Round 1

Reviewer 1 Report (Previous Reviewer 1)

I see no restricttions to publishing

Author Response

No Comment 

Reviewer 2 Report (New Reviewer)

The research topic of the manuscript is novel and it fits on the journal purpose.
The reviewer recommends the publication of this paper after solving the following issues:
1. The material properties of steel and concrete are not clarified - what kind of concrete classes are considered as NSC, and what kind of concrete classes are considered as HSC? The same refers to the steel - what kinds and what strengths of steels are considered in this study?
2. There are numerous editorial errors, such as writing Celsius degrees either with a gap or without a gap. In reviewer opinion, the temperature values always should be separated from units with a gap, e.g. 1050 oC.
3. Also other editorial issues shall be addressed, such as:
- in row No. 151, under instead of Under,
- in row No. 161, Full-lenght (with a dash) instead of Full lenght - compare to: Half-length (with a dash) in the same row No. 161,
- Figures No. 1, No. 2, No. 3 and No. 4 lack graphical resolution which shall be improved,
- in row. 233 density is written incorectly as 2400 kg/m2; the weight of concrete shall be given in [kg/m3];
- in rows 239 and 242, in the text the incorect, undefined symbols are written, such as "f_cm" in row No. 242,
- in row No. 448 there is a reference to Figure 4.27 which is not present in the text. It shall be clarify where it is to be found; in the Eurocode 2?
- there is a spelling error in Figure 6: "Soncrete Slab" instead of "Conrete Slab",
- there are numerous spelling errors in Figures 25 and 26,
- the Figures 28-39 shall be changed; the results can be presented in a more clear and elegant form on a single or at most on a couple of diagrams.

Overall, text editing needs significant improvement.

Author Response

Dear Reviewer 

We appreciate the time and effort that you have dedicated to providing your valuable feedback on the manuscript.

Kindly find the attachment. 

Warmest Regards,

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

The topic is interesting and addresses an issue that requires in-depth research.

However, the current article has some shortcomings that need to be addressed by the authors.

The objective is not clearly stated, so it is not possible to assess whether the research achieves them.

There is important research that is not cited such as "Application of support vector machine with firefly algorithm for investigation of the factors affecting the shear strength of angle shear connectors, Chahnasir et all." Or "Behavior of Tilted Angle Shear Connectors, Khorramian et all." 

Row 128 indicates that the shear decreased by 155% and 179% what does a value greater than 100% mean?

Item 3 what characteristics does an AP concrete imply.

Item 5.2 talks about reinforcing bars to check if an element is embedded, its implication is not clear and requires further explanation.

Point 6.1 states "Based on the results of experimental study and comparison 394 with FE modelling, FE modelling exhibited a reasonable elastic and plastic behavior of the stiffened shear connector". However, the validation shows qualitative, but not quantitative behavior, so its validity is highly questionable. In addition, in the cited research several tests have been carried out in different conditions and for several types of connectors, and the current research does not indicate which are the dimensions of the connectors and which characteristics of the concrete and steel have been considered.

On the other hand, neither in Figures 10 11 and following nor in the text are the units of the stresses indicated. Furthermore, in row 396 it is indicated that the von Mises stresses of the concrete are shown. This type of failure criterion should be justified in detail, since it is not used for materials of the type such as concrete and is used for steel. The lack of units occurs in the rest of the figures, so that the results cannot be evaluated.

Figures 12 and 13 show images that are not from this research; their origin should be explicitly indicated in the text of the image. In addition, some of the images shown in this research do not appear in the reference [17] cited.

In point 6.2 it is stated that the dimensions of the tests are between 75-100 but in the modeling 120 mm is used, the decision should be justified in more detail, since in the cited research the C-connectors are also stiffened and are 75-100.

In point 6.2.1. mention is made of failure modes of cracks, which are not the subject of this investigation, it should be made very clear which are results of the investigation and which are not.

In line 448 there is a reference to a figure that is not located in the document (Figure 4.27).

In lines 450 to 461 it is not clear if the behavior is that of the specimens that were tested, which is not the object of the investigation, or if it is that of the models. The stresses in the finite element model are mentioned, but no reference is made to which one. In addition, only figures are shown with the stresses in the steel and none are shown with the stresses or level of damage in the concrete, which justifies that the failure is caused by the stresses in the connector.

In Figures 15 to 18 in the legends, some show a minimum temperature of 20ºC and in others 0ºC. Why is this?

The lack of units in Figures 19 and following does not allow us to evaluate the results.

There is no discussion linking the results to previous research.

Author Response

Dear Reviewer 

We appreciate the time and effort that you have dedicated to providing your valuable feedback on the manuscript.

