Assessment and Fragility of Byzantine Unreinforced Masonry Towers

Round 1

Reviewer 1 Report

Manuscript investigates seismic response of five cultural heritage towers. Very interesting study with proper writing. There are minor issues that need to be addressed and added into discussion that is missing:

• add discussion and relate your findings with similar studies from introduction and suggested
• https://www.researchgate.net/publication/326679135_AMBIENT_VIBRATION_TESTS_ON_NEW_ZEALAND_UNREINFORCED_MASONRY_CHURCHES_USING_LOW_COST_SENSORS
• https://www.sciencedirect.com/science/article/abs/pii/S0950061806001097
• ambient noise measurements related to earthquake modelling can be used for dynamic monitoring prior and post earthquake event, please see: https://link.springer.com/article/10.1007/s12665-015-5185-x
• Application of HBIM as a Research Tool for Historical
  Building Assessment can be useful for model building approach for valorisation and interpretation of constructive changes over time, through the modelling logic, closely relating to the logic of construction https://civilejournal.org/index.php/cej/article/view/836
• Please see also general equation system for linear dynamic soil-structure interaction (SSI) in frequency domain https://hrcak.srce.hr/202605
•  

Author Response

We deeply thank the reviewer for his time and efforts to improve the paper. Below follow point-by-point responses to the reviewer’s comments.

Manuscript investigates seismic response of five cultural heritage towers. Very interesting study with proper writing.

We thank the reviewer for his positive comment.

There are minor issues that need to be addressed and added into discussion that is missing:

• add discussion and relate your findings with similar studies from introduction and suggested: https://www.researchgate.net/publication/326679135_AMBIENT_VIBRATION_TESTS_ON_NEW_ZEALAND_UNREINFORCED_MASONRY_CHURCHES_USING_LOW_COST_SENSORS
• https://www.sciencedirect.com/science/article/abs/pii/S0950061806001097
• ambient noise measurements related to earthquake modelling can be used for dynamic monitoring prior and post earthquake event, please see: https://link.springer.com/article/10.1007/s12665-015-5185-x

The dynamic monitoring is further discussed now in the document with additional citations, see lines 83-85.

• Application of HBIM as a Research Tool for Historical
  Building Assessment can be useful for model building approach for valorisation and interpretation of constructive changes over time, through the modelling logic, closely relating to the logic of construction https://civilejournal.org/index.php/cej/article/view/836

A discussion about the HBIM  is made, see lines 85-86.

• Please see also general equation system for linear dynamic soil-structure interaction (SSI) in frequency domain https://hrcak.srce.hr/202605

The SSI is discussed in the paper, see lines 166-168.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper is valuable and delivers interesting conclusions about masonry towers. Still, the paper's object does not present novelties in the methods, which are standard in structural engineering. The manuscript refers to a case study, but the authors do not provide sufficient details about the masonry towers. The analysis is numerical; there are no experimental tests to endorse the mechanical parameters or modal testing values to estimate the experimental modal parameters. This aspect weakens the credibility of the results. The reviewer suggests proving the values adopted in the FE modelling of the tower if possible. Are there any experimental outcomes?

Except for this, the paper is well written and presents interesting contents. There are a few minor concerns to be addressed:

The author suggests including the following reference about the fragility of ancient masonry towers:

Aloisio, A., Capanna, I., Cirella, R., Alaggio, R., Di Fabio, F., & Fragiacomo, M. (2020). Identification and model update of the dynamic properties of the san silvestro belfry in l’aquila and estimation of bell’s dynamic actions. Applied Sciences, 10(12), 4289.

 

Is it possible to improve the resolution of Fig.1?

The resolution of almost all the figures is meagre! The enhancement of their quality is mandatory!

Line 271- the authors left a Greek expression, revise

The authors must clarify how they estimated the fragility functions. How they estimated the parameters of the lognormal distribution? Did they carry out nonlinear dynamic analysis? Did they follow a Monte Carlo approach? This paragraph is not clear and must be expanded since the paper's primary focus should be the fragility estimate.

 

Some references:

https://www.tandfonline.com/doi/abs/10.1080/15583058.2014.951792?casa_token=7mbHKsxQ5I8AAAAA:SVAGflaOAh5dHqh-j-15qasgIupvNUrZH87xgwyT-2lWWXN8RwKFrmTC_24EqgrYxo5k_7fiRAmphDU

Author Response

We deeply thank the reviewer for his time and efforts to improve the paper. Below follow point-by-point responses to the reviewer’s comments.

The paper is valuable and delivers interesting conclusions about masonry towers.

 

We thank the reviewer for the positive comment.

