Chapter 7. Fastenings. Contents. Lawrence A. Soltis

Transcription

1 Fastnings Lawrnc A. Soltis Chaptr 7 Contnts Nails 7 Withdrawal Rsistanc 7 Latral Rsistanc 7 5 Spiks 7 8 Stapls 7 8 Drift Bolts 7 9 Wood Scrws 7 9 Withdrawal Rsistanc 7 9 Latral Rsistanc 7 1 Lag Scrws 7 11 Withdrawal Rsistanc 7 11 Latral Rsistanc 7 1 Bolts 7 14 Baring Strss of Wood Undr Bolts 7 14 Loads at an Angl to th Grain 7 14 Stl Sid Plats 7 15 Bolt Quality 7 15 Effct of Mmbr Thicknss 7 15 Two-Mmbr, Multipl-Mmbr Joints 7 15 Spacing, Edg, and End Distanc 7 16 Effct of Bolt Hols 7 16 Pr-1991 Allowabl Loads 7 17 Post-1991 Yild Modl 7 18 Connctor Joints 7 18 Paralll-to-Grain Loading 7 18 Prpndicular-to-Grain Loading 7 18 Dsign Loads 7 Modifications 7 1 Nt Sction 7 3 End Distanc and Spacing 7 3 Placmnt of Multipl Connctors 7 3 Cross Bolts 7 4 Multipl-Fastnr Joints 7 4 Mtal Plat Connctors 7 5 Fastnr Had Embdmnt 7 6 Rfrncs 7 7 h strngth and stability of any structur dpnd havily on th fastnings that hold its parts togthr. On prim advantag of wood as a structural matrial is th as with which wood structural parts can b joind togthr with a wid varity of fastnings nails, spiks, scrws, bolts, lag scrws, drift pins, stapls, and mtal connctors of various typs. For utmost rigidity, strngth, and srvic, ach typ of fastning rquirs joint dsigns adaptd to th strngth proprtis of wood along and across th grain and to dimnsional changs that may occur with changs in moistur contnt. Maximum latral rsistanc and saf dsign load valus for small-diamtr (nails, spiks, and wood scrws) and largdiamtr dowl-typ fastnrs (bolts, lag scrws, and drift pins) wr basd on an mpirical mthod prior to Rsarch conductd during th 198s rsultd in latral rsistanc valus that ar currntly basd on a yild modl thory. This thortical mthod was adaptd for th 1991 dition of th National Dsign Spcification for Wood Construction (NDS). Bcaus litratur and dsign procdurs xist that ar rlatd to both th mpirical and thortical mthods, w rfr to th mpirical mthod as pr-1991 and th thortical mthod as post-1991 throughout this chaptr. Withdrawal rsistanc mthods hav not changd, so th pr- and post-1991 rfr only to latral rsistanc. Th information in this chaptr rprsnts primarily Forst Products Laboratory rsarch rsults. A mor comprhnsiv discussion of fastnings is givn in th Amrican Socity of Civil Enginrs Manuals and Rports on Enginring Practic No. 84, Mchanical Connctions in Wood Structurs. Th rsarch rsults of this chaptr ar oftn modifid for structural safty, basd on judgmnt or xprinc, and thus information prsntd in dsign documnts may diffr from information prsntd in this chaptr. Additionally, rsarch by othrs srvs as a basis for som currnt dsign critria. Allowabl strss dsign critria ar prsntd in th National Dsign Spcification for Wood Construction publishd by th Amrican Forst and Papr Association; limit stats dsign critria ar prsntd in th Standard for Load and Rsistanc Factor Dsign (LRFD) for Enginrd Wood Construction publishd by th Amrican Socity of Civil Enginrs. 7 1

2 Nails Nails ar th most common mchanical fastnings usd in wood construction. Thr ar many typs, sizs, and forms of nails (Fig. 7 1). Th load quations prsntd in this chaptr apply for bright, smooth, common stl wir nails drivn into wood whn thr is no visibl splitting. For nails othr than common wir nails, th loads can b adjustd by factors givn latr in th chaptr. Nails in us rsist withdrawal loads, latral loads, or a combination of th two. Both withdrawal and latral rsistanc ar affctd by th wood, th nail, and th condition of us. In gnral, howvr, any variation in ths factors has a mor pronouncd ffct on withdrawal rsistanc than on latral rsistanc. Th srvicability of joints with nails latrally loadd dos not dpnd gratly on withdrawal rsistanc unlss larg joint distortion is tolrabl. Th diamtrs of various pnny or gaug sizs of bright common nails ar givn in Tabl 7 1. Th pnny siz dsignation should b usd cautiously. Intrnational nail producrs somtims do not adhr to th dimnsions of Tabl 7 1. Thus pnny sizs, although still widly usd, ar obsolt. Spcifying nail sizs by lngth and diamtr dimnsions is rcommndd. Bright box nails ar gnrally of th sam lngth but slightly smallr diamtr (Tabl 7 ), whil cmnt-coatd nails such as coolrs, sinkrs, and coatd box nails ar slightly shortr (3. mm (1/8 in.)) and of smallr diamtr than common nails of th sam pnny siz. Hlically and annularly thradd nails gnrally hav smallr diamtrs than common nails for th sam pnny siz (Tabl 7 3). Withdrawal Rsistanc Th rsistanc of a nail shank to dirct withdrawal from a pic of wood dpnds on th dnsity of th wood, th diamtr of th nail, and th dpth of pntration. Th surfac condition of th nail at th tim of driving also influncs th initial withdrawal rsistanc. Figur 7 1. Various typs of nails: (lft to right) bright smooth wir nail, cmnt coatd, zinc-coatd, annularly thradd, hlically thradd, hlically thradd and barbd, and barbd. Tabl 7 1. Sizs of bright common wir nails Siz Gaug Lngth (mm (in.)) Diamtr (mm (in.)) 6d 11-1/ 5.8 ().87 (.113) 8d 1-1/ (-1/) 3.33 (.131) 1d (3) 3.76 (.148) 1d (3-1/4) 3.76 (.148) 16d (3-1/) 4.11 (.16) d (4) 4.88 (.19) 3d (4-1/) 5.6 (.7) 4d (5) 5.7 (.5) 5d (5-1/) 6. (.44) 6d 15.4 (6) 6.65 (.6) Tabl 7. Sizs of smooth box nails Siz Gaug Lngth (mm (in.)) Diamtr (mm (in.)) 3d 14-1/ 31.8 (1-1/4) 1.93 (.76) 4d (1-1/).3 (.8) 5d (1-3/4).3 (.8) 6d 1-1/ 5.8 ().49 (.98) 7d 1-1/ 57. (-1/4).49 (.98) 8d 11-1/ 63.5 (-1/).87 (.113) 1d 1-1/ 76. (3) 3.5 (.18) 16d (3-1/) 3.43 (.135) d (4) 3.76 (.148) Tabl 7 3. Sizs of hlically and annularly thradd nails Siz Lngth (mm (in.)) Diamtr (mm (in.)) 6d 5.8 () 3.5 (.1) 8d 63.5 (-1/) 3.5 (.1) 1d 76. (3) 3.43 (.135) 1d 8.6 (3-1/4) 3.43 (.135) 16d 88.9 (3-1/) 3.76 (.148) d 11.6 (4) 4.5 (.177) 3d (4-1/) 4.5 (.177) 4d 17. (5) 4.5 (.177) 5d (5-1/) 4.5 (.177) 6d 15.4 (6) 4.5 (.177) 7d (7) 5.6 (.7) 8d 3. (8) 5.6 (.7) 9d 8.6 (9) 5.6 (.7) 7

3 For bright common wir nails drivn into th sid grain of sasond wood or unsasond wood that rmains wt, th rsults of many tsts hav shown that th maximum withdrawal load is givn by th mpirical quation p=54 1G 5 /. DL p=7 85G 5 /, DL (mtric) (inch pound) (7 1a) (7 1b) whr p is maximum load (N, lb), L dpth (mm, in.) of pntration of th nail in th mmbr holding th nail point, G spcific gravity of th wood basd on ovndry wight and volum at 1% moistur contnt (s Ch. 4, Tabls 4 to 4 5), and D diamtr of th nail (mm, in.). (Th NDS and LRFD us ovndry wight and volum as a basis.) Th loads xprssd by Equation (7 1) rprsnt avrag data. Crtain wood spcis giv tst valus that ar somwhat gratr or lss than th quation valus. A typical load displacmnt curv for nail withdrawal (Fig. 7 ) shows that maximum load occurs at rlativly small valus of displacmnt. Although th quation for nail-withdrawal rsistanc indicats that th dns, havy woods offr gratr rsistanc to nail withdrawal than do th lowr dnsity ons, lightr spcis should not b disqualifid for uss rquiring high rsistanc to withdrawal. As a rul, th lss dns spcis do not split as radily as th dnsr ons, thus offring an opportunity for incrasing th diamtr, lngth, and numbr of th nails to compnsat for th wood s lowr rsistanc to nail withdrawal. Th withdrawal rsistanc of nail shanks is gratly affctd by such factors as typ of nail point, typ of shank, tim th nail rmains in th wood, surfac coatings, and moistur contnt changs in th wood. Withdrawal load (N) Displacmnt (in.) 6d smooth box nail.49-mm (.98-in.) diamtr 31.8 mm (1-1/4 in.) pntration dpth Douglas-fir 1% moistur contnt.54 spcific gravity Displacmnt (mm) Figur 7. Typical load displacmnt curv for dirct withdrawal of a nail Withdrawal load (lb) Effct of Sasoning With practically all spcis, nails drivn into grn wood and pulld bfor any sasoning taks plac offr about th sam withdrawal rsistanc as nails drivn into sasond wood and pulld soon aftr driving. Howvr, if common smooth-shank nails ar drivn into grn wood that is allowd to sason, or into sasond wood that is subjctd to cycls of wtting and drying bfor th nails ar pulld, thy los a major part of thir initial withdrawal rsistanc. Th withdrawal rsistanc for nails drivn into wood that is subjctd to changs in moistur contnt may b as low as 5% of th valus for nails tstd soon aftr driving. On th othr hand, if th wood fibrs dtriorat or th nail corrods undr som conditions of moistur variation and tim, withdrawal rsistanc is rratic; rsistanc may b rgaind or vn incrasd ovr th immdiat withdrawal rsistanc. Howvr, such sustaind prformanc should not b rlid on in th dsign of a naild joint. In sasond wood that is not subjctd to apprciabl moistur contnt changs, th withdrawal rsistanc of nails may also diminish du to rlaxation of th wood fibrs with tim. Undr all ths conditions of us, th withdrawal rsistanc of nails diffrs among spcis and shows variation within individual spcis. Effct of Nail Form Th surfac condition of nails is frquntly modifid during th manufacturing procss to improv withdrawal rsistanc. Such modification is usually don by surfac coating, surfac roughning, or mchanical dformation of th shank. Othr factors that affct th surfac condition of th nail ar th oil film rmaining on th shank aftr manufactur or corrosion rsulting from storag undr advrs conditions; but ths factors ar so variabl that thir influnc on withdrawal rsistanc cannot b adquatly valuatd. Surfac Modifications A common surfac tratmnt for nails is th so-calld cmnt coating. Cmnt coatings, contrary to what th nam implis, do not includ cmnt as an ingrdint; thy gnrally ar a composition of rsin applid to th nail to incras th rsistanc to withdrawal by incrasing th friction btwn th nail and th wood. If proprly applid, thy incras th rsistanc of nails to withdrawal immdiatly aftr th nails ar drivn into th softr woods. Howvr, in th dnsr woods (such as hard mapl, birch, or oak), cmnt-coatd nails hav practically no advantag ovr plain nails, bcaus most of th coating is rmovd in driving. Som of th coating may also b rmovd in th sid mmbr bfor th nail pntrats th main mmbr. Good-quality cmnt coatings ar uniform, not sticky to th touch, and cannot b rubbd off asily. Diffrnt tchniqus of applying th cmnt coating and variations in its ingrdints may caus larg diffrncs in th rlativ rsistanc to withdrawal of diffrnt lots of cmnt-coatd nails. Som nails may show only a slight initial advantag ovr plain nails. In th softr woods, th incras in withdrawal rsistanc of 7 3

