Joint Design 2 (2001) - Nails, Staples & Screws

2Contents

Introduction

Fastener Specification and Application

NailsScrews

Joint Design

Lateral LoadsWithdrawalFastener Spacings

Connection Design

Direct Force ConnectionsAxial TypeMoment ConnectionsComputer Design of Moment Joints

Specifications

Other References

COVER PHOTO: Commercial hardwooddecking fixed to sub-structure with hot dippedgalvanised decking spikes

Nail Fixed plywood shearwalls and nailfabricated plywood box-beams

Nailed plywood gussets provide momentjoints for portal frames

TIMBER JOINT DESIGN-2

3Introduction

In domestic, industrial and commercialconstruction, nails are the most commonly usedand economical of all fasteners. If it is possible tomake any choice in fastener type on economicgrounds, nails should be selected.

Staples are also used extensively and may beinstalled for a similar cost to nails. Their use isusually restricted to specific details of lightweightconstruction including flooring, diaphragms andsheathing in addition to furniture, joinery and thefixing of sheeting and upholstery to framing.

Plain screws are used in special situations buthave a higher installation cost than nails.Typically, they are used for attaching hinges andother fixtures where it may be necessary toremove these objects at some later stage. Thedevelopment of Type 17 self-drilling power-drivenscrews has led to more extensive use of screws infixing roof sheeting, roof battens, wall boards and,more recently, heavy timber decking.

Type 17 screws provide a higher strength and amore reliable form of fastening under withdrawalloads.

All fasteners described herein are characterisedby having maximum loads limited by thebending strength of the fastener rather thanbearing or cleavage failure of the wood. Theload capacity is independent of the direction ofload relative to the grain. Accordingly, it mightbe expected that timber shrinkage underadverse conditions will merely result in thefastener bending rather than in the timbersplitting. While nails, staples and screws aremore accommodating than bolts and other highcapacity fasteners, large shrinkage strains inpoorly detailed joints can still cause splittingproblems if care is not exercised by designersand builders.

Nails, staples and screws offer the followingadvantages: low installation cost per unit shear strength rapid installation high fire resistance low joint deformation.

Nails, staples and screws may be used in arange of timber connections including thosewhich transfer large force components. Costsare minimal and the connections can be neat ifcarefully detailed. Where space is limited andloads high, designers should consider the useof bolts and other high capacity fasteners.

Light framed construction uses nail fixings for most joints


4Fastener Specification andApplication

Nails

Applications and Head TypesIn AS 2334, the principle nail classification is onthe basis of application type. Refer Table 1.Application type is associated principally with thehead type but is also affected by shank type andsurface treatment such as galvanising.

For pneumatic driving, a further range of nail headtypes is available. The T-nail is used to fix flooringbut this has reduced resistance to pull-through.Other pneumatically driven types include D-head,flat head, pin head, and pinless head.

Point TypesIn addition to nail types based on head shape, AS2334, includes different point types. The standardpoint type is the diamond with the point angleformed at 35 but alternative types are illustrated inAppendix D of AS 2334, which include pencil(which penetrate concrete more readily and areused on masonry nails), chisel and dump points.Refer Figure 1. Blunt (shear) point nails are alsoreadily available. These alternatives are importantin timber construction. Diamond pointed nailsfracture brittle sheeting and experience shows theyalso have a greater tendency to split hardwoodsand cypress. If designers, constructionsupervisors or builders find they are experiencingdifficult in nailing hardwood with conventional nailsa switch to dump, chisel or blunt pointed nails willoften solve the problem without there being anyneed to resort to techniques such as pre-drilling. Itis claimed that these nails have reduced holding(pull-out) power but this is not a seriousdisadvantage.

FIGURE 1 NAIL POINT TYPES

Shank and Head TypesNails can also be characterised by shank andhead type. The standard, called plain shankin AS 1720.1, is smooth and should be used fortemporary work and general construction. Nailswith annular ring and screw (or spiral) shanksare also available which provide superiorholding power to plain shank nails. There is atendency to use ring shank nails in softwoodand screw shank nails in hardwood.

