Experimental Investigation on Dowel Laminated Timber Made of Uruguayan Fast-Grown Species

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In your introduction, Line 94-97 seems to lack merit to me. Plenty of mass timber products such as glulam and CLT have passed fire tests and been shown to perform well in fire over many studies conducted in many different countries. To suggest otherwise, as if DLT has a “distinct advantage” of fire performance needs a reference if it is going to be stated. Additionally, all wood products benefit from biophilia as an aesthetic property, you haven’t supported why DLT would have a “distinct advantage” compared to glulam or CLT.

As a general comment, I found the introduction a bit long and wandering. I think it could be made more concise to get to the topic at hand, which is DLT using low-value Uruguayan timber.

Line 143: Equilibrating to MC of 16% seems pretty high. Is that close to the EMC of Ecuador?

Line 149: Equilibrating the dowels to 8% seems high also, could they not be dried down lower?

In the methods, your process effectively is E-grading the lamella. Is this representative of what a production DLT panel would use? If visual grade lumber would be used in commercial DLT panels, would your results on E-grade panels be equivalent or would the greater variability of stiffness between the lamella create differences? 

Line 348-358: So basically, there is little to know difference between laminating the 7 lamellas with a dowel or just stacking them next to each other with no connection at all? That would make sense to me because your dowels are at the neutral axis.

Line 408-411: Yes, this should be somewhat obvious from the start, that since these lamellas are oriented to behave as a series of parallel beams, the composite connection and connection stiffness between the layers matters much less.

Some of the big issues with DLT are related to across the width shrinkage and across the depth shrinkage of the panels. Your paper does not discuss this at all. I think at a minimum this limitation and challenge should be discussed somewhere. What would be the approximate shrinkage of pine and eucalyptus?

Your introduction has a long explanation of the use of mass timber being motivated by the need to reduce emissions. Then in the conclusion you say using a topping slab to control vibration and deflection should be explored. These two statements seems to conflict, as adding the slab back goes against the motivation of using mass timber in the first place. What about increasing the depth of the DLT? What about different E-grade species for DLT? I think a better conclusion could be written that provides potential solutions that don't conflict with the initial premise of needing sustainable solutions.

Author Response

Reviewer #1

- In the introduction, Line 94-97 seems to lack merit to me. Plenty of mass timber products such as glulam and CLT passed fire tests and been shown to perform well in fire over many studies conducted in many different countries. To suggest otherwise, as if DLT has a “distinct advantage” of fire performance needs a reference if its I going to be stated. Additionally, all wood products benefit from biophilia as an aesthetic property, you have[t supported why DLT would have a “distinct advantage” compared to glulam or CLT.

- Agree. The statement (Line 94-97) was removed.

- As a general comment, I found the introduction a bit long and wandering. I think it could be made more concise to get to the topic at hand, which is DLT using low/value Uruguayan timber.

- Ok. The introduction was modified.  

- Line 143: Equilibrating to MC of 16% seems pretty high. Is that close to the EMC of Ecuador?

- Thanks for the question. The EMC in Uruguay is close to 16%.  The text was modified:  “All lamellae were equilibrated to a target moisture content (MC) of 16%, typical for indoors in Uruguay.”

In addition, in the Introduction section, Line 89 was modified and a reference was included: “Typical MC of 6-8% for dowels and 12-16% for lamellas are preferred in the manufacturing process [13].”

- Line 149: Equilibrating the dowels to 8% seems high also, could they not be dried down lower?

-. The MC % adopted in this work was similar to those found in the literature (Sotayo et al 2020, Derikvand et al 2021).

Line 89 was modified and a reference was included:  “Typical MC of 6-8% for dowels and 12-16% for lamellas are preferred in the manufacturing process [13].”

 

- In the methods, your process effectively is E-grading the lamella. Is this representative of what a production DLT panel would use? If visual grade lumber would be used in commercial DLT panels, would your results on E-grade panels be equivalent or would the greater variability of stiffness between the lamella create differences?

- Thanks for the question. After line 326, a text was added.

