Copyright © 1999, 2004 by American Forest & Paper Association, Inc., Washington, D.C.
ADS Commentmy
PART XI: WOOD SCREWS
11.1-GENERAL
11.1.1-Quality of Wood Screws
In the 1986 and earlier editions, woodscrewswere
not required to meet particular dimensional and thread
type standards to qualify for the design values given in
the Specification. The general performance requirement
inthese
editions was that the woodscrewsbeof
sufficient strength to cause failure in the wood rather
than the metal.
-
The 1991 edition requires wood screws to conform
to the dimensional data of
ANSVASME
Standard
B18.6.1-1981in order to qualify for tabulated design
values and related design provisions. Standard B18.6.1,
whichcovers both cut and rolled thread screwtypes,
does not specifyminimum metal strength properties.
However,bendingyield
strength of the screwisa
required input to the lateral designvalueyield
mode
equations of
11.3.1.
Additionally, the actual tensile
stressin the screw at the root diameter isrequired to
be checked
when
designing
the connection for withdrawal loads (see 11.2.3of the Specification).
Tabulated lateral design values for woodscrewsin
Tables 11.3A and 11.3Bapply to screwswithspecified
strength properties.Irrespective of whether the lateral
designvaluesinthesetables
are used or lateral design
values are developeddirectly
from the yield mode
equations of 11.3.1, it is the designer’s responsibility to
specify the metal strength properties of the wood screws
that are to be employed for the job.
11.1.2-Fabrication and Assembly
-
11.1.2.1 Prior
to
the 1962 edition, lead
hole
requirements for woodscrewswere 90 percentof the
screw root diameter for hardwoods and 70 percentof
the root diameter for softwoodspecies.Theseprovisionswerebased on early research involving flat head
woodscrews up to 24 gage and 5 inchesinlengthin
seven species, including southern pine, cypress and oak
(55). In the 1962 edition, the leadholerequirements
werereferenced to new fastener species groups established on the basisofspecificgravity.
The 90 percent
of root diameter requirementwasapplied
to Group I
species,thosewithaspecificgravity
greater than 0.60;
and the 70 percent
of
root diameter requirement
was
applied to speciesoflowerspecificgravityin
Groups
11, I11 and IV.
In the 1982 edition, the provisionallowingthe
insertion of wood screws in
Group I11 and IV species
without aleadholewhen
the screwwassubjectto
withdrawal loads onlywas
introduced. The specific
gravity of speciesinthese groups wasless than 0.5 1.
This provision for use of screws without aleadhole
paralleled that made for 3/8 inch and smaller diameter
lagscrewsinthesame
edition and was supported by
both research results and field experience (see Commentary for 9.1.2.2).
The leadholeprovisions for screwsinwithdrawal
in the 1991 edition continue the requirements of the
1982 and earlier editions except that the species group
designationshavebeenreplaced
by specific
gravity
ranges.
11.1.2.2 In the 1960 and earlier editions, wood
screwsresisting
lateral loads were requiredtohave
shank and threaded portion leadholesin
hardwoods
equal to the shank and thread root diameters, respectively; and insoftwoodspecies equal to seven-eighths
the shank and thread root diameters, respectively.
These provisions were based on early lateral load tests
wood
of screws
(57,62,98).
The hardwoods and
softwoods
designations
were
replaced
the
in1962
edition withspecies Group I and Groups 11, I11 and
IV, respectively,
based
on specific
gravity.
Species
classifiedin Group I werethosewithspecificgravities
greater than 0.60
while
those
with
lower
specific
gravities were classified in the higher numbered groups.
In the 1991 edition, lateral designvalues for wood
screws are no longer tabulated in terms ofspecies
groups but are given for each individual species combination. Thus the leadholerequirements
for screws
resisting lateral loads that were
given
in
previous
editions are appliedintermsofwhetherthe
specific
gravity of the speciesis greater than 0.60 or equalto
or less than 0.60. It is to be noted that leadholesare
required for allwoodscrewssubject
to lateral loads
regardless of wood specific gravity.
