Seismic Retrofit Technique Using Plywood and Common Nails for Connections of Low-Rise Timber Frame Construction

Round 1

Reviewer 1 Report

In this manuscript, the P&N technology is proposed, the research contents is relatively detailed but less innovative, and I have the following questions about the study.

(1) Regarding the P&N retrofit technique used in this test, how was the material determined for the plywood and nails? In addition, how is the length of nails determined?

(2) The study did not mention the strength of plywood and nails, and this part needs to be added.

(3) All the pictures in the full-scale test are schematic diagrams, so it is suggested to add physical pictures to prove that the test was carried out.

Author Response

Thank you for giving us the comments. We appreciate the time and effort to review. Here is a point-by-point response to the comments.

(1) Regarding the P&N retrofit technique used in this test, how was the material determined for the plywood and nails? In addition, how is the length of nails determined?

The plywood and nail used in the P&N retrofit technique were determined by the Japanese Building Standards Act and by nail guns that Japanese carpenters widely used. Since the Act was revised in 2000, plywood has been widely used in Japanese new build TF houses to ensure wall shear capacity in place of braces. Because installing plywood can use general nail guns and is much easier than hammering STCs at post-beam-brace connections. Also, many specifications of plywood shear walls in the Act use 50-mm length nails; therefore, many Japanese carpenters use nail guns for CN50. For those reasons, the 12-mm thickness of the plywood and CN50 conforming to the Japanese Agricultural Standard: "Plywood," and the Japanese Industrial Standard: JIS A 5508 "Nails," respectively, were determined as the materials for the P&N. I added the sentence above to the section “2. Materials and Methods”.

(2) The study did not mention the strength of plywood and nails, and this part needs to be added.

As written in (1), the plywood used in this study conformed to the Japanese Agricultural Standard. Also, the timbers conformed to the Japanese Agricultural Standard: "Sawn Lumber." All nails used in this study conformed to the Japanese Industrial Standard: JIS A 5508 "Nails." I added the above two information to the section "2.1. Pullout tests on the post-beam connection."

(3) All the pictures in the full-scale test are schematic diagrams, so it is suggested to add physical pictures to prove that the test was carried out.

I added the P&N specimen photos as new Figure 10.

Reviewer 2 Report

This paper proposed a simple and easy seismic retrofit technique for earthquake-prone existing houses in Japan. The proposed technique can reinforce timber frame connections using only plywood and common nails. The study is well designed, but more discussions are needed, especially about the failure modes.

 1) In the pullout tests of post-beam connections, the plywood was bearing the transverse force.

2) Fig. 6 should give a setup of proposed P&N specimens. In addition, is the the flexible jointed jig a pinned joint fixture?

3) Similarly, Fig.9 should show the test setup of P&N specimens.

4) The material properties are suggested to be provided.

5) The load-displacement curves are suggested to use legends but not only distinguished by colors.

6) Figs.12 and 13 could be combined in single figure.

7) The failure modes should be compared and discussed.

8) More analysis and discussions are needed to show the advantages of the proposed method.

9) Please explain the validity of the proposed method based on such few specimens

Author Response

Thank you for giving us the comments. We appreciate the time and effort to review. Here is a point-by-point response to the comments.

1) In the pullout tests of post-beam connections, the plywood was bearing the transverse force.

The word “flexible jointed jig” in Figure 6 was wrong. ”Anti-inclination fixture” is correct, and I corrected the illustration in Figure 6.

2) Fig. 6 should give a setup of proposed P&N specimens. In addition, is the flexible jointed jig a pinned joint fixture?

I added the P&N specimen in Figure 6 and corrected the “flexible jointed jig” to ”Anti-inclination fixture.”

3) Similarly, Fig.9 should show the test setup of P&N specimens.

I changed the Figure 9 illustration to the P&N specimen.

4) The material properties are suggested to be provided.

The plywood and timbers used in this study conformed to the Japanese Agricultural Standard, and the nails conformed to the Japanese Industrial Standard. I added information on the material standards to the sections “2. Materials and Methods” and “2.1. Pullout tests on the post-beam connection.”

5) The load-displacement curves are suggested to use legends but not only distinguished by colors.

I added legends to all Figures.

6) Figs.12 and 13 could be combined in single figure.

I combined Figure 12 and 13, also Figure 14 and 15.

7) The failure modes should be compared and discussed.

I added all failure modes were pulling out of the nails in pullout test.

8) More analysis and discussions are needed to show the advantages of the proposed method.

The advantage of the proposed technique is the labor-saving of retrofit working than the STCs’ installation with equivalent seismic performance. I added this advantage and the background on why plywood and common nail for this technique to the study’s objective and section “2. Materials and Methods,” respectively.

