| | II Ith essa lll Redo. SbALOCNO ME) KOLOLS LDN PONS ENTE P.C.RORK, J.A.PRASER 1903 04 CO. AND -BLANK KEARS, MICH. 4 sesis THESIS ] ty shed , * 7 ~lC. BORK and J.A.PRASER, a7 4 CHRSIS, (2 S | — 4 Efficiency of Wooden Tension Joints, ——— -- ro determine the efficiency of wooden tension joints and to compare the relative strengths of long leaf yellow pine and oak Also to determine whether the values scnerally used for compres- Sion and tension of oak and pine Gre good averaze values for wood Such as is uSed in ordinary practice and obtainable at any good ‘ lumber yard. a “Nathod:- We used the Tinius Olsen testine machine in the Mechanic al Laboratory at M.A.C. This machine is constructed to break xké@ Steel and iron and is not axactly suitable for 4 test of wood. The first difficulty was in holdirg the ends of the joint. We first tried bolting two pieces of iron on the joint and allowing the strain to come against these irons. This method failed because the bolts and friction of the iron on the wood was not sufficient to stand the strain though we endeavored to incre- ase the friction bv roughing the surface of the iron with a chisel Tne machine not being built for this purpose did not provide suffl cient room for more bolts and it was quite difficult to put in the 108476 4 two that we used. This method was tnen &nardoned and we decided to grip the ends of the joint with wedses és that is the way in é which iron and steel are fripped in the machine. The pulling apparatus on the machine consisted of two plates with 2-3/en x 2-3/8" holes in the center. It was necessa- 4 ry to make some smaller wedres than those belonging to the machine These wa mado of cast iron and cut grooves in them to increase the s friction of the wedrees arainst the wood. The wedrees had & sur- face of about 4 inches by 2 inches which pressed azainst the wood. "hore was no accurate way in which we could calculate the erushing force appliand to the wood,but We concluded that the é elght sq. inches on the Wedges vould cive the wood sufficient areca }-1- 4 to resist crushinec. ve found by trial that the wood did rot crush evenly and besides breaking our wedres the eruskin= allow- ed the wedrees to slip through the plate on the machine,v.us losing ‘ te 4 treir hold on the wood. Te tested three joints by this method however and then some of the stronper ones cave us trouble. We then bored two 3 /en holes in the partof the wood subjected to crushing and inserted two 3/8 " rods so that wren the wood would @ not stand the crushing force the pressure would be partially sus- 4 tained by these rods. This method was purstied to tne end of our experiments. The timber used in the tests was of sood quality put was arhe as f «gs would ordinarily not thoroushly ceasoned thoush perhaps as food 4S WO a be used in construction. In the desifn of the Joints we took the followins values Tension = ITI00 * per sq. inch Compression = I300 #! per sa. inch. 3 e -. e _ ro JY. . Crushing on pins =750 :" per sq. inch. é 4 Shearing in plane of fibres £130 = per sq. inch. 4 Crushin> asainst ends of fibres -I290 per Sq. inch. In order to deatermine the efficiency it was necessary to aseertahk the strensth of