4 cmnt-coatd nails is not prmannt but drops off significantly aftr a month or so. Cmnt-coatd nails ar usd primarily in construction of boxs, crats, and othr containrs usually built for rough handling and rlativly short srvic. Nails that hav galvanizd coatings, such as zinc, ar intndd primarily for uss whr corrosion and staining rsistanc ar important factors in prmannc and apparanc. If th zinc coating is vnly applid, withdrawal rsistanc may b incrasd, but xtrm irrgularitis of th coating may actually rduc it. Th advantag that uniformly coatd galvanizd nails may hav ovr nongalvanizd nails in rsistanc to initial withdrawal is usually rducd by rpatd cycls of wtting and drying. Nails hav also bn mad with plastic coatings. Th usfulnss and charactristics of ths coatings ar influncd by th quality and typ of coating, th ffctivnss of th bond btwn th coating and bas fastnr, and th ffctivnss of th bond btwn th coating and wood fibrs. Som plastic coatings appar to rsist corrosion or improv rsistanc to withdrawal, whil othrs offr littl improvmnt. Fastnrs with proprly applid nylon coating tnd to rtain thir initial rsistanc to withdrawal compard with othr coatings, which xhibit a markd dcras in withdrawal rsistanc within th first month aftr driving. A chmically tchd nail has somwhat gratr withdrawal rsistanc than som coatd nails, as th minutly pittd surfac is an intgral part of th nail shank. Undr impact loading, howvr, th withdrawal rsistanc of tchd nails is littl diffrnt from that of plain or cmnt-coatd nails undr various moistur conditions. Sand-blastd nails prform in much th sam mannr as chmically tchd nails. Shap Modifications Nail shanks may b varid from a smooth, circular form to giv an incras in surfac ara without an incras in nail wight. Spcial nails with barbd, hlically or annularly thradd, and othr irrgular shanks (Fig. 7 1) ar commrcially availabl. Th form and magnitud of th dformations along th shank influnc th prformanc of th nails in various wood spcis. In wood rmaining at a uniform moistur contnt, th withdrawal rsistanc of ths nails is gnrally somwhat gratr than that of common wir nails of th sam diamtr. For instanc, annular-shank nails hav about 4% gratr rsistanc to withdrawal than common nails. Howvr, undr conditions involving changs in moistur contnt of th wood, som spcial nail forms provid considrably gratr withdrawal rsistanc than th common wir nail about four tims gratr for annularly and hlically thradd nails of th sam diamtr. This is spcially tru of nails drivn into grn wood that subsquntly dris. In gnral, annularly thradd nails sustain largr withdrawal loads, and hlically thradd nails sustain gratr impact withdrawal work valus than do th othr nail forms. Nails with dformd shanks ar somtims hardnd by hat tratmnts for us whr driving conditions ar difficult or to obtain improvd prformanc, such as in pallt assmbly. Hardnd nails ar brittl and car should b xrcisd to avoid injuris from fragmnts of nails brokn during driving. Nail Point A smooth, round shank nail with a long, sharp point will usually hav a gratr withdrawal rsistanc, particularly in th softr woods, than th common wir nail (which usually has a diamond point). Howvr, sharp points accntuat splitting in crtain spcis, which may rduc withdrawal rsistanc. A blunt or flat point without tapr rducs splitting, but its dstruction of th wood fibrs whn drivn rducs withdrawal rsistanc to lss than that of th common wir nail. A nail taprd at th nd and trminating in a blunt point will caus lss splitting. In havir woods, such a taprd, blunt-pointd nail will provid about th sam withdrawal rsistanc, but in lss dns woods, its rsistanc to withdrawal is lss than that of th common nail. Nail Had Nail had classifications includ flat, oval, countrsunk, dp-countrsunk, and brad. Nails with all typs of hads, xcpt th dp-countrsunk, brad, and som of th thin flathad nails, ar sufficintly strong to withstand th forc rquird to pull thm from most woods in dirct withdrawal. Th dp-countrsunk and brad nails ar usually drivn blow th wood surfac and ar not intndd to carry larg withdrawal loads. In gnral, th thicknss and diamtr of th hads of th common wir nails incras as th siz of th nail incrass. Th dvlopmnt of som pnumatically opratd portabl nailrs has introducd nails with spcially configurd hads, such as T-nails and nails with a sgmnt of th had cut off. Corrosion and Staining In th prsnc of moistur, mtals usd for nails may corrod whn in contact with wood tratd with crtain prsrvativ or fir-rtardant salts (Chs. 14 and 17). Us of crtain mtals or mtal alloys will rduc th amount of corrosion. Nails of coppr, silicon bronz, and 34 and 316 stainlss stl hav prformd wll in wood tratd with ammoniacal coppr arsnat and chromatd coppr arsnat. Th choic of mtals for us with fir-rtardant-tratd woods dpnds upon th particular fir-rtardant chmical. Staining causd by th raction of crtain wood xtractivs (Ch. 3) and stl in th prsnc of moistur is a problm if apparanc is important, such as with naturally finishd siding. Us of stainlss stl, aluminum, or hot-dippd galvanizd nails can allviat staining. In gnral, th withdrawal rsistanc of coppr and othr alloy nails is comparabl with that of common stl wir nails whn pulld soon aftr driving. Driving Th rsistanc of nails to withdrawal is gnrally gratst whn thy ar drivn prpndicular to th grain of th wood. Whn th nail is drivn paralll to th wood fibrs (that is, 7 4

5 into th nd of th pic) withdrawal rsistanc in th softr woods drops to 75% or vn 5% of th rsistanc obtaind whn th nail is drivn prpndicular to th grain. Th diffrnc btwn sid- and nd-grain withdrawal loads is lss for dns woods than for softr woods. With most spcis, th ratio btwn th nd- and sid-grain withdrawal loads of nails pulld aftr a tim intrval, or aftr moistur contnt changs hav occurrd, is usually somwhat gratr than that of nails pulld immdiatly aftr driving. To nailing, a common mthod of joining wood framwork, involvs slant driving a nail or group of nails through th nd or dg of an attachd mmbr and into a main mmbr. To nailing rquirs gratr skill in assmbly than dos ordinary nd nailing but provids joints of gratr strngth and stability. Tsts show that th maximum strngth of tonaild joints undr latral and uplift loads is obtaind by (a) using th largst nail that will not caus xcssiv splitting, (b) allowing an nd distanc (distanc from th nd of th attachd mmbr to th point of initial nail ntry) of approximatly on-third th lngth of th nail, (c) driving th nail at a slop of 3 with th attachd mmbr, and (d) burying th full shank of th nail but avoiding xcssiv mutilation of th wood from hammr blows. Th rsults of withdrawal tsts with multipl nail joints in which th pic attachd is pulld dirctly away from th main mmbr show that slant driving is usually suprior to straight driving whn nails ar drivn into drywood and pulld immdiatly, and dciddly suprior whn nails ar drivn into grn or partially dry wood that is allowd to sason for a month or mor. Howvr, th loss in dpth of pntration du to slant driving may, in som typs of joints, offst th advantags of slant nailing. Cross slant driving of groups of nails through th sid grain is usually somwhat mor ffctiv than paralll slant driving through th nd grain. Nails drivn into lad hols with a diamtr slightly smallr (approximatly 9%) than th nail shank hav somwhat gratr withdrawal rsistanc than nails drivn without lad hols. Lad hols also prvnt or rduc splitting of th wood, particularly for dns spcis. Clinching Th withdrawal rsistanc of smooth-shank, clinchd nails is considrably gratr than that of unclinchd nails. Th point of a clinchd nail is bnt ovr whr th nail protruds through th sid mmbr. Th ratio btwn th loads for clinchd and unclinchd nails varis normously, dpnding upon th moistur contnt of th wood whn th nail is drivn and withdrawn, th spcis of wood, th siz of nail, and th dirction of clinch with rspct to th grain of th wood. In dry or grn wood, a clinchd nail provids 45% to 17% mor withdrawal rsistanc than an unclinchd nail whn withdrawn soon aftr driving. In grn wood that sasons aftr a nail is drivn, a clinchd nail givs 5% to 46% gratr withdrawal rsistanc than an unclinchd nail. Howvr, this improvd strngth of a clinchd-nail joint dos not justify th us of grn lumbr, bcaus th joints may loosn as th lumbr sasons. Furthrmor, laboratory tsts wr mad with singl nails, and th ffcts of drying, such as warping, twisting, and splitting, may rduc th fficincy of a joint that has mor than on nail. Clinching of nails is gnrally confind to such construction as boxs and crats and othr containr applications. Nails clinchd across th grain hav approximatly % mor rsistanc to withdrawal than nails clinchd along th grain. Fastning of Plywood Th nailing charactristics of plywood ar not gratly diffrnt from thos of solid wood xcpt for plywood s gratr rsistanc to splitting whn nails ar drivn nar an dg. Th nail withdrawal rsistanc of plywood is 15% to 3% lss than that of solid wood of th sam thicknss. Th rason is that fibr distortion is lss uniform in plywood than in solid wood. For plywood lss than 1.5 mm (1/-in.) thick, th gratr splitting rsistanc tnds to offst th lowr withdrawal rsistanc compard with solid wood. Th withdrawal rsistanc pr unit lngth of pntration dcrass as th numbr of plis pr unit lngth incrass. Th dirction of th grain of th fac ply has littl influnc on th withdrawal rsistanc from th fac nar th nd or dg of a pic of plywood. Th dirction of th grain of th fac ply may influnc th pull-through rsistanc of stapls or nails with svrly modifid hads, such as T-hads. Fastnr dsign information for plywood is availabl from APA Th Enginrd Wood Association. Allowabl Loads Th prcding discussion dalt with maximum withdrawal loads obtaind in short-tim tst conditions. For dsign, ths loads must b rducd to account for variability, duration-of-load ffcts, and safty. A valu of on-sixth th avrag maximum load has usually bn accptd as th allowabl load for long-tim loading conditions. For normal duration of load, this valu may b incrasd by 1%. Normal duration of load is dfind as a load of 1-yar duration. Latral Rsistanc Pr-1991 Tst loads at joint slips of.38 mm (.15 in.) (approximat proportional limit load) for bright common wir nails in latral rsistanc drivn into th sid grain (prpndicular to th wood fibrs) of sasond wood ar xprssd by th mpirical quation p= KD 3 / (7 ) whr p is latral load pr nail, K a cofficint, and D diamtr of th nail. Valus of cofficint K ar listd in Tabl 7 4 for rangs of spcific gravity of hardwoods and softwoods. Th loads givn by th quation apply only whr th sid mmbr and th mmbr holding th nail point ar of 7 5

6 Tabl 7 4. Cofficints for computing tst loads for fastnrs in sasond wood a (pr-1991) Spcific Latral load cofficint K (mtric (inch pound)) gravity rang b Nails c Scrws Lag scrws Hardwoods (1,44) 3.17 (3,36) 6.34 (3,8) (,) (4,64) 9.51 (4,8) (,7) (6,4) (4,95) Softwoods (1,44) 3.17 (3,36) 3.3 (3,38) (1,8) 9.79 (4,3) 6.34 (3,8) (,) 36.4 (5,8) 9.51 (4,8) a Wood with a moistur contnt of 15%. b Spcific gravity basd on ovndry wight and volum at 1% moistur contnt. c Cofficints basd on load at joint slip of.38 mm (.15 in.) approximatly th sam dnsity. Th thicknss of th sid mmbr should b about on-half th dpth of pntration of th nail in th mmbr holding th point. Th ultimat latral nail loads for softwoods may approach 3.5 tims th loads xprssd by th quation, and for hardwoods thy may b 7 tims as grat. Th joint slip at maximum load, howvr, is mor than tims.38 mm (.15 in.). This is dmonstratd by th typical load slip curv shown in Figur 7 3. To maintain a sufficint ratio btwn ultimat load and th load at.38 mm (.15 in.), th nail should pntrat into th mmbr holding th point by not lss than 1 tims th nail diamtr for dns woods (spcific gravity gratr than.61) and 14 tims th diamtr for low dnsity woods (spcific gravity lss than.4). For spcis having dnsitis btwn ths two rangs, th pntration may b found by straight lin intrpolation. Post-1991 Th yild modl thory slcts th worst cas of yild mods basd on diffrnt possibilitis of wood baring and nail bnding. It dos not account for nail had ffcts. A dscription of th various combinations is givn in Figur 7 4. Mod I is a wood baring failur in ithr th main or sid mmbr; mod II is a rotation of th fastnr in th joint without bnding; mods III and IV ar a combination of wood baring failur and on or mor plastic hing yild formations in th fastnr. Mods I m and II hav not bn obsrvd in nail and spik connctions. Th yild modl thory is applicabl to all typs of dowl fastnrs (nails, scrws, bolts, lag scrws), and thus th wood baring capacity is dscribd by a matrial proprty calld th dowl baring strngth. Load (kn) Slip in joint (in.) Th yild mod quations (Tabl 7 5) ar ntrd with th dowl baring strngth and dimnsions of th wood mmbrs and th bnding yild strngth and diamtr of th fastnr. Th dowl baring strngth of th wood is xprimntally dtrmind by comprssing a dowl into a wood mmbr. Th strngth basis is th load rprsnting a 5% diamtr offst on th load dformation curv (Fig. 7 3). Dowl baring strngth F (Pa, lb/in ) is mpirically rlatd to spcific gravity G by F F x fastnr Slip in joint (mm) diamtr Yild strngth 184. =114. 5G 184. =16, 6G 8d common nail Figur 7 3. Typical rlation btwn latral load and slip in th joint and 5% offst dfinition. (mtric) (inch pound) whr spcific gravity is basd on ovndry wight and volum Load (lb) (7 3a) (7 3b) Spacing End distanc, dg distanc, and spacing of nails should b such as to prvnt unusual splitting. As a gnral rul, nails should b drivn no closr to th dg of th sid mmbr than on-half its thicknss and no closr to th nd than th thicknss of th pic. Smallr nails can b drivn closr to th dgs or nds than largr ons bcaus thy ar lss likly to split th wood. Grain Dirction Effcts Th latral load for sid-grain nailing applis whthr th load is in a dirction paralll to th grain of th pics joind or at right angls to it. Whn nails ar drivn into th nd grain (paralll with th wood fibrs), limitd data on softwood spcis indicat that thir maximum rsistanc to latral displacmnt is about two-thirds that for nails drivn into th sid grain. Although th avrag proportional limit loads appar to b about th sam for nd- and sid-grain nailing, th individual rsults ar mor rratic for nd-grain nailing, and th minimum loads approach only 75% of corrsponding valus for sid-grain nailing

