Causes of the Collapse of the Polcevera Viaduct in Genoa, Italy

Round 1

Reviewer 1 Report

The submitted manuscript is very similar to the following one:

Rymsza, Janusz. Causes of the Morandi viaduct disaster in Genoa as a contribution to the design of pre-stressed structures. Roads and Bridges - Drogi i Mosty, [S.l.], v. 19, n. 1, p. 5-25, mar. 2020. ISSN 2449-769X.

https://www.rabdim.pl/index.php/rb/article/view/v19n1p5/542

DOI: 10.7409/rabdim.020.001

Author Response

The author would like to thank the Reviewer for the comment. The article submitted to MDPI is a version enriched compared to the article from the Road and Bridges - Drogi i Mosty quarterly with information related to the design and construction technology in chapter 1.4. "Construction of the main structural elements of the bridge in Genoa" (entirely new). Other sections are also improved compared to the previous publication. The proper reference is added in section 4.

The article includes the following additional drawings related to the design of the viaduct and flyover:

Fig. 3a Overpass support (longitudinal and cross-section).

Fig. 3b Viaduct support (longitudinal and cross-section).

Fig. 4b Schematic anchoring of the cable in the deck and at the top of the pylon.

In addition, drawings related to the technology of the viaduct construction have been added:

Fig. 5a Placing the span on the cantilevers of supports No. 6 and 7 of the overpass.

Fig. 5b Construction of pylon and cantilevers of support No. 9 of the viaduct.

Fig. 5c Pre-stressing temporary tendons laid on top of the cantilevers during the construction of the cantilevers.

Fig. 5d Viaduct supports at different stages of construction: support No. 9 – completely executed, support No. 10 – with the two-sided cantilevers made, and support No. 11 – with the pylon made.

Fig. 5e Viaduct supports at different stages of construction: support No. 10 – with concreted cables and support No. 11 – with steel tendons before concreting.

Fig. 5f Placing the span on cantilevers of supports  Nos. 10 and 11 of the viaduct.

Reviewer 2 Report

The author presents a case study paper on the collapse of the Polcevera Viaduct In Genoa, Italy.

The theme is interesting and current. The approach used is equally interesting as it recovers a proposal for reinforcement made a few years ago for bridges of this type.

The article is well-written and well-presented. Only one main question arises for me:

It is referred to in the abstract that the concept of strengthening the structure, as proposed by the author of the article 25 years ago, would be addressed in this paper, however, this approach is simple and very superficial, and may, however, be an interesting topic about this Subject.

 

Author Response

The Author would like to thank the Reviewer for the positive comments.

In April 1993, the author of the article was at Italstrade, visiting the reconstruction of the Polcevera viaduct. During this period, the diagonal stay cables of the viaduct were strengthened according to the design by Pisani. The author correctly suggested that this solution is not proper as it could lead to a bridge failure.

The motivation of this paper is to present findings of the condition of the Polcevara Viaduct before a disaster and the concept of strengthening this type of structure. This is very important because two more bridge structures of the same design by Morandi still exist.

It seems that the author's concept of adding more steel cables mounted in a pylon could be successfully implemented on one of these structures after a thorough analysis of the structural behavior and load distribution in individual technological and operational phases of the viaduct.

Reviewer 3 Report

Thanks to the author for investigating the causes of the disaster of the Polcevera viaduct in Genoa, Italy. The following comments need to be addressed:

• I suggest changing ‘disaster’ with ‘collapse’ in the manuscript Title as well as line 6 of Abstract.
• The statement in lines 15 and 16 is not strong. What is the analytical data to back up the concept of adding cables to prevent the support collapse?
• Please provide a reference for your proposed concept, 25 years ago, if any.
• Please explain what the practical challenges of the proposed concept are.
• The reference in line 579 need to be numbered at the end of manuscript.

The proposed concept can be considered in an analytical study but without the results and a comparative study with other possible approaches it is not backed up. Highlighting the imperative need to address the issue must be the main focus of the manuscript.

Author Response

The Author would like to thank the Reviewer for the comments.

1. I suggest changing ‘disaster’ with ‘collapse’ in the manuscript Title as well as line 6 of Abstract. – The Author would like to thank the Reviewer for the comment, the change has been implemented

2. The statement in lines 15 and 16 is not strong. What is the analytical data to back up the concept of adding cables to prevent the support collapse? - The Author would like to thank the Reviewer for the comment. First of all, introducing additional structure elements would relieve the damaged stays. Strengthening the corrosion-damaged cable and stressing the already bent stays was not correct; therefore could not be effective. Secondly, additional elements in the structure allow for better stress distribution and redundancy - if one fails, the other will take on a greater load, and the viaduct will not be susceptible to sudden failure.
3. Please provide a reference for your proposed concept, 25 years ago, if any. Please explain what the practical challenges of the proposed concept are. - The proposed solution would consist of the following stages: unloading the cantilever supports by removing the suspended span and then strengthening the supports by adding additional stay cables. The additional elements of the structure would need to be placed symmetrically and parallel to prevent twisting and destruction of the pylon. This solution could extend the life of the facility and reduce the risk of a sudden failure.

