Timber

Construction
Connection Design
according to AS1720.1
using SPAX screws
SPAX Advantages
Guaranteed quality and innovation since 1823

Ground Seration
T-STAR plus 4CUT
/ 4CUT

Ensures maximum torque From screw lengths No pre-drilling (wood Certified proof of origin
transfer when driving over 160mm. Reduces dependent), reduces offers a high degree of
screws. the screwing-in torque splitting. Square end safety, quality and continuity.
significantly. displaces the fibres and
reduces screwing in torque.

Superior corrosion protection,

especially in CCA/ACQ treated timber

High corrosion protection from the exclusive DELTA-SEAL coating, providing twice the corrosion protection
compared to hot-dipped galvanised products. Ideal for CCA and ACQ treated timbers, all hardwoods and
suitable for any external use away from direct exposure to salt water. Large range of stainless steel screws
also available.

Screw types & applications

Partial Thread

Washer head Countersunk head

The partial thread screw works like a clamp, pulling the two timber components together tightly. To achieve this
clamping effect, the threadless shank must be equivalent to the thickness of the upper component.
• Washer head - the large bearing area of the head provides a high clamping force
• Countersunk head - used for flush fixings
Ideal for frame and roof structures, pergolas, boardwalks, retaining walls.

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Screw types & applications (cont.)
Full Thread

Cylinder head Countersunk head

Fully threaded screws are available in countersunk and cylinder head screws up to 600mm long. They are ideal
for three main applications:

• Joining two components together for a very high load capacity

• Tensile re-inforcement to prevent cracking of timber
• Compression re-inforcement to prevent crushing of timber
The cylindrical head can sink into the timber below the surface providing a fully concealed fixing.

T-joint Beam Beam to Upright

Clamp the two pieces together first with Insert screw from below at a 45o angle
a SPAX partial thread washer head screw

Compression Reinforcement Notched Beam

Prevents crushing of the timber Reinforcement and strengthening
of notch or recess

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 Connection Design According to
AS1720.1 Using SPAX Screws
Introduction
This design guide is derived from testing SPAX screws installed in Australian and New Zealand timber
species and is designed to be used in conjunction with AS1720.1-2010 for quick predesign of load bearing
connections with SPAX screws but is not intended to replace appropriate engineering and design by a design
professional.

Testing was conducted according to AS1649-2001 and DIN EN 1382 to determine the limit state design lateral
and withdrawal load capacities of SPAX screws in various timber types.

This guide has been established in good faith and to the best of our knowledge. No liability is, therefore,
engaged or accepted for any errors.

Characteristic Capacities for SPAX Screws

(read in conjunction with Sections 4.3 and 4.5 of AS1720.1 – 2010)
Type 1 Joints (fastener subjected to shear)
a) Lateral loads in side grain

Table 1 – Characteristic Capacity for Single Screw in Side Grain Laterally Loaded in Single Shear

Partial Thread Screws Full Thread Screws

Characteristic Shear Capacity per Screw (Qk)N* Characteristic Shear Capacity per Screw (Qk)N*
Nominal Diameter d1 (mm) Nominal Diameter d1 (mm)
Joint Joint
6.0 8.0 10.0 12.0 6.0 8.0 10.0 12.0
Group Group
Shank Diameter D (mm) Core Diameter d2 (mm)
4.3 5.7 6.8 8.5 3.8 5.0 6.1 7.5
JD1 3788 6238 8447 12483 JD1 3051 4932 6985 10027
JD2 2846 4686 6346 9378 JD2 2292 3705 5247 7533
JD3 2237 3685 4990 7373 JD3 1802 2913 4126 5923
JD4 1597 2630 3561 5263 JD4 1286 2079 2945 4228
JD5 1138 1875 2538 3751 JD5 917 1482 2099 3013
JD6 822 1398 1834 2710 JD6 780 1010 1620 2290

* Capacities for partial thread screws assume the shear plane is in line with the unthreaded screw shank.
These capacities are based on interpolation of capacities provided in AS1720.1. Actual values from test results vary slightly.

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Timber Dimensions
Dimensions such as minimum thickness and depth of penetration as
per clause 4.3.5 of AS1720.1.

For the characteristic capacities given in Table 1 to be applicable,

timber thicknesses and screw length as shown in Figure 1 below
shall be such that—

(a) thickness of first member .......................................t1>10D; and

(b) depth of penetration into second member.............tp>7D.

where D = shank diameter

For lesser values of t1 and tp, the characteristic capacity shall be

reduced in proportion to the decrease in t1 or tp and the screw shall be Figure 1
considered as non-load-bearing if t1 or tp is less than 4D.

As SPAX screws with 4-CUT or CUT points significantly reduce the risk of splitting, the prescribed minimum
thicknesses may be reduced.

b) Lateral loads in end grain

The characteristic capacities for screws laterally loaded in the end grain shall not exceed 60% of the values
provided in Table 1 above determined in accordance with Clause 4.3.2.2(b) of AS1720.1.

Type 2 Joints (fastener subjected to tension)

a) Withdrawal loads from side grain

The characteristic capacities for SPAX screws axially loaded in withdrawal from the side grain of seasoned
timber are provided in Table 2 below.

b) Withdrawal loads from end grain

The characteristic capacities for SPAX screws axially loaded in withdrawal from the end grain of seasoned
timber shall not exceed 60% of the values provided in Table 2 below determined in accordance with Clause
4.3.2.3(b) of AS1720.1.