Screw nails provide greater withdrawalresistance than plain shank nails and areparticularly effective against shock loads andreduce wood splitting. Some appropriateapplications are flooring, panelling, gussetplates, cladding, underlay, finishing, roofing andplasterboard. A related nail type is the twist nailwhich is easier to drive than the smooth shanknail. The twist used is a less intense form ofspiral.

Ring type nails have high holding powergenerated by the keying action of displacedfibres acting against the nail grooves. Inwithdrawal, resistance drops sharply after initialslip due to the rings tearing the wood fibres.Accordingly, ring shank nails are notrecommended where shock loads are involvedbut are suitable in high wind areas especiallywhere softwood framing is used. Data onwithdrawal capacities must be obtained fromnail manufacturers. Other applications includeunderlay for flooring, plasterboard and pallets.

Plain, screw and ring nails are available for bothhand and pneumatic driving.

Refer Table 1 for schedule of nails types asdefined in AS 2334, STEEL NAILS METRICSERIES.

MaterialsThe most common material used in nailmanufacture is cold drawn, low carbon steel.Refer AS 2334. Such nails are sufficientlyductile to bend through 90 degrees at a radiusequal to their diameter without fracture orcracking. Although not covered by thestandard, this ductility requirement is only metby plain and screw shank nails. Ring shanknails, because they are formed by a workhardening process, are more brittle and oftensnap if bent in this way. This lack of ductility isnot a problem in most timber construction.


5It is also possible to purchase nails made ofaluminium, copper, brass, silicon-bronze, stainlesssteel and monel. Aluminium nails are used forfixing aluminium sheeting and fittings and theothers in boat building and where especiallycorrosive environments exist e.g., swimming pools.

Monel nails have been used for the fixing ofwestern red cedar panelling. Because of theirsmoother surface it is usually necessary for thespecial type nails to have annular ring shanksto improve withdrawal resistance.

TABLE 1 NAIL TYPES (AS 2334)

Type Application IIlustration

Bullet head nail Timber framing and general finishing

Flat head nailMetal connectors, containers and

softwood framing

Hardboard nail Hardboard fixing

Wallboard nail Wallboard fixing

Cement sheet nail Cement sheeting

Flex sheet nailGalvanised sheeting, other flexible

sheeting

Soft sheet nailLow density materials

eg. plastics

Clout

General fixing of thin sheets notrecommended for structural connectors

such as framing anchors

Plasterboard nail Plasterboard fixing

Decking spike Timber deck fixing

Duplex nail Concrete formwork can be withdrawn

Roofing nailFix galvanised roof or wall sheeting

(non-cyclone areas only)

Fencing staple Fix fencing wire


6In exterior applications, the metal in some nailsreacts with extractives in the wood and formsstains; e.g., uncoated steel nails can cause blackstains and copper nails leave green stains. Thesolution to this problem is to use galvanised orother nail types excluding copper.

Finishes and CoatingsVarious special coatings and treatments alsoincrease nail holding power, provide corrosionresistance and improve appearance. Thetreatments include: plating hot dipped galvanising polymer and other coatings

Nickel and cadmium are the most commonly usedplating treatments. These improve appearanceand provide slightly improved corrosion resistance.

Hot dipped galvanised nails or screws shouldbe used in weather exposed situations

Hot dipped galvanising involves the application ofa zinc coating by hot dipping in a zinc bath. Itleaves a rough surface with enhanced withdrawaland corrosion resistance characteristics.

Manufacturers also coat pneumatically driven nailswith plastics which are claimed to improvewithdrawal resistance. The coatings are activatedby the friction heat generated during driving andmanufacturers indicate they increase short termwithdrawal resistance by around 150 percent. Aprocess called phoscoating is also in use. Thisinvolves the surface etching of an iron phosphatecoating, which tends to roughen the surface andenhance the withdrawal resistance arising fromfriction.

Preferred Diameter-Length CombinationsIn selecting nails, designers should be aware thatdiameters and lengths are available only in certaincombinations. Refer Table 2 for bullet head nailsand AS 2334, for details of other hand-driven nails.