 

Still, the paper's object does not present novelties in the methods, which are standard in structural engineering. The manuscript refers to a case study, but the authors do not provide sufficient details about the masonry towers. The analysis is numerical; there are no experimental tests to endorse the mechanical parameters or modal testing values to estimate the experimental modal parameters. This aspect weakens the credibility of the results. The reviewer suggests proving the values adopted in the FE modelling of the tower if possible. Are there any experimental outcomes? Except for this, the paper is well written and presents interesting contents.

 

The point of the reviewer is valid. The investigation is based on in-situ measurements of the geometrical properties. Material testing has not been carried out due to the monumental restrictions of the structures.

To alleviate this deficiency of the paper, a thorough literature review of modal measurements of towers with similar characteristics has been now added. Moreover, empirical formulas have been used to estimate the modal frequencies. A comparison with experimental and empirical values is now made which justifies the assumptions for the material properties.

However, it should be highlighted that the focus of the current investigation is on the collapse and overturning which involves large displacements and rotations due to cracking. Therefore, the influence of the elastic properties (and elastic strains) is very limited as can be seen in the following sections.

 

 

There are a few minor concerns to be addressed:

The author suggests including the following reference about the fragility of ancient masonry towers:

Aloisio, A., Capanna, I., Cirella, R., Alaggio, R., Di Fabio, F., & Fragiacomo, M. (2020). Identification and model update of the dynamic properties of the san silvestro belfry in l’aquila and estimation of bell’s dynamic actions. Applied Sciences, 10(12), 4289.

 

The reference was found relevant and was included in the manuscript. 

 

Is it possible to improve the resolution of Fig.1?

The resolution of almost all the figures is meagre! The enhancement of their quality is mandatory!

 

The figures are now vectorized to guarantee major resolution.

 

Line 271- the authors left a Greek expression, revise.

Amended.

 

The authors must clarify how they estimated the fragility functions. How they estimated the parameters of the lognormal distribution? Did they carry out nonlinear dynamic analysis? Did they follow a Monte Carlo approach? This paragraph is not clear and must be expanded since the paper's primary focus should be the fragility estimate.

 

The fragility analysis is based on the capacity curves derived from NL static (pushover) analyses as presented in section 6.1 and Figure 11. This is now clearly stated in lines 460-461.

In section 6.2 the derivation of the fragility curves is presented in lines 456-466 based on the capacity curves estimated in section 5. On the capacity curve of each tower clearly two damage-states are defined: damage-state 2 (the yield point) and damage-state 4 (the collapse point). The other two damage-states are related to these two as a fraction (see line 464-465). Therefore, the average values of each damage-state are estimated along with the corresponding variability (see lines 467-478). Then, the lognormal distribution is applied to generate the curves shown in Figure 13.

 

Some references:

https://www.tandfonline.com/doi/abs/10.1080/15583058.2014.951792?casa_token=7mbHKsxQ5I8AAAAA:SVAGflaOAh5dHqh-j-15qasgIupvNUrZH87xgwyT-2lWWXN8RwKFrmTC_24EqgrYxo5k_7fiRAmphDU

The reference was found relevant and was included in the manuscript. 

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript treats a paramount issue of architectural heritage preservation. Fragility analyses are conceived based on limit analyses for different failure mechanisms. Five real case studies have been considered, dealing with five iconic masonry towers of the byzantine age. Generally speaking, the article is well-conceived and deserves the attention of the editorial board. Some comments must be addressed before publication.

• Section 2.2, represents the modal analysis. It seems that no experimental campaign is carried out to investigate the eigenmodes of the structures. The references in this section do not justify the selection of the mechanical properties. The construction ages are different thenceforth is expected that the material for different towers is different. A further explanation should be provided.
• From line 181 – 187 the explanation is not fully reliable. For instance, the difference between the 0.44s and 0.65s of the towers, with the 0.1s and 0.44 s of the range of seismic severity, is not so great as to conclude that “are still standing avoiding the collapse over the centuries as they are out of the most critical frequency content of strong motions in Greece”. Moreover, considering the higher modes which have a corresponding period lower than 0.4s, consequently would a cause for high seismic demands in terms of forces or local collapses. There are controversial justifications that could be found for both scenarios, either confirm their safety or that they are unsafe. More explanation is deemed required. The mass activation for each mode could be e relevant information.
• From line 198 – 203 the authors refer to the observed failure mechanism in the Italian context. The authors say are three failure mechanisms and they list four, while according to reference 36, there are 5 failure mechanism. The authors should clarify this aspect.
• The acronyms: ANA, APO, DP and KPO are unclear.
• Figure 12 should be before figure 13 in the text, an error of the caption.
• Figure 12 was not found referred in the text. However, this figure is wrong. The graph presents fragility curves, and as depicted in the graph, all five towers are considered. The formulation of a fragility curve for each damage level is explained in section 6.2 and table 6, however, it is not explained how these fragilities could be interconnected for the five towers. In any case, it doesn’t seem reasonable to have a fragility curve for all of them but separately for each case study.

