Behavior of Self-Tapping Screws Used in Hybrid Light Wood Frame Structures Connected to a CLT Core

Round 1

Reviewer 1 Report

This paper presents an interesting topic on screwed connection details to transfer diaphragm forces into CLT shear walls. The paper is well written and contains publishable contents. The reviewer’s questions and comments are listed as follows:

1.       The authors may need to clarify if these connections between the diaphragms and the vertical CLT core-wall systems are specified as one source of energy dissipation for seismic design. In other words, what is the main performance objective of these connection details?

2.       Line 154 and Line 156, please correct the typos, “strew spacing”

3.       Line 157, timber splitting was observed in some specimens, which apparently affected the displacement capacity and caused pre-mature failure. The screw spacing and end distance seemed to well exceed the minimum requirements in most design standards. What about the edge distance? Do you reckon predrilling in lumber can help? More discussion on this will help readers understand the reason.

4.       In Figure 4f, note some mixed angle connections had 20% load drops after the first peak at very small displacements. However, failure points seemed to be defined after the connections reached the second peak with much larger displacement. Please clarify this. In fact, we can optimise the inclined to 90-degree screw ratio to avoid too much load drop after the first peak.

5.       It was mentioned in the conclusion part that the 90-degree connections had similar ductility to the 45-degree connections. In my opinion, this is caused by the fundamental flaws of the definition of the ductility. 45-degree connections had very limited deformation capacity, very few would consider they can provide ductile connection solutions for energy dissipation.

Author Response

The authors thank the reviewer for their time and effort in reviewing the manuscript. We hope the changes listed have made the manuscript suitable for publication and we look forward to your response.

Response to Reviewer 1 Comments

 

Point 1: The authors may need to clarify if these connections between the diaphragms and the vertical CLT core-wall systems are specified as one source of energy dissipation for seismic design. In other words, what is the main performance objective of these connection details?

 

Response 1: The objective of the connection test is to develop a ductile connection system that can be used as one source of energy dissipation for the seismic design of hybrid buildings. Clarifications have been added in lines 50-51 and 85-87.

 

Point 2:  Line 154 and Line 156, please correct the typos, “strew spacing”

Response 2: ”strew spacing” has been replaced with “screw spacing”, see lines 172-175.

 

Point 3:  Line 157, timber splitting was observed in some specimens, which apparently affected the displacement capacity and caused pre-mature failure. The screw spacing and end distance seemed to well exceed the minimum requirements in most design standards. What about the edge distance? Do you reckon predrilling in lumber can help? More discussion on this will help readers understand the reason.

Response 3: The edge distances has been added in lines 167-169. Predrilling can also help prevent splitting and has been added as another option in lines 176.

 

 Point 4:  In Figure 4f, note some mixed angle connections had 20% load drops after the first peak at very small displacements. However, failure points seemed to be defined after the connections reached the second peak with much larger displacement. Please clarify this. In fact, we can optimise the inclined to 90-degree screw ratio to avoid too much load drop after the first peak.

Response 4: Authors agree with reviewer’s point. Clarifications have been added in lines 161-165 and 193-194.

 Point 5:  It was mentioned in the conclusion part that the 90-degree connections had similar ductility to the 45-degree connections. In my opinion, this is caused by the fundamental flaws of the definition of the ductility. 45-degree connections had very limited deformation capacity, very few would consider they can provide ductile connection solutions for energy dissipation.    

Response 5: Authors agree that the ductility ratio may have fundamental flaws. Time history analysis is needed to evaluate the reliability of these parameters for quantifying the energy dissipation capacity of a system. Additional discussions on this have been added in lines 208, 263-266, and 277-281.

Please see the attachment which is the revised paper

Author Response File: Author Response.docx

Reviewer 2 Report

This article gives an interesting experimental research on the behavior of self-tapping screw connection between light-frame wood diaphragm and CLT core. Series of tests were conducted with the consideration of several variables, like STS insertion angle, STS type, STS size. Some valuable conclusions on the effects of variables were obtained. This basic research is of great significance for the application of such connecting method in CLT and light-frame structure hybrid system. However, deep-going discussion on the mechanical properties and equivalent hysteretic damping is still needed to draw more useful conclusion. Moreover, theoretical calculation on the stiffness and load-carrying capacity is deserved to guide the designation of such STS connection.

Author Response

The authors thank the reviewer for their time and effort in reviewing the manuscript. We hope the changes listed have made the manuscript suitable for publication and we look forward to your response.

 

Response to Reviewer 2 Comments

 

Point 1: This article gives an interesting experimental research on the behavior of self-tapping screw connection between light-frame wood diaphragm and CLT core. Series of tests were conducted with the consideration of several variables, like STS insertion angle, STS type, STS size. Some valuable conclusions on the effects of variables were obtained. This basic research is of great significance for the application of such connecting method in CLT and light-frame structure hybrid system. However, deep-going discussion on the mechanical properties and equivalent hysteretic damping is still needed to draw more useful conclusion.

