Climate Change Impact on Corrosion of Reinforced Concrete Bridges and Their Seismic Performance

Reviewer #1

This paper presents a study on the influence of corrosion effects due to carbonation on the seismic performance of existing RC motorway bridges considering the climate change impact, several scenarios are evaluated, and some useful results are obtained. The paper exhibits clear writing logic and rigorous numerical analysis. However, to improve the academic quality and persuasiveness, some revisions are suggested as follows:

A: The authors gratefully acknowledge the reviewer for his/her time and suggestions. The authors have addressed the proposed comments that have let the paper improve.

R1: The literature review on the topics of structural health monitoring are insufficient, some topics should be considered in the section of Introduction, such as the development of SHM (The Current Development of Structural Health Monitoring for Bridges: A Review), the variation of temperatures on the performance of damage identification (Temperature Effect on Vibration Properties and Vibration-Based Damage Identification of Bridge Structures: A Literature Review, Damage detection under varying temperature using artificial neural networks), and time domain-based damage identification (Statistical pattern recognition for Structural Health Monitoring using time series modeling: Theory and experimental verifications).

A: As suggested by the reviewer, the following consideration has been added in the Introduction:

“Moreover, also the growing use of Structural Health Monitoring (SHM) techniques is fundamental to be able to evaluate the maintenances state of existing RC bridges over time [26-28].”

Considering the following new references:

[26] Deng, Z.; Huang, M.; Wan, N.; Zhang, J. The Current Development of Structural Health Monitoring for Bridges: A Review. Buildings 2023, 13(6), 1360.

[27] Luo, J.; Huang, M.; Lei, Y. Temperature Effect on Vibration Properties and Vibration-Based Damage Identification of Bridge Structures: A Literature Review. Buildings 2022, 12(8), 1209.

[28] Gul, M.; Necati Catbas, F. Statistical pattern recognition for Structural Health Monitoring using time series modelling: Theory and experimental verifications. Mechanical Systems and Signal Processing 2009, 23(7), pp. 2194-2204.

R1: Line 59, [2627] should be [26, 27].

Line 63: The comma is not necessary.

Line 142: [55,55] should be wrong.

Line 189: “an” should be “and”.

A: Done.

R1: In Equation (1), K should be a coefficient, not a function, so K(T(t)-20) need to be simplified as K, and Equations (1) and (2) can be combined; What’s the meaning of T, daily maximum or minimum temperature, daily mean temperature, annul mean temperature or gradient temperature for box girder bridge? Please clarify it.

A: As suggested by the reviewer Eq. 1 and 2 are combined as follows:

Trepresents the annual mean temperature which characterize the area where the bridge was built.

R1: The captions of many figures are not correct, some sub-caption is missing, such as figure 1.

A: The numbering of the figures has been corrected in the new version of the paper.

R1: In lines 277-278, if the bridge is a highway bridge, the traffic load can be neglected, if not, such as subway viaduct, the traffic load should be considered, please clarify.

A: In the evaluation of the seismic vulnerability of bridges, the traffic load can be neglected according to as reported in the Italian Design Code,

[22] Decreto Ministeriale 17/01/2018, Ministero delle Infrastrutture e dei Trasporti, G.U. Serie Generale n.42 del 20/02/2018 – S.O.8.

R1: Lines 317-318, the first three natural periods are very close, please explain the reason and provide the mode shapes.

A: The mode shapes of the first natural periods are reported in the new Figure 11 added in the revised version of the manuscript.

As it is possible to notice from the Figure 11, the natural periods are very close because they are related to the piers 2 and 3.

R1: Lines 331-332, “are presents” may not correct.

A: “are presents” has been replaced with “is present” in the new version of the manuscript.

R1: The first paragraph in the section of Conclusions is too long, please simplify it.

A: As suggested by the reviewer, Section 5 has been simplified in the new version of the manuscript.

Reviewer #2

The paper under review aims to investigate the impact of climate change on the corrosion effects due to carbonation and its subsequent influence on the seismic performance of existing reinforced concrete (RC) motorway bridges. The study explores various scenarios involving changes in carbon dioxide concentrations, temperature, and relative humidity, with a particular focus on Italian RC motorway bridges constructed between the 1960s and 1970s.

