THE SHEAR STRENGTH, AND FAILURE MODES, OF TIMBER JOISTS OBTAINED FROM THE TORSION TEST METHOD

Transcription

1 THE SHEAR STRENGTH, AND FAILURE MODES, OF TIMBER JOISTS OBTAINED FROM THE TORSION TEST METHOD Aami Khokha 1, Hxin Zhang 2, Danil Ridly-Ellis 3 ABSTRACT: This pap psnts dtails of th xpimntal mthod and tst slts fom a sis of tosion tsts ndtakn to valat th sha stngth of timb joists. Th fail mods and th colation of sha stngth and tosional sha modls w also stdid. Tst slts obtaind indicat that sha stngth of tstd joists was high than th pblishd vals in EN 338 and in th USDA Wood Handbook. Th tst joists factd mostly at th middl with cacks popagatd towads ith sppots o dgs. Howv, combind tnsion sha and cshing fail mods w somtims obsvd at sppots. A good colation was fond btwn tosional sha stngth and th sha modls, bt, it appad that knots do not hav sbstantial inflnc on th sha stngth. Th cnt vision of th tsting standad EN48 inclds th tosion tsting appoach to obtain th sha modls of timb. It is poposd that a tosion tst also b adoptd as a mthod fo valating th sha stngth of timb. KEYWORDS: Tosion tst, Sha stngth, Sha modls, Dsign vals, Fail mchanism 1 INTRODUCTION 123 Th sha stngth paalll to gain o sha stngth is a fndamntal mchanical popty of wood and is sd in gnal timb stctal dsign. Th sha stngth can b dtmind by tsting small cla wood blocks ( sha blocks ) as commndd by tsting standads sch as EN48 [1] and ASTM D [2].Th sha block tst mthod allows th sha stngth vals to b obtaind f fom inflnc of wood dfcts and, thfo, th tst pocd ndstimats th htognos nat of wood. To accont fo th possibl inflnc of wood dfcts and htognity of wood, fll siz stctal lmb can b tstd nd bnding (th o fo point) o in tosion [3] to obtain th sha stngth. In pactical tms, th application of th sha stngth vals in EN338 [4] is on th basis of th bnding stngth of timb, both via th allocation of timb to a gad in th stngth gading pocss and by th s of th ls in EN384 [5]. Th cnt vsion of th standad ss th 1 Aami Khokha, School of Engining and th Bilt Envionmnt, Edinbgh Napi Univsity, 1 Colinton Road, Edinbgh, EH1 5DT, UK a.khokha@napi.ac.k 2 D. Hxin Zhang, School of Engining and th Bilt Envionmnt, Edinbgh Napi Univsity, 1 Colinton Road, Edinbgh, EH1 5DT, UK j.zhang@napi.ac.k 3 D. Danil Ridly-Ellis, Cnt fo Timb Engining, Edinbgh Napi Univsity, 1 Colinton Road, Edinbgh, EH1 5DT, UK d.idlyllis@napi.ac.k following ation to calclat sha stngth fom th bnding stngth, obtaind by tsting fll siz stctal timb in fo point bnding: f v, k f v, k f m, k Wh f v,k is th chaactistic sha stngth and f m,k is th chaactistic bnding stngth. Th pcoming visions of EN338 [6] and EN384 [7] apply a slightly diffnt lationship, bt to th sam nd: sha stngth is obtaind on th basis of bnding stngth.. 8 (1) A shot-span flxal tst might b clos to th al-lif loading condition bt wold not povid a simpl to analys stat of sha d to th intaction of tnsil, ppndicla compssiv and sha stsss that tak plac. On th oth hand althogh a tosion tst dos not psnt an actal al-lif loading condition it dos podc a p and mo nifom systm of sha stsss in th spcimn allowing masmnt of th p sha stngth. Howv, ntil cntly, vy littl attntion has bn paid to s th tosion tst mthod. Vaios sachs hav xamind diffnt tst mthods fo obtaining th sha stngth, and compad sha stngth vals with bnding stngth. Nois [8] intodcd a panl sha tst mthod. Mandy [9] and Knn [1] obtaind sha stngth of Doglas-fi bams by tsting thm nd th point bnding tsts. Ramm t al. [11] sd a fo point bnding tst appoach on Doglas-fi and compad th slts with th sha block sha stngth vals. Cof t al. [12] sd a finit lmnt appoach to valat th