7 (a) (b) (Not applicabl) Mod I m Mod I s Mod II Mod I m Mod I s Mod II (Not applicabl) Mod III m Mod III s Mod IV Mod III m Mod III s Mod IV Figur 7 4. Various combinations of wood-baring and fastnr-bnding yilds for (a) two-mmbr connctions and (b) thr-mmbr connctions. Moistur Contnt Effcts Nails drivn into th sid grain of unsasond wood giv maximum latral rsistanc loads approximatly qual to thos obtaind in sasond wood, but th latral rsistanc loads at.38 mm (.15 in.) joint slip ar somwhat lss. To prvnt xcssiv dformation, latral loads obtaind for sasond wood should b rducd by 5% for unsasond wood that will rmain wt or b loadd bfor sasoning taks plac. Whn nails ar drivn into grn wood, thir latral proportional limit loads aftr th wood has sasond ar also lss than whn thy ar drivn into sasond wood and loadd. Th rratic bhavior of a naild joint that has undrgon on or mor moistur contnt changs maks it difficult to stablish a latral load for a naild joint undr ths conditions. Structural joints should b inspctd at intrvals, and if it is apparnt that th joint has loosnd during drying, th joint should b rinforcd with additional nails. Dformd-Shank Nails Dformd-shank nails carry somwhat highr maximum latral loads than do th sam pnnywight common wir nails, but both prform similarly at small distortions in th joint. It should b notd that th sam pnnywight dformd-shank nail has a diffrnt diamtr than that of th common wir nail. Ths nails oftn hav highr bnding yild strngth than common wir nails, rsulting in highr latral strngth in mods III and IV. Latral Load Slip Modls A considrabl amount of work has bn don to dscrib, by mathmatical modls, th latral load slip curv of nails. Ths modls hav bcom important bcaus of thir nd as input paramtrs for advancd mthods of structural analysis. On thortical modl, which considrs th nail to b a bam supportd on an lastic foundation (th wood), dscribs th initial slop of th curv: δ= P + ( J J ) ( L L ) 1 1 ( K1+ K) (7 4) whr P is th latral load and δ is th joint slip. Th factors L 1, L, J 1, J, K 1, and K (Tabl 7 6) ar combinations of hyprbolic and trigonomtric functions of th quantitis λ 1 a and λ b in which a and b ar th dpth of pntration of th nail in mmbrs 1 and, rspctivly. For smooth round nails, 4 k λ = (7 5) 3 πed whr k is lastic baring constant, D nail diamtr, and E modulus of lasticity of th nail. For sasond wood, th lastic baring constant k (N/mm 3, lb/in 3 ) has bn shown to b rlatd to avrag spcis spcific gravity G if no lad hol is usd by k = 58G (mtric) (7 6a) k =, 144, G (inch pound (7 6b) If a prbord lad hol qual to 9% of th nail diamtr is usd, k = 869G (mtric) (7 7a) k = 3,, G (inch pound) (7 7b) Othr mpirically drivd modls attmpt to dscrib th ntir load slip curv. On such xprssion is P = A log 1 ( 1+ Bδ ) (7 8) whr th paramtrs A and B ar mpirically fittd. 7 7

8 Tabl 7 5. Th 5% offst latral yild strngth (Z) for nails and scrws for a two-mmbr joint Mod Z valu for nails Z valu for scrws I s III m III s IV Dfinitions D Spiks Dt F s s Dt F s s k1dpf 1+ R kdtf s + R D m m FmFyb 31 ( + R ) Common wir spiks ar manufacturd in th sam mannr as common wir nails. Thy hav ithr a chisl point or a diamond point and ar mad in lngths of 76 to 35 mm (3 to 1 in.). For corrsponding lngths in th rang of 76 to 15 (3 to 6 in.), thy hav largr diamtrs (Tabl 7 7) than common wir nails, and byond th 6d siz thy ar usually dsignatd by diamtr. kdtf 3 s + R m 175. FmF D 31 ( + R ) nail, spik, or scrw diamtr, mm (in.) (for annularly thradd nails, D is thrad-root diamtr; for scrws, D is ithr th shank diamtr or th root diamtr if th thradd portion of th scrw is in th shar plan) F m dowl baring strss of main mmbr (mmbr holding point), kpa (lb/in ) F s dowl baring strss of sid mmbr, kpa (lb/in ) F yb bnding yild strss of nail, spik, or scrw, kpa (lb/in ) p pntration of nail or spik in main mmbr, mm (in.) t s thicknss of sid mmbr, mm (in.) Z offst latral yild strngth R = F m /F s k k k 1 3 Fyb( 1+ R ) D = 1+ ( 1+ R) + 3F p = 1+ = 1+ m 1 ( + R ) F ( + R ) D yb + R 3F t m s 1 ( + R ) F ( + R ) D yb + R F t m s yb Tabl 7 6. Exprssions for factors in Equation (7 4) Factor Th withdrawal and latral rsistanc quations and limitations givn for common wir nails ar also applicabl to spiks, xcpt that in calculating th withdrawal load for spiks, th dpth of pntration is takn as th lngth of th spik in th mmbr rciving th point, minus two-thirds th lngth of th point. Stapls Exprssion a L1 λ1 sinhλ1a cosh λ1a sinλ1a cos λ1a k 1 sinh λ1a sin λ1a L λ sinhλb cosh λb sinλb cos λb k sinh λb sin λb J1 λ1 sinh λ1a + sin λ1a k 1 sinh λ1a sin λ1a J λ sinh λb + sin λb k sinh λb sin λb K1 3 λ1 sinhλ1a cosh λ1a + sinλ1a cos λ1a k 1 sinh λ1a sin λ1a K 3 λ sinhλb cosh λb + sinλb cos λb k sinh λb sin λb a k 1 = k 1 d and k = k d, whr k 1 and k ar th foundation moduli of mmbrs 1 and, rspctivly. Diffrnt typs of stapls hav bn dvlopd with various modifications in points, shank tratmnt and coatings, gaug, crown width, and lngth. Ths fastnrs ar availabl in clips or magazins for us in pnumatically opratd portabl staplrs. Most factors that affct th withdrawal and latral loads of nails similarly affct th loads on stapls. Th withdrawal rsistanc, for xampl, varis almost dirctly with th circumfrnc and dpth of pntration whn th typ of point and shank ar similar to nails. Thus, Equation (7 1) has bn usd to prdict th withdrawal load for on lg of a stapl, but no vrification tsts hav bn don. Th load in latral rsistanc varis approximatly as th 3/ powr of th diamtr whn othr factors, such as quality of mtal, typ of shank, and dpth of pntration, ar similar to nails. Th diamtr of ach lg of a two-lggd stapl must thrfor b about two-thirds th diamtr of a nail to provid a comparabl load. Equation (7 ) has bn usd to prdict th latral rsistanc of stapls. Howvr, yild modl thory quations hav not yt bn xprimntally vrifid for stapls. 7 8

9 Tabl 7 7. Sizs of common wir spiks Lngth Diamtr Siz (mm (in.)) (mm (in.)) 1d 76. (3) 4.88 (.19) 1d 8.6 (3-1/4) 4.88 (.19) 16d 88.9 (3-1/) 5.6 (.7) d 11.6 (4) 5.7 (.5) 3d (4-1/) 6. (.44) 4d 17. (5) 6.68 (.63) 5d (5-1/) 7.19 (.83) 6d 15.4 (6) 7.19 (.83) 5/16 in (7) 7.9 (.31) 3/8 in (8-1/) 9.53 (.375) In addition to th immdiat prformanc capability of stapls and nails as dtrmind by tst, factors such as corrosion, sustaind prformanc undr srvic conditions, and durability in various uss should b considrd in valuating th rlativ usfulnss of a stapld connction. Drift Bolts A drift bolt (or drift pin) is a long pin of iron or stl, with or without had or point. It is drivn into a bord hol through on timbr and into an adjacnt on, to prvnt th sparation of th timbrs connctd and to transmit latral load. Th hol in th scond mmbr is drilld sufficintly dp to prvnt th pin from hitting th bottom. Th ultimat withdrawal load of a round drift bolt or pin from th sid grain of sasond wood is givn by p= G DL (mtric) (7 9a) p= 6, 6G DL (inch pound) (7 9b) whr p is th ultimat withdrawal load (N, lb), G spcific gravity basd on th ovndry wight and volum at 1% moistur contnt of th wood, D diamtr of th drift bolt (mm, in.), and L lngth of pntration of th bolt (mm, in.). (Th NDS and LRFD us ovndry wight and volum as a basis.) This quation provids an avrag rlationship for all spcis, and th withdrawal load for som spcis may b abov or blow th quation valus. It also prsums that th bolts ar drivn into prbord hols having a diamtr 3. mm (1/8 in.) lss than th bolt diamtr. Data ar not availabl on latral rsistanc of drift bolts. Th yild modl should provid latral strngth prdiction, but th modl has not bn xprimntally vrifid for drift bolts. Dsignrs hav usd bolt data and dsign mthods basd on xprinc. This suggsts that th load for a drift bolt drivn into th sid grain of wood should not xcd, and ordinarily Gag or diamtr of shank /3 lngth should b takn as lss than, that for a bolt of th sam diamtr. Bolt dsign valus ar basd on th thicknss of th main mmbr in a joint. Thus th dpth of pntration of th drift bolt must b gratr than or qual to th mainmmbr thicknss on which th bolt dsign valu is basd. Howvr, th drift bolt should not fully pntrat its joint. Wood Scrws Th common typs of wood scrws hav flat, oval, or round hads. Th flathad scrw is most commonly usd if a flush surfac is dsird. Ovalhad and roundhad scrws ar usd for apparanc, and roundhad scrws ar usd whn countrsinking is objctionabl. Th principal parts of a scrw ar th had, shank, thrad, and cor (Fig. 7 5). Th root diamtr for most sizs of scrws avrags about two-thirds th shank diamtr. Wood scrws ar usually mad of stl, brass, othr mtals, or alloys, and may hav spcific finishs such as nickl, blud, chromium, or cadmium. Thy ar classifid according to matrial, typ, finish, shap of had, and diamtr or gaug of th shank. Currnt trnds in fastnings for wood also includ tapping scrws. Tapping scrws hav thrads th full lngth of th shank and may hav som advantag for crtain spcific uss. Withdrawal Rsistanc Cor or root diamtr Exprimntal Loads Th rsistanc of wood scrw shanks to withdrawal from th sid grain of sasond wood varis dirctly with th squar of th spcific gravity of th wood. Within limits, th withdrawal load varis dirctly with th dpth of pntration of th thradd portion and th diamtr of th scrw, providd th scrw dos not fail in tnsion. Th scrw will fail in tnsion whn its strngth is xcdd by th withdrawal strngth from th wood. Th limiting lngth to caus a tnsion failur dcrass as th dnsity of th wood incrass sinc th withdrawal strngth of th wood incrass with dnsity. Th longr lngths of standard scrws ar thrfor suprfluous in dns hardwoods. Lngth A B C Figur 7 5. Common typs of wood scrws: A, flathad; B, roundhad; and C, ovalhad. 7 9

