Numerical Analysis of CFST Column with PBL Stiffeners under Axial Compression

Round 1

Reviewer 1 Report

This paper conducted numerical investigations on the axial compression behaviors of concrete-filled steel tubular columns with PBL stiffeners. The research topic is of interest; however, this paper cannot be accepted in its current state, needing major revisions.

(1)    Section 1. The necessity of the research should be introduced in detail.

(2)    Section 2. Please briefly clarify the design philosophy of the test specimens, such as the decision of stiffener dimensions and configurations.

(3)    Section 3.1.1. For the steel material model, the steel strength has different strength and response in the corner and flat zones of the square steel tube according to several studies in the open literature. Have the authors considered these differences?

(4)    Section 3.1.2. Has the concrete damage been considered in this model? Please clarify the concrete damage modeling.

(5)    Section 3.2.1. Please briefly introduce the “Solid shell” function in ANSYS. The information can help readers who have little knowledge of ANSYS to understand its function.

(6)    Section 3.2.2. Was the contact between steel tube and concrete simulated in both normal and tangential directions? Please describe more details.

(7)    Sections 3.3 and 4. The validation studies should be introduced before the analysis results.

(8)    Section 4.1. The overall failure modes of the columns were validated. However, this study numerically examined the damage patterns of concrete and stiffeners. The validation studies are encouraged to include the comparisons of tested and simulated concrete and stiffener behaviors.

(9)    Application range of the proposed formula should be clarified.

Author Response

Dear reviewer,

We gratefully thank you for your time spend making your constructive remarks and valuable suggestions, which has significantly raised the quality of the manuscript and has enable us to improve the manuscript. Each suggested revision and comment was accurately incorporated and considered. Below the comments are response point by point and the revisions are indicated.

This paper conducted numerical investigations on the axial compression behaviors of concrete-filled steel tubular columns with PBL stiffeners. The research topic is of interest; however, this paper cannot be accepted in its current state, needing major revisions.

(1)    Section 1. The necessity of the research should be introduced in detail.

Thanks for reviewer’s comments. The content of necessity of the research has been added and introduced in detail.

(2)    Section 2. Please briefly clarify the design philosophy of the test specimens, such as the decision of stiffener dimensions and configurations.

Thanks for reviewer’s comments. Relevant content has been added to Section 2.

(3)    Section 3.1.1. For the steel material model, the steel strength has different strength and response in the corner and flat zones of the square steel tube according to several studies in the open literature. Have the authors considered these differences?

Thanks for reviewer’s comments. I am sorry that the tests focus on the effect of different stiffening rib methods on members' ultimate strength and ductility while ignoring the fact that steel strength has different strengths and responses in the corner and flat zones of square steel tubes. The relevant literature has been reviewed [1-4]. They all focus on the different strengths and responses of stainless steel strengths in the corner and flat zones of square steel tubes, while this factor is less discussed in carbon steel, e.g., literature [5,6].

[1] Huang Y, Young B. Material properties of cold-formed lean duplex stainless steel sections. J Thin-Walled Struct 2012;54:72–81.

[2] Theofanous M, Gardner L. Testing and numerical modelling of lean duplex stainless steel hollow section columns. Eng Struct 2009;31(12):3047–58.

[3] Chen J, Young B. Corner properties of cold-formed steel sections at elevated temperatures. Thin-Walled Struct 2006;44:216–23

[4] Afshan S, Rossi B, Gardner L. Strength enhancements in cold-formed structural sections— Part I: Material testing. J Constr Steel Res 2013;83:177–88.

[5] C. Petrus, H.A. Hamid, A. Ibrahim, et al., Experimental behaviour of concretefilled thin walled steel tubes with tab stiffeners, J. Constr. Steel Res 2010;66 (7):915–922.

[6] Zhou X H, Zhou Z, Gan D. Analysis and design of axially loaded square CFST columns with diagonal ribs. J Constr Steel Res, 2019, 167:105848.

 

(4)    Section 3.1.2. Has the concrete damage been considered in this model? Please clarify the concrete damage modeling.