Line 326: “In addition, the variability of lamella stiffness (Ed=21 % for pine and Ed=10% for eucalyptus) corresponded to low grade timber which will not be representative of commercial DLT production. Nevertheless, in general, the variability of lamella stiffness determined by E-grading could lead to differences compared to values of commercial DLT panels, if in the industry lamella would be sorted by visual grading. On the other hand, lumber stiffness within a visual grade has also a certain degree of variability due to its inherent natural grown characteristics. The variation in MOE of glued laminated beams, made of visually graded lumber was evaluated by Moody et al [33]. They compared the experimental stiffness for laminating grades of lumber with industry values and found differences of 4% -16% for Douglas Fir/Larch and 2% -19% for Southern Pine, respectively.”

- Line 408-411: Yes, this should be somewhat obvious from the start, that since these lamellas are oriented to behave as a series of parallel beams, the composite connection and connection stiffness between the layers matters much less.  

OK.

- Some of the big issues with DLT are related to across the width shrinkage and across the depth shrinkage of the panels. Your paper does not discuss this at all. I think at a minimum this limitation and challenge should be discussed somewhere. What would be the approximate shrinkage of pine and eucalyptus?

- Thanks for the comment. A paragraph was added.

Line 386: “Furthermore, no physical sign of dowel withdrawal in none of the panels was observed. However, during service life, changes in the RH of the environment would affect the dimension stability of the panel and its components, i.e., individual lamellas and dowels. In this study where flatsawn boards were used, radial shrinkage/swelling across the width and tangential shrinkage/swelling across the depth of panels would occur over time. The dimensional instability could lead to separation between adjacent lamellas and to loosen of dowels. Previous studies [37] on dimension stability of drilled holes on softwoods showed that swelling of the wood material reduced the hole diameter and shrinkage increase the diameter. For pine 3.59% and 6.02 % of radial and tangential shrinkage, respectively, can be expected. For eucalytptus the respective percentages would be 4.54% and 8.80%. The mechanosorptive behavior of DLT panels will be investigated in further works.”

- Your introduction has a long explanation of the use of mass timber being motivated by the need to reduce emissions. Then in the conclusion you say using a topping slab to control vibration and deflection should be explored. These two statements seems to conflict, as adding the slab back goes against the motivation of using mass timber in the first place. What about increasing the depth of the DLT? What about different E-grade species for DLT? I think a better conclusion could be written that provides potential solutions that don´t conflict with the initial premise of needing sustainable solutions.

- Thanks for the comment. Conclusion section was modified having in consideration the reviewer´s comment. In particular:

Lines 446-454: The structural performance of DLT could be improved by using better timber quality. Increasing the depth of the boards or using different E-grade species for DLT production could be potential solutions to fulfil the structural requirements. Since the design of DLT panels is usually driven by serviceability limit states, the addition of multiple layers of plywood to the top side of the panel would increase the overall stiffness and probably would reduce vibrations. Further work on sustainable materials as a replacement of concrete for a typical compression slab that comply with the requirements of the serviceability limit states of the EC-5 will be very valuable.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The work is appropriate to the scope of the magazine. It presents essential information that can contribute to advances in connecting doweled wooden parts. However, some adjustments are necessary: - Citations adopted as references must be improved, with greater emphasis on the use of scientific works published in consolidated international journals. Talks at events, technical notes, or other types of communications that do not go through peer review must be avoided; Conclusions must be objective and direct, responding in a linear way to the question addressed in the research (This study aims to evaluate the structural behavior of Dowel Laminated Timber (DLT) made of fast-growing pine and eucalyptus lamellae, and different dowel diameters.

Comments on the Quality of English Language

The work is appropriate to the scope of the magazine. It presents essential information that can contribute to advances in connecting doweled wooden parts. However, some adjustments are necessary: - Citations adopted as references must be improved, with greater emphasis on the use of scientific works published in consolidated international journals. Talks at events, technical notes, or other types of communications that do not go through peer review must be avoided; Conclusions must be objective and direct, responding in a linear way to the question addressed in the research (This study aims to evaluate the structural behavior of Dowel Laminated Timber (DLT) made of fast-growing pine and eucalyptus lamellae, and different dowel diameters.