One commendable aspect of the paper is its timely and relevant topic. Climate change and its impact on infrastructure, especially in the context of seismic performance. The emphasis on bridges, directly vulnerable to weather effects, enhances the study's significance, highlighting potential repercussions for public safety and transportation due to structural degradation.

A: The authors gratefully acknowledge the reviewer for his/her time and suggestions. The authors have addressed the proposed comments following in a hopefully improved version of the paper.

R2: The abstract lacks clarity concerning the utilized research methods. To enhance clarity and conciseness, specifically elaborate on the comparison of results with prior research. Provide additional details on the nature, scope, and findings of previous studies for a more comprehensive understanding.

A: The abstract has been modified adding the following sentences:

“…. the implementation of 3D simplified Finite Element Models and the use of analytical relation to obtain the reduction of steel reinforcement diameter as a function of the age of the bridge and of the considered corrosion scenario”

“The results obtained using the projection of the climate change impact are compared with those calculated considering the corrosion scenarios resulting from the DuraCrete research project to understand if the evolution of climate leads to worse scenarios than those previously assessed.”

R2: What are the importance and timeliness of comparative analysis and practical implications?

A: To clarify this aspect, the following sentence is added at the end of the Section 5:

“Finally, it is important to highlight that the comparison of the results obtained considering the different scenarios analyzed is useful to improving the maintenance and management of these strategic structures in order to always guarantee an adequate safety level.”

R2: What are the key assumptions made in evaluating climate evolution, how might uncertainties in these assumptions affect the reliability of the study's conclusions?

A: As reported in Section 2, the key assumptions used for the evaluation of the climate evolution are presented in reference [43-45, 47]:

[43] van Vuuren, D.P.; Edmonds, J.; Kainuma, M.; Riahi, K.; Thomson, A.; Hibbard, K.; Hurtt, G.C.; Kram, T.; Krey, V.; Lamarque, G.F.; Masui, T.; Meinshausen, M.; Nakicenovic, N.; Smith, S.J.; Rose, S.K. The representative concentration pathways: an overview. Climatic Change 2011, 109, pp. 5-31. https://doi.org/10.1007/s10584-011-0148-z.

[44] O’Neill, B.C., Carter, T.R., Ebi, K. et al. Achievements and needs for the climate change scenario framework. Nat. Clim. Chang. 2020, 10, 1074–1084. https://doi.org/10.1038/s41558-020-00952-0

[45] Schwalm, C.R.; Glendon, S.; Duffy, P.B. RCP8.5 tracks cumulative CO2 emissions. Proc. Natl. Acad. Sci. USA 2020, 117, 19656–19657. https://doi.org/10.1073/pnas.2007117117"https://doi.org/10.1073/pnas.2007117117

[47] Jacob, D.; Petersen, J.; Eggert, B.; et al. EURO-CORDEX: new high-resolution climate change projections for European impact research. Regional Environmental Change 2014, 14, pp. 563-578. https://doi.org/10.1007/s10113-013-0499-2.

The main effect due to the climate change impact hypotheses used in this study is that the corrosion levels obtained from DuraCrete leads to more critical scenarios compared to those obtained with climate change projections for the considered area. This aspect is highlighted in the conclusions of the revised version of the paper as follows:

•  the corrosion levels obtained from DuraCrete leads to more critical scenarios compared to those obtained with climate change projections for the area where the analysed viaduct was built.

R2: How were the Representative Concentration Pathways (RCPs) chosen, and what specific considerations led to the selection of RCP4.5 and RCP8.5? How well do RCP4.5 and RCP8.5 reflect medium and maximum pathways?

A: To clarify this aspect, the following sentence has been added in Section 2:

“According to the last IPCC report [IPCC, 2021], an average increase of global mean surface air temperature of 2.7°C and 4.4°C is expected at the end of the century (period 2081-2100) for RCP4.5 and RCP8.5 respectively”

R2: Has a sensitivity analysis been conducted to assess the impact of uncertainties in climate projections on the study's outcomes?