TABLE 2 BULLET HEAD NAILS SIZE/LENGTH

Diameter Lengths

2.0 30 40 45 50

2.5 40 45 50 65

3.15 45 50 65 75

3.75 65 75 90 100

4.5 75 100 - -

5.0 100 125 - -

5.6 125 150 - -

Pneumatically driven nails are also available ina wide range of length-diameter combinationswith a common range of diameters being 2.0 3.3 mm and lengths in the range of 50 90mm.

Screws

Applications and Head TypesPlain wood screws are described in AS 1476,and self-drilling types in AS 3566. As with nails,plain screws are commonly classified by headtype and, herein, this same description isextended to self-drilling types. Refer Table 3.

In addition to head type, screws are alsoclassified by the method of driving.

Plain screw types are driven with aconventional screw driver in the case of aslotted head and with a Phillips driver in thecase of cross-recessed heads. Refer Figure 2.

FIGURE 2 SLOTTED AND CROSS RECESSED SCREW HEADS


7Self-drilling (Type 17) screws are available in awide variety of head shapes and driving typesappropriate to the particular application.

In general, the external and hexagonal recesseddrives are used where a high degree of directionalcontrol and high torque is necessary during theinstallation process.

The cross-recessed head is used where lessdirectional control and torque is needed.

Point TypesPlain wood screws have sharp conical (describedas Gimlet) points. The self-drilling types have aspecial drilling point which can penetrate thin metalsheet or wood without there being any need to pre-drill holes.

Power driven screws provide secure fixing.Countersunk heads may be appropriate forsome applications

TABLE 3 SCREW TYPES

Type Application Illustration

TRADITIONAL (AS 1746)

Countersunk head slotand cross-recessed drive

General finishing where the headmust be flush

Raised counter-sunk head slot and cross-recesseddrive

General finishing where the head isfeaturing

Round head slot drive Use is not recommended

SELF-DRILLING (AS 3566) TYPE 17

Hexagon washer head external hexagon drive

Roof sheet fixing. Used withneoprene washer under head

Countersunk head cross-recessed drive

General fixing in wood to woodconnections

Wafer head cross-recessed drive

General fixing of proprietary metalfastener to wood connections, whereroof sheeting rests on fastener

Bugle head cross-recessed and hexagonalrecessed heads

General fixing in wood to woodconnections where uplift may besevere


8Shank TypesShank size is specified by a gauge number asindicated in Table 4.

TABLE 4 SCREWS SHANK/GAUGE

Shank Size (mm) Gauge

2.74 4

3.45 6

4.17 8

4.88 10

5.59 12

6.30 14

7.72 18

The root diameter (the diameter at the base of thethread) is specified in the respective standards butthe capacities provided in AS 1720, are in terms ofthe screw gauge.

In plain wood screws a taper is used in thethreaded portion. The taper angle is chosen at thediscretion of the screw manufacturer.

The common Type 17 screws have parallelshanks.

An alternative shank is available with two threads,one with a high and one with a low profile which isclaimed to have increased holding power.

With hexagonal roof fasteners, a shank isavailable with threaded portions near the tipand head but with an unthreaded portion in themiddle. The upper threaded section preventsmetal roofing sliding down the screw shank andbreaking the washer seal under localisedloading such as is caused by tradesmanwalking on the ridges of roof sheeting.

MaterialsPlain screws are manufactured in low-carbonsteel, brass and stainless steel. Type 17screws are available in low carbon steel andstainless steel.

FinishesElectroplated finishes applied to screws includezinc, zinc-chromate, cadmium, nickel andchromium. These improve corrosion resistanceand appearance. For higher corrosionresistance in marine, salt or chemicalenvironments hot dipped galvanised, plated orstainless steel screws should be used. Hotdipped galvanised Type 17 screws are alsoavailable.

Preferred Diameter-Length CombinationsScrew diameters (defined by the size or gaugenumber) are manufactured only in a limitedrange of lengths. Refer Table 5 for traditionalwood screws. Diameters may vary betweenmanufacturers.

