Development of fragility curves for road bridges exposed to volcanic lahars

Dagá, Joaquín; Chamorro, Alondra; de Solminihac, Hernán; Echaveguren, Tomás

doi:https://doi.org/10.5194/nhess-18-2111-2018

Articles | Volume 18, issue 8

https://doi.org/10.5194/nhess-18-2111-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-18-2111-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 8

Research article

|

08 Aug 2018

Research article |

| 08 Aug 2018

Development of fragility curves for road bridges exposed to volcanic lahars

Joaquín Dagá, Alondra Chamorro, Hernán de Solminihac, and Tomás Echaveguren

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Final revised paper (published on 08 Aug 2018)
Preprint (discussion started on 12 Oct 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Interesting contents but difficult to read', Anonymous Referee #1, 08 Dec 2017
- AC1: 'REPLY TO REFEREES AND GUIDE TO THE REVISION OF THE PAPER - Referee #1', Joaquin Daga, 19 Feb 2018
RC2: 'Review of "Development of bridge failure model and fragility curves for infrastructure overturning and deck sliding due to lahars"', Anonymous Referee #2, 09 Jan 2018
- AC2: 'REPLY TO REFEREES AND GUIDE TO THE REVISION OF THE PAPER - Referee #2', Joaquin Daga, 19 Feb 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (26 Feb 2018) by Thom Bogaard

AR by Joaquin Daga on behalf of the Authors (26 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Apr 2018) by Thom Bogaard

RR by Anonymous Referee #2 (23 Apr 2018)

Suggestions for revision or reasons for rejection

This revised manuscript focuses on the development of fragility curves for Chilean bridges affected by lahars. The main damage mechanisms considered are pier or abutment overturning and deck sliding. Development of the fragility curves follows a process of developing a conceptual model and limit state functions, incorporating analytical models of scour and pressure and finally, Monte-Carlo simulation. These curves (for bridges without (C1) and with (C2) piers) are then parametrised and tested against bridge failure data. I believe this is a useful contribution, as while results are specifically for Chilean bridges (where the authors have data), the method and process is outlined well enough for it to be translated to other regions. Previous concerns highlighted by myself (Referee #2) and referee #1 have been addressed (see the attached for some smaller issues) and the language has greatly improved. The additional detail on methodology and validation, as requested, clarifies many of the previously highlighted issues. However, validation of the fragility curves (Section 6.2) is fatally flawed:

The number of empirical samples n_e in each test (Tables 3 and 4)is too small to draw any statistical conclusion. From n_a, x_a, n_e and x_e provided, the power of each Z test is around 0.05 (5%). That is, the probability of a Type II error (not rejecting the null hypothesis when it is actually false) is around 95%. Note this does not necessarily mean that the parametric curves (and failure model) are incorrect, but it indicates there is insufficient empirical data to provide a statistical validation of the model.

The lack of data is common in similar studies of fragility, and is not a problem which I expect the authors to solve. Rather, the bridge failure model should be well grounded in physical principles and critically evaluated against any sources of data. From my assessment, I believe the failure/limit state model is sufficiently comprehensive (keeping in mind the need for some level of simplicity) and the evaluation against empirical data in section 6.1 provides some level of (qualitative) support. Therefore, I recommend the manuscript could be published, subject to the following critical changes:

- Section 6.2, and all references to the statistical validation (p. 1, lines 27-29; section 6.3 first paragraph; p. 22, line 16) should be removed completely.
- In section 6.3, the authors should additionally highlight the data-deficiency issue (possibly as a source of future work) and critically evaluate the success of the model in reference to Table 2. How representative is the empirical data of the range of conditions used to generate the analytical fragility curves? Are the main sources of force/vulnerability sufficiently explored with the empirical data and/or could qualitative 'bounds' on the reliability of these curves be determined?

Referee Report: PDF

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RR by Anonymous Referee #1 (03 May 2018)

Suggestions for revision or reasons for rejection

In general, this study provides interesting and useful information for engineers responsible for design, operate and maintain the road network under the risk of lahar impacts. In my view, as a research engineer in the field of river engineering, the paper has some difficulties to read, each can be easily improved. Before the publication, such weakness should be dealt with.

Point to point comments

Title: the concept of 'bridge failure model', the difference between 'bridge failure' and 'infrastructure overturning and deck sliding', the definition of 'infrastructure' are not clear, this leads the reader to imagine what will come from the manuscript from the title difficult. My suggestion is, something like, 'Development of failure model and fragility curves for road bridges under lahar impact' or simpler 'Development of fragility curves for road bridges under lahar impact'. The ambiguity of terminologies makes difficult to follow the meaning of not only title but remaining part of the manuscript. E.g. 'infrastructure' covers a broad sense. Road network itself can be included in the concept of 'infrastructure' (as used in the first line of the abstract). 'infrastructure' is mainly used to mean a foundation of something in this manuscript, especially for a bridge. If so, it is better to describe 'bridge infrastructure' or 'bridge foundation'.