A: The parameters have been calibrated to best reproduce the climatic evolution of the area in order to be able to make a correct comparison with the more general scenarios hypothesized by DuraCrete, considering as reported in

[60] Stewart, G.M.; Wang, X.; Nguyen, M.N. Climate change impact and risks of concrete infrastructure deterioration. Engineering Structures 2011, 33(4), pp. 1326-1337. https://doi.org/10.1016/j.engstruct.2011.01.010"https://doi.org/10.1016/j.engstruct.2011.01.010.

An ensemble of climate projections is considered in the study for both scenarios and average temperature values are used for the computations. A full probabilistic approach could be considered in a future study relying also on weather generation techniques as introduced in Section 2 (see reference [48]) and evaluating prediction intervals for corrosion rates.

R2: What considerations were made to ensure a meaningful correlation between climate change and corrosion effects?

A: The fundamental parameter considered in this research work is the value of the mean corrosion current density (i_corr) which is present in the formulation of the simplified analytical model used to obtain the reduction of the steel reinforcement diameter due to carbonation phenomenon and which define the considered corrosion level.

R2: Use high-quality images for Figures 1, 2, 3, ,4, 5, 6, 7, 8 and 11

A: As suggested by the reviewer, the quality of the Figures is improved in the revised version of the manuscript.

R2: Please elaborate on the rationale behind the use of Timoshenko beam elements to schematize the main structural elements, how do these elements accurately capture the behavior of the viaduct under seismic loads, especially considering the complexities introduced by corrosion effects?

A: The use and the validity of this approach is discussed in detail in the following research works:

Crespi, P.; Zucca, M.; Longarini, N.; Giordano, N. Seismic assessment of six typologies of existing RC bridges. Infrastructures 2020, 5(6), 52. 10.3390/INFRASTRUCTURES5060052.

Crespi, P.; Zucca, M.; Valente, M. On the collapse evaluation of existing RC bridges exposed to corrosion under horizontal loads. Engineering Failure Analysis 2020, 116, 104727. 10.1016/j.engfailanal.2020.104727.

Crespi, P.; Zucca, M.; Valente, M.; Longarini, N. Influence of corrosion effects on the seismic capacity of existing RC bridges. Engineering Failure Analysis 2022, 140, 106546. 10.1016/j.engfailanal.2022.106546.

Zucca, M.; Reccia, E.; Longarini, N.; Eremeyev, V.; Crespi P. On the structural behaviour of existing RC bridges subjected to corrosion effects: Numerical insight. Engineering Failure Analysis 2023, 152, 107500. 10.1016/j.engfailanal.2023.107500.

As reported in Section 3, the choice of Timoshenko beam elements for the implementation of the main structural elements of the viaduct is due to the reduced computational effort that characterize this approach. Furthermore, the corrosion effects have been considered only in terms of reduction of steel reinforcement diameter which influence the trend of the moment-curvature diagram of the section which regulate the concentrated plastic hinges that represent the ductile collapse mechanism and the shear resistance of the monitored structural element which govern the concentrated plastic hinges that represent the brittle failure mechanism.

R2: How were the corrosion effects induced by carbonation integrated into the structural models?

A: As mentioned in the previous point, the corrosion effects have been introduced in the analysis only in terms of reduction of steel reinforcement diameter which influence the trend of the moment-curvature diagram and of the shear resistance of the monitored structural element. This aspect is considered in the FEM varying the main points which define the concentrated plastic hinges whose behavior is described in Figure 9.

R2: The observation that corrosion effects significantly influence the brittle failure mechanism more than the ductile one is intriguing. What underlying factors contribute to this discrepancy?

A: This discrepancy is due to the poor construction details which characterize the viaducts built in Italy between the 1960’s and 1970’s especially regarding the stirrups. In fact, these structures have been designed to resist only to low values of horizontal loads because they are designed without considering the presence of seismic actions.

R2: What are the  limitations of the study? What key considerations or challenges should be addressed in future investigations?

A: The limitations of the study are due to the presence of a single case study. As highlighted in the conclusions of the revised version of the manuscript “Further developments of this research work are related to the generalization of the results obtained considering other viaducts built in different years and located in different seismic zones.” 

R2: Please add a notation section

A: As suggested by the reviewer, a notation section is added in Appendix A

Reviewer #3

The paper “Climate change impact on corrosion of r.c. bridges and their seismic performance” is a good paper and well written, but there are many issues that should be treated as the following points:

A: The authors gratefully acknowledge the reviewer for his/her time and suggestions. The authors have addressed the proposed comments following in a hopefully improved version of the paper.

