A?DS Commentay

PART XII: NAILS AND SPIKES

12.1-GENERAL nails to attach studs tobottom and top plates are standard practices accepted by most building codes. 12.1.1-General Provisions The provisionrecognizing the useof standard Provisions for common steelwire nails and spikes nailingschedules (126) inlieu of designing joints for havebeen part of the Specificationsince the 1944 specific loads was first introduced in the 1982 edition. edition. Threaded hardened-steelnails and boxnails were added in the 1962 edition and the 1977 edition, 12.1.2-Quality of Nails and Spikes respectively. 12.1.2.1 Standard diameters for thevarious types Differences in Nail Types. For thesame penny- of nails and spikes were tabulated in previous editions weightclassification and length, round spikeshave a ofthe Specification. In the 1991 edition, Federal larger shank diameter than common nails and may Specification FF-N-1O5B (70) is referenced as the basic have either a point and countersunk oval head or dimensional standard. Paragraphs 3.6.5, 3.6.11.2, 3.16.9 a diamond point with a flat head. Spikes over 60d are and 3.9-Style 3 of this Federal Specification cover steel generally specified by length (57,70). wirebox nails, steel wire common nails,pallet or threadedhardened steel nails, andround steelwire Threaded or deformed shank hardened-steelnails spikes,respectively. Nails or spikes outside the diame- include both ring or annularly threaded and helically ter and length classes covered in the Federal Specifica- threaded nails. For equivalent pennyweight and length, tion for each type may be available. Provisions of the hardened-steel nails have a smaller shank diameter than 1991 editionmay be applied to suchnails or spikes common nails for pennyweights of 8d and larger. The when the applicable diameters and lengths are specified head diameter of 20d and smaller hardened-steel nails and used to detennine designvalues. is larger than that ofthe corresponding common nail but is smaller for largersizes (those over 4 inchesin The nailprovisions of the 1991 editionalso apply length) (70). to common wire nails made of copper or aluminum alloy conforming to the sizes given for such metals in Box nailshave smallera shank diameter than FederalSpecification FF-N-105B. It isthe designer’s commonnails of equivalent pennyweight. The head responsibility to use appropriate bending yield strengths diameter ofbox nails is larger than that ofcommon for such metals when determining lateral design values nails for sizesless than 10d, is thesame for the 10d in accordancewith 12.3 andto assurethe tensile, to 16d sizes and issmaller for sizes 20d and larger bearing and shear strengths of the fastener are adequate (70). to resist loads being transferred through the fastener to Nail Specifications. The requirement that nails the members in the joint (see 7.2.3 of Specifica- intended for use in engineering construction be specified tion). by length and diameter wasintroduced in the 1986 12.1.2.3 The requirements for threadedhardened- edition. The specificationalso should include head steelnails have remain unchanged since the 1962 diameter if the nail is produced in more than one head edition. diameter for the same length and shank diameter; and thread type or head and pointtype if other than 12.1.3-Fabrication and Assembly common or box nails are to be used (70). 12.1.3.1 A limitation on the size of prebored holes General Construction. Most nailed joints in light for nails and spikeswas first introduced in the 1952 framewood construction are not engineered but are edition.Such holes werelimited to 75 percent of the made in accordancewith standard practices that have diameterof the fastener. In the 1962 edition, the been established from manyyears of field experience limitation waschanged to 90 percent forGroup I (126). Such practices are expressedin terns ofnailing species, those having a specific gravity of 0.62 or larger; schedules which give the number, size and type of nail, and 75 percent for Group 11, I11 and IV species, those and the direction of driving (e.g. face nailing, toenail- havinga specific gravity of 0.59 or less.These provi- ing) to be used for different connections. For example, sions were carried forward unchanged through the 1986 use of three 8d toenails to attach to a sill plate; edition. The limitation on preborednail and spike anduse of four 8d toenails or two 16d face or end holes remains the same in the 1991 edition except that

