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KOMATSU, Kohei

MORI, Takuro

NODA, Yasunobu

Kyoto University Research Information Repository

TitleReinforcement of Large Finger Joint for ProgressingMechanical Properties of Glued Laminated Timber CornerJointsAuthor(s)NODA, Yasunobu; KOMATSU, Kohei; MORI, TakuroCitationWood research : bulletin of the Wood Research Institute KyotoUniversity (2003), 90: 25-26Issue Date2003-09-30URL http://hdl.handle.net/2433/53097RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityPreliminaryReinforcement of Large Finger Joint for Progressing MechanicalProperties of Glued Laminated Timber Corner JointsYasunobu NODA*1,2, Kohei KOMATSU*l and Takuro MORI*l(Received May 31, 2003)Keywords: glued laminated timber, frame corner, wooden dowel, reinforcement, open-mode momentWooden dowelFig. 1. left: The mechanism of radial stress, right: Theimage of failure caused by radial stress. M:Moment.Japanese larch(E105-f300, 150mmX 300mm)Large Finger JointIntroductionLarge Finger Joints (LFJ) have been used in Europeancountries for large scale Glued Laminated Timber (GLT)frame structures. Distinction of LFJ frame corner isadhesive typejoint and no steel wares are used. This typejoint, therefore, has been considered as another type ofGLT frame corner in Japan. There are some reports andpapers about LFJ in European countriesl), however,almost all their concern is limited to the case of close-modefailure and open-mode failure is not important becausethere is no earthquake. In contrast, we have beenattacked by earthquakes so that it is necessary to evaluateboth cases of open- and close-mode failures, especially foropen-mode failure. Prelimina,ry test showed that open-mode failure was brittle, and maximum load was almosthalf of that of close-mode failure. To resolve thisundesired property, we insist on reinforcement for open-mode failure.Former research result2) suggested that open-modebrittle failure was coursed by the stress perpendicular tothe grain. This stress is, what we called, radial stress,which is seen in curved G LT on open-mode failure and isto be neglected in simple bending test on straight G LTbeam. We recognized that most important things wouldbe to prevent failure from radial stress for improving framecorner strength property. In this paper, we reportpossibilities of reinforcement by inserting wooden dowelsto prevent conventional LFJ flame corner joints frombrittle failure.The Mean of ReinforcementFig. 2. Design of LFJ frame corner reinforced withwooden dowel (Unit: mm).Fig. 1 shows how radial stress occurs by subjected toopen-mode moment. When LFJ flame corner is exposedunder open-mode moment, the forces shown in Fig. 1 (left)are caused by the resultant force of compression stress atoutside of corner and the resultant force of tensile stress atinside of corner. Radial stress -is caused by this pair offorces. If this radial stress is prevented, it will be possibleto evaluate the ultimate strength of LFJ corner frame byshear failure of bonded layer of LFJ.Fig. 2 shows design of LFJ frame corner reinforced withwooden dowels. The largest radial stress will be occuredbe happened on LFJ area, it will be, therefore, the most*1 Laboratory of Structural Function.*2 Present address: Hokkaido Forest Products ResearchInstitute.effective to reinforce III this area. However, ifreinforcement is designed on LFJ area, it will be difficult tofabricate LFJ frame corner. We, therefore, adopted themean of reinforcement that wooden dowel can be bondedbefore jointing LFJ.At first, we did tensile tes ts of G LT block with 45 degreesofgrain angle with wooden dowel for the reinforcement, formaking sure preliminary the effect of dowel reinforcementto reveal the availability of reinforcement with woodendowel.ExperimentsTensile test of GLT block with 45 degrees of grainangle reinforced with wooden dowelThe tensile test of GLT block with 45 degrees of