A Study on the Charring Properties of Glued Laminated Korean Larch Timber Columns

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

Thank you for the information, I have reviewed the article.

The present revised manuscript has provided a careful point-to-point response to the questions I raised earlier and has provided new insights into the fire resistance of timber structures.

A new 5th reference has been added with an incorrect author and the page number of that reference is missing and needs to be corrected.

With this minor issue corrected, I believe the manuscript can be accepted for publication.

Author Response

thank you for your review.

reference modify complete.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

-Based on your comment pertaining to the lack of including the zero-strength layer, it seems as though this has been considered when calculating the effective cross-section. Therefore, the authors should specify how exactly the authors discerned between char layer, char base, and pyrolysis zone. This is not described in the manuscript. This should not be left to the reader's imagination or guesswork.

-Limitation (again), pertaining to how the authors assess strength/quantify the load factors. This is done based on the KS, on specified strengths/design values. The authors are advised to compare their experimental moduli with code, to provide verification that the comparisons with KS values is indeed appropriate.

-Limitations and scope of the current study are obvious to the reviewer (based on these comments and reading the paper twice now), but this must be explicitly stated in the manuscript. Recommend placing this within the conclusions.

Comments on the Quality of English Language

Please conduct a final readthrough prior to resubmission, for good measure.

Author Response

Comment1. 

Based on your comment pertaining to the lack of including the zero-strength layer, it seems as though this has been considered when calculating the effective cross-section. Therefore, the authors should specify how exactly the authors discerned between char layer, char base, and pyrolysis zone. This is not described in the manuscript. This should not be left to the reader's imagination or guesswork.

 

A1. I explained about the character layer and the residual section in Figure 2.

In this study, the measurement was conducted only for the residual section without considering the zero-strength layer. (line 205)

 

Comment2. 

Limitation (again), pertaining to how the authors assess strength/quantify the load factors. This is done based on the KS, on specified strengths/design values. The authors are advised to compare their experimental moduli with code, to provide verification that the comparisons with KS values is indeed appropriate.

 

A2. According to KS F 1611-3, the average charring rate of the Glued laminated timber(Korean larch) is 0.60mm/min. The reason for comparing the Euro code and the fire resistance test data in this study was that there was no prior experimental study on the 2-hour fire resistance test of Glued laminated timber(Korean larch), so the 2-hour fire resistance test data and the Euro code were compared.

 

Comment3. 

Limitations and scope of the current study are obvious to the reviewer (based on these comments and reading the paper twice now), but this must be explicitly stated in the manuscript. Recommend placing this within the conclusions.

 

A3. The scope of this study was laminated lumber using Korean larch. Although there are limit in GLT from Korean larch, most of the collection material in Korea is made using larch. Therefore, I think this study is valuable.(line 391)

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

N/A

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

(1) The introduction to previous research is relatively limited, and it is necessary to supplement the conclusions of other researchers while highlighting the innovative aspects of this study. If the innovation is mainly due to the use of domestic Larch, it is essential to explain why this tree species was chosen, discussing aspects such as resource distribution and mechanical properties. 

(2) The sample size of the experiment needs clarification. Was there only one set of experiments conducted with a single sample? If not, please add Figure 6 to present the displacement-load curves for all samples.

(3) Currently, this paper's research is primarily focused on the description of experimental content and phenomena, lacking in theoretical models and numerical simulations. The depth of the paper needs to be further enhanced.

(4)  If European standards or South Korean national standards are used, designers could calculate the carbonization rate of Douglas-fir glued laminated timber based on the regulations, even without this experimental research. If the intention is to compare differences between tree species, it might be more pertinent to supplement the discussion with the differences in combustion performance of different species. This point is provided for the author's consideration.

Comments on the Quality of English Language

Language needs to be more concise and complete, and basic knowledge for popularization can be simplified

Reviewer 2 Report

Comments and Suggestions for Authors

Different tree species have varying levels of fire resistance, and even for the same tree species, different weather or climate of the region in which it grows, can lead to significant differences in fire resistance. The author's research is very interesting and the article is worth publishing, but it needs to be revised and improved according to the following suggestions.

 

 

1. The content described in "Introduction" is the research background and basic knowledge of fire resistance of timber structures. However, there is no relevant description of the fire resistance performance of components related to this article's topic. The existing "Introduction" has incomplete coverage and needs to be expanded. Suggest focusing on the research on the impact of different factors on the fire resistance performance of wooden components, with a particular emphasis on introducing them.

