# Strength Properties of Structural Glulam Manufactured from Pine (Pinus sylvestris L.) Side Boards

^{1}

^{2}

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## Abstract

**:**

^{2}.

## 1. Introduction

## 2. Experimental Material

^{2}to 19.7 kN/mm

^{2}were used. The pieces were selected so that the faces were characterised by a comparable modulus of elasticity (E +/− 0.2 kN/mm

^{2}). Narrow timber (85 mm) was not tested and it was collected from the stack at random. It was assumed that narrow timber will have the modulus of elasticity ranging from 4.7 kN/mm

^{2}to 7 kN/mm

^{2}, i.e., from the value of the 5% quantile to the mean value specified in the EN 338 standard [37] for timber grade C14. The equivalent value of the modulus of elasticity for the beam was calculated from Equation (1):

^{2}to 13.45 kN/mm

^{2}and under advantageous conditions such beams should meet the requirements for glulam grade GL24c elements, since the mean value for this range of values is 11.65 kN/mm

^{2}.

^{2}, KS 11 kN/mm

^{2}and KG 9 kN/mm

^{2}(EN 338 [37]) and applying the known Equation (2) [14]:

_{ef}—effective/substitute modulus of elasticity, N/mm

^{2},

_{x}—area moment of inertia, mm

^{4},

_{i}—modulus of elasticity of layer, N/mm

^{2},

_{i}—cross-sectional area, mm

^{2},

^{2}. Thus both variants should exhibit similar ranges of strength and modulus of elasticity.

^{2}. Melamine-urea-formaldehyde resin MUF 1247 was used as a bonding agent together with the dedicated hardener 2526. Both products were manufactured by Akzo Nobel (Amsterdam, Netherlands). The mixture was prepared taking into consideration the conditions found in the laboratory room. It was assumed that 20 g of the hardener need to be added to 100 g resin. The adopted amount of the hardener is consistent with the recommendation for this resin by Akzo Nobel. The adhesive was applied using a glue roller applicator. Manufactured beams were subjected to a 4-point bending strength test according to the diagram presented in Figure 3. Beams were tested in the upright position.

## 3. Results and Discussion

^{2}to 24.1 kN/mm

^{2}(Figure 4). It should be noted that the analysis was done only for wide boards. However, it does not have a normal distribution, although the median is 13.96 kN/mm

^{2}and it is only slightly lower than the mean (14.21 kN/mm

^{2}). Skewness is 0.405 and kurtosis is 0.202. Over 50% of the batch is timber with the modulus of elasticity between 12 kN/mm

^{2}and 16 kN/mm

^{2}and these are very high values, while only approximately 1% tested pieces had the modulus of elasticity below 8 kN/mm

^{2}in the case of side boards with width exceeding 100 mm.

^{3}and the characteristic value (5-percentile) is 480 kg/m

^{3}. Moreover, almost 75% of tested timber pieces had a density between 500 kg/m

^{3}and 650 kg/m

^{3}, while only 8% of pieces had a density below 500 kg/m

^{3}(Figure 6). However, according to the data given in Figure 5, timber with a density below 500 kg/m

^{3}is characterised by the modulus of elasticity from 7 kN/mm

^{2}to almost 15 kN/mm

^{2}and these are relatively high values.

^{2}(Figure 4), thus it is 2-fold higher than it had been assumed. However, when assuming the mean value the modulus of elasticity when calculated according to formula 1 and beams of type CW-V at approximately 15.7 kN/mm

^{2}should be expected, whereas the obtained value is much lower. Nevertheless, the modulus of elasticity was assessed only for sawn timber with width over 100 mm. Wider sawn timber probably originates from deeper located log layers, thus it may exhibit better mechanical properties. In the latter case, i.e., BW-H beams, the assumed values of the modulus of elasticity for a given grade during visual grading are underestimated. However, it may be assumed that this difference, amounting, for these beams, to approximately 10%, is a factor increasing certainty of the required quality for the manufactured elements. In the case of glulam elements and the modulus of elasticity evaluated according to the PN-EN 14080:2013 standard [40], not only the mean modulus of elasticity is assessed, but it is also the value of the 5th percentile. In the case of the analysed beams, these values are 11.3 kN/mm

^{2}and 12.1 kN/mm

^{2}for BW-H and CW-V beams, respectively.

^{2}, while for BW-H beams it is 59.2 N/mm

^{2}(Figure 9). Although the difference is approximately 8%, there are no grounds to state that both batches differ statistically. Recorded values are very high because they account for approximately 50% bending strength of pine wood. However, a statistically significant value for bending strength is the value of the (5-percentile). In the case of analysed beam types, these values amount to 42.0 N/mm

^{2}and 43.2 N/mm

^{2}for BW-H and CW-V beams, respectively. In both cases characteristic bending strength is also very similar; nevertheless, a more advantageous value for obtained for CW-V beams. Thanks to such ranges of strength and the modulus of elasticity both beam types are characterised by a greater load carrying capacity than that required for GL24c beams.

## 4. Conclusions

- -
- the modulus of elasticity of side boards falls within a very wide range of values, from approx. 5.5 kN/mm
^{2}to 24 kN/mm^{2}; however, over 60% of the material is sawn timber with the modulus of elasticity over 11 kN/mm^{2}, - -
- side boards are characterised by high elastic properties,
- -
- in accordance with the assumptions, both variants were characterised by a comparable modulus of elasticity, although it was much higher than it had been expected,
- -
- static bending strength of beams manufactured in the vertical timber arrangement system is slightly higher than that of beams produced from horizontally arranged timber,
- -
- beams manufactured from horizontally arranged timber layers shows a smaller confidence interval for static bending strength,
- -
- the difference in the value of the (5-percentile) for both beam types is slight and it needs to be stated that both beam types exhibit a high bending strength exceeding 40 N/mm
^{2}.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Sawn timber arrangement in the manufacture of structural beams (A,B,D,E), C—direction of loading; ((

**a**)—quality in the bend test, (

**b**)—waste timber, unclassified, (

**c**)—visual assessment-class KW, (

**d**)—visual assessment-class KS, (

**e**)—visual assessment-class KG).

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**MDPI and ACS Style**

Mirski, R.; Dziurka, D.; Kuliński, M.; Trociński, A.; Kawalerczyk, J.; Antonowicz, R.
Strength Properties of Structural Glulam Manufactured from Pine (*Pinus sylvestris* L.) Side Boards. *Materials* **2021**, *14*, 7312.
https://doi.org/10.3390/ma14237312

**AMA Style**

Mirski R, Dziurka D, Kuliński M, Trociński A, Kawalerczyk J, Antonowicz R.
Strength Properties of Structural Glulam Manufactured from Pine (*Pinus sylvestris* L.) Side Boards. *Materials*. 2021; 14(23):7312.
https://doi.org/10.3390/ma14237312

**Chicago/Turabian Style**

Mirski, Radosław, Dorota Dziurka, Marcin Kuliński, Adrian Trociński, Jakub Kawalerczyk, and Ryszard Antonowicz.
2021. "Strength Properties of Structural Glulam Manufactured from Pine (*Pinus sylvestris* L.) Side Boards" *Materials* 14, no. 23: 7312.
https://doi.org/10.3390/ma14237312