Author Response

Reviewer #2

- Citations adopted as references must be improved. Ok. References were improved.

- Conclusions must be objective and direct, responding in a linear way to the question addressed in the research (This study aims to evaluate the structural behaviour of Dowel Laminated Timber (DLT) made of fast-growing pine and eucalyptus lamellae, and different dowel diameters.

- Thanks for the comment. The Conclusion section was modified as follows:

“This study aims to evaluate the structural behaviour of Dowel Laminated Timber made of fast-growing pine and eucalyptus lamellae, and different dowel species and diameters. The test specimens were constructed using low grade timbers.  Based on the results and observations the following conclusions can be drawn:

• The mean modulus of elasticity and the bending strength of DLT panels were similar to those of the individual lumbers suggesting that no composite action was achieved.
• Dowel species and dowel diameter had no substantial influence on the bending properties of structural size panels, yet showed an effect on the slip modulus and shear capacity of the dowelled connections.
• The most common failure mode under bending indicates that some lamellas within the DLT panel are weaker than others, and as they fail by tension, the stress is transferred through the dowels to the adjacent lamellas until complete panel failure occurs.
• A good match between the analytical estimation and the experimental results of the bending stiffness of structural size panels was found.
• The structural performance of DLT could be improved by using better timber quality. Increasing the depth of the boards or using different E-grade species for DLT production could be potential solutions to fulfil the structural requirements. Since the design of DLT panels is usually driven by serviceability limit states, the addition of multiple layers of plywood to the top side of the panel would increase the overall stiffness and probably would reduce vibrations. Further work on sustainable materials as a replacement of concrete for a typical compression slab that comply with the requirements of the serviceability limit states of the EC-5 will be very valuable.

On-going research focusing on embedment strength and dimensional stability of dowels will address important issues previously mentioned and will contribute to a better understanding on the overall performance of DLT systems.”

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Experimental investigation on dowel laminated timber made of Uruguayan fast-grown species

 

Research on the use of wood raw materials from fast-growing species for the production of building materials is an interesting and future-oriented alternative for today's construction. Materials that do not contain harmful chemicals (e.g. adhesives) are particularly desirable. The material solution proposed by the authors in the form of dowel laminated timber meets the expectations of modern construction, in particular wooden construction based on fully ecological materials. Although the technology for producing building elements made of 100 percent wood (so-called Holz100%) is already known around the world, it uses a typical coniferous raw material. The authors' use of fast-growing species to produce laminated timber sets new research directions of significant scientific and utilitarian importance. In this context, the article should be considered interesting and valuable. The methodology and analysis of the results are generally unobjectionable. Nevertheless, the authors should supplement the presented methodology and analysis of results with more detailed information, in particular:

·       description of the raw material used during the research: age and diameter of the trees from which the lamellas were obtained for the study, average width of annual rings, share of late wood, etc.;

·       How was the moisture content measured? Was the spread of moisture content in all pieces of wood actually only 1%?

·       When producing the test specimens, were the drilled holes for the pins exactly the same diameter as the pin, or was there a slight clearance?

·       It would be good to supplement the analysis of the results with at least a basic statistical analysis describing the significance of the differences.

Taking into account the above remarks, the article requires a minor revision.

Author Response

Reviewer #3

- Description of the raw material used during the research: age and diameter of the trees from which the lamellas were obtained for the study, average with of annual rings, share of late wood, etc.

- Thanks for the comment. The first paragraph of the sub section 2.1 was modified.