Kindly find the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

The shear connector between concrete slabs and steel beams is one of the major components in composite constructions and play an important role in the behavior of structure. The authors designed two novel types of stiffened angle connectors with full-length and half-length stiffeners and conducted push-out experiments to study their behavior under isothermal fire loading, proving that they have superior performance compared to traditional shear connectors. The authors used finite element analysis (FEA) to study the performance of the new stiffened shear connectors again with the height, width of the shear connectors and temperature as variables. The work is interesting, but there are some comments must be addressed:

1. The two shear connectors have been studied extensively in experiments (e.g. Ref. 17), what’s the new in current study?

2. Please revised the introduction, highlight the unsolved issues in current stage, and why your work are so important, this will make te current work more attractive.

3. Please check and improve the logic of the introduction and the English expression of the whole text, for example:

In lines 21-22 on page 1, “ The results indicate that the ultimate strength stiffened angle shear connector drops by 92% in 1050℃”. The preposition "of" may be missing between “ultimate strength” and “stiffened angle shear connector”.

In lines 105-107 on page 3, “ As temperatures rise, researchers discovered that the shear strength of both the concrete and the connector significantly declines at a faster pace than that of the connector”. There are two “connector”s, are they the same?

……

4. Please check grammar and wordiness throughout the text, for example:

In lines 50-51 on page 2, “material qualities that vary, failure mechanisms are more complex”, "vary" is a verb;

In line 54 on page 2, “whereas shear connectors indirectly faces the increase in temperature”, the verb form is wrong;

……

5. Please check and explain the letters in the equations, for example:

In lines 183-184 on page 4, What does λ_a in the equations represent?

In line 210 on page 5, What do a, b, and c in the equation represent?

……

6. There are so many figures that it is not easy to read, Maybe it is better to integrate comparative pictures of the same variables, such as Figures 15-18.

7. Please check and improve the Figures details, for example:

In line 172 on page 4, There are two punctuation marks at the end of the sentence;

The color scales in Figures 10, 11, etc. have no units;

In Figures 22, 23, etc., The abscissa scale values overlap with the figures;

In Figures 28, 29, etc., The titles overlap with the figures;

……

8. The number in the fourth row of Table 3 is wrong.

9. In line 441 on page 14, Missing the other half of the square brackets.

10. In line 441 on page 14, Missing the punctuation mark at the end of the sentence.

11. Citation of previous work shall be marked with references, For example:

In lines 463-465 on page 14, “In recent studies, comparing the results of 60-120 mm height of typical shear connector found that the height of the angle shear connector does not play a vital role on shear strength, but heights of 75 and 100 mm were optimal.”

Author Response

Dear Reviewer 

We appreciate the time and effort that you have dedicated to providing your valuable feedback on the manuscript.

Kindly find the attachment.

Author Response File: Author Response.pdf

Reviewer 5 Report (New Reviewer)

Dear Authors 

In this auricle, authors applied a numerical study to investigate the behavior of novel stiffened angle shear connectors embedded in solid concrete slabs at both ambient and elevated. An advanced nonlinear finite element model is developed and validated with available experimental work by Nouri, K., et al. [17]. Also, parametric studies are performed to evaluate the variations in concrete strength and connector’s dimensions. The results indicate that the ultimate strength stiffened angle shear connector drops by 92% in 1050℃. Comparing studies shows the strength of the stiffened shear connector at 700-850℃ is equivalent to the ordinary C-shaped shear connectors. The stiffened shear connector is more ductile at elevated temperature as compared to ambient temperature. The shear strength raised to 66% and 159.7% by increasing the height and width of the stiffened shear connector, respectively. Furthermore, the height of stiffened shear connector is crucial to enhance the shear strength capacity as compared to the ordinary C-shaped shear connector.

In my opinion this paper is suitable for publication in “Sustainability”, but before publication of this paper in this journal, authors should index references [39] , [40] in the text. These references are not cited in the text.

Author Response

Dear Reviewer 

We appreciate the time and effort that you have dedicated to providing your valuable feedback on the manuscript.

Kindly find the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report (New Reviewer)

For example, the objective is explained but it is not correctly stated in the text.
The new version of the document does not justify why the von Mises concrete rupture criterion is used, the quantitative validation of the finite element model against the tested model is not justified, as only the comparison of the deformation of the finite element model and the photograph is made qualitatively.
The strength of the concrete taken is said to be 40 MPa, indicating that it is usual. However, in the design of bridge decks or floor slabs of buildings, a strength of 25 or 30 MPa is very common.
It is indicated that reinforcing bars have been modelled, but the temperatures and stresses to which they are subjected are not reflected in the model.
There is no section in which the results are discussed in relation to the state of the art and which demonstrate that the research represents an advance in knowledge.
Therefore, from the point of view of this reviewer, there are deficiencies in the validation of the model that do not allow the validity of the conclusions obtained, and therefore the publication of the research in its current development is recommended.

