Evaluation of Influence of the Integrated Welded Handrail System in the Bus Body Frame on Strength and Passive Safety

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments of the Reviewer

The authors of the manuscript ‘Evaluation of influence of the integrated welded handrail system in the bus body frame on strength and passive safety’ presented a study in which they used the finite element method analysis in the Ansys Static Structural system to evaluate the integration of a welded handrail system into the bus body frame to increase its overall rigidity and passenger safety. In addition, the authors of this article use parametric mathematical modelling, an effective step preceding the finite element method (FEM), to approximate the loads, accelerations, and the number of vertical posts in the bus body handrail system. This, in turn, allowed for further simulation modelling. The relevance of this study lies in the need to redesign bus frames to strengthen them and subsequently install electric or gas energy sources on bus roofs, which are the main alternative to low-emission diesel engines. This concept is quite relevant, as it contributes to achieving the EU's 2030 target of reducing CO₂ emissions by 30% and to switching intercity buses to compressed natural gas or fuel cells, and city buses to electric drive, in accordance with UNECE standards R110 and R100. The data obtained provide valuable information for the further design of bus bodies, including the use of handrails to reinforce the body structure, as a reinforced structure will allow the placement of alternative power sources for environmentally friendly bus engines. The technical solution proposed by the authors appears complete, and the research described in the manuscript is relevant.

The manuscript has a classic research paper structure. In the introduction, the authors provide a comprehensive literature review, including information about the second chapter, devoted to research materials and methods, in which they describe the main methods of their research. The third chapter is devoted to the modelling results and their discussion. The fourth chapter is devoted to discussing the results obtained. And the fifth contains conclusions.

Overall, the authors' study is comprehensive and provides a thorough overview of the topic. It is complete and relevant to the modern scientific community.

Although the authors adhere to the recommendations of the Applied Sciences journal and correctly structure the article, there are several aspects that need improvement:

1. The authors of the study need to clearly define the purpose of the study. In its current form, it is unclear why the authors are conducting it. This study of bus frame deformation is necessary for the further manufacture of new buses powered by alternative, environmentally friendly energy sources or the conversion of existing buses. What specific task are the authors of the study aiming to achieve?
2. In the first section, it is advisable for the authors to indicate the advantages of placing gas cylinders and batteries on the roof of the bus in order to prove the relevance of the study. Since batteries can be placed in the passenger compartment under the seats and cylinders at the rear of the bus
3. If possible, please highlight the handrail system in Figure 2a in a different colour. This will make the figure more informative and render Figure 2b irrelevant.
4. Please provide information in section 2 and accordingly in table 1 regarding whether the weight of the cylinders (700 kg) is empty or full.
5. Please add labels to the front and rear parts of the bus frame in Figures 5-11 for better clarity.
6. In Figure 5b, option 1.1 N, and Figure 7b, option 2.1 N, the handrails are difficult to see. It is advisable to place the image at a different angle so that the load on the handrails is visible.
7. The authors of the study should indicate in their conclusion what specific result they achieved by conducting this study. What exactly is the optimal handrail design for this type of bus frame?
8. The authors of the study should formulate a clear research objective and obtain research results in line with this objective. At present, it is unclear what the specific purpose of this series of studies was. Was it to determine the optimal design of handrails, or something else?

Comments for author File: Comments.pdf

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, the research topic is interesting and relevant. However, to improve the quality of the manuscript, I suggest working together:

1. Abstract:

1) should be rewritten according to the Instructions for Authors

https://www.mdpi.com/journal/applsci/instructions

• Abstract: … 1) Background: Place the question addressed in a broad context and highlight the purpose of the study; 2) Methods: Describe briefly the main methods or treatments applied. Include any relevant preregistration numbers, and species and strains of any animals used; 3) Results: Summarize the article's main findings; and 4) Conclusion: Indicate the main conclusions or interpretations. The abstract should be an objective representation of the article: it must not contain results which are not presented and substantiated in the main text and should not exaggerate the main conclusions.