Response 1:

Additional discussion on mechanical properties combined with the failure modes has been added in lines 247-249 and 253-255. Additional discussion on equivalent hysteretic damping has been added in lines 265-267 and 277-283.

Point 2: Moreover, theoretical calculation on the stiffness and load-carrying capacity is deserved to guide the designation of such STS connection.

 

Response 2:

This paper is mainly focused on developing a ductile connection system that can be used as one source of energy dissipation in a hybrid CLT-wood frame structure. Theoretical calculation is not the focus of this research, so authors prefer not to include it in this paper. However, the test results derived from this research can be used as database for developing and verification of theoretical calculation.

Please see the attachment which is the revised paper

Author Response File: Author Response.docx

Reviewer 3 Report

I thoroughly enjoyed reading this work. I would like to appreciate the authors for clear drawings, and great discussions. I have some minor comments:

1. Fig 2 c Distance between two angled screws was not mentioned like the one mentioned in Fig 2 b

2. Table 1 45° + 90° assembly had STS PT + FT, I think it would be FT+PT in this order

 

3. Line 153 and that whole paragraph has “strew” typo instead of screw 

 

 

Author Response

The authors thank the reviewer for their time and effort in reviewing the manuscript. We hope the changes listed have made the manuscript suitable for publication and we look forward to your response.

Response to Reviewer 3 Comments

 

Point 1: Fig 2 c Distance between two angled screws was not mentioned like the one mentioned in Fig 2 b

Response 1: The screw distance has been added in Figure 2c.

Point 2: Table 1 45° + 90° assembly had STS PT + FT, I think it would be FT+PT in this order

 Response 2: Thanks for pointing out the typo. It has been revised. See Table 1.

Point 3: Line 153 and that whole paragraph has “strew” typo instead of screw 

Response 3: “strew spacing” has been replaced with “screw spacing”.

Please see the attachment which is the revised paper

Author Response File: Author Response.docx

Reviewer 4 Report

Dear Authors,

It is an interesting and well-prepared article, presenting the current achievements in the field of research on wood connectors with the use of modern research methods. methods but it needs some improvement and some additions. However, I propose a few minor additions and corrections, which I present in a synthetic way. 

Line 90
It should be explained what it means by the term “The panel is E1 stress grade…” (class according to which standard, possibly basic data such as density, modulus of elasticity - MOE, bending strength - MOR). The mechanical properties of CLT are of significant importance for the obtained test results - the destruction process of screw connections takes place mainly in CLT (crushing, cracks, tears)

Line 93
The description of the screws should be supplemented with several basic data (type of steel, e.g. shear strength perpendicular to the axis).

 

Minor editing comments:

Lines 5-7
The data should be supplemented with the initials of the Authors: A.E.; L.Z.; C.N.

Figures 2, 3 4 and 8
Some inscriptions (dimensioning or markings) are very small and difficult to read. These inscriptions should be enlarged.

Lines 281-285
Here, instead of the authors' full names, the initials should be given.

Yours sincerely
Reviewer

 

Author Response

The authors thank the reviewer for their time and effort in reviewing the manuscript. We hope the changes listed have made the manuscript suitable for publication and we look forward to your response.

Response to Reviewer 4 Comments

 

Point 1: Line 90
It should be explained what it means by the term “The panel is E1 stress grade…” (class according to which standard, possibly basic data such as density, modulus of elasticity - MOE, bending strength - MOR). The mechanical properties of CLT are of significant importance for the obtained test results - the destruction process of screw connections takes place mainly in CLT (crushing, cracks, tears)

Response 1: The E1 stress grade is according to ANSI/APA PRG 320 [16]. The detailed mechanical properties of CLT has been added in Table 1.

Point 2: Line 93
The description of the screws should be supplemented with several basic data (type of steel, e.g. shear strength perpendicular to the axis).

 Response 2: Additional information of screws has been added in lines 100-101, and the machinal properties has been added in Tabel 1.

Point 3: Lines 5-7
The data should be supplemented with the initials of the Authors: A.E.; L.Z.; C.N.

Response 3: We can upload the data files as a supplement but the journal template has the full author names on the first page.

 

 Point 4: Figures 2, 3 4 and 8. Some inscriptions (dimensioning or markings) are very small and difficult to read. These inscriptions should be enlarged.

Response 4: Larger size of fonts have been used in Figures 2, 3, 4 and 8.

Point 5: Lines 281-285
Here, instead of the authors' full names, the initials should be given.

Response 5: Thanks for pointing it out. Initials are used now.

Please see the attachment which is the revised paper

Author Response File: Author Response.docx