a solid picee of wood che Same size as the joint. ‘J CD 4S we could not test such a larre picce on account of the diffi- culty of holding the ends we made six tost picees of wood with # 4 three quartors of inch eross seation and portion enlareed where é wedzes were applied. Tests of sticks of oak and yellow pine ; area of cross 4 4 Section of each stick is 3/4 Sqe in. No. of stick.Kind of wood. Fallod at, Stress per Avorace Sq, inch. po oak ”~*~ failed bv Shearilnr of C2.o tables «as shown 4 és @ 7 « « e _ c, d. - ; - e a. rep . e nl Js. Mm --r ~ wt in skatch | Mo ermishine “st env point wes cvidenvt . “O bolts me ” + a 7? . - = ¢ iL 7 7 r > . 4a. only vare used and thay Seetred emply sufficicnit to hold tre jolne 4 torether, - - remo St Strength = 5000 :". ‘ 4 peal Practor of safety = 5050 # Iooo = 5,05. mfPicio.ey x1 1/2 Y 11/2 % 5578 = 20.61 55. 4 é / Arch of Paibirs = 4.1/6 5 LY. hrs, 4 4 Shoarine value per sa,ineh - 3000 # 4 1/5 "ast of oak voodon fish plsto join’ desiznedt for 2000. . v e e ° 4. 3 AY ~ ‘oint failed by breskin in tvo in @ Section Snrouch ad first bol® hols. Used 5 a fan bolts on seach Side. Soo diasram f. In this eas2 tho vood erusked quite, « Little in frons of é the bolts. The bolts also wore bent all out of Shape, Tne joint pulled apart abou / Strain of 7,°90-4, é 1 a ee 7 ane) ‘ mGilure occurred under a Roal feetor of safcty was 7200 4 2000 - 5.6. d 4 ciency Te 1/2 I 1/2 X 4244 = 56,05 jp wPL Lei an oe _ 1200 T bk x { 2° ae e je e 4. “ ry ‘ an ~ o Area crushed arainst bolts = 1/* x 3/9 Xo sa I 7/8. 4 ‘ rr rN wk. - 7900 ¢ 1 7/8 = 3840 Hpor soq/inch. " Slened for 2000 =" s abou 6. Using c a vollow pine joint with wooden fish plate de- ; > ~ 7 acd 4. r " Sakine safe valuos Nnaving G faetor of safety of l 4 3 1/4 " bolts on cach side, Sae diagram G- wa wara unable to pull tre joint ontirely intwo but wo a) i reachod itg ultimate stransth, Thea tivo parts of the joint separa- 4 fed one inch whon undor maximum strain, -railure occurred by crush 4 ine of bolts in wood also bolts Wore bont. Wltimate stranucti qa ct » 1~ it C CD C4 > ws 4 / ,rea crushed x 1/4 x 3/2 xX Os [ 7/8 Sq inchos or A778 4 to sa inch resistance to crushing at ends of fabric, L ; / Ranl factor of safety - 8960 < 2000 = A 48 4 Prficiency - 8950 # 11/2 xX I 1/2 xX 6578 = 6054 7. 4 = gem ome ees oe -* om we ee es 8 ee es ow SE a ee 8 oe aw ee ew oe ee ee ee 8 ~~) ee On ot OR 8 ew oe mast of a table scarf joint of wellow pine desiined for é 4 I000 =". See dia-ram h. Toint failed at °450:5 bz Shearing of? a table. There were no signs of crushing nor of breakine at secteé tion. ™19 bolts soomed sufficient to hold the joint tocether 4 f This is a s&kmple joint ,vary oasily madq which produces 4 compar- f atively food strength, i -- 4 r J Ultimate strencth = 4460 34 é 4 y = “460 $ I000 =-4.4:. é cr Peal factor of safe mactor of safety uscd in design = &. 4 wr r¢ Efficioney = 14460 $2 X I 3/4 % 5578 = 19.37 js, Y uw ry! @ ea % f-te 5) wi? < qs }- ma ¢) 2 % Q 2 be ~~ C2 1 fe Cc C e host of a yellow pine iron fish plete join" desirned sed $ 1/4 imch bolts on each side. See diacram i. n 2, ot Dnroke &t point whare bolt taka I lfe Xx I Vf =2 1/4 so / incenes Ia to ,-3fe a © 7/2, é ta ~ cn re /. * y - 6335 $ I f° = 5579 “ pes Sq inch was all the wood stood s ° in tonsion. are re '} ’ a 3 4. 