Some similar or interconnected literature to your work are: 10.1007/s10518-019-00732-y; 10.1016/j.soildyn.2019.105752 ; 10.1080/15583058.2020.1805045 ; 10.1080/15583058.2020.1723735  ; 10.3389/fbuil.2019.00033 ; 10.1016/j.ymssp.2019.04.038 ; 10.1007/s10518-017-0222-7 ; 10.1080/15583058.2019.1645241 ; 10.1007/s10518-014-9595-z ; 10.1007/s00419-015-1027-2

Author Response

We deeply thank the reviewer for his time and efforts to improve the paper. Below follow point-by-point responses to the reviewer’s comments.

The manuscript treats a paramount issue of architectural heritage preservation. Fragility analyses are conceived based on limit analyses for different failure mechanisms. Five real case studies have been considered, dealing with five iconic masonry towers of the byzantine age. Generally speaking, the article is well-conceived and deserves the attention of the editorial board.

We thank the reviewer for the positive comment.

Some comments must be addressed before publication.

• Section 2.2, represents the modal analysis. It seems that no experimental campaign is carried out to investigate the eigenmodes of the structures. The references in this section do not justify the selection of the mechanical properties. The construction ages are different thenceforth is expected that the material for different towers is different. A further explanation should be provided.

The analytical results are now compared with results from the literature and are found in good agreement. Despite the time difference, all the structures are in a very close vicinity and the materials are found from close quarries as the land offers good quality marble and raw materials. This is practice was followed during Ottoman conquest and is well documented.

• From line 181 – 187 the explanation is not fully reliable. For instance, the difference between the 0.44s and 0.65s of the towers, with the 0.1s and 0.44 s of the range of seismic severity, is not so great as to conclude that “are still standing avoiding the collapse over the centuries as they are out of the most critical frequency content of strong motions in Greece”. Moreover, considering the higher modes which have a corresponding period lower than 0.4s, consequently would a cause for high seismic demands in terms of forces or local collapses. There are controversial justifications that could be found for both scenarios, either confirm their safety or that they are unsafe. More explanation is deemed required. The mass activation for each mode could be e relevant information.

This has been an introductory comment based on the elastic properties and a force-based philosophy. The thorough displacement-based analysis and the proper justification follows afterwards, see Section 6.1.

Therefore, to avoid any misunderstanding of the reader, the comment is now omitted.

• From line 198 – 203 the authors refer to the observed failure mechanism in the Italian context. The authors say are three failure mechanisms and they list four, while according to reference 36, there are 5 failure mechanism. The authors should clarify this aspect.

We thank the reviewer for the careful reading. We amended the oversight, and we added a comment about the fifth type (see line 230-233).

• The acronyms: ANA, APO, DP and KPO are unclear.

The acronyms are presented in Table 1.

• Figure 12 should be before figure 13 in the text, an error of the caption.

Amended.

• Figure 12 was not found referred in the text. However, this figure is wrong. The graph presents fragility curves, and as depicted in the graph, all five towers are considered. The formulation of a fragility curve for each damage level is explained in section 6.2 and table 6, however, it is not explained how these fragilities could be interconnected for the five towers. In any case, it doesn’t seem reasonable to have a fragility curve for all of them but separately for each case study.

An error occurred in the numbering of figures resulting in the non-reference of Figure 12 which is now corrected accordingly.

In section 6.2 the derivation of the fragility curves is presented in lines 456-478 based on the capacity curves estimated in section 6.1. On the capacity curve of each tower two damage-states are defined: damage-state 2 (the yield point) and damage-state 4 (the collapse point). The other two damage-states are related to these two as a fraction (see line 464-466).

As the fragility curves are a practical statistical means to estimate the vulnerability, they are of a more general nature without precisely following one tower’s architectural characteristics and response. Therefore, the average values of each damage-state are estimated along with the corresponding variability (see lines 467-478).

Some similar or interconnected literature to your work are: 10.1007/s10518-019-00732-y; 10.1016/j.soildyn.2019.105752 ; 10.1080/15583058.2020.1805045 ; 10.1080/15583058.2020.1723735  ; 10.3389/fbuil.2019.00033 ; 10.1016/j.ymssp.2019.04.038 ; 10.1007/s10518-017-0222-7 ; 10.1080/15583058.2019.1645241 ; 10.1007/s10518-014-9595-z ; 10.1007/s00419-015-1027-2

The proposed papers were found relevant and added in the manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The paper is now suitable for publication in Infrastructures.

Reviewer 3 Report

The raised comments have been correctly addressed by the authors. A sound justification is provided and the manuscript is enhanced.

I suggest to accept the paper for publication.

The authors should correct any typos like:

simper-with simple