11.1.2.3 Insertion of
wood
screws
by turning
rather than driving has beenarequirementsincethe
1944 edition. All tests on which wood screw provisions
in the Specification are based involved joints made with
this method ofassembly(55,62,98).
11.1.2.4 Use of lubrication to
facilitate
screw
insertion and avoidscrew damage, arecommendation
since the 1944 edition, has been made mandatory in the
Wood Screws
~~
133
NDS Commentary
1991 edition.Earlytestsshowthe
lubricant has no
significanteffect on designvalues (55,57,98).
11.2-WITHDRAWAL DESIGN VALUES
Background
for wood
screws
w = K,G~D
are
(C11.2-1)
where:
W
K,
G
D
= nominalwithdrawaldesignvalueperinch
of screw length or per inch of penetration
of the threaded portion, lbs
= constant basedonultimate
load tests and
screw length basis
= specific
gravity,
oven
dry
weight
and
volume
= shank diameterofthescrew,in.
This equation wasbasedonearlyextensivetesting
with cut thread woodscrews and sevenwoodspecies
(55). In the 1960 and earlier editions, the equation was
published
in
the
Specification
in
lieu
of
tabulated
withdrawaldesignvalues. In the 1944 edition, avalue
of 2040 wasused for the constant K,.
This value
gave a withdrawal design value per inch
of total screw
length assuming the depth of penetration into the piece
receiving the point was at least two-thirds the length of
thescrew; and awithdrawaldesignvalue
whichwas
approximatelyone-fifththeultimate
load determined
fromscrewwithdrawaltests
(55). The one-fifth factor
represented an originally recommended one-sixth factor
onultimate load (57) increased by twentypercent as
part of theWorld War I1 emergencyadjustmentin
1.2 factor was
designvalues.Followingthewar,this
codified as 10 percent for thechangefrompermanent
to normal loading and 10 percent for experience(see
Commentary for 2.3.2).
In the 1950 edition, the basis for W waschanged
fromdesignvalueperinchof
total screw length to
designvalueperinchofpenetrationofthethreaded
part of the screw. The value of the constant K , was
changed to adjust the equation for this new index point
(57,62). The equation became
W = 2850 G 2 D
where:
134
Wood s%rews
penetrationofthethreaded
screwinthepiecereceivingthe
portion ofthe
point, lbs
A table of allowable screw withdrawal design values
based on Equation C11.2-2 also was introduced inthe
1950 edition.
11.2.1-Withdrawal from SideGrain
Withdrawal design
values
basedonthe equation
W = nominal withdrawal design value per inch of
(C11.2-2)
In the 1960 edition, the table ofscrewgages
and
lengths, which had been part of the Specification since
the 1944 edition, was dropped. In the 1962 edition,
Equation C11.2-2 also was dropped from the Specification in favor of the tabulated withdrawal design values
alone.
1991 Edition
The wood screw withdrawal design values in Table
1 1.2A ofthe
1991 edition are basedonEquation
C11.2-2 and remainunchanged from those givenin
earlier editions. The specific application of the tabulated withdrawaldesignvalues
to rolledthreadwood
screws as well as cut thread screws is a new provision.
Previous editions did not specify thread type, although
theearlyresearch
on whichwoodscrewwithdrawal
designvalues are basedwasconducted
on cutthread
screws.
The shank or body diameter of a cut thread screw
is the same as the outside diameter of the thread. The
shank or bodydiameter of therolledthreadscrewis
the same as the root diameter. For the same gage and
nominaldiameterofscrew,
both screwthreadtypes
havethesame
threads per
inch,
the
same
outside
diameter of thread and thesamethread depth. If the
tensilestrengthofthescrewis
adequate and thelead
holeprovisionsbased on root diameter are employed,
is
thewithdrawalresistance
ofrolledthreadscrews
consideredequivalent
to that of cut thread screws.