The word 'abutment' has potentially two meaning, one is the foundation of bridge pier and other is the marginal area between a river bank and the bridge. So the reader wonders what you want to say using the word 'abutment', so it is needed to clarify which do you want to mean or use another word.

You used 'failure model' (singular) so maybe you want to define 'failure model' as the toolbox to identify damage or non-damage for all possible types of failure mode. On the other hand, 'fragility curves' (plural) were made for each failure type. This means, the failure model was actually composed of several sub-models corresponding to each failure mode, and the sub-models were used to develop each fragility curve, if my understanding is correct. What I want to say is that it is better to use 'failure models' instead of 'failure model'.

Page 1, line 35, I'd like to replace 'losses' --> 'restrictions' and remode 'permanent'.
Page 1, line 35, It is not clear how 'highway' and 'road' distinguished in the manuscript.
Page 2, line 2, 'temporary' --> 'temporal'?
Page 2, line 3, 'loss of surface friction' --> 'loss of friction between (road) pavement and tires'?
Page 2, line 10, 'affect(ed)' is quite neutral but here you want to say some negative meaning so ''damaged' or something like this may be better to use here. (not only here but other sentences using 'affect(ed)')
Page 2, line 14, The meaning of 'critical' here is not clear.
Page 2, line 16, put 'a' before 'consequence'.
Page 2, line 27, 'studies' --> 'covers'?
Page 2, line 33, 'effects' --> 'interruption'
Page 2, line 36, 'and' --> 'nor'?
Page 2, line 40, It is not clear how 'calibration' and 'parameterization' distinguished.
Page 3, line 7, What do you mean by 'analytical models'?
Page 3, lines 21-22, 'Debris flows are highly viscous slurries of sediment and water'. I think 'deris' is explained but not about 'flows'.
Page 3, line 28, I think you can remove 'so'.
Page 3, lines 36-37, 'scour of the riverbed drags massive material blocks' doesn't make sense.
Equation (1): Is DS defined? What is the meaning of subscript i?
Page 4, line 26, 'the recently described approaches' --> 'the approaches described above'?
Title of Section 3. I'd like to suggest to replace as '(Development of) failure model(s) for bridge pier/abutment overturning and deck sliding due to lahars'
Page 5, The first paragraph of section 3.1, so do you define that g(X)=D(X)-S(X)? If so, it is better to describe so using equation.
Figure 1: It is not clear how the abutment overturning and the pier overturning were distinguished. Maybe, it is better to specify where are the deck, pier and abutment in Figure 1. Can we discuss the pier overturning using the moment Mn defined in Figure 1? Can you define Fwi, Fws, Fr in Figure 1?
Equations (3) and (5) Are Yso and Fr function of X? If so, how do you change Yso and Fr depending on X?
Page 8, line 5, 'produced' --> 'caused'
Title of Section 4. It is not clear what do you want to mean by 'experiment'.
Page 9, line 10, 'For this case' --> 'In this study'?
Page 9, line 22, 'this study' --> 'Muller (1996)'?
Page 9, line 24, 'the magnitude of the scour' --> 'the scor depth'?
Page 9, line 27, The meaning subscript of Y is not clear. (c-d, e-d, c-o, e-o, etc.) Maybe you can specify this by a figure.
Page 9, line 27, Eq. (8) and (9) --> Eqs. (8) and (9).
Page 11, Can you define h_design, e_super, h_imp etc. using figure?
Page 11, 'grava'-->'gravel'
Table 1, Definition of numbers in Deterministic value/probabilistic distribution is not clear. E.g. what is the meaning of 1.0 and 1.9 for K_gr? What 1.0, 1.06 and 1.06 mean for K_R? What is the meaning of '1,1' for K_3?
Table 2, can you show the type of failure (actual and predicted) for each bridge? Also can you show the predicted failure probability for each bridge?

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ED: Reconsider after major revisions (further review by editor and referees) (08 May 2018) by Thom Bogaard

AR by Joaquin Daga on behalf of the Authors (19 Jun 2018) Manuscript

ED: Referee Nomination & Report Request started (22 Jun 2018) by Thom Bogaard

RR by Anonymous Referee #2 (02 Jul 2018)

ED: Publish subject to technical corrections (10 Jul 2018) by Thom Bogaard

ED: Publish subject to technical corrections (11 Jul 2018) by Thom Bogaard

AR by Joaquin Daga on behalf of the Authors (14 Jul 2018) Manuscript

Short summary

One of the main volcanic processes affecting road bridges are lahars, which are flows of water and volcanic material running down the slopes of a volcano. In this paper, bridge failure models due to lahars are proposed and, based on these, fragility curves are developed. Fragility curves are parameterized by maximum likelihood estimation, assuming a cumulative log-normal distribution. Bridge failure models are empirically evaluated using data of 15 bridges that were affected by lahars.