Lines 138-144: “The lumber for this study came from two commercial plantations, devoted to pine (Pinus elliotti) and eucalyptus (eucalyptus grandis), respectively. Climate and soil conditions lead to fast growth rates, which in turn produce high percentage of juvenile wood. Both plantations have sawmills and are located in Rivera province (30°54’09”S, 55°33’02”W,  and 30°56’13”S, 55°33’35”W) at the northeast of Uruguay. The pine and eucalyptus plantations comprised of 27-year old and 19-year old trees, respectively. One hundred and forty 2-by-6 pine boards and one hundred 2-by-4 eucalyptus boards that have been previously kiln-dried at the mills, having none or negligible face knots near to the neutral axis, and/or with minimal deformations, were selected. The sawing pattern of the majority of boards was flatsawn. The width of the annual rings for pine ranged from 10 mm to 15 mm, while no distinct growth rings in eucalyptus was appreciated.All boards were covered with plastic film and transported to the LATU for further processing and evaluation. The boards were 4S-planned and cut to final lamellae dimensions of 138 x 50 x 2850 mm³ and 89 x 36 x 1900 mm³ for pine and eucalyptus, respectively. All lamellae were equilibrated to a target moisture content (MC) of 16%, typical for indoors in Uruguay. The MC of the lamellas was assessed by a resistance xilohigrometer (Lignomat) with a tolerance of (±1.5%). Three measurements per piece were taken and the corresponding average was computed. The lamellas were divided in two groups per species, to prepare connection specimens and DLT panels.”

 

- How was the moisture content measured? Was the spread of moisture content in all pieces of wood actually only 1%?

- Thank for the question. The text was modified and more information was included.

(Line 143-145):  “All lamellae were equilibrated to a target moisture content (MC) of 16%. The MC of the lamellas was assessed by a resistance xilohigrometer (Lignomat) with a tolerance of (±1.5%). Three measurements per piece were taken and the corresponding average was computed. The lamellas were divided in two groups per species, to prepare connection specimens and DLT panels”.

- When producing the test specimens, were the drilled holes for the pins exactly the dame diameter as the pin, or was there a slight clearance?

- Thanks for the question. The drilled holes have a 0.5 mm tolerance for the dowel to expand. A sentence addressing this matter was included.

Lines 181-183: “A row of holes with 0.5 mm tolerance with respect to the dowel size was drilled at the mid-height of the panel (i.e., mid-height of face laminations and perpendicular to the loading direction) and dowels were inserted manually with a rubber hammer. Therefore, an efficient connection by the swelling of the dowel was expected.

- It would be good to supplement the analysis of the results with at least a basic statistical analysis describing the significance of the differences.

- Thanks for the suggestion. Statistical analysis was performed and included in the text.

After Line 281, a new sub section (“2.3. Statistical analysis”) in M&M was included.

Following are the changes:  “2.3. Statistical analysis

            The mechanical properties and density of the dowelled connections within each lamella species group (i.e., pine or eucalyptus) were compared (p<0.05) using analysis of variance (ANOVA). For pine, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the joint, were analysed.

            Similarly, the mechanical properties and density of the DLT panels within each lamella species group (i.e., pine or eucalyptus), were compared (p<0.05) using ANOVA. For pine DLT, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus DLT, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the panel, were analysed.”

-Lines 288-293. The paragraph was modified as follows: “The shear capacity (Fs) was defined as the maximum load detected during the tests.  ANOVA results indicated that pine joints assembled with guatambú dowels (PG20p) showed significant higher (p<0.05) load-carrying capacity and stiffness compared to those corresponding to pine lamellas and eucalyptus dowels (PE20p). The eucalyptus joints assembled with 18 mm diameter dowels (ET18p) showed significant superior load carrying capacity and stiffness (p<0.05) compared to its counterpart jointed with 15 mm dowels (ET15p). Comparison of density within each lamella species group (i.e., PG20p vs PE20p, and ET18p vs ET15p) indicated no significant difference regardless of dowel species or dowel diameter.”

- Lines 327-329 were modified as follows: “Analysis of variance established that the bending properties of pine panels fastened with guatambú dowels had no significant difference (a=0.05) with those of panels jointed with eucalyptus dowels.”

- Line 335-337 was modified as follows: “For eucalyptus DLT ANOVA results indicated that panels fastened with 15 mm diameter dowels showed no significant differences (a=0.05)  compared to those fastened with 18 mm diameter dowels, indicating that dowel diameter did not affect the bending properties of the panels.”

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The topic of the paper is for sure interesting and Authors depicted its importance to a large extent in the introduction section. However in my opinion the manuscript is shaped more as a technical report than as a scientific manuscript. I don't see any hypothesis-driven experimental design, any trace of statistical analysis of the results and, mostly, any discussion in comparison to the current literature. Therefore I think that the manuscript cannot be accepted in this form...