140 Nails and Spikes NDS Comentary the separation between the most densespecies and was dropped from the Specificationin favor ofthe other speciesis defined in terms of specific gravity withdrawal design value table alone. rather than fastener species groups. The latter are no longer used for connection designin the 1991 edition. Also inthe 1962 edition, provisions for assigning withdrawaldesign values to threaded hardenednails 12.1.3.2 Toenailing proceduresconsisting of slant were introduced. Suchnails were assigned the same drivingof nails at a 30” angle from theface of the withdrawaldesign values as those for common wire attached memberwith an end distance(distance be- nailsof the samepennyweight class. However, the tween end of side member and initial point of entry) of procedure was modified in the 1968 edition to account one-third the nail length have been part of the Specifi- for the fact that although the diameter of common wire cation since the 1952 edition. Based on lateral and nails increases as pennyweight class increases from 20d withdrawal tests of nailed joints in frame wall construc- to 60d, the diameters of threaded hardened nails in this tion (62,160), the toenail factors of12.2.3 and 12.3.7 range and larger do not. The diameter of 30d, 40d, presume use ofthese driving procedures and the 50d and 60d threaded hardened nailsis the same as absenceof excessive splitting. If suchsplitting does that (0.177inches) for the 20d nail of thistype, and occur, a smaller nail should be used. the diameter for 80d and 90d threaded hardened nails was the same as that (0.207inches) for the 70d size. 12.2-WITHDRAWAL DESIGN VALUES To adjust for these differences, the 20d to 60d thread- 12.2.1-Withdrawal fromSide Grain ed hardened nails wereassigned the samewithdrawal designvalue as that for20d commonnails having a Background diameter of0.192 inches. The 70d to 90d threaded hardenednails were assigned the samewithdrawal Withdrawal designvalues for nails and spikes are designvalue as that for acommon nail having a based on the equation diameter whichwas in the same ratio tothe 70d (C12.2-1) threaded hardenednail diameter of0.207 as the W = 1380 G5”D common to threaded nail diameter ratio for 20d nails, where: or 0.192/0.177. This equivalent diameter 0.225is inches, the diameter of a 40d common nail. For 20d W = nail or spikewithdrawal design value per and smallerpennyweights of threaded hardenednails, inch of penetration in member holding point, thesame withdrawal design values as those for the lbs equivalentsize common nails were used as inthe G = specificgravity of member holding point previous edition. based on oven dry weight and volume D = shank diameter of the nail or spike,in. Withdrawal designvalues for boxnails based on Equation C12.2-1were introduced inthe 1977 edition. Equation C12.2-1was based on earlyresearch The foregoingprocedures for establishingwithdrawal (56,64) and has beenused to establishnail and spike design values for nails and spikes were carried forward withdrawaldesign values since the1944 edition. unchanged through the 1986 edition. Withdrawal designvalues obtained from the equation represented about one-fifth average ultimate test values 1991 Edition

Both Equation C12.2-1 and resultant tabulated mine which diameters apply to box nails, common nails withdrawaldesign values for common wirenails and and spikes. Withdrawal designvalues for threaded spikes by species were presented in the 1944 and 1948 hardened nails are givenin a separate portion of Table editions. In 1950, tabulated withdrawaldesign values 12.2A because of their different basis.

Nails and Spikes 141 NDS Commentmy values for smooth-shank nailsinserted inpartially Ln /3 seasoned or wet wood that will seasonin service or p, = Ln - - (C12.2-2) cos 30" installedin dry wood that willbe subject to wetting and drying inservice (see 7.3.3). = 0.615 Ln

Clinching. It is to be noted that the withdrawal where: resistance of smooth-shank nails can besignificantly increased by clinching(35). Increases in withdrawal p, = penetration of nail in member holding point, resistanceof 45 to 170percent due to clinchinghave in. been reported when nails are tested soon after driving. Ln = lengthof nail, in. Wheninstalled in unseasoned or partiallyseasoned wood and tested after seasoning,increases of250 to 12.3-LATERAL DESIGN VALUES 460 percent as a result of clinching have been observed. 12.3.1-Wood-to-Wood Connections Clinching across the grain was found to give 20 perceut higherwithdrawal design values than clinchingalong Background the grain. When a greater assurance of a givenlevel of withdrawalresistance is needed with smooth-shank From the 1944 through the 1986 editions, lateral nails, clinching should be considered. design values for nails and spikes loaded at any angle to grain werebased on the equation 12.2.2-Withdrawal from EndGrain Z = KLD3" (C12.3-1) Reduction of withdrawaldesign values up to 50 percenthave been reported for nailsdriven in end where: grain surfaces (radial-tangential ) as comparedto side grain (radial-longitudinal or tangential-longitudinal 2 = nominalnail or spike lateral designvalue, planes)surfaces (57,160). When coupled with the Ibs effectsof seasoning in service after fabrication, such KL = species group constant based on specific reductions are considered too great for reliable design. gravity (G) of wood members It is considered to be on this basis that loading of nails = 2040 Group I G = 0.62 - 0.75 2ndspikes in withdrawal from end grain has been = 1650 Group I1 G = 0.51 - 0.55 prohibitedin the Specificationsince the 1944 edition. = 1350 Group I11 G = 0.42 - 0.49 = 1080 Group IV G = 0.31 - 0.41 12.2.3-Toe-NailFactor, Ctn D = nail or spike shank diameter, in. The 0.67 adjustment of withdrawal design values for Equation C12.3-1was based on earlynail tests toenailing has been a provision of the Specification (5739) and assumed certain minimum penetrations of since the 1951 edition. The adjustment is based on the the fastener in the main member (see Commentary for resultsof joint tests comparing slant driving and 12.3.4).Values assigned to the constant KL gave straight driving (57) and oftypical toenailed and end lateral design values that were approximately 75 percent nailed joints usedin frame wall construction (160) of proportional limit test values. These values included wherethe attached memberis pulled directly away the originallyrecommended adjustment of1.6 (57) from the main member. It isapplicable to joints increased 20 percent as part of the World War I1 fabricated at alllevels of seasoning. This includes emergencyincrease in wood design values. The latter multiple nail joints fabricated of unseasoned wood and adjustment wassubsequently codified as a 10percent then loaded after seasoning (57,66,160). When properly increase for thechange from permanentto normal driven(see Commentary for 12.1.3.2),toenailing with loading and 10 percent for experience (see Commentary cross slant driving can produce stronger joints than end for 2.3.2). Nail lateral designvalues of 75 percent of or facenailing. For example, a stud to plate joint proportional limit values are about one-fifth maximum made of four 8d toenails was reported to be stronger testvalues for and about one-ninth maxi- than the same joint made withtwo 16d endnails mum test values for (57). (62,160). From the 1944 through the 1960 editions, the - Where toenailing is employed, the depth of penetra- individual group equations werepresented thein tion of the nail in the member holding the point may Specification along with the listof species to which be taken as the actual length of nail in the member as each applied. Beginning with the 1950 edition, tabulat- shownin Figure C12.3-1, or (see12.1.3.2) ednail and spike lateral designvalues based on the