2. The article compared the research results with the European standard, and the European standard cited in the article also clarified that wood density is an important parameter affecting the charring rate of wood components by dividing them into two charring rates based on wood density. However, in this article, it is not mentioned what the density of Korean larch is. In addition, important information on its moisture content, the type of adhesive used in glulam preparation, the thickness of the layer, and whether it has the same composition is missing. It is recommended to provide additional clarification.

3. Are the three photoes in Figure 5 taken during the author's experimental process? As shown in Figure 5b, it is evident that there is a significant difference in the width of the wood growth ring among different laminates, which will result in differences in the density and charring rate of the wood in different laminates. Has the wood been graded or selected based on its density before preparing laminated timber?

4. I think the author had significant issues with the design of the test plan when conducting fire resistance tests on load-bearing components. Whether it is fire resistance or creep testing, the load level of components in the field of timber structures is usually measured as a percentage of the test value, rather than a percentage of the design value. Because the design values of the mechanical properties of wooden components are usually about one-third of the test values, the load levels of the components in this article are taken as 0.5, 0.6, 0.7, 0.9, and 1.3 of the design values, which are actually only about 0.15, 0.18, 0.21, 0.27, and 0.39 of the test values. These levels are very similar, and in addition, the wood properties themselves have significant variability. Therefore, the charring rate of the components under different load levels tested shows very similar values.

5. The author mentioned that the European standard considers the phenomenon of corner charring of wooden components under double-sided and above exposure to fire. Has this been found in this investigation, and how many are specifically mentioned? There is no relevant description in the main text.

6. The charring rate and depth of load-bearing wooden components are greater than those of non load-bearing components, and need to be discussed and analyzed in the main text.

7. At the beginning of the article, the authors mentioned that the same tree species with different growth environments can also lead to performance differences. Is there any difference between the glulam made from larch wood in Korea and those from other regions, and what is the difference? Additional explanation is required. In addition, it is recommended to discuss and analyze the reasons for the differences. Previous studies have suggested that wood density and chemical composition content are the main reasons for the differences in fire resistance performance of different wood components. It is recommended to refer to them.

Relationships between wood properties and fire performance of glulam columns made from six wood species commonly used in China. Case Studies in Thermal Engineering, 2024, 54, 104029. https://doi.org/10.1016/j.csite.2024.104029

Experimental investigation into fire performance of mixed species glulam beam under three-side fire exposure. European Journal of Wood and Wood Products, 2022, 80, 235-245. https://doi.org/10.1007/s00107-021-01746-7

Reviewer 3 Report

Comments and Suggestions for Authors

- The load ratio, what is the baseline of this? I believe the authors are using design-level strength and calculations. Does the Korean fire code consider statistical factors (5th percentile to average)? No mention of this is discussed, and this needs to be clarified in the manuscript.

- Line 82, "almost unstable". WHat does this mean??

- Line 131, Korean accreditation, please provide reference

- Please do not use the "we" and other personal pronouns in the manuscript (e.g. Line 173, etc)

- The cross section of your test specimens are full-scale, large-scale, etc? Please discuss how representative these specimens are, particularly for a structure that can be built in Korea.

- Line 190, what is peak compression length? 1m is considerable!! Please clarify. Is this for the actuator? If so, why is this relevant?

- The amount of char depth measurements, are they significant enough? 4 locations for 3000mm long specimens.

- No mention or discussion of zero-strength layer. THis is critical and plays a huge role in determining residual capacity.

- UNclear how the residual capacity was calculated. This is critical, since your load ratio is (seemingly) based on this.

- Typo "laminar" throughout the manuscript.

- Line 239, please explain and elaborate on the displacement criterion. For the reviewer, this seems odd. Why is displacement being used and not capacity?

- Table 2, the loads applied seem very low versus what the reviewer anticipates for the size of the specimens. Calculations/equations are required to demonstrate how these numbers came about. See my comment regarding design vs. actual strength.

- Related to the previous comment, has the quasi-static compression capacity of such specimen been assessed previously? What is the typical overstrength factor?

- Figure 6 should also include axial load vs. time and axial load vs. axial displacement.

- The authors measured axial load and displacement but do not report on mechanical properties such as the modulus of elasticity.

- Line 268 to 275, no mention of zero strength layer playing a role in the calculation. See my previous comment.

- Figure 7, Clearly there is localized charring occuring in specimen C-L-1, of 100+ mm versus average of 85mm. This should be discussed, particularly with relation to the lower than average performance of this specimen.

- Figure 9, typos in graph legend. 

Comments on the Quality of English Language

Please consider the typos mentioned previously and perform a general readthrough for structure phrasing, pronouns, and typos.