Thanks for reviewer’s comments. Damage to concrete is considered in the intrinsic model of concrete, where the stress in the early stages increases with strain, while after the stress peak, the stress decreases with increasing strain.

 

(5)    Section 3.2.1. Please briefly introduce the “Solid shell” function in ANSYS. The information can help readers who have little knowledge of ANSYS to understand its function.

Thanks for reviewer’s comments. The introduction of “Solid shell” function in ANSYS has been added to section 3.2.1.

(6)    Section 3.2.2. Was the contact between steel tube and concrete simulated in both normal and tangential directions? Please describe more details.

Thanks for reviewer’s comments. A contact surface pair comprised of the steel tube's inner surface and the concrete core's outer surface can be defined. Because of the high modulus of elasticity of the steel tubes and stiffeners, they are defined as the master-slave contact surface and the concrete as the slave contact surface. Meanwhile, the tangential contact is set to "Frictional" with a friction coefficient of 0.6, and the normal direction is set to "Pure Penalty" with a normal penalty stiffness (FKN) of 10, and the normal direction can be specified for the interface, which allows the separation of the interface in tension and no penetration of that in compression. This section has been added to section 3.3.2.

(7)    Sections 3.3 and 4. The validation studies should be introduced before the analysis results.

Thanks for reviewer’s comments. The content has been adjusted and validation studies has been introduced before the analysis results.

(8)    Section 4.1. The overall failure modes of the columns were validated. However, this study numerically examined the damage patterns of concrete and stiffeners. The validation studies are encouraged to include the comparisons of tested and simulated concrete and stiffener behaviors.

Thanks for reviewer’s comments. Contrast added to section 4.2.

(9)    Application range of the proposed formula should be clarified.

Thanks for reviewer’s comments. Formulas are divided into two categories, types D1 and D2 width-to-thickness ratios should conform to  [7], and other types of width-to-thickness ratios should conform to  [8]. The above has been added to section 6.5.

[7] Guo J H, Diao Y. Experimental behaviors of square concrete filled steel tubular columns with PBL stiffeners[J]. Structures, 2022, 38: 1556-1569.

[8] DBJ/T13-51-2010, “Technical Specification for Concrete-Filled Steel Tubular Structures,” The Construction Department of Fujian Province, Fuzhou, China, 2010.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper concerns an analysis of thin-walled steel columns with concrete-filled core subjected to compression. Many variants of columns under axial load were tested and verified. In my opinion, the paper provides interesting results but in general the novelty of paper is moderate. Author should more emphasise how aspects actually are a novelty in the paper and how scientific soundness is included. After major corrections, the paper might be suitable to be published in “Processes”.

Remarks/Questions:

1)    English language, spaces and style in text should be corrected. Many flaws are seen (e.g.):

- line 378: “the equations predicted the bearing capacity of CFST column are generally consist of two parts” – it is not understanding.

- line 509: „The method proposed do not need to calculate much parameters”

- line 254: “as the thickness of steel tube keep unchanged”.

- lines 274-278: “The order of  strength values of 5 groups from big to small was Type A> Type B> Type D2> Type C > 275 Type D1 in Fig5.2(c). In Fig 5.2(d), as the ?? increased from 2.75mm to 4.75mm, the ultimate strengths of Type D1 and D2 were bigger than Type A, Type B, Type C, which was  similar with Fig 5.2(b) and the order of strength values of 5 groups from big to small was  Type D2> Type D1>Type A> Type B> Type C”- it is intricate and unclear.

2)    Which algorithm of nonlinear calculation was assumed? In how many steps the simulations were conducted? It is not clear in the text.

3)     The paper should be better organised.

It is suggested, after corrections, to verify by English Proofreader.

Author Response

Dear reviewer,

We gratefully thank you for your time spend making your constructive remarks and valuable suggestions, which has significantly raised the quality of the manuscript and has enabled us to improve the manuscript. Each suggested revision and comment was accurately incorporated and considered. Below the comments are response point by point and the revisions are indicated.