142 Nails and Spikes NDS Commentary equations for each group were included in the Specifi- tional limitof a nailed joint couldbe assumed to be cation. Presentation of the lateral designvalue equa- associatedwith a slip of approximately 0.015 inches tionswas then discontinued beginningwith the 1962 (65,160). As Equation C12.3-1 isconsidered to give edition. In the 1960 and earliereditions, naila average lateral design values that are about 75 percent fastener group between Groups I1 and I11 was included of average proportional limittest values, the lateral inthe specification for intermediate density design values tabulated in previous editions would index species. This intermediate group alsowas dropped to an averageinitial slip of 0.011 inches. This defor- beginning with the 1962 edition as most of the included mation level excludes the effects of any creep occurring species were of little commercial importance. under design loads. Prior to the 1971 edition, grain type and other 1991 Edition features than specificgravity were taken into account inclassifying species into fastener groups. This was Nail and spike lateral designvalues in the 1991 evidenced by somespecies with the same specific edition are based on application of the yieldlimit gravitiesbeing classified in Group I11 and others in model (see Commentary for 7.2.1 and 8.2.1) which also Group IV (57,62). Beginningwith the 1971 edition, has been used to establish the lateral design values for specificgravity was used as thesole criterion for bolts, lagscrews and woodscrews. The yieldmode assignmentof species for nail lateral designvalue equations givenin 12.3.1 for nails and spikes in single constants. The specificgravity class limits shown in shear havebeen developed and verifiedinrecent thelegend for Equation C12.3-1 were used to classify research (27,28). The equations provide for four modes species from 1971 through the 1986 edition. of yielding: bearing in the side member being attached (Mode I, ), development of a plastic hinge in the side Provisions for establishing lateral design values for member (Mode 111, ), development of a plastic hinge threaded hardened nails were introduced in the 1962 in the main member (Mode 111, ), and development of edition. Thesenails were assigned the same lateral plastichinges in both main and sidemembers (Mode designvalues as those for common nails of the same IV). The lowest lateral design value, 2, obtained from pennyweight class. The smaller diameter of the thread- the four equations is taken as the basic lateral design ed hardened nails compared to the common nails was value for the particular connection being evaluated. It considered to be offset by the higher bending strength is to be noted that the Mode 111, equation, unlike the of the former. In the 1968 edition, assignments for other nailyield mode equations and those for other 30d and larger threaded hardened nails werereduced dowel type fasteners, includes a term to account for the to account for the fact that thediameters of the 30d length or penetration of the nail in the main member. to 60d pennyweight sizes were the same as the diame- All equations, however, require a minimum penetration ter for the 20d nail of this type, and the diameters of of six diameters in the main member. the 80d and 90d sizeswere the same as the 70d size. Under this change, the 20d to 60d threaded hardened The KO termin the denominator ofeach yield nails were assigned the same lateral design value as that mode equation represent factors to reduce yieldmode for the 20d common nail and the 70d to 90d threaded equation valuesbased on a 5 percentdiameter offset hardenednails wereassigned the same lateral design dowelbearing strength to thegeneral levelof the value as that for the 40d commonnail. The ratio of proportional limit based lateral design values tabulated the diameter of the 70d threaded hardened nail to that inprevious editions of theSpecification. Values of of the 40d common nail is the same as the ratio of the KO varydepending upon the shank diameter, D, of 20d threaded hardened nail to that of the 20d common the nail or spike, as shownbelow. nail (see Commentary for 12.2.1 - Background).These D s 0.17 K’ = 2.2 procedures for establishing lateral designvalues for 0.17 < D < 0.25 KO = 1O(D ) + 0.5 threaded hardened nailswere continued through the D L 0.25 KO = 3.0 1986 edition. The 2.2 factor for fasteners 0.17 inches or less in Lateral designvalues for boxnails based on diameterisbased on a comparison ofyield mode Equation C12.3-1 were first introduced in the 1977 lateral designvalues with nail lateral designvalues edition. published in the 1986 edition for joints made with 8d It is to be noted that lateral design values tabulated and 16d nailsin each of two species for arange of inthe 1986 and earlier editions of theSpecification side member thicknesses (117). The 0.17 diameter limit were not considered associated with a specific deforma- coversall standard boxnail sizes (up to 40d) and tionlevel. However, it was reported that the propor- common and threaded hardened nails up to 16d. Most