Author Response

Dear Reviewer 

We appreciate the time and effort that you have dedicated to providing your valuable feedback on the manuscript.

Kindly find the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

After read the revised manuscript,  the authorshave satisfactorily addressed my major concerns, thus, I believe this interesting work is worth of publication.

Author Response

No further comment.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

1. Line 656 - high...

2. Lines 738-740 - please simplify

Author Response

Comments from Reviewer 1

1.Information about the experiment must be added. Only comparison on the max load is not enough. The failure modes in numerical model and experiment must be compared in detail.

The failure mode section added as below

6.2.1 Failure mode

As earlier studies illustrated, due to the unequal thermal conductivity of steel and concrete, the temperature of concrete typically is lower than that of shear connector by ap-proximately 100°C–150°C [14,29-30]. The detail investigation in this study reveals the same pattern, as shown in Figures 15 – 18 , which causes the strength of the shear con-nector to drop faster than the surrounding concrete. Thus, concrete crushing failure mode at elevated temperature is less likely, and failure is most likely governed by steel failure. The potential damage to strength caused by heating must be considered. Heating included the vaporisation of free water at approximately 100°C, which meant that humidity had no effect on the concrete strength during the test; several aggregates underwent quartz trans-formation above 600°C; concrete started sweating and cracking at approximately 450°C [31. The failure mode observed under monotonic loading at elevated temperatures for the stiffened angle shear connectors was accompanied by a longitudinal crack throughout the slab. The observed cracks were due to concrete and steel isotropic essence. The thermal in-crease of the concrete depended on temperature alteration. Several cracks formed around the surface of the connectors and in a direction parallel to the steel I-beam. Bazant and Kaplan (1996) [32] observed that cracking occurs due to structural stresses in concrete caused by inhomogeneous thermal increases, which are expressed as a temperature func-tion based on Eurocode 2 [19]. Figure 4.27 shows the said phenomenon during the high-temperature experiments

By observing the experimental results and FEM results, at elevated temperature due to reduction of steel strength, stiffened shear connector slightly bend before failure and then sheared off (shear connector failure). Concrete crushing failure was observed at am-bient temperature where the width of the shear connector was 80 mm and occurred at el-evated temperature with full-length stiffened shear connector with 80 mm width at lower temperature where the stiffness of steel did not yet drop considerably. Most specimens failed with the same type of failure at ambient and elevated temperatures. At elevated temperatures, the shear connectors’ behaviour was more ductile due to the reduction in steel strength, and the failure was more ductile than that at ambient temperatures. The width and the height of novel stiffened shear connector play a vital role in terms of its strength. Therefore, the connector area facing the force was enhanced by increasing the width and the height of the angle profile.

3.How the heat distribution shown in Fig.18 is obtained? The detailed information must be added.

As presented in Fig.18, The heat distribution is presented and in left corner box, presented the NT11 which present the different temperatures with different colours. However, authors look forward to being advised to present details.

4. The high-strength concrete is not introduced in Materials properties section. 5. The following references about angle can be added.

This study focused on the normal concrete at ambient and elevated temperatures, and compared the results with existing research of high-strength concrete. Authors shall consider the high-strength concrete for future works as required a detailed study.

Finite-Element Simulation of Posttensioned Steel Connections with Bolted Angles under Cyclic Loading

A simplified numerical model for post-tensioned steel connections with bolted angles.

The study mostly focused on the static loading and shall proceed with cyclic loading in future studies and also take note of valuable suggestions for future studies

Reviewer 2 Report

Comment 1 suggests that only comparison on the max load is not enough and the load-displacement curves derived in experiment should be added. However, this point is not mentioned.   

The second comment is directly ignored.   

The fourth comment is not addressed.  

This paper is not obviously improved.

Author Response

Comments from Reviewer 2

Suggestions for Authors

1. Please make clear the parameters of "ordinary C-shaped shear connectors"

In this study “ordinary C-shaped shear connectors” refers to non-stiffened shear connector with same dimensions, which stated in paper line 419.

2. The crack presented on the Fig. 12 is developing not in the area predicted by simulation (Fig.11).

Authors consider figure 11 to present the concrete compression damage where concrete crushed under pressure and compared it with experimental results that occurred as shown in figure 12.

3. What is the sensibility of the calculations results to change of fundamental characteristics of the material: thermal expansion, thermal conductivity, etc.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Recommend to publishing