R3: Re-write the first sentence in the introduction part to be summarized and more understood with reduced references as much as possible

A: The first sentence of the introduction has been rewritten as follows:

“During last years, the attention in safety assessment existing reinforced concrete (RC) viaducts has significantly grown especially for the several collapses that involved this kind of structures [1-5].”

As suggested by the reviewer the references have been reduced.

R3: There are many grammar mistakes that should be corrected in the whole paper.

A: Done.

R3: All the figures need to improve the resolution and quality.

A: As suggested by the reviewer, the quality of the Figures is improved in the revised version of the manuscript.

R3: The conclusion part should summarize and contain only the important results obtained from this study.

A: As suggested by the reviewer, Section 5 has been simplified in the new version of the manuscript.

R3: The conclusion part should not contain any references. Therefore, the authors should delete all references existing in the conclusion part.

A: As suggested by the reviewer, all the references present in the conclusions have been deleted.

Reviewer #4

The manuscript deals the with the influence of corrosion effects due to carbonation on the seismic performance of existing RC motor-way bridges considering the climate change impact is investigated. Several scenarios for the expected variations in CO2 concentrations, temperature and relative humidity are evaluated considering that most of the Italian RC motorway bridges are built between 1960s and 1970s. The results obtained are compared with those calculated considering the corrosion scenarios resulting from previous research studies to understand if the evolution of climate leads to worse scenarios than those previously assessed. Explain and discuss the following queries.

A: The authors gratefully acknowledge the reviewer for his/her time and suggestions. The authors have addressed the proposed comments following in a hopefully improved version of the paper.

R4: Much discussion in the abstract is dedicated to introduction than methodology of the work, kindly discuss briefly about the methodology of the work.

A: As suggested by the reviewer the following sentences is added in the Introduction:

“The present paper analyzes the effects of the climate change impact (in terms of increase of temperature and variation of relative humidity), which influence the development of corrosion phenomena due to carbonation, on the seismic performance of existing RC viaducts. In particular, a method of investigation of RC bridges is proposed based on the literature models that relate the variation of climate parameters to corrosion processes induced by carbonation taking as benchmark a real case study: an existing RC viaduct of the Italian motorway network built around the 1970s and located in province of Massa Carrara.”

R4: This study considered many simplified assumptions in the finite element model but that can’t be the case, how can this study justify these assumptions especially for dynamic analysis? Explain

A: As reported in Section 3, the analyses performed are non-linear static. The use and the validity of this approach is discussed in detail in the following research works:

Crespi, P.; Zucca, M.; Longarini, N.; Giordano, N. Seismic assessment of six typologies of existing RC bridges. Infrastructures 2020, 5(6), 52. 10.3390/INFRASTRUCTURES5060052.

Crespi, P.; Zucca, M.; Valente, M. On the collapse evaluation of existing RC bridges exposed to corrosion under horizontal loads. Engineering Failure Analysis 2020, 116, 104727. 10.1016/j.engfailanal.2020.104727.

Crespi, P.; Zucca, M.; Valente, M.; Longarini, N. Influence of corrosion effects on the seismic capacity of existing RC bridges. Engineering Failure Analysis 2022, 140, 106546. 10.1016/j.engfailanal.2022.106546.

Zucca, M.; Reccia, E.; Longarini, N.; Eremeyev, V.; Crespi P. On the structural behaviour of existing RC bridges subjected to corrosion effects: Numerical insight. Engineering Failure Analysis 2023, 152, 107500. 10.1016/j.engfailanal.2023.107500.

R4: Does this study use any finite element software to model and analyse or it’s a finite element code?

A: In this research work MIDAS CIVIL commercial software have been used for the FEM implementation. This aspect has now been clarified in the first part of Section 3 adding the following reference:

[60] MIDAS Civil Analysis Reference, 2023, https://www.midasoft.com/bridge-library/civil/products/midascivil.

R4: Figure 8 and 9 explain what the notations represent and its axis

A: The notations of the axis of the Figures 8 and 9 are now explained in the related captions.