Nds and Spikes 143 NDS Comentaty spikesfall in the larger diameterclasses. Because side increase as diameter decreases (106). The regression of memberthickness isvariablea in the yield mode testvalues from whichnail bending yield strength equations but was not a factor indeveloping lateral values were estimated is given below. design values given in previous editions, the KD value (C12.3-2) of 2.2 gives lower lateral design values for joints made Fyb = 130.4 - 2140 with the thinnest side members (5/16 inch) than those previously tabulated for equivalent species and nail size, where: but larger lateral designvalues for joints madewith Fyb = bendingyield strength ofsteel based on 5 thickerside members (1-1/2 inch). In addition to percentdiameter offset, 1000 psi havingsubstantially higher lateral designvalues than D = naildiameter, in. thosepreviously given in the Specification,nailed and spiked joints made with the thicker side members also The increasein yield strength associated with the hadsignificantly higher lateral designvalues than lag decrease in diameter is attributed to the work harden- screw and woodscrew joints made withthe same ingof the steel as it is formed into progressively diameter fastener and side member thickness when the smaller diameters (106). KD value of 2.2 was used in the nailyield equations for thesecombinations. As the larger diameternails Bendingyield strength values for hardenedsteel and spikes are used with the thicker side members, the nailsgiven in the footnote ofTables 12.3C are based foregoinginconsistencies were addressed by increasing on bendingyield strength values for common nails of the KO factor for nail and spikediameters of0.25 equivalent diameter increased approximately 30 percent inches or more from 2.2 to 3.0, limiting the 2.2 factor (see Appendix I). to 0.17 diameters and less, and use of a linear transi- TabulatedWood-to-Wood Lateral Design tion (KD = 10d + 0.5) for intermediatediameters. Values. Lateral designvalues for single shear connec- These KD factor assignments are thesame as those tionsmade with 112 to 1-1/2inch thick side members usedwith the yield mode equations for woodscrews for each of the major individual species combinations (see 11.3.1). are givenin Tables 12.3A to 12.3D.Tables A, B, C

The nail and spike yield mode equations are applied.However, certainin designs, use ofthe enteredwith the fastenerdiameter, the side member tabulated lateral designvalues for thelowest specific thickness, the dowel bearing strengths of the main and gravitywood in the joint maybe considered overly side members (Fern and Fcs ) , and thebending yield conservative. In such cases, determining allowable joint strengthof the fastener (Fyb). Dowelbearing lateral designvalues directly from the yieldmode strengths for all species combinations are listed in Table equations may prove beneficial. The difference between 12A. These dowel bearing strength values are based on tabulated lateral designvalues and yield modelateral thesame specific gravity equation used to establish design values for mixed species joints are illustrated in dowel bearing strengths for wood screws (see Commen- the nail examples presented in Example C12.3-1. tary for 11.3.1 - 1991 Edition andEquation C11.3-2). The equation isbased on researchwhich involved The effect of side member thickness on nail lateral bearingtests of nails 12dto 40d insize and which designvalues is not linear. Tabular lateral design showed that diameter was not a significant independent valuesshould not be extrapolated to obtain lateral variable with specific gravity (203). designvalues for sidemember thicknesses larger than the maximum thickness listed in the tables (see Exam- The bending yield strength of the nail or spike, pleC12.3-1). For joints made ofspecies other than Fub , maybe specified by the designer or thevalues those tabulated, lateral design values for a listed species given in the footnotes in Tables 12.3A, 12.3B, 12.3C or combinationswith a lower specific gravity than that for -- 12.3Dmay be used (see Appendix I). The footnote the species being used, as determined from Table 12A, values are based on the results of tests of common wire maybe applied. With the highest density hardwoods, nails which showed that bending yield strength tends to NDS Commentary