2 pfomanc of th and fiv point bnding tsts to obtain sha stngth of wood bams. To valat th applicability of tosion tsting, Riyanto and Gpta [13] condctd sach to compa sha block, bnding and tosion tst appoachs fo attaining th sha stngth. Thy concldd that th tosion tst is a btt appoach than th oth mthods. Lat, Gpta t al. [14,15] sd xpimntal and finit lmnt appoachs and concldd that th tosion tst mthod was th mo applicabl tst mthod to th sha block tst mthod. Th cnt daft of EN48 [13] incldd th tosion tst mthod to obtain th sha modls of wood in plac of th pvios bnding mthod (alongsid th option of masing sha stain dictly ding bnding). Ctainly th is vidnc to sppot th jction of th old bnding mthod (.g. [17]). This stdy invstigatd th applicability of th tosion tst mthod to obtain th sha stngth of timb joists and poposs this also b incldd in th tst standad. Th main objctiv of psnting this pap is to dscib th application of th tosion tst to obtain th sha stngth vals, and to compa th slts with th pblishd vals fom EN338 [4] and in th Wood Handbook [18]. Th sconday objctivs w to xamin th fail mchanism of wood nd tosion, th colation of tosional sha stngth with sha modls, and tosional sha modls with modls of lasticity. 2 MATERIAL AND METHODS Sitka spc (Pica sitchnsis) and Noway spc (Pica abis) joists of nominal coss sction of 45 1 mm w tstd. Sitka spc timb of C16 stngth class was ct into fo diffnt lngths of 1. m, 2. m, 2.8 m and 3.6 m with 15, 1, 12 and 25 sampls, spctivly slctd fo ach lngth (dnotd h SP). Noway spc (NS) wood of stngth class C16 and C24 was ct into 2.4 m lngths with 14 and 12 spcimns spctivly. Bfo tsting, all sampls w conditiond in a contolld-nvionmnt oom (21 C and 65% lativ hmidity) ntil thy attaind constant mass (appoximatly 12% moist contnt). A 1 kn-m tosion tsting machin (Tinis Olsn, Pnnsylvania USA) was sd to tst th timb joists nd tosion and to mas th twisting displacmnt of th timb inclinomts with a ang of ± 3 w attachd to th pp dg (45 mm dimnsion) of ach sampl, as shown in Fig 1. Th monting positions fo th inclinomts dpndd on th lngth of sampl bing tstd, bt in all cass inclinomts w montd at last 1 mm fom th clamps to avoid nd ffcts. Fo 1. m long sampls, two inclinomts, ach locatd 2 mm fom th nd clamps, allowd displacmnt to b masd on a 6 mm cntal span. Fig 2 givs th positions of inclinomts fo ach lngth. Th main ppos of monting inclinomts was to obtain th lativ twist of th span f fom machin and clamp distotion to calclat sha modls (G). Th sha stngth was calclatd on th basis of th maximm to. All tst spcimns w tstd at 4 /min [3] ntil thy factd. Th sha stngth and G of ach tst spcimn was calclatd on th basis of Saint-Vnant tosion thoy fo ctangla sctions as follows: Maximm To Sha Stngth (2) d t 2 k Stiffnss G (3) d t 3 k In Eations (2) and (3), d is th dpth (majo cosssction dimnsion) and t is th thicknss (mino cosssction dimnsion) of th tst spcimn and k 1 and k 2 a constants that dpnd on th dpth thicknss atio (s.g. [19]). Tst clamps Inclinomts Tosion Tst Fig 1: Tosion tsting appaats1. m sampl Fig 2: Sha stngth tst aangmnts fo SP and NS joists (lngths in mm) Sha stngths w calclatd on th basis of th maximm applid to, as shown in Fig 3. Th stiffnss was obtaind by condcting lina gssion analysis of th applid to and th lativ twist p lngth within th lastic gion as shown in Fig

