Aerodynamic Loading and Wind-Induced Vibration Characteristics of Bridge Girders with Typical Asymmetric Configurations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript investigates the aerodynamic loading and wind-induced vibration characteristics of long-span bridge girders with asymmetric configurations. Below are my comments

1. Can the authors include specific quantitative findings (e.g., % differences in flutter velocity) to better showcase the impact?
2. I suggest including “wind direction angle” (WDA) and “angle of attack” (AOA) as keywords since they are central to the analysis.
3. The study claims a lack of prior work on asymmetric girders—can the authors further discuss any recent computational or field studies in this area?
4. Integrate more recent studies (post-2020) that use CFD or AI-based aerodynamic optimization techniques for asymmetrical configurations.
5. Can the authors elaborate on Reynolds number effects and how they ensure dynamic similarity in wind tunnel testing?
6. Could the authors include a flowchart or schematic to better illustrate the data processing pipeline?
7. Is the comparision between the girders used in the study statistically supported? COuld the authors include uncertainity analysis or confidence interval for key parameters like critical flutter velocity.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates two assymetric bridge girders under laminar flows. The reviewer has several concerns:

1. Line 149 and line 156, two length scales are used. Why not using the same length scale ratios, since different length ratios can cause some Reynolds number effects.
2. Line 185-186, the AOA is from -10 to 10 degree. In most of the studies, the AOA can be -5 to 5 degree. The authors need to clarify why they choose a larger range of AOA.
3. In reality, the wind can not be a laminar flow. The authors used a laminar flow in the experiment, but the turbulent wind field can affect the detach and reattach of the wind flows. Therefore, the authors need to discuss how their results can be applied in real engineering applicaitons.
4. In the conclusion part, the author claim that PI-shaped girder show larger discrepancy when wind is blowing in 0 and 180 degree. But this conclusion is not solid since the two girders are of different width. This really affects the flow reattachment.
5. In the literature review part, the authors listed very limited CFD studies. But CFD is widely used to study the wind effects on the bridges. For example: 1) the BARC benchmark model: Bruno, Luca, Maria Vittoria Salvetti, and Francesco Ricciardelli. "Benchmark on the aerodynamics of a rectangular 5: 1 cylinder: an overview after the first four years of activity." Journal of Wind Engineering and Industrial Aerodynamics 126 (2014): 87-106. 2) the later on study of different shapes: Ricci, Mattia, Luca Patruno, Stefano de Miranda, and Francesco Ubertini. "Flow field around a 5: 1 rectangular cylinder using LES: Influence of inflow turbulence conditions, spanwise domain size and their interaction." Computers & Fluids 149 (2017): 181-193. 3) and even study the wind effects on the auxiliary facilities of the bridge: Chen, Yanlin, Xiangjie Wang, Chao Sun, and Benrui Zhu. "Exploring the failure mechanism of light poles on elevated bridges under high winds." Engineering Failure Analysis 159 (2024): 108076.

There are also some minor writing issues:

1. line 41, “A critical…”, "A" should not be capitalized.
2. line 194, since AOA is widely used in this paper, why 'attack angle' is used here?
3. Table 1 and 2: it seems there are some footnotes abnout the length ratio since there are a '2' and '4' as superscripts. But the reviewer did not see any footnotes in the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This is an interesting and timely study that looks into how asymmetrical bridge girders behave aerodynamically under different wind direction angles (WDAs). The authors have designed a well-planned experimental program and the work addresses a clear gap in current bridge aerodynamics research, where most studies focus on symmetric configurations. The findings are significant, particularly in demonstrating how asymmetric configurations alter the aerodynamic behavior under different WDAs, affecting bridge safety and serviceability. The study is methodologically sound and well-structured, with clear experimental procedures and results presentation.

However, while the experimental work is thorough, there are several limitations in scope, methodology, and result interpretation that need to be addressed to strengthen the paper’s contribution and rigor for publication in a high-impact journal.

1. All tests were conducted in smooth flow conditions. However, real-world bridge sites experience turbulent boundary layer winds. The absence of turbulence in the test program limits the applicability of the results. The authors should discuss atmospheric turbulence intensities (10–15%).
2. While the experimental approach is solid, the paper would be stronger if it included CFD simulations or at least some form of flow. It is strongly suggested to conduct CFD simulation to explain phenomena like flow separation and vortex shedding around the bikeway and asymmetric girder.
3. The study focuses on 0° and 180° WDAs, but in real-life scenarios, winds rarely approach structures head-on or directly from behind. Intermediate WDAs (like 30°, 45°) often trigger the most complex vibration behaviors. It is strongly suggested to analyze it at different angle of attack and discuss the flow angularity.
4. The paper doesn’t mention measurement uncertainties, repeatability of tests, or how confident we can be in the flutter derivative identifications. Including some uncertainty estimates or error bars would increase trust in the results.
5. Since the models operate at relatively small scales, Reynolds number effects might influence the results, especially for bluff-body phenomena like VIV. It would be helpful if the authors could comment on whether Reynolds number independence was achieved or discuss how scale effects might affect result interpretation.
6. The literature review is quite comprehensive but could benefit from referencing some of the latest CFD-based or AI-driven studies on bridge aerodynamics.
7. At section 3.1, the authors observe significant discrepancies in drag and pitching moment coefficients for the asymmetric II-shaped girder between 0° and 180° WDAs, especially at positive AOA. How the flow separation mechanisms responsible for this behavior? Are there possible vortex formation patterns along the bikeway side that explain the higher sensitivity in positive AOAs?
8. The static lift coefficient CLC_LCL​ trends for both girders show certain symmetry in positive AOA but diverge at negative AOAs. Explain whether this suggests asymmetric flow behavior on the leeward side of the bikeway in these configurations? How might this affect local pressure distributions?
9. In section 3.2, the variation of A₂​ in 0° WDA consistently shows lower values at high reduced wind velocities, indicating enhanced aerodynamic damping. Please clarify whether this damping arises primarily from altered vortex shedding frequencies, flow separation suppression, or interaction effects between the bikeway and deck edges? A qualitative explanation would strengthen this result.
10. For the asymmetric box girder, flutter derivatives such as H₄​ show subtle differences between WDAs, unlike the more dramatic changes seen in the II-shaped girder.
    Is this simply a function of cross-sectional shape robustness, or are there specific flow interference phenomena (like sheltering effects or bilaterally balanced pressure fields) that moderate this difference?
11. The heaving VIV responses occur at more AOAs in 180° WDA than 0° WDA for the II-shaped girder, with larger lock-in ranges at 180° WDA. What aerodynamic mechanisms could explain this?
12. Interestingly, torsional VIV is absent in 180° WDA but present at specific AOAs in 0° WDA. Explain this asymmetry’s aerodynamic cause.
13. The critical flutter velocity increases at positive AOAs for both girders in 0° WDA compared to 180° WDA. How does this compare to established studies (e.g. by Chen et al. 2009 [42]) on upper stabilizer effects?
14. The most adverse flutter condition for the II-shaped girder occurs at 2.5° AOA, while for the box girder it is at -3° Explain what aerodynamic factors or flow field behaviors might be responsible for this difference in critical AOAs between girder types?
15. Across multiple sections, the results are well presented numerically but lack underlying aerodynamic flow field reasoning.

Comments on the Quality of English Language

English language is fine. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors addressed all the queries and comments satisfactorily. Paper can be published