thiswill result insignificant underestimation of joint capacity. Example C12.1-1 Yield mode lateral design values for wood-to-wood single Comparison of 1991and Earlier Edition Lateral shear nailed connections: DesignValues. Differences in lateral design values for singleshear nailed connections in the 199 1 and1986 Single andmixed speciesjoints of southernpine and editions resulting fiom the change to the yield limit model -- made with 8d common nails in side member thicknesses of 3/8, 1/2 and 5/8 inches and with 60d com- and the use of individual species rather than fastener group mon nails in side member thicknesses of 1/2, 1 - 1/2, and 2- values is illustrated in Table C 12.3-1. 112 inches Table C12.3-1- Comparison of 1991 and 1986 NDS Fen,F,, = 5550 psisouthern pine (SP) Wood-to-Wood Single Shear Nail = 3350 psispruce-pine-fir (SPF) Lateral Design Values Fvb = 100,000 psi 8d = 70,000 psi 60d Side D = 0.131 8d Member = 0.263 60d Thick- Nail Nail NailLateral Design Value, lbs KO = 2.2 8d ness,Penny- Dim. SouthernPine Spruce-Pine-Fir = 3.0 60d Weightin. in. 19911986 Ratio 19911986 Ratio p = naillength - sidemember thickness Box Nails: 1/2 8d 0.113 67 1.0663 47 51 0.92 Side Yield Mode 20d 0.148 101 1.0794 73 77 0.95 Nail MemberNail Design Values, lbs 314 8d 0.113 79 1.2563 57 51 1.12 Penny-Thickness Species 20d 0.148 121 1.2994 83 77 1.08 W eight in. MainSideWeight in. ZIII,ZIII,ZI,ZIV Common Nails: SP SP 124 242 106 2 /2 1 8d 0.131 85 78 1.09 61 64 0.95 SPF SP 124 160 92 69 20d 0.192 137 139 0.99 103 114 0.90 SP SPF 75 219 92 a 1-1/2 20d 0.192 185 139 1.33 144 114 1.26 SPF SPF 75 149 82 2 60d 0.263 262 223 1.17 191 182 1.05 112 SP SP 165 229 85 106 Threaded Hardened Nails: SPF SP 165 152 x 92 SP SPF 100 207 68 92 /2 1 8d 0.120 80 78 1.03 58 64 0.91 SPF SPF 100 141 fl 82 20d 0.177 147 139 1.06 111 114 0.97 1-1/2 16d 0.148 145 108 1.34 113 88 1.28 518 SP SP 207 216 106 94 70d 0.207 227 176 1.30 171 144 1.19 SPF SP 207 144 84 92 SP SPF 125 195 2 92 Spikes: 82 SPF SPF 125 134 a /2 1 20d 0.225 162 176 0.92 123 144 0.85 60d 112 SP SP 243 905 J.@ 262 60d 0.283 201 248 0.81 155 203 0.76 SPF SP 243 593 165 228 1-112 40d 0.263 262 223 1.17 191 182 1.05 SP SPF J4J 821 161 228 3/8 0.375 428 379 1.13 290 310 1.07 SPF SPF 147 551 144 204 1-1/2 SP SP 730 745 288 262 Theconsistently higher 1991/1986 lateral design value SPF SP 730 491 260 228 ratios for the 3/4 and 1 - 1/2 inch side member thicknesses SP SPF 441 676 207 228 relativeto the ratios for the 1/2 inch side member thick- SPF SPF 441 456 204 191 ness reflect the use of side member thickness as a variable 2- 112 SP SP 1216 588 433 262 in the yield mode equations whereas previous lateral design SPF SP 1216 391 392 228 valueswere independent of memberthickness. The SP SPF 734 533 294 228 generallylower lateral design value ratios for the fasteners SPF SPF 734 363 272 204 withdiameters over 0.25 inchesrelative to those with diametersless than 0.17 inches represents the effect of the larger KO factor (3.0) usedin the yield mode equations forthe former as comparedto the factor (2.2) usedwith thelatter.