3 Fo most of th tstd spcimns th lastic gion was fond btwn 3% and 3% of maximm applid to, and thfo, lina gssion analysis was condctd btwn 5% and 25% of th maximm applid to to obtain th stiffnss. Riyanto and Gpta [13] hav shown that in compaison to th sha block tsts, th tosional sha stngth vals of Doglas-fi w abot 18% high than th sha stngth vals of tstd sha blocks and abot 2% high than th pblishd vals in th Wood Handbook [18]. Tabl 1: Th man sha stngth vals of tstd joists Fig 3: A typical applid to and lativ twist of 2.8m tst sampl 3 RESULTS AND DISCUSSIONS 3.1 DESIGN STANDARDS AND TORSIONAL SHEAR STRENGTH VALUES Tabl 1 povids th man sha stngth vals of both Sitka Spc and Noway spc bams. Fo C16 Sitka spc, th man sha stngth of 7.2 MPa was attaind and that was abot 15% low than Noway spc of th sam gad, and 22% lss than th C24 Noway Spc. C24 class timb has th highst sha stngth (9.3 MPa), which agd with xpctations that th high stngth class wold hav high sha stngth vals. Fo th C16 of Noway spc th sha stngth was abot 9% low than C24 of th sam spcis. It was fond that diffnt spcis has diffnt sha stngth vals. This is phaps bcas th diffnt spcis hav diffnt atios of sha and bnding poptis. In th cnt EN338 [4], th chaactistic sha stngth vals fo C16 and C24 a 1.8 MPa and 2.5 MPa spctivly. Ths vals a calclatd on th basis of bnding stngth of fll siz stctal timb bams tstd nd fo point bnding tst in accodanc with EN48 [1,5] (Eation 1) althogh EN48 also povids a mthod to obtain th sha stngth by tsting a mm wood block. Mch high chaactistic sha stngth vals of 4.8 MPa (166% high) of C16 (combind SP and NS) and 7.5 MPa (2% high) of C24 w achivd whn joists w tstd nd to. Th vision of EN338 [6] has aisd vals of chaactistic sha stngth fo ths gads (3.2 MPa and 4. MPa) bt ths a still sbstantially lss than thos obsvd xpimntally in this stdy. Basd on sha block tsts of cla sampls, th Wood Handbook [18] povids th man sha stngth vals fo Sitka spc and Noway spc of 6.7 MPa and 7.4 MPa spctivly. Fom this sach, man sha stngth of SP was 7.2 MPa (8% high) and fo NS was 8.5 MPa (13% high), vn thogh th matial tstd was of stctal siz and not cla wood. Similaly, Go p SP NS Stngth Gad Lng th (m) No. of Joists Max. Applid This compaison shows that lativly high sha stngth vals w achivd whn th tosion tst appoach was sd, vn in compaison to tsts on cla timb. Althogh it shold b notd that only two spcis w tstd in this sach, a makd diffnc in sha stngth was fond compad with vals givn in EN338 [4,6]. This sggsts that th assignmnt of sha stngth vals accoding to th slts of bnding tsts may b ov-consvativ, at last fo low gads wh knots affct bnding stngth, bt not so mch th sha stngth (which may vn b impovd by knots). It may b appopiat that th tosion tst pocd b adoptd as a standad mthod to obtain th sha stngth vals, spcially in light of its inclsion as a mthod to obtain sha modls. 3.2 FAILURE MECHANISM UNDER TORSIONAL LOADING Man Sha Stngth (MPa) C C C C C16 Ovall C avag C All tst spcimns w factd whn tstd nd tosion. Sampls of shot lngth (1 to 2.4 m) factd within th ang of 3 p mt twist, whil long sampls (2.8 m and 3.6 m) factd within th ang of 2 to 3 p mt. This amonts to a high val of total twist fo long spcimns. On of th 3.6 m joists was twistd to 11 (31 p mt) bfo it bok as shown in Fig 4. Thoghot th tsts, small cacking noiss w had and it was noticd that small hoizontal hai-typ cacks appad in th tst sampls whil to was still applid on spcimns. Ding tsts, most of th joists factd with lag bang sond and a pff of wood dst in ai aond th location of fail was sn. It was fond that fail cacks, in many cass, w initiatd within th cla wood vn thogh a nmb of lag knots w psnt in tst joists.

