The delamination along the annual ring on the cross-section of laminae and the bonding strength according to the tangential angle between laminae were evaluated for the production of 3-ply cross-laminated timber (CLT) using domestic larch. Since there is no standard for CLT in Korea, the production ...
The delamination along the annual ring on the cross-section of laminae and the bonding strength according to the tangential angle between laminae were evaluated for the production of 3-ply cross-laminated timber (CLT) using domestic larch. Since there is no standard for CLT in Korea, the production and test of specimens for bonding strength followed the standard procedure of "Structural glued laminated timber" (KS F 3021). The standard specifies to exclude any measurement from the cracks of timbers resulted from drying or knots during delamination test of the glued laminated timbers. However, the failure of cross-sectional tissues along the annual rings was observed near the glue-line of all specimens during the delamination test. Because this phenomenon can generate defects in the CLT that may be exposed to various temperatures and relative humidities after the actual construction, the delamination percentage was measured by including this wood failure. As a result, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed inward was the lowest, which was around 13%, regardless of the annual ring direction of the middle lamina. On the other hand, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed outward was the highest, which was around 26%. Furthermore, end-split occurred in the outer lamina during the drying process of the boiling delamination test, which affected the delamination percentage. Therefore, the soaking delamination test was found to be more appropriate for evaluating the delamination strength of CLT. The block shear strength of larch CLT was $3.9{\pm}0.9$ MPa on average, which was 46% lower than the block shear strength requirement (7.1 MPa) of the standard, but satisfied the criteria of the block shear strength (3.5 MPa) of the European Standard (prEN 16351: 2013).
The delamination along the annual ring on the cross-section of laminae and the bonding strength according to the tangential angle between laminae were evaluated for the production of 3-ply cross-laminated timber (CLT) using domestic larch. Since there is no standard for CLT in Korea, the production and test of specimens for bonding strength followed the standard procedure of "Structural glued laminated timber" (KS F 3021). The standard specifies to exclude any measurement from the cracks of timbers resulted from drying or knots during delamination test of the glued laminated timbers. However, the failure of cross-sectional tissues along the annual rings was observed near the glue-line of all specimens during the delamination test. Because this phenomenon can generate defects in the CLT that may be exposed to various temperatures and relative humidities after the actual construction, the delamination percentage was measured by including this wood failure. As a result, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed inward was the lowest, which was around 13%, regardless of the annual ring direction of the middle lamina. On the other hand, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed outward was the highest, which was around 26%. Furthermore, end-split occurred in the outer lamina during the drying process of the boiling delamination test, which affected the delamination percentage. Therefore, the soaking delamination test was found to be more appropriate for evaluating the delamination strength of CLT. The block shear strength of larch CLT was $3.9{\pm}0.9$ MPa on average, which was 46% lower than the block shear strength requirement (7.1 MPa) of the standard, but satisfied the criteria of the block shear strength (3.5 MPa) of the European Standard (prEN 16351: 2013).
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가설 설정
For this reason, in this study, the tissues of cross-sections that are relatively weaker than tissues of radial-sections failed along the annual rings near the glue-line of all specimens during delamination test as shown in Fig. 3. This phenomenon can be a defect of CLTs that can appear according to the variations of temperature and humidity after actual construction. In this study, therefore, the wood failures along the annual rings on the cross section near the glue-line were also included in the delamination length and measured again.
제안 방법
As a result of the delamination tests for CLT combinations according to the annual ring direction of larch laminae, end-split developed in the outer lamina of specimens during the drying process of the boiling delamination test, which affected the delamination percentage of the glue-line.
The specimens were classified into four types according to the up and down directions of the annual rings on the cross section as shown in Fig. 1. Type A was combined in such a way that the annual rings of the cross sections of all layers were arranged in the same direction.
Among them, larch is acting as a substitute for imported woods together with pine trees (Statistical Yearbook of Forestry, 2014). Therefore, in order to stimulate domestic timber use and find a possible commercialization of larch CLTs, this study evaluated the delamination percentage and block shear strength of CLTs that have been combined in various ways along the annual rings of the cross section of larch laminae.
대상 데이터
Larch (Larix kaemfrei carr.) laminae with an average air-dry moisture content of 14%, an average air-dry specific gravity of 0.52, and a size of 27 mm (T) × 89 mm (W) were used.
이론/모형
For the number of specimens, a total of 80 specimens were produced with 10 soaking and boiling delamination specimens for each type. These specimens were tested according to the standard procedure (KS F 3021, 2013). After testing, the delamination length of the glue-line was measured for every glue-line of the specimens.
성능/효과
In this study, therefore, the wood failures along the annual rings on the cross section near the glue-line were also included in the delamination length and measured again. As a result, as shown in Table 1 the average soaking delamination percentage and the average boiling delamination percentage of Type A were measured at 25.6% and 10.3%, respectively. Those of Type B were measured at 1.
The delamination percentages according to the section are as follows. The average soaking delamination percentage and the boiling delamination percentage of the X section of type A were 22.0% and 11.1%, respectively and those of the Y section were 29.3% and 9.5%, respectively. Those of the X section of type B were 20.
The average soaking delamination percentage and the average boiling delamination percentage of Type A were both 1.1%, those of Type B were both 0.5%, those of Type C were 0.9% and 1.2%, respectively, and those of Type D were 1.9% and 1.1%.
). The block shear test in this study generated rolling shear failures in 57% of the specimens, and fractures in the glue-line in 37%, and general shear fracture in 6%.
Therefore, soaking delamination test was found to be more accurate than the boiling delamination test in the evaluation of CLT’s delamination strength.
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