4. . 4. a Py wae Jltimete stroneth - G6oo = ar c ct a 4 _ 7 o\ = 1 Sor of Sarecty - 62525 $2000 - 3,17 - it ° ° ry rr | - f PfPflcicncy —5555 ¢ I 1/2 xX I 1/? X 6573 = 42,30 — — = om —=— en ew ew ee ee SP ew OP we oe OP ee ee a ee Oe ee ee HW ae oe Oe ew owe owe ee ew e-em Oe oe Teste of @ Kervod searf oak tansion joint desirnad for es 7000 with a thro | 2 pote © ee + Ih co © c> O ~ O r+ mM a bt 7y Cc © CO e 9a0 dilarram j. This joint failed by breaking of fibers at section where tho bolt takes out part of the areca. Thore was also 4 bendp int moment developed in tris section causine failure at much less a tension than was expected, The resistance of the pins is to one Sige of the noautral axis and this of course causes the bendin7; mom 4 ent. Ultimate stronztth = 500 cal factor of safety - 2300 ¢ 700 -3.3. TJ oe nhe 4 21. 10 5 > ~ rh fe Cd j-4e © ™ C2 ‘ ™ I 2500 oje ty B44 = Tifyex rife x 1 Area of failur> = ZL inch 3; stress per sq,inch not con- siderbdg bending moment= oz99 "500. LO, Test of keyed fish plate ef pine designed for 2000#, See diagram k, Joint failed under a load ef 3910 in tension, We had but twe bolts in the joint as we wished te get @ value affested enly by the resistance of keys and shearing ef. the table but we feund that there sheuld be bolts in every table in erder te holgé the jeint tegetker, Under stress the kaye tend te turn up en edge causing a bending moment in the plate, Alse the keys turning as thay do when joint is insufficiently pelted presents less crudhing area fer kaya, The kays were crushed seme wut the weed at tae and ef the fivres was net erusked thus showing that the crushing strength at the ends ef the fibre en Texas pine is greater than the crushing strength en the side ef oak fibre, Ghe efficianey = 3910 » 2x1 3/4 x.6578= 16, 98%, Real facter safety = 3910 ¢ 2000= 1,88. Value ef shearing strength= 3910 @ 4= 977,85 ef oak pins, ‘™ os €: i) oat ' an’ ., I a _ 4 + tog * = "9 . e - w » 9 af ay ry oe. ; ' ~ 4 ha, ee “4 we ‘ - ’ a ‘ a 2 4 9 a> ey ~ . ’ a ‘ ’ oy Zt _ 3 “ e cy . im -e e e @ . y} a 4 . s % * ~ . 4 ‘4 h 4 ‘ ’ . 4a a | ay * t. ¢ , . ‘ e , ', 3 s. ‘ ue ® ‘ 4 fy -—y ae -— ban New t.. : « 5 2 =a ' . - . "4 . s ae @ ° . g a - ff ‘ 44 a r ' “a 4, + a | , ‘ s ¢ ‘ ~—— ft, » . . e , ‘ ' < . ' ‘ ¢ , o - ‘ ‘ ~ e ‘ -~ a) x! oo 2 te c . nd . ot t ” poy a f % . ‘ “4 > “ a 4 ~ ' - 1 a —_ a 4 re, “we! ee, h | ‘4 ” te? hee 4 as! ey a . wt . . ~ ‘ « # aa tom, ee ‘ - uy aoe om 4. « a . ax “ . 4 e 4 ‘ A - 3 ’ ' fs . « . - 4 ~~ é - * os ’ a a "@ im oF 4 7. 7... ° bo” 2 Lr ON Teer ud Yellew Pine Jeints lle Values ebtained #'s per sq, ineh Designed Kind Ultimate Efficiency Paster Com- Skear- Tension for atrength. ef prese- ing a - safety ion 10¢0 Table Fish Plate 365@ 20, 61 3.05 <---- T4 sone 2000 Weed Fish Plate 8968 60.54 4.48 4778 a2. «.W~ 1600 Table Scart 4460 19.87 4.46 ----- 558 «--- 26600 Kered Pish Plate 3010 16, 9& 1,95 $«<-<- o—- 2 8 owe 2000 Ire Fish Plate 638% 42,80 83,17 -«--- .