10 Th withdrawal rsistanc of typ A tapping scrws, commonly calld sht mtal scrws, is in gnral about 1% gratr than that for wood scrws of comparabl diamtr and lngth of thradd portion. Th ratio btwn th withdrawal rsistanc of tapping scrws and wood scrws varis from 1.16 in dnsr woods, such as oak, to 1.5 in lightr woods, such as rdwood. Ultimat tst valus for withdrawal loads of wood scrws insrtd into th sid grain of sasond wood may b xprssd as p=18. 5G DL (mtric) (7 1a) p=15, 7G DL (inch pound) (7 1b) whr p is maximum withdrawal load (N, lb), G spcific gravity basd on ovndry wight and volum at 1% moistur contnt, D shank diamtr of th scrw (mm, in.), and L lngth of pntration of th thradd part of th scrw (mm, in.). (Th NDS and LRFD us ovndry wight and volum as a basis.) Ths valus ar basd on raching ultimat load in 5- to 1-min. This quation is applicabl whn scrw lad hols hav a diamtr of about 7% of th root diamtr of th thrads in softwoods, and about 9% in hardwoods. Th quation valus ar applicabl to th scrw sizs listd in Tabl 7 8. (Shank diamtrs ar rlatd to scrw gaugs.) For lngths and gaugs outsid ths limits, th actual valus ar likly to b lss than th quation valus. Th withdrawal loads of scrws insrtd in th nd grain of wood ar somwhat rratic, but whn splitting is avoidd, thy should avrag 75% of th load sustaind by scrws insrtd in th sid grain. Lubricating th surfac of a scrw with soap or similar lubricant is rcommndd to facilitat insrtion, spcially in dns woods, and it will hav littl ffct on ultimat withdrawal rsistanc. Tabl 7 8. Scrw sizs appropriat for Equation (7 1) Scrw lngth (mm (in.)) Gaug limits 1.7 (1/) 1 to (3/4) to (1) 3 to (1-1/) 5 to () 7 to (-1/) 9 to (3) 1 to Fastning of Particlboard Tapping scrws ar commonly usd in particlboard whr withdrawal strngth is important. Car must b takn whn tightning scrws in particlboard to avoid stripping th thrads. Th maximum amount of torqu that can b applid to a scrw bfor th thrads in th particlboard ar strippd is givn by T = X (mtric) (7 11a) T = X (inch pound) (7 11b) whr T is torqu (N m, in lb) and X is dnsity of th particlboard (kg/m 3, lb/ft 3 ). Equation (7 11) is for 8-gaug scrws with a dpth of pntration of 15.9 mm (5/8 in.). Th maximum torqu is fairly constant for lad hols of to 9% of th root diamtr of th scrw. Ultimat withdrawal loads P (N, lb) of scrws from particlboard can b prdictd by 1 / 54 / P = KD ( L D 3) G (7 1) whr D is shank diamtr of th scrw (mm, in.), L dpth of mbdmnt of th thradd portion of th scrw (mm, in.), and G spcific gravity of th board basd on ovndry wight and volum at currnt moistur contnt. For mtric masurmnts, K = 41.1 for withdrawal from th fac of th board and K = 31.8 for withdrawal from th dg; for inch pound masurmnts, K =,655 for withdrawal from th fac and K =,55 for withdrawal from th dg. Equation (7 1) applis whn th stting torqu is btwn 6% to 9% of T (Eq. ( 7 11)). Withdrawal rsistanc of scrws from particlboard is not significantly diffrnt for lad hols of 5% to 9% of th root diamtr. A highr stting torqu will produc a somwhat highr withdrawal load, but thr is only a slight diffrnc (3%) in valus btwn 6% to 9% stting torqus (Eq. (7 11)). A modst tightning of scrws in many cass provids an ffctiv compromis btwn optimizing withdrawal rsistanc and stripping thrads. Equation (7 1) can also prdict th withdrawal of scrws from fibrboard with K = 57.3 (mtric) or 3,7 (inch pound) for th fac and K = 44.3 (mtric) or,86 (inch pound) for th dg of th board. Latral Rsistanc Pr-1991 Th proportional limit loads obtaind in tsts of latral rsistanc for wood scrws in th sid grain of sasond wood ar givn by th mpirical quation p= KD (7 13) whr p is latral load, D diamtr of th scrw shank, and K a cofficint dpnding on th inhrnt charactristics of th wood spcis. Valus of scrw shank diamtrs for various scrw gaugs ar listd in Tabl

11 Tabl 7 9. Scrw shank diamtrs for various scrw gaugs Scrw numbr Diamtr or gaug (mm (in.)) 4.84 (.11) (.15) (.138) (.151) (.164) (.177) (.19) (.3) (.16) (.4) (.68) (.94) 8.13 (.3) (.37) Valus of K ar basd on rangs of spcific gravity of hardwoods and softwoods and ar givn in Tabl 7 4. Thy apply to wood at about 15% moistur contnt. Loads computd by substituting ths constants in th quation ar xpctd to hav a slip of.18 to.5 mm (.7 to.1 in.), dpnding somwhat on th spcis and dnsity of th wood. Equation (7 13) applis whn th dpth of pntration of th scrw into th block rciving th point is not lss than svn tims th shank diamtr and whn th sid mmbr and th main mmbr ar approximatly of th sam dnsity. Th thicknss of th sid mmbr should b about on-half th dpth of pntration of th scrw in th mmbr holding th point. Th nd distanc should b no lss than th sid mmbr thicknss, and th dg distancs no lss than onhalf th sid mmbr thicknss. This dpth of pntration (svn tims shank diamtr) givs an ultimat load of about four tims th load obtaind by th quation. For a dpth of pntration of lss than svn tims th shank diamtr, th ultimat load is rducd about in proportion to th rduction in pntration, and th load at th proportional limit is rducd somwhat lss rapidly. Whn th dpth of pntration of th scrw in th holding block is four tims th shank diamtr, th maximum load will b lss than thr tims th load xprssd by th quation, and th proportional limit load will b approximatly qual to that givn by th quation. Whn th scrw holds mtal to wood, th load can b incrasd by about 5%. For ths latral loads, th part of th lad hol rciving th shank should b th sam diamtr as th shank or slightly smallr; that part rciving th thradd portion should b th sam diamtr as th root of th thrad in dns spcis or slightly smallr than th root in low-dnsity spcis. Scrws should always b turnd in. Thy should nvr b startd or drivn with a hammr bcaus this practic tars th wood fibrs and injurs th scrw thrads, sriously rducing th load carrying capacity of th scrw. Post-1991 Scrw latral strngth is dtrmind by th yild modl thory (Tabl 7 5). Mods I, III, and IV failurs may occur (Fig. 7 4). Th dowl baring strngth valus ar basd on th sam spcific gravity quation usd to stablish valus for nails (Eq. (7 3)). Furthr discussion of scrw latral strngth is found in ASCE Manual No. 84, Mchanical Connctions in Wood Structurs. Lag Scrws Lag scrws ar commonly usd bcaus of thir convninc, particularly whr it would b difficult to fastn a bolt or whr a nut on th surfac would b objctionabl. Commonly availabl lag scrws rang from about 5.1 to 5.4 mm (. to 1 in.) in diamtr and from 5.4 to 46 mm (1 to 16 in.) in lngth. Th lngth of th thradd part varis with th lngth of th scrw and rangs from 19. mm (3/4 in.) with th 5.4- and 31.8-mm (1- and 1-1/4-in.) scrws to half th lngth for all lngths gratr than 54 mm (1 in.). Lag scrws hav a hxagonal-shapd had and ar tightnd by a wrnch (as opposd to wood scrws, which hav a slottd had and ar tightnd by a scrw drivr). Th following quations for withdrawal and latral loads ar basd on lag scrws having a bas mtal avrag tnsil yild strngth of about 31.3 MPa (45, lb/in ) and an avrag ultimat tnsil strngth of 53.9 MPa (77, lb/in ). Withdrawal Rsistanc Th rsults of withdrawal tsts hav shown that th maximum dirct withdrawal load of lag scrws from th sid grain of sasond wood may b computd as 3 / 34 / p=15. 4G D L 3 / 34 / p=8, 1G D L (mtric) (inch pound) (7 14a) (7 14b) whr p is maximum withdrawal load (N, lb), D shank diamtr (mm, in.), G spcific gravity of th wood basd on ovndry wight and volum at 1% moistur contnt, and L lngth (mm, in.) of pntration of th thradd part. (Th NDS and LRFD us ovndry wight and volum as a basis.) Equation (7 14) was dvlopd indpndntly of Equation (7 1) but givs approximatly th sam rsults. Lag scrws, lik wood scrws, rquir prbord hols of th propr siz (Fig. 7 6). Th lad hol for th shank should b th sam diamtr as th shank. Th diamtr of th lad hol for th thradd part varis with th dnsity of th wood: For low-dnsity softwoods, such as th cdars and whit pins, 4% to 7% of th shank diamtr; for Douglas-fir and Southrn Pin, 6% to 75%; and for dns hardwoods, such as oaks, 65% to 85%. Th smallr prcntag in ach rang applis to lag scrws of th smallr diamtrs and th largr 7 11

12 Tabl 7 1. Multiplication factors for loads computd from Equation (7 15) Figur 7 6. A, Clan-cut, dp pntration of thrad mad by lag scrw turnd into a lad hol of propr siz, and B, rough, shallow pntration of thrad mad by lag scrw turnd into ovrsizd lad hol. prcntag to lag scrws of largr diamtrs. Soap or similar lubricants should b usd on th scrw to facilitat turning, and lad hols slightly largr than thos rcommndd for maximum fficincy should b usd with long scrws. In dtrmining th withdrawal rsistanc, th allowabl tnsil strngth of th lag scrw at th nt (root) sction should not b xcdd. Pntration of th thradd part to a distanc about svn tims th shank diamtr in th dnsr spcis (spcific gravity gratr than.61) and 1 to 1 tims th shank diamtr in th lss dns spcis (spcific gravity lss than.4) will dvlop approximatly th ultimat tnsil strngth of th lag scrw. Pntrations at intrmdiat dnsitis may b found by straight-lin intrpolation. Th rsistanc to withdrawal of a lag scrw from th ndgrain surfac of a pic of wood is about thr-fourths as grat as its rsistanc to withdrawal from th sid-grain surfac of th sam pic. Latral Rsistanc Pr-1991 Th xprimntally dtrmind latral loads for lag scrws insrtd in th sid grain and loadd paralll to th grain of a pic of sasond wood can b computd as p= KD (7 15) whr p is proportional limit latral load (N, lb) paralll to th grain, K a cofficint dpnding on th spcis spcific gravity, and D shank diamtr of th lag scrw (mm, in.). Valus of K for a numbr of spcific gravity rangs can b found in Tabl 7 4. Ths cofficints ar basd on avrag rsults for svral rangs of spcific gravity for hardwoods and softwoods. Th loads givn by this quation apply whn th thicknss of th sid mmbr is 3.5 tims th shank diamtr of th lag scrw, and th dpth of pntration in th main Ratio of thicknss of sid mmbr to shank diamtr of lag scrw Factor Tabl Multiplication factors for loads applid prpndicular to grain computd from Equation (7 15) with lag scrw in sid grain of wood Shank diamtr of lag scrw (mm (in.)) Factor 4.8 (3/16) (1/4) (5/16) (3/8) (7/16) (1/) (5/8) (3/4).55. (7/8) (1).5 mmbr is svn tims th diamtr in th hardr woods and 11 tims th diamtr in th softr woods. For othr thicknsss, th computd loads should b multiplid by th factors listd in Tabl 7 1. Th thicknss of a solid wood sid mmbr should b about on-half th dpth of pntration in th main mmbr. Whn th lag scrw is insrtd in th sid grain of wood and th load is applid prpndicular to th grain, th load givn by th latral rsistanc quation should b multiplid by th factors listd in Tabl For othr angls of loading, th loads may b computd from th paralll and prpndicular valus by th us of th Scholtn nomograph for dtrmining th baring strngth of wood at various angls to th grain (Fig. 7 7). 7 1