This is supported by comparative testsofonetypeof
tappingscrew and cut thread woodscrews.Although,
thethread depth of tapping and rolledthreadscrews
are not the same, both types
have
outside
thread
diameters that are larger than theirbodydiameters.
The comparativetestsshowed
that, for comparable
diameters and penetrations of thethreadedportion of
the screws, the withdrawal design values of the tapping
screw were slightly higher than those of the cut thread
fastener (65,204).
Screwlength as well as screwgage
or nominal
diametermust be specified. The ANSUASMEB18.6.1
standard requires thread length to be equivalent to at
least
two-thirds
of the
nominal
screw
length.
The
screwdiametersassociatedwiththescrewgagesgiven
in Table 11.2A are shown in Tables 1 1.3A and 1 1.3B.
-
ADS Commentary
Table 11.2Aisenteredwith
the specificgravityof
the lumber species combination receiving the threaded
portion of the screw.Specificgravityvalues
are given
for current commercial lumber species combinations in
Table 11A.Speciesspecificgravityvalues
tabulated in
the Specification have changed in various editions as a
resultofnew
property information, changesin
the
commercial importance of some
species,
and the
introduction ofnewspecies groupings. Specific gravity
values tabulated in the 1991 edition reflect a number of
such changes from valuesgiveninpreviouseditions.
11.2.2-Withdrawalfrom End Grain
Early tests of wood screws in withdrawal
from end
grain surfaces of oak, southern pine, maple and cypress
gavesomewhat
erratic resultsrelative
to those for
withdrawal from side grain (55). These irregular results
were attributed to the tendencyof the screw to split
the
wood
in
the end grain configuration. Average
ratios of end grain withdrawal resistance to side grain
withdrawalresistanceranged
from 52 to 108percent
(55). Becauseofthisvariability,
structural loading of
woodscrewsinwithdrawal
from end grain has been
prohibitedsince the 1944edition.Wheresplittingis
avoided, use of an end grain to side grain withdrawal
designvalue ratio of75percent
has beensuggested
(57,66).
11.2.3-Tensile Strength of Wood Screw
(See Commentary for 11.1.1)
11.3-LATERAL DESIGN VALUES
11.3.1-Wood-to-Wood Connections
Background
From the 1944 through the 1986 editions, lateral
designvalues for woodscrews loaded at anyangle to
grain werebased on the equation
(C11.3-1)
2 = KLD2
where:
2 = nominalwoodscrew
lateral designvalue,Ibs
'K = species group constant based on specific
=
=
=
=
D =
gravity ( G ) ofwoodmembers
4800 Group I
G = 0.62
3960 Group I1
G = 0.51
3240 Group I11
G = 0.42
2520 Group IV
G = 0.31
shank diameter, in.
-
0.75
-
0.49
0.41
- 0.55
The equation wasbased on early lateral load tests
ofwoodscrewsin
southern pine,cypress and oak in
whichthe depth of penetration of the screw into the
piece receiving the block was at least 7 times the shank
diameter (57,98). The valuesshown for the constant
KL provided lateral design values which were about 75
percent of those associated with test
proportional limit
values. The KL valuesincludedtheoriginallyrecommended adjustment of1.6(57)increased20percent
as
part of the World War I1 emergency increase in wood
designvalues. Thelatter adjustment wassubsequently
codified as a 10 percent adjustment for thechange
from permanent to normal loading and 10percent for
experience (see Commentary for 2.3.2). Lateral design
valuesof75percentof
proportional limitvalues are
about one-fifth maximum test loads (57).
Beginningwith the 1950 edition, tabulated wood
screw lateral designvaluesbased on Equation C11.3-1
were includedin the Specification. Presentation of the
equations for each group was subsequently discontinued
beginning
with
the 1962 edition. In the 1960 and
earlier editions, awoodscrewfastener
group between
Groups I1 and I11 wasprovidedintheSpecification.
This group for intermediate density hardwood species
alsowas dropped beginningwith the 1962edition.
Prior to1971, grain type and other featuresthan
specificgravitywereconsideredinclassifyingcertain
lowerdensitysoftwoodspecies into KL factor groups.