The value is the minimum permitted under AS1476. A corresponding range of preferreddiameter-length combinations is provided in AS3566, for self-drilling screws.

TABLE 5 WOOD SCREWS (AS 1476)

Length (mm)ShankDia.(mm)

Size(No.)

6 8 10 12 16 20 25 30 35 40 45 50 60 70 80 90 100 120

1.98 2 - - - - - - - - - - - - - -

2.29 3 - - - - - - - - - - - -

2.64 4 - - - - - -

2.97 5 - - - - - - - - - - -

3.33 6 - - - - - - -

3.68 7 - - - - - - - - -

4.04 8 - - - - - - - -

4.39 9 - - - - - - - - -

4.72 10 - - - -

5.38 12 - - - - -

6.05 14 - - - - - - 6.76 16 - - - - - - - - - - - -


9Joint Design

Nails and screws may be used to form joints whichresist both direct forces (shear and axial) andmoments. They are employed extensively indomestic construction for connecting framingmembers. They are also used for fabricatingplywood box-beams, stress skin panels, theconnection of sheathing, panelling and flooring andto fabricate the joints of nailed plywood and steelplate gusseted portal frames.

Lateral LoadsThe capacity of individual fasteners is determinedby procedures outlined in AS 1649. In determiningthe shear capacity the load at 0.4 mmdisplacement and at the ultimate load are dividedby appropriate safety factors and the lower of thetwo values is chosen in deriving the basic designcapacity. Usually, the relative slip of the two shearfaces increases rapidly just above the 0.4 mmrelative slip load which means that large increasesin slip, such as might be caused by moisturemovement, reduce the tendency to cause splitting.The standard test is in double shear where it isassumed that the load in single shear is half thedouble shear value. The capacity of nails andscrews is the same for fasteners of the samediameter.

For a satisfactory design it is necessary that N Nj.The design capacity Nj of a fastener iscomputed using the following procedure:

1. The species of timber being fastened mustbe known.

2. The seasoning state of the timber at thetime of driving the fasteners must also beknown and the service moisture contentestimated.

3. Reference is then made to Table 2.1 of AS1720.1, which places the fastener into aJoint Group.

The Joint Group will be one of J1 J6 forunseasoned timbers and seasoned timberswhich will have a service moisture contentover 15 percent and JD1 JD6 forseasoned timbers which remain at or below15 percent moisture content in service.

4. The characteristic capacity Qk is obtainedfrom fastener capacity tables in AS 1720.1,which is then modified by the relevant andk factors to obtain the design capacity Nj.

AS 1720.1 expresses fastener capacity in the form:Nj = k1k13k14k16k17Qk for nails (1)

= k1k13k14k16k17Qk for screws (2)Where

Nj = design capacity on an individual fastenerQk = characteristic capacityk1 = duration factork13 = end/side grain factork14 = double/single shear factork16 = side plate factork17 = multiple fastener factor

The load, N*, acting on an individual fastener is given by:

N* = ])q(q)q[q 2mydy2

mxdx +++ (3)

qdx = Fx/n (4)qdy = Fy /n (5)qmx = My m/lp (6)qmy = Mxm/lp (7)

WhereFx = direct force in the x directionFy = direct force in the y directionn = number of fasteners in the jointM = moment acting on the joint

xm,ym = x, y coordinate distances to nail furthest from joint centroidlp = polar moment of area of nail group

= ri 3/2 rm

1/2

ri = polar distance to the ith fastener

rm2 = xm

2 + ym2


10

In addition to depending on Joint Group, thecharacteristic capacities for nails and screwsdepend on their diameter. The basiccapacities for steel nails and screws are givenin Tables 4.1 4.7 of AS 1720. No data isprovided for other material types.Manufacturers test data should be consulted ifthese are being used.

The shear capacity of screws in end-grain israted as 60% to the capacity of side graindriven screws and the modification factor K13accounts for end grain effects.