13 Y P QN Load or strss paralll to grain Load or strss prpndicular to grain Load of strss at inclination θ with dirction of grain 45 b 3 15 X a Allowabl load or strss for P, Q, and N in units, tns, hundrds, or thousands Figur 7 7. Scholtn nomograph for dtrmining th baring strss of wood at various angls to th grain. Th dashd lin ab rfrs to th xampl givn in th txt. Th nomograph provids valus as givn by th Hankinson quation, PQ N = (7 16) Psin θ+ Qcos θ whr P is load or strss paralll to th grain, Q load or strss prpndicular to th grain, and N load or strss at an inclination θ with th dirction of th grain. Exampl: P, th load paralll to grain, is 6, lb, and Q, th load prpndicular to th grain, is, lb. Th load at an angl of 4 to grain, N, is found as follows: Connct with a straight lin 6, lb (a) on lin OX of th nomograph with th intrsction (b) on lin OY of a vrtical lin through, lb. Th point whr lin ab intrscts th lin rprsnting th givn angl 4 is dirctly abov th load, 3,3 lb. Valus for latral rsistanc as computd by th prcding mthods ar basd on complt pntration of th unthradd shank into th sid mmbr but not into th main mmbr. Whn th shank pntrats th main mmbr, th prmittd incrass in loads ar givn in Tabl 7 1. Whn lag scrws ar usd with mtal plats, th latral loads paralll to th grain may b incrasd 5%, providd th plat thicknss is sufficint so that th baring capacity of th stl is not xcdd. No incras should b mad whn th applid load is prpndicular to th grain. Lag scrws should not b usd in nd grain, bcaus splitting may dvlop undr latral load. If lag scrws ar so usd, howvr, th loads should b takn as two-thirds thos for latral rsistanc whn lag scrws ar insrtd into sid grain and th loads act prpndicular to th grain. Th spacings, nd and dg distancs, and nt sction for lag scrw joints should b th sam as thos for joints with bolts (discussd latr) of a diamtr qual to th shank diamtr of th lag scrw. Lag scrws should always b insrtd by turning with a wrnch, not by driving with a hammr. Soap, bswax, or othr lubricants applid to th scrw, particularly with th dnsr wood spcis, will facilitat insrtion and prvnt damag to th thrads but will not affct prformanc of th lag scrw. Post-1991 Lag scrw latral strngth is dtrmind by th yild modl thory tabl similar to th procdur for bolts. Mods I, III, and IV yild may occur (Fig. 7 4). Th dowl baring Tabl 7 1. Prmittd incrass in loads whn lag scrw unthradd shank pntrats foundation mmbr Ratio of pntration of shank into foundation mmbr to shank diamtr Incras in load (%)

14 strngth valus ar basd on th sam paralll- and prpndicular-to-grain spcific gravity quations usd to stablish valus for bolts. Bolts Baring Strss of Wood Undr Bolts Th baring strss undr a bolt is computd by dividing th load on a bolt by th product LD, whr L is th lngth of a bolt in th main mmbr and D is th bolt diamtr. Basic paralll-to-grain and prpndicular-to-grain baring strsss hav bn obtaind from tsts of thr-mmbr wood joints whr ach sid mmbr is half th thicknss of th main mmbr. Th sid mmbrs wr loadd paralll to grain for both paralll- and prpndicular-to-grain tsts. Prior to 1991, baring strss was basd on tst rsults at th proportional limit; sinc 1991, baring strss is basd on tst rsults at a yild limit stat, which is dfind as th 5% diamtr offst on th load dformation curv (similar to Fig. 7 3). Th baring strss at proportional limit load is largst whn th bolt dos not bnd, that is, for joints with small L/D valus. Th curvs of Figurs 7 8 and 7 9 show th rduction in proportional limit bolt-baring strss as L/D incrass. Th baring strss at maximum load dos not dcras as L/D incrass, but rmains fairly constant, which mans that th ratio of maximum load to proportional limit load incrass as L/D incrass. To maintain a fairly constant ratio btwn maximum load and dsign load for bolts, th rlations btwn baring strss and L/D ratio hav bn adjustd as indicatd in Figurs 7 8 and 7 9. Th proportional limit bolt-baring strss paralll to grain for small L/D ratios is approximatly 5% of th small clar crushing strngth for softwoods and approximatly 6% for hardwoods. For baring strss prpndicular to th grain, th ratio btwn baring strss at proportional limit load and th small clar proportional limit strss in comprssion prpndicular to grain dpnds upon bolt diamtr (Fig. 7 1) for small L/D ratios. Spcis comprssiv strngth also affcts th L/D ratio rlationship, as indicatd in Figur 7 9. Rlativly highr bolt proportional-limit strss prpndicular to grain is obtaind with wood low in strngth (proportional limit strss of 3,93 kpa (57 lb/in ) than with matrial of high strngth (proportional limit strss of 7,86 kpa (1,14 lb/in )). This ffct also occurs for bolt-baring strss paralll to grain, but not to th sam xtnt as for prpndicular-to-grain loading. Th proportional limit bolt load for a thr-mmbr joint with sid mmbrs half th thicknss of th main mmbr may b stimatd by th following procdurs. For paralll-to-grain loading, (a) multiply th spcis small clar comprssiv paralll strngth (Tabls 4 3, 4 4, or 4 5) by.5 for softwoods or.6 for hardwoods, (b) multiply this product by th appropriat factor from Figur 7 8 for th L/D ratio of th bolt, and (c) multiply this product by LD. Ratio of long- to short-bolt baring strss (%) For prpndicular-to-grain loading, (a) multiply th spcis comprssion prpndicular-to-grain proportional limit strss (Tabls 4 3, 4 4, or 4 5) by th appropriat factor from Figur 7 1, (b) multiply this product by th appropriat factor from Figur 7 9, and (c) multiply this product by LD. Loads at an Angl to th Grain A L/D ratio Figur 7 8. Variation in bolt-baring strss at th proportional limit paralll to grain with L/D ratio. Curv A, rlation obtaind from xprimntal valuation; curv B, modifid rlation usd for stablishing dsign loads. Ratio of long- to short-bolt baring strss (%) A-1 A- B-1 B L/D ratio Figur 7 9. Variation in bolt-baring strss at th proportional limit prpndicular to grain with L/D ratio. Rlations obtaind from xprimntal valuation for matrials with avrag comprssion prpndicular strss of 7,86 kpa (1,14 lb/in ) (curv A 1) and 3,93 kpa (57 lb/in ) (curv A ). Curvs B 1 and B, modifid rlations usd for stablishing dsign loads. For loads applid at an angl intrmdiat btwn thos paralll to th grain and prpndicular to th grain, th boltbaring strss may b obtaind from th nomograph in Figur 7 7. B 7 14

15 Ratio of bolt baring strss to comprssion prpndicular to grain proportional limit strss Stl Sid Plats Whn stl sid plats ar usd, th bolt-baring strss paralll to grain at joint proportional limit is approximatly 5% gratr than that for wood sid plats. Th joint dformation at proportional limit is much smallr with stl sid plats. If loads at quivalnt joint dformation ar compard, th load for joints with stl sid plats is approximatly 75% gratr than that for wood sid plats. Pr-1991 dsign critria includd incrass in connction strngth with stl sid plats; post-1991 dsign critria includ stl sid plat bhavior in th yild modl quations. For prpndicular-to-grain loading, th sam loads ar obtaind for wood and stl sid plats. Bolt Quality Bolt diamtr (in.) Bolt diamtr (mm) Figur 7 1. Baring strss prpndicular to th grain as affctd by bolt diamtr. Both th proprtis of th wood and th quality of th bolt ar factors in dtrmining th strngth of a boltd joint. Th prcntags givn in Figurs 7 8 and 7 9 for calculating baring strss apply to stl machin bolts with a yild strss of 31 MPa (45, lb/in ). Figur 7 11 indicats th incras in baring strss paralll to grain for bolts with a yild strss of 86 MPa (15, lb/in ). Effct of Mmbr Thicknss Th proportional limit load is affctd by th ratio of th sid mmbr thicknss to th main mmbr thicknss (Fig. 7 1). Pr-1991 dsign valus for bolts ar basd on joints with th sid mmbr half th thicknss of th main mmbr. Th usual practic in dsign of boltd joints is to tak no incras in dsign load whn th sid mmbrs ar gratr than half th thicknss of th main mmbr. Whn th sid mmbrs ar lss than half th thicknss of th main mmbr, a dsign Ratio of long- to short-bolt baring strss (%) L/D ratio Figur Variation in th proportional limit boltbaring strss paralll to grain with L/D ratio. Curv A, bolts with yild strss of MPa (15, lb/in ); curv B, bolts with yild strss of 31.6 MPa (45, lb/in ). Ratio to joint with sid mmbr half th thicknss of main mmbr load for a main mmbr that is twic th thicknss of th sid mmbr is usd. Post-1991 dsign valus includ mmbr thicknss dirctly in th yild modl quations. Two-Mmbr, Multipl-Mmbr Joints In pr-1991 dsign, th proportional limit load was takn as half th load for a thr-mmbr joint with a main mmbr th sam thicknss as th thinnst mmbr for two-mmbr joints. For four or mor mmbrs in a joint, th proportional limit load was takn as th sum of th loads for th individual shar plans by trating ach shar plan as an quivalnt two-mmbr joint. A B L/D =.67 L/D = 4. L/D = Sid mmbr thicknss/main mmbr thicknss Figur 7 1. Proportional limit load rlatd to sid mmbr thicknss for thr-mmbr joints. Cntr mmbr thicknss was 5.8 mm ( in.). 7 15

16 Post-1991 dsign for joints with four or mor mmbrs also rsults in valus pr shar plan. Connction strngth for any numbr of mmbrs is consrvativly found by multiplying th valu for th wakst shar plan by th numbr of shar plans. Spacing, Edg, and End Distanc Th cntr-to-cntr distanc along th grain should b at last four tims th bolt diamtr for paralll-to-grain loading. Th minimum cntr-to-cntr spacing of bolts in th across-th-grain dirction for loads acting through mtal sid plats and paralll to th grain nd only b sufficint to prmit th tightning of th nuts. For wood sid plats, th spacing is controlld by th ruls applying to loads acting paralll to grain if th dsign load approachs th boltbaring capacity of th sid plats. Whn th dsign load is lss than th bolt-baring capacity of th sid plats, th spacing may b rducd blow that rquird to dvlop thir maximum capacity. Whn a joint is in tnsion, th bolt narst th nd of a timbr should b at a distanc from th nd of at last svn tims th bolt diamtr for softwoods and fiv tims for hardwoods. Whn th joint is in comprssion, th nd margin may b four tims th bolt diamtr for both softwoods and hardwoods. Any dcras in ths spacings and margins will dcras th load in about th sam ratio. For bolts baring paralll to th grain, th distanc from th dg of a timbr to th cntr of a bolt should b at last 1.5 tims th bolt diamtr. This margin, howvr, will usually b controlld by (a) th common practic of having an dg margin qual to on-half th distanc btwn bolt rows and (b) th ara rquirmnts at th critical sction. (Th critical sction is that sction of th mmbr takn at right angls to th dirction of load, which givs th maximum strss in th mmbr basd on th nt ara rmaining aftr rductions ar mad for bolt hols at that sction.) For paralll-to-grain loading in softwoods, th nt ara rmaining at th critical sction should b at last 8% of th total ara in baring undr all th bolts in th particular joint undr considration; in hardwoods it should b 1%. For bolts baring prpndicular to th grain, th margin btwn th dg toward which th bolt prssur is acting and th cntr of th bolt or bolts narst this dg should b at last four tims th bolt diamtr. Th margin at th opposit dg is rlativly unimportant. Effct of Bolt Hols Th baring strngth of wood undr bolts is affctd considrably by th siz and typ of bolt hols into which th bolts ar insrtd. A bolt hol that is too larg causs nonuniform baring of th bolt; if th bolt hol is too small, th wood will split whn th bolt is drivn. Normally, bolts should fit so that thy can b insrtd by tapping lightly with a wood mallt. In gnral, th smoothr th hol, th highr th baring valus will b (Fig. 7 13). Dformations Figur Effct of rat of fd and drill spd on th surfac condition of bolt hols drilld in Sitka spruc. A, hol was bord with a twist drill rotating at a priphral spd of 7.6 m/min (3 in/min); fd rat was 1.5 m/min (6 in/min). B, hol was bord with th sam drill at a priphral spd of m/min (1,5 in/min); fd rat was 5.8 mm/min ( in/min). Load (kn) Dformation (in.) Slow fd Fast fd Dformation (mm) Figur Typical load dformation curvs showing th ffct of surfac condition of bolt hols, rsulting from a slow fd rat and a fast fd rat, on th dformation in a joint whn subjctd to loading undr bolts. Th surfac conditions of th bolt hols wr similar to thos illustratd in Figur accompanying th load ar also lss with a smoothr bolthol surfac (Fig. 7 14). Load (x1 3 lb) Rough hols ar causd by using dull bits and impropr rats of fd and drill spd. A twist drill opratd at a priphral spd of approximatly 38 m/min (1,5 in/min) producs uniformly smooth hols at modrat fd rats. Th rat of fd dpnds upon th diamtr of th drill and th spd of 7 16