This wasevidenced by somespecieshavingthesame
specific gravities as those in Group I11 beingclassified
in Group IV (57,62).Beginningwiththe
1971 edition,
specific
gravity
was
used
as the
sole
criterion
for
assignment ofspecies for woodscrew lateral design
value constants. The specificgravityclasslimits
for
KL valuesshowninthelegend
for Equation C11.3-1
wereused
toclassifyspecies
from 1971 throughthe
1986 edition.
1991 Edition
Similar to the treatment of bolts and lagscrews,
lateral design
values
for wood
screws
in
the
1991
edition are based on application ofthe
yield
limit
model (see Commentary for 7.2.1 and 8.2.1). The same
general equations used to describedifferentmodes of
yieldingoflagscrews
are alsousedwithwoodscrews
(seeCommentary for 9.3.1). Three modes ofyielding
are provided for: bearing in thesidemember or cleat
(Mode I, ), development of a plastic hinge in the screw
in the main member (Mode IIIs ), and development of
plastichingesin both main and sidemembers(Mode
IV).
The term KO in the denominator of the yield
mode equations of11.3.1relatesyieldmode
equation
designvaluesbased
on a 5 percentdiameteroffset
Wood Scmws
135
dowelbearing strength to the general levelof proportional limit based lateral design values previously given
intheSpecification.
For smalldiameterdoweltype
fasteners (wood screws and nails), this conversion factor
wasset at 2.2when the fastenerpenetrationinthe
member receiving the point is sufficient to develop the
full lateral load capacity of the joint.
In the 1986 and earlier editions of the Specification,
lateral design values for small diameter lag screws were
lower than those for wood
screws
of
comparable
diameter. This differencewasaresultofthedifferent
methodologies used to establish lateral design values for
thetwo fastener types,primarily the reduction factor
applied to proportional limittestvalues.
In the 1991
edition, this difference in lateral design values between
small diameter lag screwsloadedparallel to grain and
wood screws of similar diameter has been minimized by
usingaconversion factor, KO , of3.0 for thelargest
diameterwoodscrews.
This valuerelates to the2.8,
4.0 and 3.0 conversion factors associated
with
the
Mode Is , IIIs and IV yield mode equations, respectively, for lag screws loaded parallel to grain (see Commentary for 9.3.1 - Yield Mode Equations). To
provide for a gradual transition of KO values between
small and large diameter wood screws, a variable value
of KO is used for intermediatediameterscrews
as
shownbelow.
Unthreaded shank diameter, inches = D
Diameter coefficient for woodscrews = KO
D
0.17
0.17 c D < 0.25
D 2 0.25
s
K’’= 2.2
KO = 1O(D)
+ 0.5
KO = 3.0
No adjustment of wood screw yield mode equation
designvalues are made for varyinganglesof load to
grain. This is a continuation of procedures in previous
editions of the Specificationwhichassignedthesame
woodscrew lateral designvalues to both parallel and
perpendicular to grain loading conditions.
The lowestvalue of 2 obtained from thethree
yield mode equations of11.3.1isselected
as the
nominal lateral designvalue for the connector. The
equations are enteredwith
unthreaded screw shank
diameter,sidememberthickness
and dowelbearing
strengths, Fa and Fa , for the species of wood being
used for the
side
or main
member.
Such
dowel
bearing strength values are given in Table 11A and are
based on the equation
FG= (16,600) G
where:
136
Wood Scmws
(C11.3-2)
G = specific gravity based on oven dry weight and
volume
The research on which Equation C11.3-2isbased
involvednailbearingtests
on fivespecies(203).Tests
ofthreenaildiameters(0.148
- 0.225in.)withone
species showed diameter to have no significant effect on
smalldiameter dowel bearing strength (203).