Nails driven through pre-drilled holes inmetal connectors provide efficientconnections

Withdrawal LoadsWithdrawal loads depend on the length ofdriving, the type of fastener and whether or notthe fastener is driven into end or side grain. Itis recommended that, wherever possible, ajoint should be constructed with nails acting inshear rather than in tension. In a variety ofsituations this is not possible eg. with the fixingof roof and wall sheeting and battens. In suchsituations and especially where strong winduplift occurs the recommendations of sheetingsuppliers should be carefully followed. Incyclonic areas, Type 17 screws tend to beused for roof sheeting and batten fixing.

It should be noted that: nails have 25% withdrawal capacity

when hand driven only into end-grain.A minimum of 2 nails shall be used.

screws driven into end-grain have theirwithdrawal capacities reduced to 60percent of the side grain capacities.

withdrawal capacities for nails andscrews are given respectively by Tables4.2 and 4.6 of AS 1720.1For Type 17 screws, manufacturerscatalogues should be consulted forwithdrawal capacities.

AS 1684.2 and AS 1684.3 also giveswithdrawal capacities for nails andscrews for short duration wind loads.

Fastener SpacingsThe fastener spacings specified in AS 1720.1,for nails driven, respectively, directly into woodand into pre-drilled holes are scheduled inTable 6 for connections in rectangular patterns.The intent of AS 1720.1, is for these spacingsto apply to rectangular patterns of nails asillustrated in Figure 3 and that they applyirrespective of timber type. It is generallyaccepted this is reasonable with hardwood tohardwood connections but that softwood tosoftwood connections (density 560 kg/m3 orless) can employ closer spacings. The closerspacings in Table 6 are from the New ZealandCode NZS 3603.

Staggered patterns (refer Figure 3) aresometimes used in forming nailed plywoodmoment connections in portal frames. In suchjoints the practice has been to adopt thestaggered pattern at the 20d along grain, and10d across grain spacing but to use double thenumber of rows. Experience shows that thisworks well, a fact supported by research byTRADA in the UK.

FIGURE 3 NAILING PATTERNS

TABLE 6 FASTENER SPACINGSAS 1720.1

(All Species)NZS 3603

Softwood (density < 560 kg/m3)Along Grain Across Grain Along Grain Across Grain

Directly driven 20d 10d 12d 5dPre-drilled 10d 3d 10d 5d


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Connection Design

Direct Force Connections

Shear TypeThe design of connections subject to direct forcesis straightforward. The allowable force perfastener Q is obtained by equation 1 or 2 fornails/staples and screws respectively and use ofthe relevant tables in AS 1720.1, for thecharacteristic values Qk. The number of fastenersis calculated by dividing the total load for the mostcritical load combination by the fastener capacity.

Once the number of fasteners has beencomputed, the joint detailing can be finalised.

In connections where members cross oneanother at 90 or some angle approaching 90,the loads involved are usually not large. Insuch cases the nails can be staggered or, if theloads are large, then the options are to:

use a single or single line of highercapacity fasteners such as bolts, split-ringsor shear-plates, and/or seasoned timber

use special proprietary fasteners such asjoist hangers.

Example 1

Assume a splice joint is to carry the tension forces PDL = 4 kN, PLL = 3 kN in 90 x 35 mm seasonedsoftwood Joint Group JD4.

The load duration factor k1, for 1.25 DL + 1.5 LL is 0.77. The equivalent DL value is (1.25 x 4 + 1.53 x3)/0.77 = 12.34. The DL + LL combination will control the design. Use 3.3 diameter nails; Qk = 885 N(interpolated from AS 1720.1 Table 4.1(b)) and 25 mm side plates.

N j = 0.85 () x 0.77 ( k1) x 2 (k14) x 0.85 (k17) x 885 (Qk)

= 985 N

n = 9.5 x 103/985= 9.6 (Use 10 nails)

Minimum Nail Length = 2 x 25 + 35= 85 mm (Use 90 mm nails)

For a splice joint it is a simple matter to avoid any possibility of cross-grain shrinkage induced splitting byuse of double side plates on each side, refer Figure 5, but this is normally unnecessary, for seasoned or alow shrinkage timber.

The recommended joint is illustrated in Figure 4. The joint of Figure 5 could be considered for metal spliceplates where shrinkage may be of concern e.g., with unseasoned ash type hardwoods.