17 rotation but should nabl th drill to cut rathr than tar th wood. Th drill should produc shavings, not chips. Proportional limit loads for joints with bolt hols th sam diamtr as th bolt will b slightly highr than for joints with a 1.6-mm (1/16-in.) ovrsizd hol. Howvr, if drying taks plac aftr assmbly of th joint, th proportional limit load for snug-fitting bolts will b considrably lss du to th ffcts of shrinkag. Pr-1991 Allowabl Loads Th following procdurs ar usd to calculat allowabl bolt loads for joints with wood sid mmbrs, ach half th thicknss of th main mmbr. Paralll to Grain Th starting point for paralll-to-grain bolt valus is th maximum grn crushing strngth for th spcis or group of spcis. Procdurs outlind in ASTM D555 ar usd to stablish a 5% xclusion valu. Th xclusion valu is dividd by a factor of 1.9 to adjust to a 1-yar normal duration of load and provid a factor of safty. This valu is multiplid by 1. to adjust to a sasond strngth. Th rsulting valu is calld th basic bolt-baring strss paralll to grain. Th basic bolt-baring strss is thn adjustd for th ffcts of L/D ratio. Tabl 7 13 givs th prcntag of basic strss for thr classs of spcis. Th particular class for th spcis is dtrmind from th basic bolt-baring strss as indicatd in Tabl Th adjustd baring strss is furthr multiplid Tabl Prcntag of basic bolt-baring strss usd for calculating allowabl bolt loads Ratio L/D adjustmnt factor by class a of bolt lngth to Paralll to grain Prpndicular to grain diamtr (L/D) a Class dtrmind from basic bolt-baring strss according to Tabl Tabl L/D adjustmnt class associatd with basic bolt-baring strss Basic bolt-baring strss for spcis group (MPa (lb/in )) Loading dirction Softwoods Hardwoods L/D adjustmnt (Tabl 7 13) Paralll <7.93 (<1,15) <7.33 (<1,63) (1,15 1,54) (1,63 1,389) >1.37 (>1,54) >9.58 (>1,389) 3 Prpndicular <1.31 (<19) <1.44 (<9) (19 9) (9 319)..59 (91 375).1.84 (3 41) 3 >.59 (>375) >.84 (>41)

18 by a factor of.8 to adjust to wood sid plats. Th allowabl bolt load in pounds is thn dtrmind by multiplying by th projctd bolt ara, LD. Prpndicular to Grain Th starting point for prpndicular-to-grain bolt valus is th avrag grn proportional limit strss in comprssion prpndicular to grain. Procdurs in ASTM D555 ar usd to stablish comprssion prpndicular valus for groups of spcis. Th avrag proportional limit strss is dividd by 1.5 for ring position (growth rings nithr paralll nor prpndicular to load during tst) and a factor of safty. This valu is thn multiplid by 1. to adjust to a sasond strngth and by 1.1 to adjust to a normal duration of load. Th rsulting valu is calld th basic bolt-baring strss prpndicular to grain. Th basic bolt-baring strss is thn adjustd for th ffcts of bolt diamtr (Tabl 7 15) and L/D ratio (Tabl 7 13). Th allowabl bolt load is thn dtrmind by multiplying th adjustd basic bolt-baring strss by th projctd bolt ara, LD. Post-1991 Yild Modl Th mpirical dsign approach usd prior to 1991 was basd on a tabular valu for a singl bolt in a wood-to-wood, thrmmbr connction whr th sid mmbrs ar ach a minimum of on-half th thicknss of th main mmbr. Th singl-bolt valu must thn b modifid for any variation from ths rfrnc conditions. Th thortical approach, aftr 1991, is mor gnral and is not limitd to ths rfrnc conditions. Th thortical approach is basd on work don in Europ (Johansn 1949) and is rfrrd to as th Europan Yild Modl (EYM). Th EYM dscribs a numbr of possibl yild mods that can occur in a dowl-typ connction (Fig. 7 4). Th yild strngth of ths diffrnt mods is dtrmind from a static analysis that assums th wood and th bolt ar both prfctly plastic. Th yild mod that rsults in th lowst yild load for a givn gomtry is th thortical connction yild load. Equations corrsponding to th yild mods for a thrmmbr joint ar givn in Tabl (Equations for twommbr allowabl valus ar givn in th AF&PA National Dsign Spcification for Wood Construction) Th nominal singl-bolt valu is dpndnt on th joint gomtry (thicknss of main and sid mmbrs), bolt diamtr and bnding yild strngth, dowl baring strngth, and dirction of load to th grain. Th quations ar qually valid for wood or stl sid mmbrs, which is takn into account by thicknss and dowl baring strngth paramtrs. Th quations ar also valid for various load-to-grain dirctions, which ar takn into account by th K θ and F paramtr. Th dowl baring strngth is a matrial proprty not gnrally familiar to structural dsignrs. Th dowl baring strngth of th wood mmbrs is dtrmind from tsts that rlat spcis spcific gravity and dowl diamtr to baring strngth. Empirical quations for ths rlationships ar as follows: Paralll to grain F =77. G (mtric) (7 17a) F =11, G (inch pound) (7 17b) Prpndicular to grain 145. F = 1. G D F = 6, 1G D -.5 (mtric) (inch pound) (7 18a) (7 18b) whr F is dowl baring strngth (MPa, lb/in ), G spcific gravity basd on ovndry wight and volum, and D bolt diamtr (mm, in.). Connctor Joints Svral typs of connctors hav bn dvisd that incras joint baring and shar aras by utilizing rings or plats around bolts holding joint mmbrs togthr. Th primary load-carrying portions of ths joints ar th connctors; th bolts usually srv to prvnt transvrs sparation of th mmbrs but do contribut som load-carrying capacity. Th strngth of th connctor joint dpnds on th typ and siz of th connctor, th spcis of wood, th thicknss and width of th mmbr, th distanc of th connctor from th nd of th mmbr, th spacing of th connctors, th dirction of application of th load with rspct to th dirction of th grain of th wood, and othr factors. Loads for wood joints with stl connctors split ring (Fig. 7 15) and shar plat (Fig. 7 16) ar discussd in this sction. Ths connctors rquir closly fitting machind groovs in th wood mmbrs. Paralll-to-Grain Loading Tsts hav dmonstratd that th dnsity of th wood is a controlling factor in th strngth of connctor joints. For split-ring connctors, both maximum load and proportional limit load paralll to grain vary linarly with spcific gravity (Figs and 7 18). For shar plats, th maximum load and proportional limit load vary linarly with spcific gravity for th lss dns spcis (Figs and 7 ). In th highr dnsity spcis, th shar strngth of th bolts bcoms th controlling factor. Ths rlations wr obtaind for sasond mmbrs, approximatly 1% moistur contnt. Prpndicular-to-Grain Loading Loads for prpndicular-to-grain loading hav bn stablishd using thr-mmbr joints with th sid mmbrs loadd paralll to grain. Spcific gravity is a good indicator of prpndicular-to-grain strngth of timbr connctor joints. For split-ring connctors, th proportional limit loads prpndicular to grain ar 58% of th paralll-to-grain proportional limit loads. Th joint dformation at proportional limit is 3% to 5% mor than for paralll-to-grain loading. 7 18

19 Tabl Factors for adjusting basic boltbaring strss prpndicular to grain for bolt diamtr whn calculating allowabl bolt loads Bolt diamtr (mm (in.)) Adjustmnt factor 6.35 (1/4) (3/8) (1/) (5/8) (3/4) (7/8) (1) (1-1/4) (1-1/) (1-3/4) () (-1/) 1.3 >76. (>3 or ovr) 1. Figur Joint with split-ring connctor showing connctor, prcut groov, bolt, washr, and nut. Tabl Th 5% offst yild latral strngth (Z) for thr-mmbr boltd joints Mod Z valu for thrmmbr boltd joint Mod I m Mod I s DtmF K θ m Dt F K s s kd 4 t s F m Mod III s ( + R)K θ θ Mod IV D FmFyb K 31 ( + R ) θ Dfinitions D nominal bolt diamtr, mm (in.) F m dowl baring strngth of main (cntr) mmbr, kpa (lb/in ) F s dowl baring strngth of sid mmbrs, kpa (lb/in ) F yb bnding yild strngth of bolt, kpa (lb/in ) K θ 1 + θ/36 t m thicknss of main (cntr) mmbr, mm (in.) t s thicknss of sid mmbr, mm (in.) Z nominal singl bolt dsign valu θ angl of load to grain (dgrs) R = F m /F s k 4 = ( + R ) Fyb( + R ) D + R 3F mts Figur Joints with shar-plat connctors with (A) wood sid plats and (B) stl sid plats. 7 19

20 Load (kn) Maximum load Proportional limit load Dsign load Spcific gravity Figur Rlation btwn load baring paralll to grain and spcific gravity (ovndry wight, volum at tst) for two 63.5-mm (-1/-in.) split rings with a singl 1.7-mm (1/-in.) bolt in air-dry matrial. Cntr mmbr was thicknss 11.6 mm (4 in.) and sid mmbr thicknss was 5.8 mm ( in.) Load (x1 3 lb) Load (kn) 15 1 Bolt diamtr (mm(in.)) 19. (3/4) 15.9 (5/8) Spcific gravity Maximum load Proportional limit load Dsign load Figur Rlation btwn load baring paralll to grain and spcific gravity (ovndry wight, volum at tst) for two 66.7-mm (-5/8-in.) shar plats in air-dry matrial with stl sid plats. Cntr mmbr thicknss was 76. mm (3 in.) Load (x1 3 lb) Spcific gravity Figur Rlation btwn load baring paralll to grain and spcific gravity (ovndry wight, volum at tst) for two 11.6-mm (4-in.) split rings and a singl 19.1-mm- (3/4-in.-) diamtr bolt in air-dry matrial. Cntr mmbr thicknss was 17. mm (5 in.) and sid mmbr thicknss was 63.5 mm (-1/ in.). Load (kn) Maximum load Proportional limit load Dsign load Load (x1 3 lb) Load (kn) Bolt diamtr (mm(in.)) 19. (3/4) 15.9 (5/8) Maximum load Proportional limit load Dsign load Spcific gravity Figur 7. Rlation btwn load baring paralll to grain and spcific gravity (ovndry wight, volum at tst) for two 11.6-mm (4-in.) shar plats in air-dry matrial with stl sid plats. Cntr mmbr thicknss was 88.9 mm (3-1/ in.) Load (x1 3 lb) For shar-plat connctors, th proportional limit and maximum loads vary linarly with spcific gravity (Figs. 7 1 and 7 ). Th wood strngth controls th joint strngth for all spcis. Dsign Loads Dsign loads for paralll-to-grain loading hav bn stablishd by dividing ultimat tst loads by an avrag factor of 4. This givs valus that do not xcd fiv-ighths of th proportional limit loads. Th rduction accounts for variability in matrial, a rduction to long-tim loading, and a factor of safty. Dsign loads for normal duration of load ar 1% highr. For prpndicular-to-grain loading, ultimat load is givn lss considration and gratr dpndnc placd on load at proportional limit. For split rings, th proportional limit load is rducd by approximatly half. For shar plats, th dsign loads ar approximatly fiv-ighths of th proportional limit tst loads. Ths rductions again account for matrial variability, a rduction to long-tim loading, and a factor of safty. Dsign loads ar prsntd in Figurs 7 17 to 7. In practic, four wood spcis groups hav bn stablishd, basd primarily on spcific gravity, and dsign loads assignd for ach group. Spcis groupings for connctors ar prsntd in Tabl Th corrsponding dsign loads (for long-continud load) ar givn in Tabl Th National Dsign Spcification for Wood Construction givs dsign valus for normal-duration load for ths and additional spcis. 7