Nails and Spikes 145 A?VS Commentary

For the joint configurations compared, the averages Table C12.3-2 - Comparison of 1991 and 1986 NDS of the 1991/1986 lateral designvalue ratios were 1.13 Wood-to-Metal SingleShear Nail for southern pine and 1.02 for spruce-pine-fir. This Lateral Design Values difference reflects the fact that southern pine was at the upper limit of its 1986 fastener group (specific gravity) Stee1 class whereas spruce-pine-fir was near the lower limit of Plate Thick- Nail Nail Nail Lateral Design Value,lbs its class. By basing the dowel bearing strength used in the yield mode equations on the specific gravity of each ness,Penny- Diam. SouthernPineSpruce-Pine-Fir species combination ratherthan basing lateral design in. Weight in. 19911986 Ratio 19911986 Ratio values on specific gravity groups, the 1991 provisions &x N&: tienail lateral designvalues more closely to the performance capabilities of each species combination 0.075 8d 0.1 13 78 79 0.99 63 64 0.98 20d 0.148 124 118 1.05 99 96 1.03 than was previously the case. 0.134 8d 0.113 90 79 1.14 74 64 1.16 12.3.2-Wood-to-Metal Connections 20d 0.148 137 118 1.16 111 96 1.16 n N&: 12.3.2.1 From the 1944 through the 1986 edition, 0.075 8d 0.131 103 98 1.05 83 80 1.04 lateral design values for nails and spikes were increased 20d 0.192142141 1.01 174 176 0.99 25 percentwhen metal rather than woodside plates 60d 0.263 279248 0.89 228198 0.87 wereused (57). This is the samemetal side plate 0.134 8d 0.131 115 1.17 98 94 80 1.18 adjustment previously used with wood screws over the 20d 0.192 174188 1.08 1.07142152 sameperiod and with bolts prior to the 1982 edition. 60d 0.263 279256 0.92 228206 0.90 Recent test results indicated the 25 percent increase for w: nailed wood-to-metal joints was conservative (165). In the 1991 edition, the effectof the metal sideplates is 0.075 16d 0.207 194192 0.99 159154 0.97 accounted for directly by entering the dowelbearing 60d 0.283 310266 0.86 212254 0.83 3/8 0.375 404 474 0.85 388321 0.83 strength, Fcs , and the thickness of the metal side plate 0.134 16d 0.207 194203 1.05 1.03159 163 in the yield mode equations of 12.3.1. Onlyyield 60d 0.283 310274 0.88 254221 0.87 Modes 111, , 111, and IV are considered. The Mode 3/8 0.375 411 474 0.87 388330 0.85 I, equation for bearing in the side member is not used as this property isconsidered separately in the design of metal parts (see 12.3.2.2 and Commentary for 7.2.3). southern pine and spruce-pine-fir joints, respectively. Becausethe variation inthickness oftypical steel side Tables 12.3E,12.3F, 12.3G and 12.3H give lateral plates is small (0.036 to 0.239) relative to the variation designvalues forjoints made withsteel box nails, in thickness of wood side members (1/2 to 1-1/2), plate commonnails, threaded hardened nails and spikes, thickness has asmaller effect on 1991 joint lateral respectively, and steel side members ranging from 0.036 designvalues than does woodside member thickness inches (20 gage) to 0.239 inches (3 gage)in thickness. when both are compared to 1986 lateral design values. Tabulated lateral designvalues for allside plate As with the wood-to-wood joints, the lower 1991/1986 thicknesses are based on adowel bearing strength of lateral design value ratios for the larger diameter nails 45,000 psi applicable to ASTMA446 Grade A galva- reflect the larger adjustment factor, KO, usedwith nizedsteel. The samenail and spikebending yield thesefasteners compared to that used for thesmaller strengths, Fub , used to develop the wood-to-wood joint diameter fasteners. lateral design values in Tables 12.3A - 12.3D were used to develop the tabulated lateral design values for joints 12.3.2.2 (See Commentary for 7.2.3) made with steel side plates. 12.3.2.3 Design values for hangers, tie downs Comparison of 1991 and Earlier Edition and other similar products that involve wood-to-metal Lateral Design Values. Differences between 1991 and nailed joints often are established by testing connections 1986 lateral designvalues for joints made withsteel made with the installed product rather than by use of sideplates and common nails are illustratedin Table the provisions of the Specification. As noted inthe C12.3-2. Commentary for 12.3.1, lateral design values tabulated inthe 1991 and earlier editions are derivedfrom The average of the 1991/1986 lateral designvalue nominal proportional limitlevel values and are about ratios for the two plate thicknesses and three nail sizes one-fifth short term ultimate test values. Design values comparedin the table are 1.00 and 0.98 for the for proprietary products such as hangers and other