4 plan nding na th middl of th span dpnding pon th lngth of th tst joists. In som cass cacks w statd in th latwood zon and tavlld towads fist th LT plan (shot sid) and thn popagatd towads th LR plan nding na middl of joist span. It was obsvd that psnc of knots, inn bak o pith was casing th discontination of th cacks and sch battns faild immdiatly within th lina tootation zon as a bittl fail. Fig 4: A typical 3.6 m joists with lag otational dfomation bfo th fact Fo diffnt typs of fail mods (viz cshing (4% of tstd spcimns), sha (25%), combind tnsion sha fail (12%) and hoizontal sha fail (23%)) w obsvd as dscibd blow Cshing Fail Th cshing fail is dfind h as a fail that occs at th sppots tiggd mainly by clamps cshing th wood matial. It was noticd that 4% of SP and NS spcimns w factd ith at loading o action clamps with cshing fail mod. Th main ason bhind cshing of wood was bcas, in addition of sha stsss, th tst clamps indcd compssiv stsss on th coss sctional aa and th combind sha and compssiv stsss casd small cacks in gowth ings which, in tn, casd cshing fail. Th cacks bgan in th alywood zon in RT plan (Fig 5) and popagatd along LR plan (long sid), as shown in Fig 6. In Fig 6, th lativ to-twist gaph is givn and th odinat of th gaph psnts th applid to and th abscissa psnts th otation fom tosion tst. T o Fig 6: A cshing fail of 3.6m battn and its to-twist lationship Combind Sha Tnsion Fail Anoth typ of fail mod obsvd was th combind sha-tnsion fail and this occd mostly in Sitka spc joists. Nin ot of 46 SP joists factd with combind sha tnsion fail mod. Th applid to podcs sha stsss and ths stsss w dominant in casing this typ of fact. In th cas of cla wood, th sha cack initiatd fom th middl of th LT plan and d to tnsion popagatd towads, and was ndd, in th LR plan. This may b bcas th gain angl might not b paalll to th longitdinal axis and, thfo, gains w factd locally in tnsion and th fail tavlld diagonally along th gain diction. Cack passs aond knot Stak lik shap nd Fig 5: Schmatic diagam of timb joists showing gain diction It was obsvd that fo th cshing fail, th fact was occd within th initial plastic zon ang of to-twist lationship. Th cacks sally statd fom gowth ings and an hoizontally along th LT 4 T35 3 o Fig 7: A combind sha tnsion fail occd in 2.8m joist and cack passd thogh knot and nds p with a shap nd

5 It was also obsvd that whn a cack appoachs a knot it tavlld aond th knot ath than pass thogh it. Ths, this indicats that knots may povid som sistanc to th sha fail. Fig 7 shows a combind sha tnsion fail, and it can b sn that th cack passd aond th knot and podcd a stak shapd nd. In som sampls, howv, it was obsvd that combind knot and gain dviation on th LR plan and knot fisss initiatd th sha fail and that tst joists w factd within thi lastic ang as a bittl mmb Sha Fail Anoth typ of fail that occd was th sha fail, which was also mainly sn in th Sitka spc joists. Abot 18 ot 46 SP joists factd with sha fail mod. It was obsvd that sha stsss w th main cas of initiating th cacks fo this fail mod, and that ths cacks w sally statd at ith th top o bottom sid, d to a knot, and thn popagatd as a diagonal cack along th long sid to pt th spcimn in sha d to th knot at th oth dg. This fail taks plac bcas dg knots a sally sondd by coss gain and this coss gain baks locally in sha to initiat th fail (Fig 7). occd within initial plasticity of th joists and most of fail cvs w lik a staight lin with a slight bnd at th nd. Cack bgan d to dg knot T o Fig 8: A typical sha fail bgan d to an dg knot in 3.6m joist T5 4 o T6 5 o Fig 7: A typical sha fail occd in 2.8m spcimn d to top and bottom dg knots It was fond that in this typ of th fail th cacks passd aond th knots that w psnt in th long sid of th battns. This shows that knots a not th wak plan along th long sid of th battns. It was also sn that wood dfcts, spcially of combind knot