Experimental Investigation and Numerical Simulation of C-Shape Thin-Walled Steel Profile Joints

Round 1

Reviewer 1 Report

This paper presents numerical and experimental study on the C-shaped thin-walled steel profile joints. Although the workload is sufficient, this paper has a large room for improvement in terms of both the technical aspect and academic writing.  

 

1. The language is poorly written and requires substantial modification. Many grammar mistakes and incorrect prepositions/terminologies are found. The author must check the draft manuscript thoroughly and make corrections
2. Line 171, is it possible the steel plate will fail by local crushing? crushing or buckling?
3. How the engineered stress-strain curve is converted into true stress-strain curve?
4. 14 (b), what is the difference among the fiver specimens in Joint B series, how come such a considerable scatter is observed?
5. What is the abnormal failure of two specimens in Joint C series? Why the abnormal failure happens?
6. The author should state clearly what type of element is employed for each part in the modelling. Solid element or shell element…

 

Author Response

Thank you for the review and suggestions!

I tried to explain each point and modify the initial form of the paper with the suggested changes. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present a study on the behaviour of a simple cold-formed steel truss joint. Overall the paper is relatively well written and organized, however, the reviewer believes that it lacks some innovative content and or real contribution to the advancement of knowledge. 

Hence, for this paper, the Reviewer suggests "Major Revisions".

I would like the authors to consider the following topics:

1. What does this study brings to the advancement of knowledge?
2. Why weren't the results compared with formulations presented in codes, for instance, EN 1993-1-3 in conjunction with EN 1993-1-8?
3. Why DX51 steel was used? The investigated joints are part of the structural system or just part of compartmentation walls? Is it still common to use this steel in LSF? As far as the reviewer knows, at least in Europe, the most common would be S280G+Z and S350GD+Z.
4. In the Introduction the authors failed to present the relevance of this study. Why is this relevant? Does this study bring something new? The observed and reported results may contribute to any modification in existing codes?
5. Why aren't the results compares with design predictions according to Eurocodes?
6. Please explain the curves in Figure 14? Why such big oscillations?
7. In the numerical modelling, since solid elements were selected, how many through-thickness elements were considered? Shearlocking phenomenon was considered and avoided?
8. Additional details should be provided about the developed numerical models. Type of finite element, mesh dimension, sensitivity tests about the mesh, type of contacts and interaction between overlapping steel plates and steel profiles and fasteners.
9. Big differences are observed in Figure 37 and 38. This show that the developed finite element model doesn't seem to be able to accurately reproduce the observed experimental behaviour. If these simulations are not improved the Reviewer believes that the numerical study is not valid. The authors must improve the numerical modelling or provide very good explanations for such big differences in terms of stiffness and load-bearing capacity.
10. Discussion and comparisons against available design methods must be provided.

Author Response

Thank you for the review and suggestions!

Please see the attachment!

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

the revised manuscript can now be published

Author Response

I would like to thank the reviewers because in the end, after several attempts, I obtained better results regarding numerical models. More details about load - displacement comparative curves are presented in the attached file and the revised version of the manuscript.

Reviewer 2 Report

Generally, the authors addressed the comments provided by the reviewers. However, the calibration of the numerical models is not acceptable. The differences are quite big, hence the model is not able to reproduce the observed experimental behaviour. For such simple models the acceptable difference would in the worst case scenario of about 10%.

This must be improved. I recommend "Major Revisions".

Author Response

The calibration of the numerical models

I would like to thank the reviewer because in the end, after several attempts, I obtained the best results.

The initial numerical models considered that all contact surfaces were perfectly bonded by means of BONDED option in ANSYS. However, as proven by the laboratory tests, this was not entirely true and thus led to significant differences between the numerical and experimental load-displacement curves.

Subsequent numerical analyses were conducted changing the type of contact between the surfaces of the connected C elements from BONDED to FRICTIONAL. A friction coefficient of 0.2 was adopted. An improvement of the obtained results was observed but, for the case of joint C, this was still not accurate enough.

The numerical model was once again investigated and FRICTIONAL type of contact was considered only between the self-drilling screw (thread, shank and head) and the wall of the holes in the thin-walled cold formed C profiles. The newly obtained force-displacement curves are plot on the same graph with experimental and initially assumed fully-bonded curves. A significant improvement of the numerically obtained results can be seen for all three joint configurations, although a slight overestimation of the initial stiffness of the joint could be observed for joint types A and B.

More details about load - displacement comparative curves are presented in the attached file and the revised version of the manuscript.

Thank you verry much!

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The authors managed to address the previous comments and to improve the overall quality of the paper. In my opinion, the paper can be accepted in its current form.