146 Nails and SNes NVS Commentary

- connecting devices may be based on proportional limit based on recentresearch which shows that the total testvalues or on maximumtest values. It isthe yield mode load capacity of a threemember joint is responsibility of the designer to determine the appropri- equivalent to twice that of a comparable twomember ateness of the procedures used to establish such design or single shear joint (28). The sixtimes fastener values,including the adequacy ofreductions for load diameter requirement on the thickness of the center duration and variability, and the appropriateness of memberin a threemember joint isrelated to the applying other adjustments given in the Specification to requirement of 12.3.4 that the minimumnail or spike thosedesign values (see Commentary for 1.1.1.4 and penetration into the main member be at least six times 7.1.1.4). the fastener diameter. 12.3.3-Double Shear Wood-to-Wood Connections Unlike previous editions, the 1991 provisions for threemember wood-to-wood joints have no require- An increase in lateral design values for connections ments on sidemember thickness to qualify for an in double shear where the nailfully penetrated all increasein the single shear lateral designvalue if the members of a three-member joint was introduced in the third membermeets the penetration requirements of 1960 edition of the Specification. An increase of one- 12.3.4. This reflects the fact that sidemember thick- third was allowed when each side member was not less ness is a variable in the yield mode equations that are than one-third the thickness of the main or center usedto establish lateral designvalues in the 1991 member and two-thirds when the thicknesses of the side edition. Application of the 120 penetration require- memberswas equal to the thickness of the main ment of 12.3.4 to the third member of a three member member. Interpolation for intermediate sidemember joint wouldexclude use of certain panelside member thicknessessubsequently was provided for inthe 1962 materials whichqualified for the threemember joint edition. In the 1982 edition, a clarifying provision was increaseinprevious editions. To provide for such added to the Specificationwhich applied the penetra- applications, the clinchednail provisions of earlier tion requirements for single shear joints to the center editions are used as an exception to the 12.3.4 penetra- member of threemember joints. Theseprovisions tion requirements. Under this exception, three member covering the design ofnailed joints in double shear joints made with 12d or smaller size nails and 3/8 inch were carried forward unchanged to the 1986 edition. or thicker side members qualify for a doubling of the In the 1968 edition, a separate adjustment for three applicablesingle shear lateral designvalue when the member joints made with clinched nails was introduced. nailextends at least three diameters beyondthe side This new provisionallowed a doubling of thesingle member and are clinched. The waiver of the clinching shear lateral design value for joints made with 12d or requirement for threaded hardened nails that wasin smaller nails if the thickness of the side members was previous editions has been dropped as theincreased 3/8 inch or larger and the nailsextended beyond the strength of these fasteners relative to common steel wire sidemember by at least three diameters and were nails has been accounted for directly in the yield mode clinched. This addition wasbased on testsof single equations. Clinching of both common and hardened shear and clinched and unclinched double shear joints nailsis considered necessary for both to qualify for made withplywood side members (108). In the 1971 twice their respective single shear lateral design values. edition, the clinchingrequirement for threemember 12.3.4-Penetration Depth Factor, Cd joints made with threaded hardened nailswas waived if the sidemember, nail size and naillength require- In the 1960 and earlier editions of the Specification, ments for doubling of single shear lateral design values nails and spikes were required to penetrate themain were met. This change, which reflected the difficulty of member a minimum of two-thirds thefastener length clinchingthis type of fastener, wasbased on tests of for softwoods and one-half the fastener length for single and double shear joints made withunclinched hardwoods to qualify for specified lateral design values threaded hardened nails (171). The provisions allowing (5739). In the 1951 edition, provisionwas made for the doubling ofsingle shear lateral designvalues for use of lesser penetrations if the lateral design value was certainnailed joints in double shear were alsocarried reduced proportionately; but the minimumpenetration forward through the 1986 edition. was required to be at least one-half the nail length for softwoods and two-fifths the nail length for hardwoods. In the 1991 edition, a doubling of the lateral design In the 1960 edition, theminimum penetration allowed - value for single shear joints isrecognized for anythree for reduced lateral designvalues was changed to two- member wood-to-wood connectionin which thethick- fifths thenail length for softwoods and one-third the ness of the center or main member is greater than six nail length for hardwoods. times the nail or spike diameter. The provisionis

Nails and Spikes 147 NDS Commentary

Beginningin the 1962 edition, penetration require- and vertical framing members also are diaphragms. ments were changed from a fastener length to a Such shear walls or vertical diaphragms act to transfer fastener diameter basis and the -hardwood loads from horizontal diaphragms down to the support- classes were dropped in favor of fastener groups based ing foundation (182). The diaphragm factor, Cdj, on specificgravity (see Commentary for 12.3.1 - applies to both horizontal and vertical diaphragms. Background). For full lateral design value, penetration Beginning with the 1960 edition of the Specification, of the fastener in the main member of 10 diameters for an increasein normal load lateral designvalues for Group I species, 11 diameters for Group I1 species, 13 diameters forGroup I11 species and 14 diameters for nails and spikes of 30 percentwas recognized when Group IV species was required. The minimum penetra- these fasteners were used in diaphragm construction. tionallowed for reduced lateral designvalues was set The increase,which applied in addition to wind and at one-third the penetrations required for full lateral earthquake load duration increases,was based on designvalues. Based on new recommendations (62), experiencewith wood diaphragms on the west coast the 1962 penetration provisions represented a relaxation designed using code approved nail shear values approxi- of previous requirements. Expressing penetration mately 30 percent larger than thosegiven inthe requirements in terms of nail diameter rather than nail Specification (180,181). The increase also wasconsid- length made it possibleto take into account the ered appropriate in view of the fact that the lateral different diameters of fasteners that are available for design values provided in the Specification represented thesame pennyweight and length. The 1962 penetra- approximately 75 percent of joint proportional limit test tion provisions were carried forward unchanged to the values (one-fifth of maximum test values) (see Commen- 1986 edition. tary for 12.3.1 - Background) and that structural diaphragms involve use of many nails acting together In the 1991 edition, lateral designvalues are given whichwas viewed as reducing variability effects. by individual species combinations rather than by fastener groups. With this change, the penetration In the 1977 edition, theprovision for increasing requirement for full lateral designvalue has been lateral designvalues for nails and spikesused in simplified to twelve fastener diameters for allspecies. diaphragm construction by 30 percentwas revised to The minimumallowed penetration for reduced lateral clarify that the adjustment appliedonly to lateral design value has been changed from 3.3 to 4.7 fastener designvalues and not to withdrawaldesign values. diameters to 6 diameters for allspecies. This increase The diaphragm adjustment provisionwas carried in the minimum penetration requirement, based on forward tothe 1986 edition without change. consideration ofnew information available on how In the 1991 edition the adjustment for diaphragm nails perform in joints (27), serves to account for the use has beenreduced to 10 percentin recognition of consolidation of the previous four separate group the changein the load duration adjustments for wind requirements into one and for the higher lateral design and earthquake loads from 1.33 to 1.6. The 10 percent values obtained for some configurations from the new factor provides for approximately thesame effective yield mode models. wind and earthquake design load for diaphragms when 12.3.5-EndGrain Factor, Ccg used with the new load duration factor (1.6 x 1.1) as did the previous 30 percent factor when used with the The use of a 0.67 adjustment factor on lateral previous load duration factor (1.33 x 1.3). If a 1.33 design values for nails or spikes driven in the end grain adjustment for wind or earthquake load continues to be has been a provision of the Specification since the 1944 used in diaphragm design, the 1.30 Cdifactor should edition. The adjustment isbased on earlyresearch on be applied to nail lateral designvalues. joints made with softwood species (57). 12.3.7-Toe-NailFactor, Ctn 12.3.6-DiaphragmFactor, C’,. The toe nail factor of 0.83 has been an adjustment Diaphragms are large, flat structural units acting to nail lateral designvalues since the 1951 edition. like a deep relatively thin beam or girder. Horizontal This factor isbetween the full lateral designvalue wood diaphragms consist of floor or roof decks acting applicable to nailsdriven perpendicular to grain (side as webs and or glued laminated timbermem- grain) surfaces and the two-thirds of full lateral design bers acting as the flanges.Such assemblies distribute value applicable to nails driven in parallel to grain (end horizontal forces acting on the flangestovertical grain) surfaces. resisting elements (145). Shear walls consisting ofwall sheathing materials attached to top and bottom plates