and gain dviation on th LR plan, also initiatd bittl sha fail and that tst joists w faild within thi lastic ang as a bittl matial, as shown in Fig 8. An xistnc of knot in th middl of th LT plan was also fond to b ccial nd tosion. Althogh it has bn sn that most of joists w factd within cla wood, in som tst spcimns it was noticd that knots at th middl of long sid casd th fact. A clos look vals that actally th knot fisss initiatd th cack which tavlld hoizontally fo a shot distanc and thn tavlld towads th dgs, as shown in Fig 9. In this typ fail, th fail Fig 9: A typical sha cack statd fom knot fiss Hoizontal Sha Fail This typ of fail was only obsvd in Noway spc spcimns. In this typ of fail, th sha cacks w sally initiatd fom cla wood within th LR plan and tavlld paalll to th longitdinal diction towads nd sppots, as shown in Fig ot of 26 Noway spc battns factd with hoizontal sha fail mod. Th tm hoizontal sha fail is givn h bcas th sha cacks an hoizontally along th lngth of th joists. It was also noticd that som sconday cacks w also dvlopd accompanid with th majo cacks. It is thoght that this typ of fail occd bcas th NS spcimns had gain that was clos to paalll to th longitdinal axis along th joist span. Thfo, whn fail occd th cacks tavlld thogh th gain paalll to th lngth. Scondly, it was obsvd that th knots divtd th cack path in Sitka spc spcimns bt th Noway spc tst joists had no lag knots (diamt > 25mm) that cold hav divtd th cack diction. It was obsvd that most joists w faild

6 within thi plasticity with ach-typ fail. In som joists of C24 it was sn that two o th majo cacks dvlopd along th long sid bt did not initiat thogh-fact of th sampl, as shown Fig 11. Fig 1: A typical NS C16 battn with a lag hoizontal sha cack and mino cacks T o Majo cack 45 T4 35 o Fig 11: A typical wid sha cacks occd in C24 timb joists nd tosion loading 3.3 RELATIONSHIP BETWEEN SHEAR STRENGTH AND SHEAR MODULUS Mino cack Wid sha cacks Tosional Sha Modls Vals Tabl 2 psnts th man, maximm and minimm sha modls of ach lngth gop. It was claly obsvd that C24 joists hav th high sha modls vals of 76 MPa, and it was xpctd that high stngth class wold hav th high sha stiffnss vals. Fo th C16 Noway spc, G was abot 2% low than fo C24 of th sam spcis. Fo Sitka spc. th man sha modls of 52 MPa attaind, was abot 17% lss than of C16 Noway Spc and 32% lss than of C24 Noway spc. Jst as th Sitka spc joists w fond to hav low sha stngth, thy also hav low sha modls. Tabl 2: Th man sha stngth vals of tstd joists Gop Gad Lngth (mm) SP No. of Spcim ns G (MPa) Man Max Min C C C C Ovall NS C C Th chaactistic vals of th man sha modls fo C16 and C24 in EN338 [4,6] a givn as 5 and 69 MPa spctivly. Ths a dtmind fom of E:G atio of 16:1 [5,7]. Th E psnts th man modls of lasticity of timb obtaind on fo-point bnding tsts [1]. In this stdy, th ovall man G fo C16 (inclding both SP and NS spcis) of 56MPa was obtaind, abot 13% high than in EN338. Fo C24, tosion tsts podcd a man G of 76MPa which was 1% high than in EN Sha Stngth and Sha Modls Colation A lina colation btwn th sha stngth and G of Sitka spc and Noway spc joists was dvlopd, as shown in Fig 12. Th R-sad vals w calclatd withot inclding th otlying high sha stngth vals of th Noway spc tst spcimns. This is bcas only two high sha stngth vals w obtaind and this thi inclsion wold ndly bias th colation of sha stngth and G. It is thoght that th slightly high colation fo Noway spc was obtaind bcas most of ths spcimns w f of wood dfcts and joists faild within cla wood. Th Sitka spc spcimns, on th oth hand, containd mo knots slting in som spcimns failing pmatly in a bittl mann. Howv, it was also notd in this stdy that knots hav vy littl inflnc on G and on sha stngth ovall. Rath, in som Sitka spc spcimns it was fond that knots initiatd th fail and casd a low sha stngth vals bt had no majo affct on G, which may wakn th colation.