Author Response

Reviewer #4

All sections were revised. Specific reviewer suggestions were addressed as follows: 

- The reviewer asked to provide statistical analysis of the results.

- Thanks for the suggestion. Statistical analysis was performed and included in the text.

-After Line 281, a new sub section (“2.3. Statistical analysis”) in M&M was included:

“2.3. Statistical analysis

            The mechanical properties and density of the dowelled connections within each lamella species group (i.e., pine or eucalyptus) were compared (p<0.05) using analysis of variance (ANOVA). For pine, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the joint, were analysed.

            Similarly, the mechanical properties and density of the DLT panels within each lamella species group (i.e., pine or eucalyptus), were compared (p<0.05) using ANOVA. For pine DLT, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus DLT, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the panel, were analysed.”

-Lines 288-293. The paragraph was modified as follows: “The shear capacity (Fs) was defined as the maximum load detected during the tests.  ANOVA results indicated that pine joints assembled with guatambú dowels (PG20p) showed significant higher (p<0.05) load-carrying capacity and stiffness compared to those corresponding to pine lamellas and eucalyptus dowels (PE20p). The eucalyptus joints assembled with 18 mm diameter dowels (ET18p) showed significant superior load carrying capacity and stiffness (p<0.05) compared to its counterpart jointed with 15 mm dowels (ET15p). Comparison of density within each lamella species group (i.e., PG20p vs PE20p, and ET18p vs ET15p) indicated no significant difference regardless of dowel species or dowel diameter.”

- Lines 327-329 were modified as follows: “Analysis of variance established that the bending properties of pine panels fastened with guatambú dowels had no significant difference (a=0.05) with those of panels jointed with eucalyptus dowels.”

- Lines 335-337 were modified as follows: “For eucalyptus DLT ANOVA results indicated that panels fastened with 15 mm diameter dowels showed no significant differences (a=0.05)  compared to those fastened with 18 mm diameter dowels, indicating that dowel diameter did not affect the bending properties of the panels.”

- Discussion in comparison to the current literature. OK. The discussion was modified.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors the authors provided all requested corrections.

 

Author Response

Thanks for your comment stating that "the authors provided all requested corrections."

Reviewer 4 Report

Comments and Suggestions for Authors

The statistical approach introduced should be justified... Authors used ANOVA but did they perform preliminary tests for homoschedasticity and data normality? Please explain why you selected the applied statistical approach. Howerver I see the manuscript has been improved but still needs some work according to the previous comment

Author Response

Reviewer #4- Round 2

Question: The statistical approach introduced should be justified... Authors used ANOVA but did they perform preliminary tests for homoschedasticity and data normality? Please explain why you selected the applied statistical approach.

Thanks for the question. Student’s t-tests to compare the means between two groups (i.e., Pine lamelas assembled with guatambú dowels, vs Pine lamellas assembled with eucalyptus dowel) was actually performed.

 Section 2.3 was modified as follows:

- Lines 281-290: “Descriptive statistics including tests of normality with measurements ​​of skewness and kurtosis, frequency histograms and normal probability graphs, were first used to analyse the data of the dowelled connections and the panels. Shapiro-Wilk test (n ˂ 50) to confirm normality of data sets was secondly performed.  Subsequently, Levene's test to asses equality of variances (p-value>0.05) was performed.          Student’s t-test for independent samples was then used to compare (p<0.05) the mechanical properties and density of the dowelled connections within each lamella species group (i.e., pine or eucalyptus). For pine, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the joint, were analysed.

            Similarly, Student´s t-test  was used to compare (p<0.05) the mechanical properties and density of the DLT panels within each lamella species group (i.e., pine or eucalyptus). For pine DLT, the influence of the dowel species (i.e., eucalyptus or guatambu), and for eucalyptus DLT, the influence of the dowel diameter (i.e., 18 mm or 15 mm) on the performance of the panel, were analysed. The statistical analyses were carried out using Microsoft excel (2016) and InfoStat (2018) software”.

- Furthermore, in Lines 299, 352 and 361, “ANOVA” was replaced by “Student´s t’test”

Author Response File: Author Response.pdf