21 Load (kn) Bolt diamtr (mm(in.)) 19. (3/4) 15.9 (5/8) 19. or 15.9 (3/4 or 5/8) Maximum load Proportional limit load Dsign load Load (x1 3 lb) Tabl Spcis groupings for connctor loads a Connctor Spcis or spcis group Group 1 Aspn Basswood Cottonwood Wstrn Balsam fir Whit fir rdcdar Eastrn hmlock Eastrn whit pin Pondrosa pin Sugar pin Wstrn whit pin Englmann spruc Modifications Spcific gravity Figur 7 1. Rlation btwn load baring prpndicular to grain and spcific gravity (ovndry wight, volum at tst) for two 66.7-mm (-5/8-in.) shar plats in air-dry matrial with stl sid plats. Cntr mmbr thicknss was 76. mm (3 in.). Load (kn) Bolt diamtr (mm(in.)) 19. (3/4) 15.9 (5/8) 19. or 15.9 (3/4 or 5/8) Maximum load Proportional limit load Dsign load Spcific gravity Figur 7. Rlation btwn load baring prpndicular to grain and spcific gravity (ovndry wight, volum at tst) for two 11.6-mm (4-in.) shar plats in air-dry matrial with stl sid plats. Cntr mmbr thicknss was 88.9 mm (3-1/ in.). Som factors that affct th loads of connctors wr takn into account in driving th tabular valus. Othr varid and xtrm conditions rquir modification of th valus. Stl Sid Plats Stl sid plats ar oftn usd with shar-plat connctors. Th loads paralll to grain hav bn found to b approximatly 1% highr than thos with wood sid plats. Th prpndicular-to-grain loads ar unchangd. Load (x1 3 lb) Exposur and Moistur Condition of Wood Th loads listd in Tabl 7 18 apply to sasond mmbrs usd whr thy will rmain dry. If th wood will b mor or lss continuously damp or wt in us, two-thirds of th Group Chstnut Yllow-poplar Baldcyprss Yllow-cdar Port-Orford-cdar Wstrn hmlock Rd pin Rdwood Rd spruc Sitka spruc Whit spruc Group 3 Elm, Amrican Elm, slippry Mapl, soft Swtgum Sycamor Tuplo Douglas-fir Larch, wstrn Southrn Pin Group 4 Ash, whit Bch Birch Elm, rock Hickory Mapl, hard Oak a Group 1 woods provid th wakst connctor joints; group 4 woods, th strongst. tabulatd valus should b usd. Th amount by which th loads should b rducd to adapt thm to othr conditions of us dpnds upon th xtnt to which th xposur favors dcay, th rquird lif of th structur or part, th frquncy and thoroughnss of inspction, th original cost and th cost of rplacmnts, th proportion of sapwood and durability of th hartwood of th spcis (if untratd), and th charactr and fficincy of any tratmnt. Ths factors should b valuatd for ach individual dsign. Industry rcommndations for th us of connctors whn th condition of th lumbr is othr than continuously wt or continuously dry ar givn in th National Dsign Spcification for Wood Construction. Ordinarily, bfor fabrication of connctor joints, mmbrs should b sasond to a moistur contnt corrsponding as narly as practical to that which thy will attain in srvic. This is particularly dsirabl for lumbr for roof trusss and othr structural units usd in dry locations and in which shrinkag is an important factor. Urgnt construction nds somtims rsult in th rction of structurs and structural units mploying grn or inadquatly sasond lumbr with connctors. Bcaus such lumbr subsquntly dris out in most buildings, causing shrinkag and opning th joints, adquat maintnanc masurs must b adoptd. Th maintnanc for connctor joints in grn lumbr should includ inspction of th structural units and tightning of all bolts as ndd during th tim th units ar coming to moistur quilibrium, which is normally during th first yar. 7 1

22 Tabl Dsign loads for on connctor in a joint a Load (N (lb)) Connctor Minimum thicknss of wood mmbr (mm (in.)) Group 1 woods Group woods Group 3 woods Group 4 woods With on connctor only With two connctors in opposit facs, on bolt b Minimum width all mmbrs (mm (in.)) At angl to grain At 9 angl to grain At angl to grain At 9 angl to grain At angl to grain At 9 angl to grain At angl to grain At 9 angl to grain Split ring 63.5-mm (-1/-in.) diamtr, 19. mm (3/4 in.) wid, with 1.7-mm (1/-in.) bolt 5 (1) 51 () 89 (3-1/) 7,94 (1,785) 4,693 (1,55) 9,74 (,85) 5,471 (1,3) 11,3 (,48) 6,561 (1,475) 1,789 (,875) 7,673 (1,75) 11.6-mm (4-in.) diamtr, 5.4 mm (1 in.) wid, with 19.-mm (3/4-in.) bolt 38 (1-1/) 76 (3) 14 (5-1/) 15,34 (3,445) 8,874 (1,995) 17,76 (3,985) 1,75 (,31) 1,6 (4,78) 1,344 (,775) 4,81 (5,58) 14,39 (3,35) Shar plat 66.7-mm (-5/8-in.) diamtr, 1.7 mm (.4 in.) wid, with 19.-mm (3/4-in.) bolt 38 (1-1/) 67 (-5/8) 89 (3-1/) 8,47 (1,89) 4,871 (1,95) 9,74 (,19) 5,649 (1,7) 11,699 (,63) 6,784 (1,55) 11,854 (,665) 7,918 (1,78) 11.6-mm (4-in.) diamtr,16. mm (.64 in.) wid, with 19.-mm or.-mm (3/4- or 7/8-in.) bolt 44 (1-3/4) 9 (3-518) 14 (5-1/) 1,677 (,85) 7,36 (1,655) 14,71 (3,35) 8,518 (1,915) 17,637 (3,965) 1,31 (,3),573 (4,65) 11,943 (,685) a Th loads apply to sasond timbrs in dry, insid locations for a long-continud load. It is also assumd that th joints ar proprly dsignd with rspct to such faturs as cntring of connctors, adquat nd distanc, and suitabl spacing. Group 1 woods provid th wakst connctor joints, group 4 woods th strongst. Spcis groupings ar givn in Tabl b A thr-mmbr assmbly with two connctors taks doubl th loads indicatd. Grad and Quality of Lumbr Th lumbr for which th loads for connctors ar applicabl should conform to th gnral rquirmnts in rgard to quality of structural lumbr givn in th grading rul books of lumbr manufacturrs associations for various commrcial spcis. Th loads for connctors wr obtaind from tsts of joints whos mmbrs wr clar and fr from chcks, shaks, and splits. Cross grain at th joint should not b stpr than 1 in 1, and knots in th connctor ara should b accountd for as xplaind undr Nt Sction. Loads at Angl with Grain Th loads for th split-ring and shar-plat connctors for angls of to 9 btwn dirction of load and grain may b obtaind by th Hankinson quation (Eq. (7 16)) or by th nomograph in Figur 7 7. Thicknss of Mmbr Th rlationship btwn th loads for th diffrnt thicknsss of lumbr is basd on tst rsults for connctor joints. Th last thicknss of mmbr givn in Tabl 7 18 for th various sizs of connctors is th minimum to obtain optimum load. Th loads listd for ach typ and siz of connctor ar th maximum loads to b usd for all thickr lumbr. Th loads for wood mmbrs of thicknsss lss than thos listd can b obtaind by th prcntag rductions indicatd in Figur 7 3. Thicknsss blow thos indicatd by th curvs should not b usd. Whn on mmbr contains a connctor in only on fac, loads for thicknsss lss than thos listd in Tabl 7 18 can b obtaind by th prcntag rductions indicatd in Figur 7 3 using an assumd thicknss qual to twic th actual mmbr thicknss. 7

23 Prcntag of optimum load at or 9 to grain Thicknss of wood mmbr with connctor in ach fac (in.) mm (-1/-in.) 11.6-mm (4-in.) diamtr, diamtr, mm (1/-in.) 19-mm (3/4-in.) bolt bolt mm (-5/8-in.) diamtr, 19-mm (3/4-in.) bolt Split ring 11.6-mm (4-in.) diamtr, 19- or.-mm (7/8- or 3/4-in.) bolt Shar plat Thicknss of wood mmbr with connctor in ach fac (mm) Figur 7 3. Effct of thicknss of wood mmbr on th optimum load capacity of a timbr connctor. Width of Mmbr Th width of mmbr listd for ach typ and siz of connctor is th minimum that should b usd. Whn th connctors ar baring paralll to th grain, no incras in load occurs with an incras in width. Whn thy ar baring prpndicular to th grain, th load incrass about 1% for ach 5-mm (1-in.) incras in width of mmbr ovr th minimum widths rquird for ach typ and siz of connctor, up to twic th diamtr of th connctors. Whn th connctor is placd off cntr and th load is applid continuously in on dirction only, th propr load can b dtrmind by considring th width of mmbr as qual to twic th dg distanc (th distanc btwn th cntr of th connctor and th dg of th mmbr toward which th load is acting). Th distanc btwn th cntr of th connctor and th opposit dg should not, howvr, b lss than half th prmissibl minimum width of th mmbr. Nt Sction Th nt sction is th ara rmaining at th critical sction aftr subtracting th projctd ara of th connctors and bolt from th full cross-sctional ara of th mmbr. For sawn timbrs, th strss in th nt ara (whthr in tnsion or comprssion) should not xcd th strss for clar wood in comprssion paralll to th grain. In using this strss, it is assumd that knots do not occur within a lngth of half th diamtr of th connctor from th nt sction. If knots ar prsnt in th longitudinal projction of th nt sction within a lngth from th critical sction of on-half th diamtr of th connctor, th ara of th knots should b subtractd from th ara of th critical sction. In laminatd timbrs, knots may occur in th innr laminations at th connctor location without bing apparnt from th outsid of th mmbr. It is impractical to assur that thr ar no knots at or nar th connctor. In laminatd construction, thrfor, th strss at th nt sction is limitd to th comprssiv strss for th mmbr, accounting for th ffct of knots. End Distanc and Spacing Th load valus in Tabl 7 18 apply whn th distanc of th connctor from th nd of th mmbr (nd distanc ) and th spacing s btwn connctors in multipl joints ar not factors affcting th strngth of th joint (Fig. 7 4A). Whn th nd distanc or spacing for connctors baring paralll to th grain is lss than that rquird to dvlop th full load, th propr rducd load may b obtaind by multiplying th loads in Tabl 7 18 by th appropriat strngth ratio givn in Tabl For xampl, th load for a 1-mm (4-in.) split-ring connctor baring paralll to th grain, whn placd 178 mm or mor (7 in. or mor) from th nd of a Douglas-fir tnsion mmbr that is 38 mm (1-1/ in.) thick is 1.3 kn (4,78 lb). Whn th nd distanc is only 133 mm (5-1/4 in.), th strngth ratio obtaind by dirct intrpolation btwn 178 and 89 mm (7 and 3-1/ in.) in Tabl 7 19 is.81, and th load quals.81 tims 1.3 (4,78) or 17. kn (3,87 lb). Placmnt of Multipl Connctors Prliminary invstigations of th placmnt of connctors in a multipl-connctor joint, togthr with th obsrvd bhavior of singl-connctor joints tstd with variabls that simulat thos in a multipl-connctor joint, ar th basis for som suggstd dsign practics. Whn two or mor connctors in th sam fac of a mmbr ar in a lin at right angls to th grain of th mmbr and 7 3

24 C A s c B D a a ar baring paralll to th grain (Fig. 7 4C), th clar distanc c btwn th connctors should not b lss than 1.7 mm (1/ in.). Whn two or mor connctors ar acting prpndicular to th grain and ar spacd on a lin at right angls to th lngth of th mmbr (Fig. 7 4B), th ruls for th width of mmbr and dg distancs usd with on connctor ar applicabl to th dg distancs for multipl connctors. Th clar distanc c btwn th connctors should b qual to th clar distanc from th dg of th mmbr toward which th load is acting to th connctor narst this dg. In a joint with two or mor connctors spacd on a lin paralll to th grain and with th load acting prpndicular to th grain (Fig. 7 4D), th availabl data indicat that th load for multipl connctors is not qual to th sum of th loads for individual connctors. Somwhat mor favorabl rsults can b obtaind if th connctors ar staggrd so that thy do not act along th sam lin with rspct to th grain of th transvrs mmbr. Industry rcommndations for various angl-to-grain loadings and spacings ar givn in th National Dsign Spcification for Wood Construction. c c c a a Figur 7 4. Typs of multipl-connctor joints: A, joint strngth dpnds on nd distanc and connctor spacing s; B, joint strngth dpnds on, clar c, and dg a distancs; C, joint strngth dpnds on nd and clar c distancs; D, joint strngth dpnds on nd, clar c, and dg a distancs. Cross Bolts Cross bolts or stitch bolts placd at or nar th nd of mmbrs joind with connctors or at points btwn connctors will provid additional safty. Thy may also b usd to rinforc mmbrs that hav, through chang in moistur contnt in srvic, dvlopd splits to an undsirabl dgr. Multipl-Fastnr Joints Whn fastnrs ar usd in rows paralll to th dirction of loading, total joint load is unqually distributd among fastnrs in th row. Simplifid mthods of analysis hav bn dvlopd to prdict th load distribution among th fastnrs in a row. Ths analyss indicat that th load distribution is a function of (a) th xtnsional stiffnss EA of th joint mmbrs, whr E is modulus of lasticity and A is gross cross-sctional ara, (b) th fastnr spacing, (c) th numbr of fastnrs, and (d) th singl-fastnr loaddformation charactristics. Thortically, th two nd fastnrs carry a majority of th load. For xampl, in a row of six bolts, th two nd bolts will carry mor than 5% of th total joint load. Adding bolts to a row tnds to rduc th load on th lss havily loadd intrior bolts. Th most vn distribution of bolt loads occurs in a joint whr th xtnsional stiffnss of th main mmbr is qual to that of both splic plats. Incrasing th fastnr spacing tnds to put mor of th joint load on th nd fastnrs. Load distribution tnds to b wors for stiffr fastnrs. Th actual load distribution in fild-fabricatd joints is difficult to prdict. Small misalignmnt of fastnrs, variations in spacing btwn sid and main mmbrs, and variations in singl-fastnr load dformation charactristics can caus th load distribution to b diffrnt than prdictd by th thortical analyss. For dsign purposs, modification factors for application to a row of bolts, lag scrws, or timbr connctors hav bn dvlopd basd on th thortical analyss. Tabls ar givn in th National Dsign Spcification for Wood Construction. A dsign quation was dvlopd to rplac th doubl ntry rquird in th National Dsign Spcification for Wood Construction tabls. This quation was obtaind by algbraic simplification of th Lantos analysis that ths tabls ar basd on C g = n m ( 1 m ) n n ( 1+ REAm )( 1+ m) 1+ m n [ ] 1+ R EA 1 m (7 19) whr C g is modification factor, n numbr of fastnrs in a row, R EA th lssr of (E s A s ) / (E m A m ) or (E m A m ) / (E s A s ), E m 7 4