7 Fig 12: Lina lationship btwn G and th sha stngth of SP and NS joists 3.4 CORRELATION OF SHEAR MODULUS AND MODULUS OF ELASTICITY A lationship of G and E was dvlopd to obsv if both mchanical poptis hav any colation. Th G of 6 mm and 18 mm potions of som of th C16 and C24 joists was obtaind sing tosion tsts and compad to masmnts of local and global E fom bnding tsts. Fthmo, th G of th whol spans (2.8 m and 3.6 m) was compad to dynamic E dtmind fom sonanc acostic tsts. Mo dtails can b fond in [2] and [17]. Lina colation slts a shown in Figs 13, 14 and 15 Fig 15: Lina lationship btwn G and th (dynamic acostic) E at span lvl No colation was fond btwn G and E and this sggsts that G is indpndnt of E within th C16 to C24 ang. As mntiond ali that in EN338 [4] th man G vals w dtmind fom E:G atio of 16:1. Howv, this stdy has fond no vidnc of any colation btwn E and G within tstd gad. Thfo, it bcoms mo impotant to obtain G vals sing th tosion tst mthod (o dict sha stain masmnt) as in th visd EN48 [16]. 4 CONCLUSION This pap has psntd th otlin slts of a sis of tosion tsts to dtmin th sha stngth of Sitka spc and Noway spc joists. Th tosion tst pocd has bn sn to podc high stngths than vals pblishd basd on bnding and sha block tsts. In th tst mthod, it was fond that sampls factd within th long sid wh sha stsss a psmd to b maximm nd applid to (xcpt in th cass wh fact was initiatd by cshing at th sppot). Fig 13: Lina lationship btwn G and th (local) E of 6 mm sctions Fig 14: Lina lationship btwn G and th (global) E of 18 mm sctions It was noticd that th cacks w commonly initiatd within cla wood and casd sha fail, bt that, in som spcimns, cacks statd d to sha and thn popagatd as a tnsil fail. Sppot conditions w fond to b impotant. It was noticd that tsting clamps indcd additional compssiv stsss which lad to cshing of th wood at th sppots and pmat fail fo som spcimns. Thfo, this is impotant to dsign sch tsting clamps so that thy minimis localisd compssiv stsss. In this pap sha modls vals w also obtaind fom tosion tsts and a psntd. It was fond that tst vals basd on tosion tsts w slightly high than th sha stngth vals in EN338. It was also fond that within th gads C16 and C24 th tosional sha modls and sha stngth a colatd to a dg simila to that btwn MoR and MoE in bnding. It was fond that G and E a not colatd with ach oth within th ang of gads tstd. Th cnt daft vision of th tsting standad EN48 [16] inclds th tosion tsting appoach to obtain th sha modls of timb. In this stdy it was fond that both sha stngth and sha modls can b obtaind fom tosion tsts and it is poposd that EN48 allow

