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KATAOKA, Yasuo

KITAMORI, Akihisa

KOMATSU, Kohei

Kyoto University Research Information Repository

Title<Preliminary>Effect of the Degree of Wedge Fixation on theRotational Behavior of Beam-Column "Nuki" Timber JointAuthor(s)KITAMORI, Akihisa; KATAOKA, Yasuo; KOMATSU, KoheiCitationWood research : bulletin of the Wood Research Institute KyotoUniversity (2002), 89: 39-40Issue Date2002-09-30URL http://hdl.handle.net/2433/53118RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityPreliminaryEffect of the Degree of Wedge Fixation on theRotational Behavior of Beam-Column"Nuki" Timber Joint*lAkihisa KITAMORI*2, Yasuo KATAOKA*3 and Kohei KOMATSU*2(Received May 31, 2002)Keywords: traditional structures, compression of wood, timber wedge, pre stressInitial stressdistributionUc (x)Uo (x)Initial stressdistributionU c (x)(Nuki)Initial stressdistributionFig. 2. Column-Beam ('Nuki') cross specimen.p/Load Cell (lOOkN)NUKI (sugi)Fig. 1. Compressive Stress Distribution in Nuki joint.ke : compressive rigidity of the beam, ke2 :secondary compressive rigidity of the beam, f3: aslope of initial stress distribution on contactsurface of the beam, (): rotational angle, e.y:deformation angle when compression yield occursfirst, Xy : length of the elastic part aftercompressive yield occurs.(1 )(3)(4)IntroductionfJo(x) = ke(fJ- B)xfJo(x) =0Nukijoint has been used to construct traditional woodenframe structures in Japan. At Nuki joint, beam memberthat penetrate column, is stiffened by wedges. Rigidity ofsuch Nuki joint mainly depends on the embedmentresistance which arises from the contact between the beamand the column, or/and the column and the wedges. Thecompression behavior perpendicular to the grain is rich inductility, so the wooden structures which have Nukijointsshow excellent performance in energy absorbing aspect!).I t is reported that the rotational rigidity of N uki joint, intowhich wedges were driven strongly, is high2). However,the role of wedges in such Nukijoints has not been clear upyet. In this study, we intended to make the effect ofwedge fixation clear theoretically, as well as experi-mentally.Estimating MethodFrom the assumed mechanical model of Nuki joint asshown in Fig. 1, following relationships were obtained.fJc(x) =ke ((3+ B)x (O~ B< By) or (O~x<Xy, By~ B)fJc(x) =ke(f3+ B)Xy+ ke2 (fJ+ B)(x- Xy)(Xy<x, By~ B)(O~B<fJ)(fJ~ B) (2)If looking at one particular contact point between Nukiand column member standing on the rotation center, thetangential force acting at the point can be separated intotwo vectors. The vertical force acts as embedment forceto the beam, and the horizontal force acts as friction loadon contact surface between beam and wedge. Thismechanism of load distribution can be expressed asparallel spring model in dependence on a rotational angle.In a certain rotational angle, two components of momentcan be induced from embedment and friction.M=Me+MrMe=Mec-MeoWhere1 3Mec=12bhc ke(fJ- B)*1 A part of this work was presented at the Annual Meeting ofthe Wood Research Society in Gifu, April, 2002.*2 Labolatry of Structural Function.*3 Faculty of Engineering, Chubu University.- 39-WOOD RESEARCH No. 89 (2002)o Experimental- CalculatedInitial Bearing Force 6kN0.05 0.\ 0.15 0.2Defonnation Angle IJ [rad]0 0OIJ--,.~-"--"""""'---'--'--"""""'--'-"""""":"""""""""""""",,~--,--.o-..JoICal.O1.5 IIeg\~5·s~0.5o'- Calculated0.05 0.\ 0.15 0.2Defonnation Angle IJ [radl1.5eg\~I'"0.5110o ExperimentalInitial Bearing Force 2kNo Experimentalo ........._..L....-'--...........--L...-'--...........--'-.........:..'~':.....-B'............~--'--........J0.05 0.\ 0.\5 0.2 0Defonnation Angle IJ fradl1.5Fig. 3. Comparison of analytical and experimental moment-deformation angle relationship at each initial bearing force level._ 1 3M eo - 12bhc (f3-8) (8~8<f3)Meo=O (f3~ 8)Mr= ChbP (p: coefficient of friction) (5)C=Cc+Co (6)Where1 3Cc=Sbhc ke(f3- 8) (O~ 8< 8y )Cc = .~ bhc 3ke(f3- 8) 12( ~:;) - ( ~:~ rf+~ b~/ke2(f3- 8) II -(~:~Yf (8y~ 8)1 .Co = Sbhc2(f3- 8) (8~ 8<(3)Co=O (f3~ 8)Here,f3 and 8y are expressed by equation (7)._ 4Co -~- .f3-~, 8y - k h f3 (7)c e, e cExperimentalThe static monotonous loading tests were carried out bythe test set-up shown in Fig. 2. We evaluated through thetest how the magnitude of initial bearing force affects onthe structur:al performance of the Nuki joint. We set 4different load levels (6,4,2 and 0 kN) for the initial bearingforce, and in t.otal 8 specimens were tested. The straingauges were attached to the surface of the Nuki member tomeasure embedment strains as well as shear strains inpanel zone.All columns (Sugi: Cryptomeria japonica) are 120 X 120 X1,200 [mm], and the size of all beams (Sugi) is 30 X 105 X700 [mm]. All wedges are Moabi (Mimusops djave Engl.)with 60 mm in width, 30 mm in depth, and 5degree inslope angle.Results and DiscussionIt was observed that moment-deformation anglerelationships were influenced by the magnitude of initialbearing force as shown iIi Fig. 3. The rotational momentat the primary yield point of specimens under the highinitial bearing force was higher than those given low initialbearing force. While initial rotational rigidity of eachspecimen was almost same and without regard to theamount of initial fixation controlled by wedges penetrationdepth into the joint. And the significant difference ,wasnot found on the amount of energy absorbing under thelarge deformation.Fig. 3 also shows the comparison between analyticalcurve and experimental value on the moment- deformationangle relationship. The analytical initial rigidity wascalculated from the elementary beam theory for cantileverbeam. From the analytical result, it was shown that thehigher the initial bearing force was given to the N uki joint,the higher the moment was obtained at primary yield pointwhich is derived from friction load. While .secondaryyield point, caused by the compression yield of the beam,appeared quickly with high initial bearing force. Thuswhen rotational angle was large, initial btmring forcehardly affects upon the moment. .In each initial bearing force level, both results showedgood agreement with respect to initial rotational rigidity,rotational moment at primary yield point, slope at plasticstage and especially the locus from the primary yield pointto the secondary' one. From these. results, it wa~confirmed that the theory based on the assumptions takenthe effects of initial bearing force into consideration couldexpresses the rotational behavior of Nuki joints very well.References1) M. INAYAMA: PhD Thesis ofTokyo Univ. (2002) (Injapanese).2) Y. KATO and K. KOMATSU: Wood Research, No. 87, 39-41(2000).- 40-

<Preliminary>Effect of the Degree of Wedge Fixation on the Rotational Behavior of Beam-Column "Nuki" Timber Joint

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<Preliminary>Effect of the Degree of Wedge Fixation on the Rotational Behavior of Beam-Column "Nuki" Timber Joint

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