FIGURE 4 SPLICE USING SINGLE TIMBERSIDE PLATES

FIGURE 5 SPLICE USING DOUBLE STEELSIDE PLATES


12

Example 2

Assume a joist is to be suspended at midspan and that the forces acting are PDL = 1 kN, PLL = 2 kN.Refer Figure 6. The DL + LL combination is critical. Using the same nails as chosen in Example 1.

Nj = 0.85 () x 0.77 (k1) x 2 (k14) x 0.94 (k17) x 885 (Qk)

= 1089 N

n = 4250/1089

= 3.9 (Say 4 nails)

The joint layout recommended on the assumption that little shrinkage will take place is illustrated in Figure6.

Where cross-grain shrinkage in the horizontal 90 x 35 mm member is likely to be of concern, thealternative is to use larger capacity fasteners such as a single bolt or a proprietary joist hanger. ReferFigure 7. For some loads and timber sizes, it may be possible to support the load on staggered fasteners;such as illustrated in Figure 8.

FIGURE 6 CROSS-JOINT FOR SEASONEDOR LOW SHRINKAGE TIMBER

FIGURE 7 CROSS-JOINT FOR HIGHSHRINKAGE TIMBER

Nail lamination of two timber members canprovide an effective means of making alarge solid section

FIGURE 8 CROSS-JOINT FOR HIGHSHRINKAGE TIMBER


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Axial Type

Nail and screws act in withdrawal mode when used to fix roof sheeting or roof battens.

Example 3

Consider roof battens at 900 mm centres spanning 600 mm between hardwood rafters of Queenslandnon-Ash Eucalyptus (J2 Joint Group) and supporting metal sheet roofing. Assume that 63 m/s is thedesign gust regional wind velocity and that Cpt = 1.8.

qz = 0.6 x 10-3 x 632 x 1.8 = 4.33 kPa

Ignoring sheeting and batten dead weight, each batten support point is loaded by a force = 4.33 x 0.9 x 0.6= 2.34 kN.

Using manufacturers literature or Table 4.8 of AS 1720.1, a Number 14 size Type 17 screw is adopted.The minimum depth of penetration is computed from Table 4.6 (A) which develops 100 N per mm ofpenetration. The withdrawal capacity of a Number 14 size Type 17 screw

Nj = 0.85 () x 1.0 (k13) x lp x 1.0 (n) x 100 = 85 lp N

Required penetration: 85

2340 = 27.5 mm Say 30 mm.

Moment ConnectionsIn practice, moment connections are usually only used to form the joints of portal frames. While suchjoints are subject to both direct forces and moment, the latter dominates and the joint may be designed, forpreliminary sizing purposes, for the moment only.

According to AS 1720.1, the force in the nail most distant from the nail group centroid is computed usingthe formula:

q =

== 1.5i

m1.5im

m

p

m

r

rM

rr

Mr

I

Mr

The depth, d, is established by design of the frame and this, in turn, fixes one dimension of the joint. Theother dimension, l, is most rapidly estimated on the basis of formulae derived by assuming the nail issmeared as shown in Figure 9 and has a shear capacity given by 2Q/s1s2 for staggered patterns and,because of the lower nail density, Q/s1s2 for rectangular patterns. The design criteria are therefore:

for staggered patterns

dAr

rM

SS2Q

1.5

m

21 = (8)

for rectangular patterns

dAr

rM

SS

Q1.5

m

21 = (9)

The integral can only be evaluated by quadrature which, for staggered patterns and using the Gaussianformula, leads to:

2Q/S1 S2 = 4.81M(l2+d2)0.25/ld[(l 2+d2)0.75-gh(g2 l2+h2d2)0.75] (10)

It is common to select g and h which control the size of the vacant central position using g = h = 0.7 whichreduces the expression for staggered patterns to:


14

2Q/S1 S2 = 6.75 M/ld )dl 22 + (11)

This equation is non-linear in l and is solved by substituting trial values of l into the right hand side until itequals the left hand side. Refer Example 4.