The bendingyield
strength value, Fyb , for the
used alsois an input to the yield
woodscrewbeing
mode equations. For screwshavingadiameterequal
toor
larger than 3/8 inch, Fyb maybetaken
as
45,000 psi (see Appendix I). Bendingtestsofnailsof
various diameters show bending yield strength tends to
increase as diameter
decreases
(106).
Wood screw
bending yield strength values based on the relationships
used to develop
found in thisnailresearchhavebeen
wood
screw
lateral design
values
tabulated
in
the
Specification for screws less than 3/8 inch diameter (see
Appendix I).
Tabulated Wood-to-Wood Lateral Design
Values. Lateral designvaluesgivenin
Table 11.3A
apply to single shear connections made onlywith cut
thread wood
screws
having
the
unthreaded shank
diameters tabulated. The table
provides
lateral design
values for screwgages from 6 to 24 and for major
individual
species
combinations.
In earlier
editions,
lateral designvalueswere
tabulated intermsof
four
fastener groups based on specificgravityclasses.
-
Tabulated lateral design values apply to connections
made with side member and main member of the same
species.
Where
different
species
are used, tabulated
lateral designvalues for thespecieswiththelowest
specific gravity may be applied or lateral design values
may
be
determined
from the yield modeequation
directly. For connections involving species not listed in
thetable, lateral designvaluesgiven
for aspecies of
lowerspecificgravitymaybeused.
Lateral design
values
in
Table 11.3A
apply
to
screwshavingthebendingyield
strengths, Fyb , given
in footnote 2ofthetable.
For screwgages 6 to 20,
the strengths shown are based on Equation C12.3-2 (see
Commentary for 12.3.1)developedfromthetests
of
commonnails.
For screws,this equation isentered
withthe unthreaded shank diameter as D.
Comparison of 1991 and Earlier Edition
Lateral Design Values. The lateral designvaluesin
the1991edition
are based on sidememberthickness,
screw shank diameter,dowelbearing
strengths of the
side and main members, and the bending yield strength
of the woodscrew.
Lateral designvaluesinearlier
-
NDS Commentary
editions were
based
on screw shank diameter and
fastener group or specificgravityclass.Both
the 1991
and earlier editions assume wood screw penetration into
the main member of at least 7 times the shank diameter. The effect of these different bases
and the conversion factors, KO , used to relate yield mode lateral
design values to the level of previous tabulated lateral
designvalues are shownby the comparisons of 1991
and 1986 lateral design values in Table C11.3-1.
Table C11.3-1- Comparison of 1991 and 1986 NDS
Wood-to-Wood Wood Screw Lateral Design Values
Side
Member
Thickness,
in.
_-
-
wood
Screw
Gage
wood
screw
W o o d Screw Lateral
lbs
Diameter,
in.1986 1991
0.164
0.216
0.294
0.372
108
138
190
Ratio
-
106
185
342
548
1.02
0.75
0.56
0.164
0.216
0.294
0.372
132
159
210
283
106
185
342
548
1.25
0.86
0.61
0.52
0.164
0.216
0.294
0.372
148
200
284
394
106
185
342
548
1.40
1.08
0.83
0.72
0.164
0.216
0.294
0.372
79
103
145
87
151
280
448
0.9 1
0.68
0.52
0.164
0.216
0.294
0.372
90
112
152
207
87
151
280
448
1.03
0.74
0.54
0.46
0.164
0.216
0.294
0.372
115
155
204
268
87
151
280
448
1.32
1.03
0.73
0.60
-
-
-
The lower 1991/1986 lateral design value ratios for
the larger gagewoodscrewsrelative
to the lateral
designvalue ratios for the 8 g screwreflectthe use of
larger KO factors in the yield mode equations for the
larger gages in order to bring wood screw lateral design
values in line with
lateral design values for lag screws
similar
of
diameter. The differences
between
the
1991/1986 lateral designvalue ratio for the joint with
8 g screw and 1/2 inch side members and that with 8 g
screw and 1-1/2 inchsidemembers (1.02 vs. 1.40 and
0.91 vs. 1.32 for southern pine and spruce-pine-fir
respectively)
indicates
the significant
effect
of
side
memberthickness.