grain- 25WOOD RESEARCH No. 90 (2003)wooden dowel (cb 28 hard maple)0.06andM:0.05- non-reinforcement- reinforcement0.02 0.03 0.04e(rad)0.01Comparison between non-reinforcementreinforcement type LFJ frame corner tests.Moment, f): Rotational Angle.o5oTable 2. The result of LFJ frame corner test.301035Fig. 4.Non-reinforcement ReinforcementAverage C.V Average C.VMmax (kN'm) 27.36 0.06 28.94 0.04G (kN'm) 4,501 0.04 4,464 0.03Energy 0.39 0.35 0.79 0.07fl 3.50 0.39 5.41 0.10M: Moment, G: Rotational Rigidity, fl : Ductility Factor.25E20z...lr:::~151) For examples, S. AICHER, V. BORNSCHLEGL and J. HERR:International. Conference of IUFRO S5.02 TimberEngineering, Copenhagen, 239-258 (1997).2) A. NITTA and K. KOMATSU: Wood Research, 88, 56-57 (1999).3) S. AICHER and G. DILL-LANGER: Otto GrafJournal, 6, 246-274 (1995).Referencesincrease 1.2 times. We presumed that inserting woodendowel was effective to prevent G LT from cracking.The result of LFJ frame corner reinforced withwooden dowelsFig. 4 and Table 2 show the results of LFJ frame cornerreinforced and non-reinforced with wooden dowel. Thereis little distinction between non-reinforced ones andreinforced ones on maximum moment and rotationalrigidity. However, energy stored up to failure wasthought to be increased, which might bring ductile failure.The reason why maximum moment did not increase will bethat wooden dowel inserted did not prevent radial stressperfectly. Actually, the crack which caused radial stresswas observed even in reinforced specimens. On the otherhand, it was also observed that wooden dowel enduredfrom pull-out by the role of polyurethane adhesive evenafter cracking occurred. Thus, if more rigid adhesivesuch as epoxy type adhesive is used for connecting woodendowel, the failure from radial stress might be prevented,and maximum moment might be increased. As analternative ways, it might be effective to insert woodendowel (s) to another direction. This will be furtherresearch subject.Reinforcementpolyurethane adhesivespec imencyanoacrylate adhes iveNon-reinforcementlag screwFV:!;w:~ft-_s tee Iintermediate block of GLTE (GPa) 6max (MPa) E (GPa) 6max (MPa)1.16 1.461.15 2.09 1.44 1.721.04 1.521.25 1.46 1.23 2.22Average 1.15 1.41E: Young's Modulus, 6: Tensile Strength.angle was referred to prEN 1,193, European Standard3).Fig. 3 shows the design of specimen. Left one is non-reinforcement, right one is reinforcement type specimen.As shown in Fig. 3 two intermediate blocks of G LTareglued both side of specimen as recommended ininformative annex B of prEN 1,193 for avoidingconcentration of tensile stress on specimen. Andconnection between intermediate block and test machinewere fixed by lag screws. Wooden dowel used is hardmaple, which inserted simultaneously with bondingintermediate block with polyurethane adhesive. Thereason of the wooden dowel extended into the eachintermediate blocks is that polyurethane adhesive layershould not become the weakest point. The elongation ofspecimen was measured by displacement transducer.Table 1. Results of tensile test ofGLT block 45 degrees tothe grainTensile test of GLT block with 45 degrees of grainangle reinforced with wooden dowelTable 1 shows results of reinforcement and ~on­reinforcement type GLT block tensile test. In some ofspecimens, failure occurred in bonded layer betweenspecimen and intermediate block so that it is difficult toconclude about strength of material, although it is likely tobe increased. On the other hand, Young's modulusResults and DiscussionsFig. 3. Tensile test of GLT block cut off at 45 degrees tothe grain (Unit: mm).- 26-

Reinforcement of Large Finger Joint for Progressing Mechanical Properties of Glued Laminated Timber Corner Joints

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Reinforcement of Large Finger Joint for Progressing Mechanical Properties of Glued Laminated Timber Corner Joints

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