Analytical and Measured Effects of Short and Heavy Rail Cars on Railway Bridges in the USA

Round 1

Reviewer 1 Report

Brief summary

The research focussed on studying the effects of freight railcars on two-span bridges employing numerical and monitoring investigations. The study is based on the fact that in the last years in North America the gross weight railcars increased consistently, mainly in the shorter ones. Numerical analyses predicted significant differences between maximum effects of shorter and standard railcars. Moreover, the outcomes of the structural monitoring confirmed that short railcars cause higher stresses.

Broad comments

The topic of the study is interesting and worthy of investigation. The study presented is meaningful and useful for understanding the impact of the increased load on bridges. The article outcomes could be considered by the stakeholders involved in managing bridges to reduce the damage and fatigue effects on such infrastructures. In a broader sense, the paper is convincing, yet the Authors should address few comments listed below.

Besides, the article needs some sentences rephrasing and corrections. Some of them are listed in the Specific comments section.

Moreover, the Authors could complete the conclusion section with considerations regarding the implications and consequences of the paper finding for stakeholders and/or engineers encompassed in bridge retrofitting, design and management.

Specific comments

Keywords: Please consider replacing the keyword: “civil engineering”; it is excessively general.

Line 11. Remove the reference.

Line 33-35. This sentence is already used in the abstract; please rephrase it.

Line 49. Please consider replacing “Other research” by “Other researches”.

Line 56. Please replace “Nort” by “North”.

Line 96. Please consider replacing “include” by “including”.

Line 102. Please remove the hyphen.

Figure 3. The authors should describe this figure more in detail. The nomenclature (M1, L0, L1, etc.) is not described in the text when the picture is introduced (it is clear only reading lines 182-186 and section 3.1.2), as well as the colours adopted for representing the trusses and beams.

Figure 4. The authors should add more information regarding the steel profile characteristics. For instance, the profile dimensions in Figure 4 could be shown.

Figure 5. Please consider increasing the text font.

Line 134. Please replace “Rriveted” by “Riveted”.

Line 140-142. This sentence is repeated (line 89-91). Please be careful and replace/remove it.

Line 145. Please add a reference for the software adopted for the analysis.

Line 150-155. The authors declared that if the analysis’s focus is to find critical components and connections, it is necessary to model connections between members with appropriate details. Is this statement meaning that authors modelled connections without appropriate details? Moreover, the authors also indicated that the best results are obtained with the model without deck and ballasted track. Could it be possible that the lack of appropriate details of the connections led to inaccurate results? In addition, what do authors mean by “best results”? What did the authors compare in order to declare which model is more appropriate? Please clarify it.

Line 165-166. Please consider replacing “but also influenced” by “but also influencing”.

Figure 11. Please consider adopting the same axes limits and intervals of Figure 8 in order to simplify the comparison.

Line 314. Please replace “Rriveted” by “Riveted”.

Section 4. Please use a consistent font with the other sections.

Author Response

The authors would like to thank a Reviewer for the constructive comments. The changes in the manuscript were made and below are descriptions of specific changes. Also, the word file with “track changes” is attached. We hope that both Reviewers are satisfied with an improved version of the paper. If any additional changes are recommended to improve our paper, we will be happy to do so.

Broad comments

The topic of the study is interesting and worthy of investigation. The study presented is meaningful and useful for understanding the impact of the increased load on bridges. The article outcomes could be considered by the stakeholders involved in managing bridges to reduce the damage and fatigue effects on such infrastructures. In a broader sense, the paper is convincing, yet the Authors should address few comments listed below. - Authors thank the Reviewer for these comments.

Besides, the article needs some sentences rephrasing and corrections. Some of them are listed in the Specific comments section.

Moreover, the Authors could complete the conclusion section with considerations regarding the implications and consequences of the paper finding for stakeholders and/or engineers encompassed in bridge retrofitting, design, and management.

Here are some implications for bridge owners and bridge engineers that were added to the conclusion section:

• Bridge load capacity ratings and railway operating restrictions need to consider railcar length in addition to railcar weight.
• Railway bridge engineers need to consider that shorter rail cars can limit the carload capacity of a bridge, due to additional load on a span.
• Railway bridge engineers need to consider that longer rail cars can shorten the fatigue life of a bridge, due to larger stress ranges caused by greater unloading between axles.
• The ratio of rail car length to span length is a key parameter.

Specific comments

Keywords: Please consider replacing the keyword: “civil engineering”; it is excessively general. – the word “Civil Engineering” was changed to “Rail car length”

Line 11. Remove the reference. – the reference is removed

Line 33-35. This sentence is already used in the abstract; please rephrase it. – The sentence was changed to: “In the last years in North America the number of railcars increased consistently: from 2010 to 2015 increased about 5 percent and the number of all HAL railcars increased 19 percent.”