2) Currently contains many detailed numerical values. Some of these numerical results should be shortened or summarized. This will enable the abstract to focus more clearly on the study's main contributions and conclusions.

2. References:

1) The manuscript contains an adequate literature review. However, the References should be expanded. Accordingly, "1. Introduction" should be expanded as well.

2) "The planned EU targets are to reduce CO2 by 15% till 2025 and by 30% till 2030 among trucks and buses ...". Where did you get this data? It should also be added to the References.

3. The manuscript describes a finite element analysis performed in ANSYS. However, the description of the finite element model could be improved by providing additional information about the finite element mesh (e.g., element type, mesh density, or general approach to mesh construction). Including a brief description of the mesh would improve the transparency and reproducibility of the numerical model.
4. The Discussion section mainly focuses on the numerical results of the finite element analysis. The discussion should be expanded to highlight the practical engineering implications of the results for bus body design and structural optimization.
5. I recommend adding a separate paragraph, "Key assumptions and limitations" at the beginning of the manuscript. This will improve the methodological transparency of the study.
6. The manuscript presents several load regimes (No. 1.1–3.2) that are used in the results section and in the figures. For better readability, the meaning of these regimes should be explained directly in the figure captions or in the corresponding text.
7. The manuscript states that the simulation was performed in the ANSYS Static Structural module. The rationale for using a static analysis approach to represent inertial loading conditions (e.g., 5g and 6.6g accelerations) should be explained to better justify the adopted modeling strategy.
8. The manuscript presents a strength uniformity parameter (SU) based on the root-mean-square deviation of von Mises stresses. A clear explanation of its physical interpretation and advantages over traditional stress evaluation metrics used in structural analysis should be provided.
9. Some of the figure captions are relatively short and could be expanded to better explain the stress and strain maps presented. This would improve the readability and clarity of the figures.

Respectfully, your Reviewer

Comments on the Quality of English Language

English needs improvement.

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper the authors studied whether integrating a welded handrail system into the structural frame of a low-floor city bus could improve stiffness and safety when additional roof loads (such as gas cylinders or battery packs) are installed. They develop a simplified dynamic model to estimate loads and then perform Finite Element Analysis (FEA) using popular commercial s ANSYS for multiple loading scenarios, comparing bus frames with and without the integrated handrail truss to evaluate stresses, displacements, and safety factors. The paper is interesting but there are several drawbacks that need to be addressed before it could be considered for publication:

1. The study relies entirely on FEA simulations  and no experimental validation or physical testing of the bus frame or handrail structure is presented. Without experimental validation, it is difficult to assess whether the FEA model accurately represents real structural behavior.
2. The proposed welded handrail integration is evaluated on a single bus model and geometry, which limits the generality of the conclusions. Different bus architectures, materials, or frame layouts may respond very differently to the same structural modification.
3. The modeling approach uses a simplified rod-based structural representation of the bus frame, which may neglect local structural details such as joint stiffness, weld behavior, and local shell effects that can significantly influence stress distributions in real structures.
4. The load cases are derived mainly from regulatory accelerations (UNECE R100/R110) and simplified dynamic assumptions. Real vehicle operation involves complex dynamic loading, fatigue, and multi-directional impacts that are not captured in the current framework.
5. The proposed “strength uniformity” metric (SU) is introduced using only three stress values (maximum, minimum, and average), which may be an oversimplified indicator of structural efficiency and may not provide a meaningful statistical description of stress distribution in a large FE model.
6. The design implications of integrating the handrail system into the structural frame are not discussed from a manufacturing or practical engineering perspective. Issues such as welding feasibility, weight increase, passenger safety regulations, and maintenance considerations remain unaddressed.
7. The organization of the paper is somewhat uneven, with a very long introduction and modeling section but relatively limited critical interpretation of the results. A clearer separation between modeling assumptions, numerical results, and engineering implications would improve readability and technical clarity.

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript in line with the previous comments. In its current form, the manuscript is suitable for publication in the journal Applied Sciences.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, my congratulations!
We worked very well together!

Respectfully, your Reviewer

Reviewer 3 Report

Comments and Suggestions for Authors

Accept.