Review Reports - Recreation of Gap Test with Damaged Plasticity Model

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present the details of the numerical simulation of the gap test with the concrete damaged plasticity model in ABAQUS. The topic is interesting, the writing is clear, and the organization is done well. However, the following items need to be addressed:

Further analysis of additional tests from the literature is necessary to support the conclusions drawn.
Can authors compare and discuss critical effective crack extension cf? It is also important, and equations are already given.
The authors should define the fracture energy Gf and ensure it has the same meaning in the software.
The pad width is not clearly described. Is it adjusted across different sets of specimens (Line 192) or of a constant of 50mm (Line 226)?
More information should be provided for the simulation. For example, what is the width of the region modelled by CDP in Figure 5? How was the dilatancy angle of 15 degrees determined in Table 1? If it were not the default value, how would this parameter affect the results? A few other important parameters, such as the viscosity parameter, were missing. How were the values in Tables 2 and 3 derived? There are very few data points; compression damage in concrete is not considered, nor is a stress versus cracking strain curve provided. Figures might help show the stress-inelastic/cracking strain-damage relationship.
More recent references should be included to ensure the research’s cutting-edge nature, particularly for CDP analysis (11-23).

Author Response

Please, see the attachement.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This study attempts to re-simulate the gap test using the Concrete Damaged Plasticity (CDP) model in Abaqus, exploring the influence of the normal stress parallel to the crack (T-stress) on Mode I fracture energy. It has certain innovativeness and engineering application value. The research design is reasonable and the method is feasible, and the results are in good agreement with the existing experimental data. However, there are obvious deficiencies in the paper in terms of method description, figure and table quality, and the depth of result analysis and discussion. A major revision is recommended. The main revision suggestions are as follows:：

1 The current explanation of the basis for setting key parameters of the CDP model (such as damage evolution criteria and stiffness recovery functions) is insufficient, which weakens the credibility of the model. The calibration process or sources of these parameters should be described in detail. At the same time, the finite element modeling part needs to supplement the basis for selecting mesh sizes (it is best to provide mesh insensitivity verification) and clarify the setting details of boundary conditions such as "Tie" constraints, to ensure that other researchers can reproduce the numerical model.

2 The readability of the existing figures and tables is poor. The force-displacement curves lack clear legends to distinguish between different specimen sizes and working conditions. All figures and tables must follow a unified format and include complete axis labels (with units). In particular, the graphs used for regression analysis of the size effect must clearly indicate the fitting equation and correlation coefficient (R^2). It is recommended to supplement the error analysis for the comparison results in Figure 13 to demonstrate the degree of agreement more rigorously.

3 The description of phenomena in the results is more than the explanation of mechanisms. It should combine the damage evolution mechanism of the CDP model to deeply analyze why the force-displacement curves of medium and large-sized specimens do not show obvious plateau segments. The comparison with the experimental results of Nguyen et al. should not only be consistent in trend, but also require quantitative error analysis, and the mechanism of how T-stress affects fracture energy should be explained from the mechanical level. In addition, the limitations of the CDP model in this study should be objectively discussed, such as its position when compared with other models.

4 There are issues in the manuscript such as undefined formula symbols (e.g., h, s, β in Formula (3))，occasionally unclear language expression, and imprecise use of technical terms. It is recommended to conduct a unified check of the entire text, define all mathematical symbols, and thoroughly polish the language to make the expression more accurate and professional.

5 to enhance the completeness and persuasiveness of the research, it is recommended that the author consider supplementing some important content. Supplement the verification details of the model and test results (such as the force-displacement curve and fracture energy comparison of typical specimens); carry out sensitivity analysis of key parameters (such as the initial damage strain). Especially, since the CDP model has many parameters and the damage parameters have a relatively significant impact on the softening behavior, the sensitivity analysis of damage parameters is crucial for proving the robustness of the current parameter set and the credibility of the results.

Major revision is recommended. This study has good academic value, but it still needs to be strengthened in terms of method details, result presentation, and discussion depth. It is recommended that the author revise the manuscript item by item according to the above comments and, when resubmitting, provide a point-by-point response letter stating the modified content.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Most of the reviewer’s comments have been addressed, and the revised manuscript has undergone substantial modification. However, the following issues should be clarified:

Is the gap test modeled by the authors the only gap test on concrete available in the literature? If not, it is advisable to conduct additional gap tests to support the conclusions.
There are two types of pads in the manuscript: the loading pad and the supporting poly-propylene pad. The dimensioning of these pads, particularly the latter, still seems confusing.
Seven more references were added; however, only two are within the past 10 years, with the latest one in 2021. More recent references will help show the research’s cutting-edge nature, particularly for CDP analysis.

Author Response

Comment 1: Is the gap test modeled by the authors the only gap test on concrete available in the literature? If not, it is advisable to conduct additional gap tests to support the conclusions.

Response 1: The gap test is a relatively new test proposed by prof. Bazant and his co-workers. It is the only type of such a test known in the literature.

Comments 2: There are two types of pads in the manuscript: the loading pad and the supporting poly-propylene pad. The dimensioning of these pads, particularly the latter, still seems confusing.

Response 2: The dimensioning of the pads has been explained in the subsection 3.3.

Comments 3: Seven more references were added; however, only two are within the past 10 years, with the latest one in 2021. More recent references will help show the research’s cutting-edge nature, particularly for CDP analysis.

Response 3: A few more recent papers have been cited in the manuscript, especially in the subsection 3.2.