Line 49. Please consider replacing “Other research” with “Other researches”. – the word “research” was changed to “researchers”

Line 56. Please replace “Nort” with “North”. – the word “Nort” was changed to “North”

Line 96. Please consider replacing “include” by “including”. – the word “include” was changed to “including”

Line 102. Please remove the hyphen. – the hyphen is removed

Figure 3. The authors should describe this figure more in detail. The nomenclature (M1, L0, L1, etc.) is not described in the text when the picture is introduced (it is clear only reading lines 182-186 and section 3.1.2), as well as the colors adopted for representing the trusses and beams. – Additional information was provided: “Fig. 3 presents the general dimensions of the bridge, the colors on the diagram represent different cross-sections. (symbol “U” refers to the connection of upper chords, symbol “L”- refers to connections of lower chords and “M” is a connection on the middle of a diagonal). This truss numbering scheme (nomenclature) is standard in North America.

Figure 4. The authors should add more information regarding the steel profile characteristics. For instance, the profile dimensions in Figure 4 could be shown. – Additional information was provided, including the built-up shape components for each truss member.

Figure 5. Please consider increasing the text font. - the drawings were enlarged

Line 134. Please replace “Rriveted” with “Riveted”. – the word “Rriveted” was changed to “Riveted”

Line 140-142. This sentence is repeated (lines 89-91). Please be careful and replace/remove it. - the sentence was removed

Line 145. Please add a reference for the software adopted for the analysis. – the reference is added

Line 150-155. The authors declared that if the analysis’s focus is to find critical components and connections, it is necessary to model connections between members with appropriate details. Is this statement meaning that authors modelled connections without appropriate details? Moreover, the authors also indicated that the best results are obtained with the model without deck and ballasted track. Could it be possible that the lack of appropriate details of the connections led to inaccurate results? In addition, what do authors mean by “best results”? What did the authors compare in order to declare which model is more appropriate? Please clarify it.

• The analysis was focused on the effect of load on the main members; therefore, the truss connections were simplified to free-end-rotation. However, the floor-system that is showing a partial fixity in the connection between stringers and floor beams was modeled using the shell elements and the connections replicated the continuous behavior of the stringers (instead of simply supported beams).
• Changes into the text were made as follow:” The stringer-to-floor-beam connections were defined to replicate the continuous behavior of the stringers. However, the focus of the analysis was to find load effects on the main bridge components, not connection”
• “The best results” were changed to “The analytical results that match the stresses calculated from measured strains were obtained using the model without the deck and ballasted track.”
• An additional recommendation was formulated: “It is recommended to investigate further this issue by measuring strains in the components of the floor system with a focus on connection behavior and potential composite action of stringers and floor-beam with the track system.”

Line 165-166. Please consider replacing “but also influenced” by “but also influencing”. ”. – the phrase “but also influenced” was changed to “but also influencing”

Figure 11. Please consider adopting the same axes limits and intervals of Figure 8 in order to simplify the comparison. – The axes limits on Figures 8 and 11 are changed to 5 ksi = 34.5 MPa.

Line 314. Please replace “Rriveted” by “Riveted”. – the word “Rriveted” was changed to “Riveted”

Section 4. Please use a consistent font with the other sections. – the correction to the font was made

Author Response File: Author Response.docx

Reviewer 2 Report

Paper consists of a lot of "statistical" data, which are quite obvious and it is not neccessary to coment in text each aspect of presented charts. More interesting part about measurement design and verification and validation results between field measuremnt and FEA is quite brief. I miss some comment why the measurement of deflection of bridges was not conducted, because for overall comparision between model and real structure with deflection is quite easy and reliable. The conservative model for shorter bridges and non consevative model for longer bridges is mentioned in discussion but not explained. 

Author Response

The authors would like to thank a Reviewer for the constructive comments. The changes in the manuscript were made and below are descriptions of specific changes. Also, the word file with “track changes” is attached. We hope that both Reviewers are satisfied with an improved version of the paper. If any additional changes are recommended to improve our paper, we will be happy to do so.

1. The measurement of deflection was not performed on the considered truss bridge due to the accessibility under the bridge and also the method of long-term measurements and data collection. The focus of the study was the load effects on main bridge components; therefore, for a truss bridge, the strain measurements on individual chords, diagonals, and stringers provided more information. Also, for the DPG span, the multiple locations of strain gages along the length, and on the cover plate terminations provided more information that deflection measured on the middle of the span.
2. In the discussion section explanation was provided for the potential cause of the discrepancy between analytical results and the stress calculated from measured strains: “In the calculations, the assumption was made that each of the C-shapes in built-up members of diagonals takes 50 percent of the load; however, it is possible that the axial force is not distributed equally between two parts of the members. The measurements were taken only from one side of the C-shapes so this cannot be verified using the available data.” The additional text was added: “It is recommended to investigate further this issue by measuring strain on the elements with two components and analyze the load distribution between them. In addition, the strains can be measured close by the connection to ensure the model was used properly with the free-end-rotation at the connections”.

Round 2

Reviewer 1 Report

The Reviewer appreciates the efforts to revise the manuscript. The Authors have addressed the reviewers' comments adequately.

Author Response

The Authors thank the Reviewer for the second round review and positive comments.

Author Response File: Author Response.docx