The generallyhigher lateral design
value ratios for southern pine compared to spruce-pinefiris due to the fact southern pinewas at theupper
limit of its 1986 fastener group (specific gravity ) class
whereas spruce-pine-fir was near the lower limit of its
class. In the 1991 edition, use of the specificgravity
value for eachspecies combination to establishdowel
bearing strength valuestieswoodscrew
lateral design
values for each combination more closelyto its own
properties.
11.3.2-Wood-to-Metal Connections
11.3.2.1 In the 1986 and earlier editions ofthe
Specification,designvalues for woodscrewsinlateral
resistance were increased 25 percentwhenmetalside
plates were used (57). This adjustment wassimilarto
that used for bolted joints with metal side plates prior
to 1982 (see Commentary for 8.2.2).
Under the provisionsof the 1991 edition, wood
screw lateral design values for joints made with metal
side members are determined from the Mode 111, and
Mode IV equations of 11.3.1. The Mode Is equation
is not used as bearingin the metalsidemembers
is
considered separately in the design of metal parts (see
11.3.2.2). The yield mode equations are enteredwith
the dowel bearing strength of the metal as Fcs and the
thicknessofthe
metal as thesidememberthickness.
Earlier editions did not account for the effectofthe
metal gage used.
Table 11.3B gives lateral designvalues
for cut
thread wood screw joints made with steel side members
from 0.048 inches (18 gage) to 0.239 inches (3 gage)
thick. A dowel bearing strength of 45,000 psi, applicable to ASTM A446 Grade A galvanizedsteel,was
assumed for allthicknesses.
The samewoodscrew
bending yield strengths, F , used to develop
the
wood-to-wood joint lateral dsign values in Table 11.3A
were used todevelop the Table 11.3B lateral design
values.
Comparison of 1991 and Earlier Edition
Lateral Design
Values.
Differences
in
1991 and
earlier edition woodscrew
lateral designvalues are
illustrated
in
Table Cll.3-2. Lateral design
values
shown for both editions are based on a penetration of
the threaded portion of the screw in the main member
ofseventimes
the shank diameter. The 1986 lateral
designvalues are applicable to anymetalsideplate
thickness that permitsthisscrew
penetration requirement to be met.
Wood Scmws
137
ADS Commentmy
Table C11.3-2 - Comparison of 1991 and 1986 NDS
Wood-to-Metal WoodScrew Lateral Design Values
Stee1
Side
Member
Thickness,
in.
wood
wood
screw
Screw
Diameter,
Gage
in.
1986
W o o d Screw
Lateral
Design Value, lbs
1991
Ratio
0.075
(148)
8g
12g
18g
0.164132
0.216
231
0.294 428
132
176
249
1.00
0.76
0.58
0.134
(log)
8g
12g
18g
0.372 24g
0.164132
0.216
231
0.294 428
685
147
188
260
356
1.11
0.81
0.61
0.52
0.075
(1 4g)
8g
12g
18g
0.164109
0.216 189
0.294350
106
141
199
0.97
0.75
0.57
0.134
(108)
8g
12g
18g
0.372 24g
0.164109
0.216
189
0.294350
560
119
152
209
286
1.09
0.80
0.60
0.51
woodscrewsinsertedin
the end grain of the main
member has been a provision of the Specification since
the 1944 edition. This isthesameend grain factor as
that used for lag screws.
11.3.5-Combined Lateral and Withdrawal Loads
Earlier editions of the Specificationassumedthe
capacityofwoodscrewssubject
to withdrawal and
lateral loads at the sametimewasthesame
as the
capacity of the screw under each load acting separately.
In the 1991 edition, the interaction equation introduced
for combinedwithdrawal and lateral loading onlag
screws (see Commentary for 9.3.5) has been applied to
woodscrews.
