Dynamic Response Analysis of Mega-Sub Isolated Structures under Multiaxial Earthquakes

Round 1

Reviewer 1 Report

A) General remarks

The research presents in this paper a very interesting topic, as well as results that are of wider significance when it comes to the numerical prediction of ground motion effects on civil engineering structures. The paper is concise and clear. The literature in the paper is adequately cited, however, some comments on the choice and significance of cited sources will be articulated in the points below.
1.     In the case of literature, it must be pointed out that most of the positions are from local, Chinese research groups. It is suggested to include some additional, relevant papers from other regions. Citing almost only authors from the same country may be considered a citation only members of the same academic community who have personal ties. Some ideas will be suggested below.
2.    The abstract is well-written The role of the abstract is to give a basic overview of the paper. In this case, this role is evident.
3.    The introduction needs some improvements. It is clear that the authors are focusing on a specific field of application of their findings. However, the reviewer would suggest extending the introduction :
a)    The authors' focus is on the civil engineering side of the problem and with no information about why the dynamic conditions of earthquakes are dangerous. What are the classification of earthquakes and especially what is a multi-dimensional earthquake?  Thus the authors are evaluating the problem which was not explained in detail in the introduction.
b)    While evaluating the need for structure design taking into account multi-dimensional earthquakes some attention must be given to special cases and events like earthquake swarms (e.g DOI: 10.3390/en15103705 ) which usually are omitted in the design processes.
c)    In the abstract authors write that it is necessary to consider the effect of the vertical component of the earthquake on the structure but do not elaborate on it in the abstract and this is crucial thing not only for some structures but e.g. for underground research facilities like accelerators (look: Effect of ground motion introduced by HL-LHC CE work on LHC beam operation, IPAC2019).
In general, the introduction needs to be more informative describing not only the problem but also the context with a description of the field of seismic problems and measurements. Suggest incorporating some ideas mentioned above.
4.    Materials and methods are well explained. No comments on the methodology used.
5.    Results are very well presented
6.    The conclusions - the novelty must be presented strongly and with proper attention to the application of the results. Additionally, the conclusions end with strange phrasing “Important reference”. Please improve this part

B) Item remarks
The graphical part of the article is one of its advantages.
No changes are necessary.
Small editing problem in Fig.17 where the “Time” caption is overlining the X-axis values.

C) Conclusions:
The article is well executed with not many changes needed in the case of the research plan and its execution. Not much editing is needed as well.
The biggest problem is the introduction which focuses on one aspect of the paper and does not give the background fully allowing us to understand the problem and the solution. This must be improved.
The reviewer marks the paper for minor revisions but hopes that the author will improve according to the suggestions above.  

Author Response

see word response to reviewer 1#.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents a topic of current interest. However, there are important issues to be addressed by following comments in the attached pdf file.

Comments for author File: Comments.pdf

none

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Despite the first round of revision the work is not suitable to be published in such a version. It can be useful to try to improve its quality by addressing the following issues:

1) The introduction section is too long. It is necessary to reduce its length.

2) In the entire work, the expression “multidimensional earthquake” needs to be substituted by “multiaxial earthquake”.

3) In the Introduction section, the authors need to mention the importance of taking into account the REAL biaxial behavior of seismic isolation bearings that has been investigated in few recent works [https://doi.org/10.1016/j.engstruct.2022.115118]. Otherwise, what is the sense of talking about “multidimensional earthquake” if the authors do not remember that the real transverse behavior exhibited by such bearings is a coupled biaxial hysteretic behavior influenced by the axial load?

4) A great limit of the work is that the real behavior of the elastomeric bearings is not modelled properly at all. As a matter of fact, linear elastic models are employed. It is crucial to: a) repeat all the analyses by considering the real hysteretic behavior of the isolation devices or b) specify, in the conclusions section, that this is a strong limit of the work that can be addressed, in the future, by using recent, accurate and efficient hysteretic models [https://doi.org/10.1016/j.ymssp.2023.110448].

 

5) Please, repeat the analyses for different types of earthquake excitations.

 

Revise the entire paper.

Author Response

Despite the first round of revision, the work is not suitable to be published in such a version. It can be useful to try to improve its quality by addressing the following issues:

Question 1:  

The introduction section is too long. It is necessary to reduce its length.

Response 1: 

The content of the introduction section has been adjusted, resulting in a 21% reduction in total length.

Question 2:  

In the entire work, the expression “multidimensional earthquake” needs to be substituted by “multiaxial earthquake”.

Response 2:

Thank you for your suggestions, the “multidimensional earthquake” has been replaced by “multiaxial earthquake”.

Question 3:  

In the Introduction section, the authors need to mention the importance of taking into account the REAL biaxial behavior of seismic isolation bearings that has been investigated in few recent works [https://doi.org/10.1016/j.engstruct.2022.115118]. Otherwise, what is the sense of talking about “multidimensional earthquake” if the authors do not remember that the real transverse behavior exhibited by such bearings is a coupled biaxial hysteretic behavior influenced by the axial load?

Response 3:

In the introduction section, relevant research on the mechanical properties of the bearing was added, and it was explained that vertical seismic action can affect the horizontal mechanical properties of the support. The mechanical model of the support should be nonlinear and cannot be analyzed solely using linear elastic models.

 

Question 4:  

A great limit of the work is that the real behavior of the elastomeric bearings is not modelled properly at all. As a matter of fact, linear elastic models are employed. It is crucial to: a) repeat all the analyses by considering the real hysteretic behavior of the isolation devices or b) specify, in the conclusions section, that this is a strong limit of the work that can be addressed, in the future, by using recent, accurate and efficient hysteretic models [https://doi.org/10.1016/j.ymssp.2023.110448].

Response 4: 

I apologize for the incorrect response to the previous question "It is necessary to specify if are low or high damping elastomeric bearings. The detailed explanation is as follows.

Our parameter analysis work for the mega sub-structure isolation system is divided into two parts. The first part involves solid modelling analysis, where a bilinear mechanical model simulates the seismic isolation bearings. In the modelling analysis, we do not specify the type of seismic isolation bearings but rather the relevant parameters for their horizontal and vertical mechanical properties. The second part involves parameter analysis based on a simplified mechanical model; the solid modelling analysis and the simplified mechanical model analysis results have been mutually validated. However, the research presented in this article only includes the simplified mechanical model analysis in the second part. During the analysis process, only the required parameters, such as [K], [M], and [C], need to be set without the need to set up the specific mechanical model of the seismic isolation bearings.

 

Question 5:

Please, repeat the analyses for different types of earthquake excitations.

Response 5: 

In this paper analyzing collision parameters for the main and substructure, we have considered the impact of different seismic wave inputs on their collision. Due to limitations in length, we will only supplement the analysis of collision parameters in this paper and will not repeat the analysis of horizontal and vertical parameters. Research on collision under other seismic waves has been supplemented in the paper. Please refer to the revised original text for details.

 

In addition, we have checked the whole paper to correct English defects.