The paper concerns an analysis of thin-walled steel columns with concrete-filled core subjected to compression. Many variants of columns under axial load were tested and verified. In my opinion, the paper provides interesting results but in general the novelty of paper is moderate. Author should more emphasise how aspects actually are a novelty in the paper and how scientific soundness is included. After major corrections, the paper might be suitable to be published in “Processes”.

(1)    English language, spaces and style in text should be corrected. Many flaws are seen (e.g.):

 

- line 378: “the equations predicted the bearing capacity of CFST column are generally consist of two parts” – it is not understanding.

Thanks for reviewer’s comments. We have made the change. The new sentence reads as follows：

“The bearing capacity of CFST column generally consists of two parts: concrete and steel tube.”

- line 509: „The method proposed do not need to calculate much parameters”

Thanks for reviewer’s comments. We have made the change. The new sentence reads as follows：

“The Equation is suitable for different types of PBL stiffeners, and the Equation of the formula is relatively simple compared to [5,8].”

- line 254: “as the thickness of steel tube keep unchanged”.

Thanks for reviewer’s comments. The sentence has been rewritten.

- lines 274-278: “The order of strength values of 5 groups from big to small was Type A> Type B> Type D2> Type C > 275 Type D1 in Fig5.2(c). In Fig 5.2(d), as the ?? increased from 2.75mm to 4.75mm, the ultimate strengths of Type D1 and D2 were bigger than Type A, Type B, Type C, which was similar with Fig 5.2(b) and the order of strength values of 5 groups from big to small was Type D2> Type D1>Type A> Type B> Type C”- it is intricate and unclear.

Thanks for reviewer’s comments. We agree and have updated the intricate sentences to clear ones.

 

2)    Which algorithm of nonlinear calculation was assumed? In how many steps the simulations were conducted? It is not clear in the text.

Thanks for reviewer’s comments. This thesis uses the Newton-Raphson non-linear algorithm. Also, load sub-steps are set with minimum substeps of 200 and maximum substeps of 10000.

 

3)     The paper should be better organised.

Thanks for reviewer’s comments. We have fixed the issues you pointed out, simplified intricate and tedious sentences, and prettified the expression of the English language. The article has been checked repeatedly, and the existing grammar and punctuation flaws have been corrected.

It is suggested, after corrections, to verify by English Proofreader

Thanks for reviewer’s comments. The English language has been further refined and proofread.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The paper numerically, by Ansys, investigated ultimate strength of the CFST stub column with stiffeners. Bellow revision should be applied.

-In order to provide a more comprehensive literature review, the authors should cite and discuss the following relevant papers in their revised manuscript:

Fu, G., Fu, G., Yu, C., Li, S., Wang, F. and Yang, J., 2021. Behaviour of rectangular concrete-filled steel tubular slender column with unequal wall thickness. Engineering Structures, 236, p.112100.

Nassiraei, H. and Rezadoost, P., 2021. Static capacity of tubular X-joints reinforced with fiber reinforced polymer subjected to compressive load. Engineering Structures, 236, p.112041.

Nassiraei, H., Zhu, L. and Gu, C., 2021. Static capacity of collar plate reinforced tubular X-connections subjected to compressive loading: study of geometrical effects and parametric formulation. Ships and Offshore Structures, 16(1), pp.54-69.



-Why the steel yield strength values were selected 397.82MPa and 349.72MPa?

- In section 3.1.1, “Fig.3.1.” should be “Fig. 3.1.”. Also, “Eq.(3.3)” should be “Eq. (3.3),”. Please revise all issues in the texts.

-Section 3.2.1, Solid 186 element was used for FE modeling. The element cannot simulate rotation at nodes. But, in experimental tests and real conditions, the rotation happen. How can the authors explain this problem?

-Why was friction coefficient of 0.6 considered in numerical modeling?

- More discission is essential on Fig. 5.2.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

This manuscript has addressed most of the reviewers’ concerns and questions during the previous review. Thus, I recommend the publication of this revised manuscript.

Reviewer 2 Report

Paper can be considered to be published after minor revision.

I don't have more questions.

Reviewer 3 Report

The paper is ready for publication.