-— 93999 Cak Joints Values ebtained ~ eect ‘s per aq, inek esigned for # Rind Ultimate Efficioney Facter Com Shear- Tensien - gtrength z ef press ing __. ~. _ _ asecue a satcty sion 1000 Teble Fish Plate 3396 30, 3 3.2 7040 828 cone 700 Keyed Start 2300 21.18 $3 n-ne woe 2300 2000 fish Plate T7208 66, 06 3.6 2384 — once 1060 Table Spart 8328 19, &2 3.3 «--- a 2648 2000 Keped Pick Plate 9600 84, 66 4,65 «--. 516 — 2000 Ivren Fish Plate 8206 75, 23 4.40 en-we ane 4373 ® 7 _ _ = - - ~ « ro. r d ] eterw ~ 2 wo ¢ . . . - ® . ars : #8 : e . , e ~y : + i? , “wow, ’ we Poeb ee + ey \ « ' ‘ ‘ 7 - tae ‘ . 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( . - a? : “ =“ . . - oe eect * - . y _— .? > &» ' oe ao -~ i , - =e ———_ uw, -@ @ar-_- eee a +. Sap Po. “eee © a= — Quan ~Qeegre-die—e- ae sree on eee es owe SF PO + eine ~_ = - fy te ty . - 2 ‘ ¢ w-- e - 1 Oe mre ot ' “a * » ° “ &\ ie Mo us 7 dbp tis: a or re arm = Ceo. ad —~- wt as oi" ® 9 - a ° ’ *~ rr ~ F _——— ° --9 “7% . if i eile ae = —_ oe ’ . oto. ‘w~ & ss ae 7 Ne Oe ere -- of cee : . . ~ a _— /é= o ", ; ‘ ~~ SO, * ! ‘ 3 . . 3 wioo7a m4 eu. ~ wae Fe ler ww 2 aw ww we — —: ae a ' @ e-’ & @ . - : . ~ mere a 7 Fe oN © . See rr ‘ ay = . ‘ —_ = "oo 7 mtb . a - A. wer tt Ne acer lf ~~ . F°.t _ « So e es - . , ~~ ° rr a ’ ees go 2 7 _— + “ a*™ > _ F 4 + . v ‘ 4 . ao: ~ —_ oi» ‘ ‘ << we es Ut te wee we ee te - + _-_ ww w ae a> ow qe oz se =~? _™ wey we oF - = o- - - o- . * bee roo morn roe Toad wae o. - ° , wie wo - ~- - whe - : . a) ap oo = & ow - mb ~. ‘ e~ ono . - pwn. aac = = . -~ = <- - | , - a . & oe ° 2 - - ~ a ae - a ee ee - -_—- 12, _ Conelusions 1, Our results indicate that a higher factor ef safety sheuld be wsed in timber eonstruetion en acceunt ef the varying strength, As an example of this tee of eur test pieses cut from same pleee ef timber showed a differmece in tensile strength ef 5006}, 2, Seuthern pine or yellew pine is strenger in tension then eak but weaker. in crushing and shearing strength, 3, Oak timber is more liable te eantain flaws then pine, 4, Taat Trantroine's values for ultimate strengths are rather higa fer the timear ebtainable nowadays, 5, That the very best jeint will be enly avout three- quarters as atreng as @ selid stiek ef same sise, 6, That our irem fidkh plate gives higher effieimey and bolts are net as liable to beeene bent allowing the joint to give, 7, Taat it is better te use iren or steel fer tension on aseount of the diffieulty in making wooden tension joints streng qeugh for required strain, ey Bg eee, ee ll " fs rvs eSied poe - = TABLE SCARF JoInT DESIGNED FoR 1000 # TENSION SCALE 477 a. a Odd Steed Set a cl . 2 Ae P72 ~ a m4 opto a ries ike al iOS Pie We Ye tL . Vas rs \ . N ¢ Cia SCALE 4+ DESIGNED FOR 2000 # TEWS/ON HEYED FISH FLATE et LA “ | TABLE FISH PLATE SCALE §*-/ DESIGNED FOR | a | 1000 #* TE/WVS/O/V es at er lon Me ee! ” “f -<—-- oe ae ee Ep : gj RS SSSED “ eS “Hh a, ee ‘9 ee, For eee ees Re wes, ieee. eo oe Pe a Dar! eaten 3 Se ec . CELE : 2 ise i en a a a eee al So ee ee Db 7 : a b 3 : S 5 + Speen) = se oy ot er ae — oe re eects re FFs oe sj 5 eee p rae nn ee ee = i sy ee cos io 5 ae ee =D c a ee an Fa i WOODEN FISHPLATE JOINT DESIGNED FOR /000™* 4 x BolLTs VSFD (N BOTH OF ABOVE JOINTS Fd pr TOP VIEW SAME AS* FIGURE AHBOVE 4 ete: feted yeaa ea ica a Tve