4. The reference in line 579 need to be numbered at the end of manuscript. - The author would like to thank the Reviewer for the comment, the change has been implemented
5. The proposed concept can be considered in an analytical study but without the results and a comparative study with other possible approaches it is not backed up. Highlighting the imperative need to address the issue must be the main focus of the manuscript. - After the bridge collapse in Genoa, it is not possible to verify the author's considerations with in-situ research. The author recommends that the proposed concept be implemented in specific cases of two existing bridge structures of the same Morandi project after a thorough analysis of the structure and making calculations in the specific conditions of reconstruction and operation. Other authors have presented studies on the analysis after the Polcever Morandi overpass disaster in Genoa in Italy [9]. In their research, they used existing knowledge to estimate the remaining life of the bridge, including existing bridge design information; crash investigation report of the Ministry of Infrastructure and Transport [10]; and archive data on truck traffic and axle loads. However, these considerations are theoretical and based on many assumptions. The additional reference is added: [9] Morgese, M., Ansari, F., Domaneschi, M. et al. Post-collapse analysis of Morandi’s Polcevera viaduct in Genoa Italy. J Civil Struct Health Monit 10, 69–85 (2020). https://doi.org/10.1007/s13349-019-00370-7 [10] Ministero delle Infrastrutture e dei Trasporti, Commissione Ispettiva Ministeriale, “Comune di Genova, Autostrada A10—Crollo del Viadotto Polcevera, Evento Accaduto il 14 Agosto 2018”, 14 Settembre 2018, Roma.

Round 2

Reviewer 1 Report

I still consider that the revised article is very similar to the previous one published by the author (Rymsza, Janusz. Causes of the Morandi viaduct disaster in Genoa as a contribution to the design of pre-stressed structures. Roads and Bridges - Drogi i Mosty, [S.l.], v. 19, n. 1, p. 5-25, mar. 2020. ISSN 2449-769X. DOI: 10.7409/rabdim.020.001). The topic and goal of the article is still the same. Many figures, texts, discussions and conclusions are repeated. The used methodology is also the same. Hence, I still consider that the article submitted to Applied Sciences does not bring sufficient novelty when compared to the previous one.

Author Response

The Author would like to thank the Reviewer for the comment.

The motivation of this paper is to present findings of the condition of the Polcevare Viaduct before a disaster and the concept of strengthening these structures. This is very important because two more bridge structures of this same design by Morandi still exist.

The article submitted to MDPI Applied Sciences is an improved and extended version of the article in RaBDiM - three drawings related to the project and six drawings about the technology of the viaduct construction are incorporated into the manuscript. A chapter on the design and construction technology of the viaduct and flyover has also been added. Additional, precise information about the design and construction of the structure in Genoa can help in strengthening the existing structures of this type in Libya and Venezuela. This information also enables the design principles of prestressed structures from half a century ago to be compared with those used today.

RabDiM quarterly is not as popular as MDPI, and thus its audience is quite limited. The author hopes that the publication in MDPI Applied Sciences will have a wider audience; therefore, more interested in the topic of prestressed structures will be able to learn about the causes of the spectacular, world-famous disaster of a facility designed by a recognized designer.

Reviewer 3 Report

Thanks for your responses. The author need to reconsider comments 2 and 3 and provide more thoughts on the analytical and practical aspects of the proposed method. Also, these comments must be implemented in the manuscript text. In the next response, please mention where you addressed these comments in the manuscript.

Author Response

The Author would like to thank the Reviewer for the comment. Text in lines added:

Line 424 – 426 : Strengthening the curvilinear, corrosion-damaged cable could not be effective - sectional stressing was difficult for technological reasons, and the stress level of the external tendons was low due to the poor technical condition of the concrete.

Line 437 – 447: Additional suspension cables in the structure allow for better load distribution and redundancy - if one element is damaged, other elements will take a greater load and the object will not suddenly crash.

The method of strengthening the structure of the facility could be as follows:

• removing the suspended span - unload the support, including brackets,
• repair and reinforce of concrete supports, including brackets and concrete tendons,
• adaptation of the pylon and brackets to attach additional steel tendons suspending the brackets,
• fixing additional steel tendons to the pylon and brackets,
• strengthening the suspended span (or replacing it with a lighter one) and placing it on the reinforced joints at the ends of the supports.

Such a solution would extend the life of the structure and reduce the risk of a sudden failure.

Line 619-628:

The Author recommends removing the suspended span and placing a span that would not be suspended but would be pulled in (the hinges would be removed - the static scheme of the platform would not be a Gerberian beam, but a continuous beam). In such a situation, additional steel tendons could be evenly distributed over the entire length of the span.

Regardless of which of the solutions is adopted (repair of a suspended span or the use of a continuous structure), there will still be difficulties related to the poor technical condition of all structural elements (damage to concrete and steel corrosion) and the need to perform construction on both sides simultaneously to prevent the destruction of a pylon with too little stiffness.

Round 3

Reviewer 3 Report

Thanks for addressing the comments.