9) Please explain the validity of the proposed method based on such few specimens

The Japan Building Disaster Prevention Association (JBDPA) reviews, evaluates and approves seismic evaluation and seismic retrofit proposals. Their publication “The Detailed Seismic Evaluation and Retrofit of Wooden Houses” is the standard for the seismic retrofit design of existing TF houses in Japan. The TF connections’ benchmarks, including safety factors by JBDPA, appear in the publication. Those benchmarks are the reason to validate with a few specimens. I added the benchmark diagrams to the figures and the publication to the reference.

Reviewer 3 Report

Author Response

Thank you for giving us the comments. We appreciate the time and effort to review. Here is a point-by-point response to the comments.

1-      The authors should work on the objective of the present research and should highlight how they have achieved that.

I rewrote this study’s objective and added the proposed technique’s advantage. Also, I added the background on why plywood and common nail for this technique to the section “2. Materials and Methods.”

2-      The authors confront different retrofitting types of timber nodes. It is mandatory to highlight the pross and cons of each type. It would be interesting to note better how these elements, playwood, CP-T, BP and SC, are conceived and how do they work.

Installing the STCs requires hammering many nails by hand, which is heavy work, especially for elderly carpenters. The aim of the proposed technique is the labor-saving of retrofit working than the STCs’ installation with equivalent seismic performance. “CP-T type,” “VP type” and “BP type” appeared in the early 1980s. These initial STCs have been the benchmark for developing new STCs, and improved designs of STCs are used for new build TF houses now.

3-      Section 2.1 is not very clear how it correlates to the full research, especially to the cyclic test. Is this correlated to figure 12 and 13? If yes, it is better to re-arrange the text's structure and group the results close to the test explanation. Add some images related to different phases of failures.

As you have raised, we first wrote Sections 2.1 and 3.1 close. However, we finally followed the Sections "Materials and Methods" and "Results and Discussion" style because many references and the MDPI template are written in this style. I added all failure modes were pulling out of the nails in the pullout test.

4-      Regarding the seismic response, the results and the benefits are not very clear. What is shown in figure 11, cannot be correlated to the figures 12 and 13 because the uplift is not a parameter that is related to the classical seismic response, estimated by pushover analysis. See for instance: https://doi.org/10.3390/buildings12050583 ; https://doi.org/10.3390/buildings11020071 ; https://doi.org/10.3390/buildings12020240 . It is important that the obtained results in terms of force-displacement curves obtained by the experiment could be useful for being implemented in the numerical analysis of larger scales.

The CP-T type STC performance is the benchmark for post-beam connections in Japan. We performed the pull-out tests in this study to compare the P&N performance with the CP-T type as benchmark. Our purpose is not to obtain the element data of the connections. I rewrote this study’s objective and added the proposed technique’s advantage.

5-      The registered ductility for the VP&BP connection typology is very scarce, so the retrofitting efficiency is missing. How would the authors justify this result? Is it related to the selected steel plates specimen, or it is related to the technology itself? The first case means the specimen is not appropriately designed for the test. In the second case means that the retrofitting strategy is not persuasible. A more insight analysis is required.

The combination of VP and BP type performance is Japan's benchmark for post-beam-brace connections. We performed the full-scale in-plane cyclic tests in this study to compare the P&N performance with the combination of VP and BP type as benchmark. I added the P&N is better for reducing the risk of brace buckling with excellent ductility.

6-      More additional explanations should be provided for the failure type.

I added all failure modes were pulling out of the nails in pullout test.

7-      The conclusions should be rewritten. It is essential that the authors highlight their contributions.

This study presents the retrofit technique to reinforce TF connections only using plywood and common nails without STCs. This simplifies retrofit work and many carpenters will accept when retrofitting earthquake-prone exiting houses. I added the above to the conclusion.

8-      The authors should enhance their literature review with more relevant articles. It is important to highlight the authors' contribution in correlation with the cutting-edge research on the subject.

We think our contribution is to present retrofit technique using conventional plywood and nails without STCs.

Round 2

Reviewer 2 Report

The revision has addressed all comments.

Author Response

Thank you for taking the time to review. The manuscript has been carefully reviewed by an experienced editor whose first language is English and who specializes in editing papers written by scientists whose native language is not English.

Reviewer 3 Report

The authors have addressed all the raised comments. 

The title should be changed because is not conform the scope and the context of the article.

I would suggest that the title is should contain the key words:

Test (experimental), steel timber connectors (STCs), timber frame construction

Author Response

Thank you for giving us the comments. We appreciate the time and effort to review. Here is a point-by-point response to the comments.

• The title should be changed because is not conform the scope and the context of the article.

We revised the article title to “Seismic retrofit technique using plywood and common nails for connections of low-rise timber frame construction.”

• I would suggest that the title is should contain the key words: Test (experimental), steel timber connectors (STCs), timber frame construction

We added the keywords that you suggested.