Optimization of Inspection Period in Natural Stone Claddings

Round 1

Reviewer 1 Report

Authors have used a multi-objective optimization procedure to schedule inspection interventions on natural stone claddings in order to understand whether there is an optimal time interval for performing the inspections, considering the several conflicts that the building owners are subjected to. Authors were successful in analysing the results based on the used case studies. They found that implementing maintenance strategies with more maintenance activities was successful and advantageous leading to higher impact on the improvement of NSC. Also, they found that a cost-saving of 36-58% can be achieved if the inspection period is increased, with a lower impact on
the aesthetic appearance. 

Accordingly, I would like to recommend this paper for publication in its current form.

Author Response

Authors have used a multi-objective optimization procedure to schedule inspection interventions on natural stone claddings in order to understand whether there is an optimal time interval for performing the inspections, considering the several conflicts that the building owners are subjected to. Authors were successful in analysing the results based on the used case studies. They found that implementing maintenance strategies with more maintenance activities was successful and advantageous leading to higher impact on the improvement of NSC. Also, they found that a cost-saving of 36-58% can be achieved if the inspection period is increased, with a lower impact on the aesthetic appearance. 

Point 1: Accordingly, I would like to recommend this paper for publication in its current form.

Response 1: The authors would like to thank the Reviewer for his/her comments.

Reviewer 2 Report

This is an interesting paper. I have several suggestions:

Please change the structure of your manuscript: 1) Introduction 2) Materials and Methods 3) Results 4) Discussion 5) Conclusions

Introduction: insert hypothesis and aims of your study

Discussion: You should discuss better your results. Please compare your results with previous studies. Insert study limitation.

Conclusion: discuss future research.

Author Response

This is an interesting paper. I have several suggestions:

Point 1: Please change the structure of your manuscript: 1) Introduction 2) Materials and Methods 3) Results 4) Discussion 5) Conclusions

Response 1: Done as suggested.

 

Point 2: Introduction: insert hypothesis and aims of your study

Response 2: Done as suggested. The following was added to the revised version of the manuscript (line 63): “Therefore, the aim of this study is to develop a framework, based on multi-objective optimization procedures, to optimize the inspection period in Natural Stone Claddings (NSC). As buildings’ constructive solution, NSC is widely used; however, little information is available in the literature about the inspection periods, and the values available are deterministic and based on the experience of experts. Therefore, one of the hypotheses behind this study is to understand whether there is an optimal time interval for performing the inspections on NSC, whether it is in agreement with the values available in the literature, and whether these values are constant over time or are changed according to the owners’ requirements and demands.”

 

Point 3: Discussion: You should discuss better your results. Please compare your results with previous studies. Insert study limitation.

Response 3: The Authors agree with the Reviewer’s comment. However, regarding the issue of comparing the results with previous studies, the Authors would like to refer that they are not aware of any other similar study, with regard to NSC or other building component, so that it is not possible to compare results. From the Authors’ knowledge, there are some studies that address inspection periods (please see Section 2.1.1 of the revised version of the manuscript), but these values are deterministic. However, to clarify this question, the following was included in the revised version of the manuscript (line 487): “However, the values provided by the literature review (Section 2.1.2) are deterministic values, defined based on the experience of experts or suggested based on users’ requirements. The main advantage of this study is the probabilistic framework of the methodology that allows encompassing the uncertainty related with the inspection periods, proposing an optimization process to find the most adequate time intervals between inspections. In terms of constraints, as with other probabilistic methodologies, the main limitation of this methodology is the size and quality of the samples. If the sample in which the analysis is based is biased or with influential case studies, the results provided by the methodology will not be realistic.”

 

Point 4: Conclusion: discuss future research.

Response 4: This issue had been dealt with superficially in the conclusions. However, to clarify it, the following sentence has been reformulated in the revised version of the manuscript (line 543): “As future research, this methodology can be used to analyse other maintenance strategies, in terms of the type of actions, the minimum requirements or the environmental context; allowing considering different conflicting parameters; and applied to others buildings’ constructive solutions or even the building as a whole.”

Reviewer 3 Report

The manuscript reports the design of a Petri net condition maintenance model to evaluate the effects of different maintenance plans of cladding made of natural stone. The topic is very interesting, and it is in line with the aims of the journal. The manuscript is well written, clear, and innovative.

I have only few comments:

1. Can you describe better the degradation conditions in each figure in fig 1.
2. Can you please add more information and comments about the data in Table 2? I know the Authors wrote “. A more detailed explanation of these 256 assumptions is provided in Ferreira et al. [58].” But I think this part deserves more explanation.
3. Can you please comment on the high standard deviation of the Ta value in Table 2?
4. Line 398-403 the Authors report that the model is dynamic and can be set-up according to the specific situations. Can you comment on how different parameters (the different type of stones, the use of the cladding, the presence of protective treatments on stone, the environment ) influence the model?
5. As a general curiosity: do you think this model could be implemented also for historical buildings, with decayed stones?