8 th tosion tst to b sd to dtmin sha stngth as wll. Howv it is also notd that th tosion tsting appoach is cafl application to avoid pmat fail d to cshing at th spcimn gips. ACKNOWLEDGEMENT Athos wold lik to acknowldgd th Cnt fo Timb Engining, Edinbgh Napi Univsity fo fininacial sppot fo th sach. Thanks a also d to D. John Moo fo poviding th facility fo condcting tosion tsting. REFERENCES [1] EN 48:23: Timb stcts-stctal timb and gld laminatd timb - dtmination of som physical and mchanical poptis ppndicla to th gain, Eopan Committ fo Standadization, Bssls, Blgim, 23. [2] ASTM D : Amican Socity fo Tsting and Matials Standads Mthods of Tsting Small Cla Spcimns of Timb Volm 4.1 Wood, Wst Conshohockn, PA. USA, [3] ASTM D : Amican Socity fo Tsting and Matials Standad Mthods of Static Tst of Lmb in Stctal Siz, Volm 4.1 Wood, Wst Conshohockn, PA. USA, [4] EN338:23: Timb Stcts - Stngth Classs, Eopan Committ fo Standadization, Bssls, Blgim, 23. [5] EN384:24: Stctal timb - Dtmination of chaactistic vals of mchanical poptis and dnsity, Eopan Committ fo Standadization, Bssls, Blgim, 24. [6] pen338:28: Timb Stcts - Stngth Classs, Eopan Committ fo Standadization, Bssls, Blgim, 28. [7] pen384:28: Stctal timb - Dtmination of chaactistic vals of mchanical poptis and dnsity, Eopan Committ fo Standadization, Bssls, Blgim, 28. [8] Nois, C. B.: Compaison of standad block-sha tst with th panl-sha tst. Fost Podcts Jonal, 7(9): , [9] Mandy, W. L.: Rlationship btwn ppndicla compssiv stss and sha stngth of wood. Wood Scinc, 1(3): , [1] Knn, F. J.: Sha stngth of wood bams. Fost Podcts Jonal, 24(9):63-7, [11] Ramm D. R., L. A. Soltis and P. K. Lbow.: Expimntal Sha Stngth of Unchckd Solid- Sawn Doglas-fi. Rsach Pap FPL-RP-553, Fost Podct Laboatoy, Madison, Wisconsin, USA, [12] Cof, W. F., F. D. Pocto and D. I. Mclan.: Pdiction of th sha stngth of wood bams sing finit lmnt analysis. Mchanics of Clllosic Matials, ASME, AMD-Vol 221/MD- Vol-77:69-78, [13] Riyanto, D. S., and R. Gpta.: A compaison of tst mthods fo valating sha stngth of stctal lmb. Fost Podcts Jonal, 48 (2): 83-9, 1998 [14] Gpta, R., L. R. Hck, and T. H. Mill: Expimntal valation of th tosion tst fo dtmining sha stngth of stctal lmb. Jonal of Tsting and Evalation, 3(4): , 22. [15] Gpta, R., L. R. Hck, and T. H. Mill: Finitlmnt analysis of th stss distibtion in a tosion tst of fll-siz stctal lmb. Jonal of Tsting and Evalation, 3(4):291-3, 22. [16] pen 48:29: Timb stcts-stctal timb and gld laminatd timb- dtmination of som physical and mchanical poptis ppndicla to th gain, Eopan Committ fo Standadization, Bssls, Blgim, 29. [17] Ridly-Ellis, D., Moo, J. and Khokha, A.: Random acts of lasticity: MoE, G and EN48. COST Action E53 "Qality Contol fo Wood and Wood Podcts" and Wood Dying Smina, Bld, Slovnia, 29. [18] USDA Wood Handbook: Wood as Engining Matial, Fost Podct Laboatoy, Gn. Tch. Rp. FPL GTR 113, USDA Podct Socity, Madison, Wisconsin, USA, [19] Bickfod W. B.: Advancd Mchanics of Matials. Addison Wsly Longman, Inc. Califonia, USA, [2] Khokha A., Zhang H., Ridly-Ellis D., Moo J.: Dtmining th sha modls of Sitka spc fom tosion tsts. In: Pocdings of th 1th Wold Confnc on Timb Engining, Miyazaki, Japan, 28.