presented in terms of testing speed. Could the authors please revise it to load versus vertical deflection measurement for better comprehension?

·       Lines 212-213 mention that the vertical deformation shows that the panel behaves fully composite, but the introduction and methods describe composite action in terms of strain reading and lack of slip between the concrete layers. Could the authors be uniform when explaining the composite action? Because there could be uniform deformation, and the panel would still be unable to achieve fully composite behavior.

·       Lines 216-2021: could the authors mention the cracking loads?

·     Lines 242-244: From the reviewer's experience, the lack of slip in this panel is due to the strong steel truss used as a connector and the four lifting devices implemented near the ends of the panel. The insulation has little effect, if any, on the results.

 

Finite Element Analysis and Modeling:

·       Why weren’t the material model assumptions for the finite element model?

·         A table comparing the full-scale tests and the FEM would greatly help a reader visualize the accuracy.

·       Could the authors explain why the FEM can’t predict the strain in the steel for the panels? See Figure 21.

·       Please use the literature to justify the finite element model chosen to predict the large-scale tests. The model is not cited, and the literature has a very long list of models with their validations.

Conclusions:

·       For clarity, please mention the load value in kN units instead of later or earlier. If the authors used percentages, please put the numerical value in kN and the percentage to be more effective.

·       The results of the FEM cannot back up the conclusion stated in line 370 because only one model is compared.

·       The last conclusion is premature for the state of this work. Please consider removing it.

 

Comments on the Quality of English Language

Typos, spelling, grammar, and phrasing issues:

·      The citations go before the period.

·      Revise the article to ensure it does not look like a set of instructions.       To give a few examples:

o   Line 52.

o   Lines 187-189.

o   Lines 257-259.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Response 8: I don't quite understand which aspect of comparison you are referring to. 

A table comparing the full-scale tests to the FEM must include at which point cracking happens, the slope of the load vs deflection curve prior to cracking, cracking load and deflection, and ultimate load and displacement. That helps the reader understand the accuracy of your model.

Comments on the Quality of English Language

No more comments.

Author Response

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Author Response File: Author Response.pdf