Seismic Performance of Space-Saving Special-Shaped Concrete-Filled Steel Tube (CFST) Frames with Different Joint Types: Symmetry Effects and Design Implications for Civil Transportation Buildings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please refer to the attached file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript investigates the seismic performance of space-saving CFST (concrete-filled steel tube) columns with special cross-sections (L-, T-, and cruciform shapes) in two-story, single-bay frame specimens. Six frame tests were conducted under low-cycle reversed loading with three different beam–column connection details (hoop + ribs, fully bolted, and replaceable flange plates). Experimental results were compared with ABAQUS and OpenSees models, and parametric analyses were performed to suggest optimal design ranges in terms of axial load ratio, slenderness, and steel ratio.

Please update literature review with recent (2020–2025) contributions on L-, T-, and cruciform CFST columns and joints.

Provide quantitative validation: include error metrics (MAE, MAPE) and calibration parameters for ABAQUS and OpenSees models.

Clarify the repairability: for the replaceable flange plate detail, provide at least an analytical or conceptual demonstration of the repair process and expected performance recovery.

Expand discussion on axial load ratio: since it was constant in experiments, numerical findings should be summarized in clear design charts/diagrams.

Add local behavior data if available (panel zone shear, rib/hoop stresses, bolt behavior); alternatively, provide numerical contour plots

Add uncertainty/variability discussion for ductility and damping ratios.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper, low-cycle fatigue tests and numerical simulations were conducted on CFST frames. The effects of connection type and column geometry on hysteresis loops, stress-deformation curves, energy absorption, ductility, and failure modes were investigated. The results are interesting and contain practically important information, so I recommend the paper be published. However, there are some unclear points. Therefore, I would like to ask you to improve the paper by referring to the comments below to deepen readers' understanding.

(1) In Section 2.1, please use a schematic diagram of the "frame-test specimen" to provide a more specific and clear explanation of the arrangement of the M-columns and S-columns, the arrangement of the actuators, and the method of fixing the sample.

(2) Please correct "CFSST" to "CFST" in the caption of Figure 1.

(3) The text states that the elastic modulus of steel is 184 GPa. However, according to Table 2, isn't Es about 200 GPa?

(4) In Section 2.3, please add a schematic diagram and detailed explanation of the "bilinear energy method" to make it clearer to readers. Also, please improve the quality of Figure 2.

(5) Please indicate which parts of the test structure schematic diagram (comment (1)) correspond to the photographs in Figures 3(a)-(e).

(6) The numbers on the vertical and horizontal axes in Figure 4 are small, so I would like them to be improved so that they are easier to read.

(7) Section 6.3 states that there is a scale effect between the "model specimen" and the "real building." Since it is stated that the model study does not take into account weld defects, it would be desirable to conduct probabilistic research that takes into account defect distribution and extreme value statistics. If the above points were also mentioned, the depth of the paper would be increased.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revision satisfactorily addresses my major concerns.