Author Response

The manuscript reports the design of a Petri net condition maintenance model to evaluate the effects of different maintenance plans of cladding made of natural stone. The topic is very interesting, and it is in line with the aims of the journal. The manuscript is well written, clear, and innovative.

I have only few comments:

Point 1: Can you describe better the degradation conditions in each figure in fig 1.

Response 1: Done as suggested. The following was added to line 138 of the revised version of the manuscript: “In Figure 1, some examples of the visual condition of NSC in each degradation level are presented. Condition A (Figure 1a) represents a NSC with no visible degradation; in Condition B (Figure 1b), the NSC begins to present some visual anomalies (superficial dirt and stains) and some loss of integrity anomalies (material degradation and cracking), which do not put at risk the NSC’ performance; Condition C (Figure 1c) corresponds to a NSC with slight degradation, with anomalies related with joints and substrate degradation and loss of integrity, such as: open joint, scaling of the edges and fracture; Condition D (Figure 1d) corresponds to a NSC with moderate degradation, where there is an evolution of the Condition C anomalies; and finally, Condition E (none of the case studies within the sample belongs to Condition E), the NSC show a generalised degradation, with severe loss of adherence anomalies.”

 

Point 2: Can you please add more information and comments about the data in Table 2? I know the Authors wrote “. A more detailed explanation of these assumptions is provided in Ferreira et al. [58].” But I think this part deserves more explanation.

Response 2: The Authors agree with the Reviewer when he/she states that an explanation should be added about the data in Table 2. The following was added to line 272 of the revised version of the manuscript: “Specifically, according to a Weibull distribution, for a NSC, a transition between condition A and B takes, on average, 4.1 years to occur, with a standard deviation of 7.0 years. The same analysis can be used for the other condition transitions. The choice of the best probability distribution that describes the degradation process is performed through the maximization of the logarithm of the likelihood [59].”

Reference:

59. Kalbfleisch, J.D.; Lawless, J.F. The analysis of panel data under a Markov assumption. J. Am. Stat. Assoc. 1985, 80, 863–871, DOI: 10.1080/01621459.1985.10478195.

 

Point 3: Can you please comment on the high standard deviation of the Ta value in Table 2?

Response 3: Done as suggested. The following was added to line 277 of the revised version of the manuscript: “However, in relation to the data shown in Table 2, the high standard deviation of T_a is due to the reduced interval associated with the severity of degradation, S_w, and the anomalies considered to quantify the severity of degradation in conditions A and B. From Table 1, the severity of degradation of condition A varies between 0 and 1%, showing that the deposit of surface dirt is sufficient to move the NSC from condition A to B. Moreover, the classification of a NSC is highly dependent on the inspector, geographic location, exposure conditions and time of the year.”

 

Point 4: Line 398-403 the Authors report that the model is dynamic and can be set-up according to the specific situations. Can you comment on how different parameters (the different type of stones, the use of the cladding, the presence of protective treatments on stone, the environment) influence the model?

Response 4: These different parameters (such as: the different type of stones or claddings, the use of the cladding, the presence of protective treatments on stone, the environment, among others) influence the model through the degradation process and the impact of the maintenance strategies. The degradation process, in the methodology proposed in this study, is responsible for modelling the sojourn time of the cladding in each degradation condition. But, naturally, the degradation process of different type of stones or claddings are different, also depending on the exposure conditions, such as: the distance from the sea, the moisture, the orientation, the wind-rain action, among others. Therefore, if the model fits the degradation process according to these parameters, the results of the model will be different, they will be adjusted to that specific situation. Furthermore, if protective treatments are used in the claddings, this can be considered in the impact of the maintenance strategies, since these treatments will modify the way the cladding deteriorates after the interventions. To clarify this issue in the manuscript, the following was added (line 501): “These parameters will influence the degradation process and the impact of the maintenance strategies and, consequently, different conclusions can be achieved.”.

 

Point 5: As a general curiosity: do you think this model could be implemented also for historical buildings, with decayed stones?

Response 5: Although the methodology developed by the Authors has so far only been applied to current buildings, the Authors believe that it can be also implemented in historic buildings. However, the Authors also believe that some changes must be made, to ensure an adequate modelling of historic building, mainly in terms of the classification system of the degradation condition of these buildings and the maintenance strategies applies over the years. For example, inspections and requirements with historic buildings are different from those of current buildings; in historic buildings, the stakeholders’ never reach an instant in time in which they decide that it is better to demolish and replace it with a new one.

Round 2

Reviewer 2 Report

L 63 - 70: "Therefore, the aim of this study is to develop a framework, based on multi-objective optimization procedures, to optimize the inspection period in Natural Stone Claddings (NSC). As 65 buildings’ constructive solution, NSC is widely used;, however, little information is available in the  literature about the inspection period, and the values available are deterministic and based on the
 experience of experts" this paragraph should be at the end of your introduction line 122.

Reviewer 3 Report

It is a very interesting manuscript, and I would like to thank the Authors for considering my comments.