Although availablelagscrewtest
dpta
indicate
withdrawal
and lateral load components
interact only at total load anglesless than 45" and
onlywith larger diameter screws(115), the lag screw
interaction equation has beenapplied to woodscrews
for purposes of uniformity and conservatism. The
equation, which is of similar form to the bearing angle
to grain equation (see Appendix J), is
The lower lateral design
value
ratios in Table
C11.3-2 for the larger screwgages are aresultof the
procedures introduced in the 1991 edition to bring
lateral designvalues for the larger woodscrews into
linewith those for lag screwsof comparable diameter
(see Commentary for 11.3.1 - Comparison). The
comparisons made show that, for equivalent screw sizes,
an approximate 80 percent increase in steel side memberthicknessisassociatedwith
an increased lateral
designvalueof 11 percent or less.
allowable
design
value
for wood
screw
loaded at angle to the surface of main
member
lateral design value for wood screw joint
withdrawaldesignvalue
for woodscrew
joint per
inch
of
thread penetration in
main member
length of thread penetration of thewood
screwinthemainmember
anglebetweenwoodsurface
and direction
of applied load
11.3.2.2 (See Commentary for 7.2.3)
11.3.3-PenetrationDepthFactor,
C
'
Use of reduced lateral design values for penetrations
of the threaded portion ofthescrewin
the main
member ofless than 7times the shank diameter (D)
has been a provision of the Specification since the 1944
edition. The minimum penetration requirement of 4 0
and the use of the ratio of actual penetration to that
required for full lateral designvalue (p/7D)as
the
factor for adjusting lateral design values for penetration
are based on earlywoodscrewresearch(57,98).
11.3.4-EndGrainFactor,
CCg
Use of two-thirds the lateral design value for wood
screwsinsertedinside
grain as the designvalue for
138
-
Equation C11.3-3 can also be used to determine the
allowable design value of wood screws embedded at an
angle to grain in the woodmember and loadedina
direction normal to the wood
member.
For this
condition a would be defined as the angle between the
woodsurface and thelagscrew
as showninFigure
C11.3-1.
11.4-PLACEMENT OF WOOD SCREWS
11.4.1-Edge Distance, End Distance, Spacing
The absence of splitting has been used as a performance criterion to determine the adequacy ofend and
edgedistances and spacing for woodscrewssincethe
1944 edition.
Woai s%rews
~
-
ADS Commentary
Table C11.4-1 Wood Screw MinimumSpacingTables
distance
Figure CII.3-I Combined Lateral and Withdrawal Load
for
Wood ScmwInsertedat
Angle to Wood Surfice
In lieuofspecificcoderequirements
for end and
edge distance for woodscrews, Table C11.4-1 maybe
used to establish
wood
screw
patterns. Designers
should note that specietype,
moisture content and
grain orientation will affectspacing(pitch)between
distance
fasteners in a row.
11.4.2-Multiple Wood Screws
Lateral design
values
for wood
screws
are not
subject to the group action factor, C , for fasteners
alignedinthe direction of load (see 7 . f 6 ) . The design
value for a connection involving more than onewood
screw is the sum of the design values for eachline
individual wood screw when all wood screws in the connection
are of the sametype, diameter and length, join the
same members and resist load in the same shear plane.
Wood Side Members
Not
Prebored
Prebored
2.5d
2.5d
Edge
End distance
- tension load parallel to grain
15d
1 Od
- compression
load
parallel
to grain
1 Od
5d
Spacing (pitch) between fasteners in
a row
- parallel to grain
15d
1 Od
- perpendicular to grain
1 Od
5d
Spacing (gage) between rows of fasteners
- in-line
5d
3d
- staggered
2.5d
2.5d
Steel Side Members
Not
Prebored
Prebored
Edge
2.5d
2.5d
End distance
- tension load parallelto grain
1 Od
5d
- compression
parallel
load
to grain
5d
3d
Spacing (pitch) between fasteners ainrow
- parallel to grain
1 Od
5d
- perpendicular to grain
2.5d 5d
Spacing (gage) between rows of fasteners
- in
2.5d
3d
- staggered
2.5d
2.5d
Wood Screws
139