A further consideration in joints of this type is the level of joint shear. In a portal joint, a very rapid build upof bending stress occurs over the length of the gusset. The joint shear is given by:

fsj = 1.5 M/bd= 1.5M/lbd (12)

FIGURE 9 IDEALISED MODEL OF NAILED MOMENT CONNENCTION USED FOR PRELIMINARYSIZING

Example 4

Assume that a 532 x 80 mm, Douglas fir, glued laminated beam carries the following factored dead andlive load moments:

MDL = 26.1 kNmMDL + LL = 68.6 kNm

The dead load plus live load moment is equivalent to a dead load moment of 68.6/0.77 = 89.1 kNm andhence the MDL + LL value controls. If 3.15 diameter nails are used then Q = 810 N (Table 4.1 B). Assumethe nails are placed in a staggered pattern at spacings 60 mm and 30 mm along and across the grainrespectively:

j = 0.8() x 0.77 (k1) x 1.1 (k16) x 1.2 (k17) x 810= 659 N

and 2Q/s1s2 = 2 x 659/60x30 = 0.73 MPad = 532 mm

The right hand side of the appropriate formulae is computed for l = 1000, 900, 800 mm where M = 0.5 x68.6 kNm since there are two nail groups sharing the joint moment.

l 2Q/S1S2 6.75 M/ld (l2=d2)0.5

1000 0.73 0.384

900 0.73 0.463

(685) 0.73 (0.733)

650 0.73 0.797


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with the solution being l = 685 mm by interpolation.

Since neither part nor an odd number of nail rows can be used, N = int (685/60) = 11.41, we use 12columns. After allowances for end distances, the gusset length required is 810 mm.

Choose a dimension l = 930 mm. After laying out the joint, it is possible to refine the design using theactual nail positions.

Computer Design of Moment JointsThe simplest method for designing moment jointsis to use a computer program. Assume that theprogram used in this instance indicates that deadplus live load is the critical condition and producesthe output below.

Gusset Detail

Length 11 of gusset = 810 mm

Nail Details

Nail diameter = 3.15 mmBasic nail capacity = 810N JD4 Joint

Group

Number of gusset nails = 236 per sideAlong grain spacing = 60 mmAcross grain spacing = 30 mm

Output from the computer program is given inFigure 10.

Joint Shear

The beam is a 532 mm x 80 mm Douglas fir ofStrength Group SD5.

fsj = 1.5M/dbI1= 1.5 x 68.6 x 106/532 x 80 x 810= 3.0 MPa

From Table 2.3A of AS 1720:

Fsj = 6.1 MPaFsj = 6.1 x 0.8 () x 0.97 (K1)

= 4.7 MPa

Hence joint shear presents no difficulty.

FIGURE 10 GUSSET DETAIL FOR EXAMPLE 4

Specifications

For detailed specification clauses, referenceshould be made to Datafile SP1, TIMBERSPECIFICATIONS.

The following is a check list of some itemswhich should be included in the specificationsof fasteners/joints or alternatively, indicated onplans:

Fastener type Fastener size/length etc. Number of fasteners, spacings etc. Material/protection e.g. galvanised,

stainless steel Joint group of timber Workmanship Pre-drilling where appropriate


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Machine nailing of multiple nail joints isstructurally efficient and allows on-sitetolerances.

Nail fixing of cladding depends on claddingand framing type

Other References

1. AS 2334, STEEL NAILS METRICSERIESStandards Australia.

2. AS 1720.1, SAA TIMBER STRUCTURESCODEStandards Australia.

3. AS 3566, SCREWS SELF DRILLING FOR THE BUILDING ANDCONSTRUCTION INDUSTRIESStandards Australia.

4. AS 1476, METRIC WOOD SCREWSStandards Australia.

5. MECHANICAL FASTENERS FORSTRUCTURAL TIMBER WORKTRADA (UK) Wood Information, Section2/3, Sheet 9.

6. AS 1684.2 and As 1684.3 ResidentialTimber Framed Construction.


Joint Design 2 (2001) - Nails, Staples & Screws

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