25 Tabl Strngth ratio for connctors for various longitudinal spacings and nd distancs a Connctor Spacing End distanc b (mm (in.)) diamtr (mm (in.)) Spacing c (mm (in.)) strngth ratio Tnsion mmbr Comprssion mmbr End distanc strngth ratio Split-ring 63.5 (-1/) (6-3/4+) (5-1/+) (4+) (-1/) 85.7 (3-3/8) (-3/4) 63.5 (-1/) (4) 8.6+ (9+) (7+) (5-1/+) (4) 13.8 (4-7/8) (3-1/) 8.6 (3-1/4) 6 Shar-plat 66.7 (-5/8) (6-3/4+) (5-1/+) (4+) (-5/8) 85.7 (3-3/8) (-3/4) 63.5 (-1/) (4) 8.6+ (9+) (7+) (5-1/+) (4) (4-1/) (3-1/) 8.6 (3-1/4) 6 a Strngth ratio for spacings and nd distancs intrmdiat to thos listd may b obtaind by intrpolation and multiplid by th loads in Tabl 7 18 to obtain dsign load. Th strngth ratio applis only to thos connctor units affctd by th rspctiv spacings or nd distancs. Th spacings and nd distancs should not b lss than th minimum shown. b End distanc is distanc from cntr of connctor to nd of mmbr (Fig. 7 4A). c Spacing is distanc from cntr to cntr of connctors (Fig. 7 4A). modulus of lasticity of main mmbr, E s modulus of lasticity of sid mmbrs, A m gross cross-sctional ara of main mmbr, A s sum of gross cross-sctional aras of sid mmbrs, m = u u 1, u = 1 + γ(s/)(1/e m A m + 1/ E s A s ), s cntr-to-cntr spacing btwn adjacnt fastnrs in a row, and γ load/slip modulus for a singl fastnr connction. For 1-mm (4-in.) split-ring or shar-plat connctors, γ = 87,56 kn/m (5, lb/in) For 64-mm (-1/-in.) split ring or 67-mm (-5/8-in.) split ring or shar plat connctors, γ = 7,5 kn/m (4, lb/in) For bolts or lag scrws in wood-to-wood connctions, γ = 46.5 D 1.5 (mtric) = 18, D 1.5 (inch pound) For bolts or lag scrws in wood-to-mtal connctions, γ = D 1.5 (mtric) = 7, D 1.5 (inch pound) whr D is diamtr of bolt or lag scrw. Mtal Plat Connctors Mtal plat connctors, commonly calld truss plats, hav bcom a popular mans of joining, spcially in trussd raftrs and joists. Ths connctors transmit loads by mans of tth, plugs, or nails, which vary from manufacturr to manufacturr. Exampls of such plats ar shown in Figur 7 5. Plats ar usually mad of light-gaug galvanizd stl and hav an ara and shap ncssary to transmit th forcs on th joint. Installation of plats usually rquirs a hydraulic prss or othr havy quipmnt, although som plats can b installd by hand. Basic strngth valus for plat connctors ar dtrmind from load slip curvs from tnsion tsts of two buttd wood mmbrs joind with two plats. Som typical curvs ar shown in Figur 7 6. Dsign valus ar xprssd as load pr tooth, nail, plug, or unit ara of plat. Th smallst valu as dtrmind by two diffrnt mans is th dsign load for normal duration of load: (1) th avrag load of at last fiv spcimns at.38-mm (.15-in.) slip from plat to wood mmbr or.76-mm (.3-in.) slip from mmbr to mmbr is dividd by 1.6; () th avrag ultimat load of at last fiv spcimns is dividd by 3.. Th strngth of a mtal plat joint may also b controlld by th tnsil or shar strngth of th plat. 7 5

26 Figur 7 5. Som typical mtal plat connctors. Load P (kn) Slip, mmbr to mmbr (in.) Plug typ plat 8. P 6.4 Toothd typ plat P Slip, mmbr to mmbr (mm) Figur 7 6. Typical load slip curvs for two typs of mtal plat connctors loadd in tnsion. Load P (x1 3 lb) Fastnr Had Embdmnt Th baring strngth of wood undr fastnr hads is important in such applications as th anchorag of building framwork to foundation structurs. Whn prssur tnds to pull th framing mmbr away from th foundation, th fastning loads could caus tnsil failur of th fastnings, withdrawal of th fastnings from th framing mmbr, or mbdmnt of th fastnr hads in th mmbr. Th fastnr had could vn b pulld compltly through. Th maximum load for fastnr had mbdmnt is rlatd to th fastnr had primtr, whil loads at low mbdmnts (1.7 mm (.5 in.)) ar rlatd to th fastnr had baring ara. Ths rlations for svral spcis at 1% moistur contnt ar shown in Figurs 7 7 and

27 Maximum mbdmnt load (kn) 6 45 Fastnr primtr (in.) Douglas-fir Wstrn hmlock Whit fir Fastnr primtr (mm) Rfrncs Rd Oak Southrn Pin Figur 7 7. Rlation btwn maximum mbdmnt load and fastnr primtr for svral spcis of wood. Load at 1.7-mm mbdmnt (kn) Fastnr had baring ara (in ) Rd Oak Southrn Pin Douglas-fir Wstrn hmlock Whit fir Fastnr had baring ara (cm ) Figur 7 8. Rlation btwn load at 1.7-mm (.5-in.) mbdmnt and fastnr baring ara for svral spcis. AF&PA National dsign spcification for wood construction. Washington, DC: Amrican Forst & Papr Association. ASCE Standard for load and rsistanc factor dsign (LRFD) for nginrd wood construction. Washington, DC: Amrican Socity of Civil Enginrs. ASCE Mchanical connctions in wood structurs. Washington, DC: Amrican Socity of Civil Enginrs. Maximum mbdmnt load (x1 3 lb) Load at.5-in. mbdmnt (x1 3 lb) ASTM. (currnt dition). Philadlphia, PA: Amrican Socity for Tsting and Matrials. ASTM F1667. Spcification for drivn fastnrs: nails, spikr, stapls. ASTM D Standard mthods for stablishing clar wood strngth valus. ASTM F547. Standard trminology of nails for us with wood and wood-bas matrials. ASTM D Standard tst mthods for boltd connctions in wood and wood-bas products. ASTM D Standard tst mthods for mchanical fastnrs in wood. Andrson, L.O Nailing bttr wood boxs and crats. Agric. Handb. 16. Washington, DC: U.S. Dpartmnt of Agricultur. Andrson, L.O Wood-fram hous construction. Agric. Handb. 73 (rv.). Washington, DC: U.S. Dpartmnt of Agricultur. Cramr, C.O Load distribution in multipl-bolt tnsion joints. Proc. Pap Journal of Structural Division, Amrican Socity of Civil Enginrs. 94(ST5): Doyl, D.V.; Scholtn, J.A Prformanc of boltd joints in Douglas-fir. Rs. Pap. FPL. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Ecklman, C.A Scrw holding prformanc in hardwoods and particlboard. Forst Products Journal. 5(6): Fairchild, I.J Holding powr of wood scrws. Tchnol. Pap Washington, DC: U.S. National Burau of Standards. Forst Products Laboratory Gnral obsrvations on th nailing of wood. FPL Tch. Not 43. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Forst Products Laboratory Nailing dns hardwoods. Rs. Not FPL 37. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Forst Products Laboratory Nail withdrawal rsistanc of Amrican woods. Rs. Not FPL RN 33. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Goodll, H.R.; Philipps, R.S Bolt-baring strngth of wood and modifid wood: ffct of diffrnt mthods of drilling bolt hols in wood and plywood. FPL Rp Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. 7 7

28 Johansn, K.W Thory of timbr connctions. Zurich, Switzrland: Publications of Intrnational Association for Bridg and Structural Enginring. 9: Jordan, C.A Rspons of timbr joints with mtal fastnrs to latral impact loads. FPL Rp. 63. Madison, WI: U.S. Dpartmnt Agricultur, Forst Srvic, Forst Products Laboratory. Kunzi, E.W Thortical dsign of a naild or boltd joint undr latral load. FPL Rp Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Kurtnackr, R.S Prformanc of containr fastnrs subjctd to static and dynamic withdrawal. Rs. Pap. FPL 9. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Lantos, G Load distribution in a row of fastnrs subjctd to latral load. Madison, WI: Wood Scinc. 1(3): Markwardt, L.J How surfac condition of nails affcts thir holding powr in wood. FPL Rp. D197. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Markwardt, L.J.; Gahagan, J.M Effct of nail points on rsistanc to withdrawal. FPL Rp. 16. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Markwardt, L.J.; Gahagan, J.M Slant driving of nails. Dos it pay? Packing and Shipping. 56(1): 7 9,3,5. McLain, T.E Curvilinar load-slip rlations in latrally-loadd naild joints. Fort Collins, CO: Dpartmnt of Forstry and Wood Scinc, Colorado Stat Univrsity. Thsis. NPA Scrw holding of particlboard. Tch. Bull. 3. Washington, DC: National Particlboard Association. Nwlin, J.A.; Gahagan, J.M Lag scrw joints: thir bhavior and dsign. Tch. Bull Washington, DC: U.S. Dpartmnt of Agricultur. Prkins, N.S.; Landsm, P.; Trayr, G.W Modrn connctors for timbr construction. Washington, DC: U.S. Dpartmnt of Commrc, National Committ on Wood Utilization, and U.S. Dpartmnt of Agricultur, Forst Srvic. Scholtn, J.A Timbr-connctor joints, thir strngth and dsign. Tch. Bull Washington, DC: U.S. Dpartmnt of Agricultur. Scholtn, J.A Strngth of boltd timbr joints. FPL Rp. R1. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Scholtn, J.A Nail-holding proprtis of southrn hardwoods. Southrn Lumbrman. 181(73): 8 1. Scholtn, J.A.; Molandr, E. G Strngth of naild joints in fram walls. Agricultural Enginring. 31(11): Soltis, L.A.; Wilkinson, T.L Boltd connction dsign. Gn. Tch. Rp. FPL GTR 54. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Strn, E.G A study of lumbr and plywood joints with mtal split-ring connctors. Bull. 53. Stat Collg, PA: Pnnsylvania Enginring Exprimnt Station. Strn, E.G Nails in nd-grain lumbr. Timbr Nws and Machin Woodworkr. 58(138): Trayr, G.W Baring strngth of wood undr bolts. Tch. Bull. 33. Washington, DC: U.S. Dpartmnt of Agricultur. Truss Plat Institut. [n.d.] Dsign spcification for mtal plat connctd wood trusss. TPI 78. Madison, WI: Truss Plat Institut. Wilkinson, T.L Baring strngth of wood undr mbdmnt loading of fastnrs. Rs. Pap. FPL 163. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Wilkinson, T.L Thortical latral rsistanc of naild joints. Procdings of Amrican Socity of Civil Enginring. Journal of Structural Division. ST5(97): (Pap. 811): Wilkinson, T.L Strngth of boltd wood joints with various ratios of mmbr thicknsss. Rs. Pap. FPL 314. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Wilkinson, T.L Assssmnt of modification factors for a row of bolts or timbr connctors. Rs. Pap. FPL 376. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Wilkinson, T.L Dowl baring strngth. Rs. Papr FPL RP 55. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Wilkinson, T.L Boltd connction allowabl loads basd on th Europan yild modl. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. Wilkinson, T.L.; Laatsch, T.R Latral and withdrawal rsistanc of tapping scrws in thr dnsitis of wood. Forst Products Journal. (7): Zahn, J.J Dsign quation for multipl-fastnr wood connctions. Nw York, NY: Journal of Structural Enginring, Amrican Socity of Civil Enginrs. Vol. 117(11): Nov. 7 8

29 From Forst Products Laboratory Wood handbook Wood as an nginring matrial. Gn. Tch. Rp. FPL GTR 113. Madison, WI: U.S. Dpartmnt of Agricultur, Forst Srvic, Forst Products Laboratory. 463 p.