148 AJds and SpiGes NDS Commentary

For toe nails subject to lateral loads, the depth of member ends and edges than larger nails as they are penetration of the nail in the member holding the point lesslikely to cause splitting. Wheresplitting can not may be taken as the vertically projected length of nail be avoided, preboring of nail holes should be used (see inthe member as shownin Figure C12.3- 1, or (see 12.1.3.1). 12.1.3.2) In lieuof specific code requirements for end and pL = LnCOS3O0 - Ln/3 (C12.3-3) edge distance for nails, Table C12.4-1 may be used to establishnailing patterns. Designersshould note that where: specie type, moisture content and grain orientation will pL = verticalprojection of penetration ofnail in affect spacing (pitch) between fasteners in a row. main member, in. Table C12.4-1 Nail Minimum Spacing Tables Ln = length of nail, in. Wood Side Members For purposes of establishing the single shear lateral Not designvalue applicable to a toe nailed joint, the side Prebored Prebored memberthickness shall be taken as thelength distance of the Edge 2.5d 2.5d nail in the side member (see Figure C12.3-1) or End distance - tension load parallel to grain . 15d 1Od ts = Ln/3 (C12.3-4) - compressionloadparallel to grain 1Od 5d Spacing (pitch) between fasteners in a row where: - parallel to grain 15d 1Od - perpendicular to grain 1Od 5d ts = effectiveside member thickness when toe- Spacing (gage) between rows of fasteners nailing is used, in. - in-line 3d 5d - staggered 2.5d 2.5d Equation C12.3-4 only applies to nails driven at an Steel Side Members - angleof approximately 30" to the face of themember Not being attached and one-third the naillength from the PreboredPrebored end of that member. The effectiveside member distance Edge 2.5d 2.5d thickness for nailsdriven at anyangle to theface of End distance the memberbeing attached should not exceed the - tension load parallel to grain Sd 1 Od actual thickness of that member. - compression load parallel to grain 5d 3d Spacing (pitch) between fasteners in a row - parallel to grain 1 Od 5d - perpendicular to grain 2.5d 5d Spacing (gage) between rows of fasteners in line - in 2.5d 3d - staggered 2.5d 2.5d

h t,=L,/3 12.4.2-Multiple Nails or Spikes \I I\ Sincethe 1944 edition, the total designvalue for a connection made with more than one nail or spike has pL determinedbeen assum the ofallowable the design V values forindividual the fasteners. In the 1992 edition, this summation provision is limited to only those nails Flgure C22.3-1Etrectivepnetration andsidemember thichess or spikes in the joint which are of the Same size and for toe nails subjkct latera//oads.to type(see Commentary for 7.2.2 and 7.1.1.1).

12.4-PLACEMENT OF NAILS AND SPIKES

- 12.4.1-EdgeDistance, End Distance, Spacing Absenceof splitting has been the performance criterion for placement of nails and spikessince the 1944 edition. Smallernails can beplaced closer to

Nails and Spikes 149

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