Table 2 – Characteristic Capacity for a Single Screw in Side Grain Loaded in Withdrawal

Characteristic Withdrawal Capacity per Screw

(Qk)N per mm Penetration of Thread
Joint
Group Nominal Diameter d1 (mm)
6.0 8.0 10.0 12.0
JD1 180 240 300 360
JD2 138 184 230 276
JD3 107 142 178 213
JD4 81 108 135 162
JD5 64 86 107 129
JD6 50 66 83 100

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Maximum Tensile Capacity

The maximum tensile capacity for a SPAX screw subject to direct axial loading shall not exceed the value
appropriate to the diameter as per Table 3 below:

Table 3 – Maximum Tensile Capacity for Screws

Design Steel Tensile Resistance Nd,tc

Nominal Diameter d1 (mm)
6.0 8.0 10.0 12.0
High-carbon steel 8800 13600 22400 30400
Stainless steel 5700 10400 16000 22400

Head Pull-Through

AS1720.1 does not consider head pull-through as a failure mode for screws but it does consider crushing
under the head for coach screws. Applying the equation Qb = f’pj x Aw, where f’pj is the stress factor from table
4.11 of AS1720.1 and Aw is the bearing area under the head from Table C6 of AS1720.1, we can provide the
head pull-through values in Table 4 below (actual values may be higher).

Table 4 – Characteristic Capacity for Head Pull-Through

Characteristic Capacity per Screw for

Head Pull-through (Qb)N
Joint Group Head Type
Nominal Diameter d1 (mm)
6.0 8.0 10.0 12.0
Countersunk 2690 4531 6945 10161
JD1
Washer Head 3857 8690 13411 NA
Countersunk 2051 3456 5297 7750
JD2
Washer Head 2942 6628 10229 NA
Countersunk 1550 2611 4002 5856
JD3
Washer Head 2223 5008 7728 NA
Countersunk 1140 1920 2943 4306
JD4
Washer Head 1635 3682 5683 NA
Countersunk 821 1382 2119 3100
JD5
Washer Head 1177 2651 4092 NA
Countersunk 556 937 1436 2101
JD6
Washer Head 798 1797 2773 NA

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Joint Groups

The corresponding joint groups for timber types is provided in Table 5 below. Radiata pine is, in most cases,
used with the heart excluded and will conform with joint group JD4 according to AS1684.2.

Table 5 – Joint Groups

Material Joint Group

MGP10 (heart excluded) JD4
MGP10 (heart included) JD5
F5 (heart excluded) JD4
F5 (heart included) JD5
LVL13 JD4
Spotted Gum JD1

Design Capacity of SPAX Screwed Joints (as per AS 1720.1 section 4.3.3)

Type 1 Joints
The design capacity (Nd,j) for a joint containing n screws to resist shear loads for Type 1 joints
shall satisfy the following:
Nd,j≥ N*

where

Nd,j = φ k1 k13k14k16 k17 n Qk

and

N* = design action effect in shear

φ = capacity factor (see Clause 2.3 of AS1720.1)

k1 = factor for duration of load for fasteners (see Clause 2.4.1.1 of AS1720.1)

k13 = 1.0 for screws in side grain

= 0.6 for screws in end grain

k14 = 1.0 for screws in single shear

= 2.0 for screws in double shear

k16 = 1.2 where the load is applied through metal side plates of adequate strength
to transfer the load and the screws are a close fit to the holes in these plates
= 1.1 for screws through plywood gusset plates
= 1.0 otherwise

k17 = factor for multiple screwed joints given in Table 4.3(A) in AS1720.1 for type 1 joints to resist direct
loads in either compression or tension.

n = number of screws in the connection

Qk = characteristic capacity given in Table 1

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Type 2 Joints
The design capacity (Nd,j) for screw joints axially loaded in withdrawal shall satisfy the following:
Nd,j ≥N*

where Nd,j is the lesser of—

Nd,j = n Nd,tc

Nd,j = φ k13 lp n Qk

or where crushing under the head poses a limit to the strength

Nd,j = φ k1 n Qb

N* = design load action effect on the joint produced by strength limit states design loads
(tension across the joint)

n = number of screws in the connection

p = penetration length of screw
Nd,tc = design maximum tensile capacity of a single screw given inTable 3
k = product of modification factors listed below:
φ = capacity factor (see Clause 2.3 of AS1720.1) (a) Green timber (see table 2.1 of NZS 3603) 0.80
(b) Duration of loading Facto
k13 = 1.0 for withdrawal from side grain (c) Screws in end grain 0.67
= 0.60 for withdrawal from end grain

lp = depth of penetration of the threaded portion of the screw into the innermost
Spacing, Edgemember
and End Distance (refer to c
Table 6
Qk = characteristic capacity given in Table 2
Spacing Minimum distance
Qb = characteristic capacity given in Table 4 End distance 10da
Edge distance 5da
NOTE: The duration of load factor k1 does not apply to withdrawal capacity.
     
Between screws      
- along grain 10da
- across grain
Spacing, Edge and End Distance (refer to section 4.3.4 of AS1720.1) 3da
da= shank diameter of screws
Table 6 – Minimum Spacing, Edge and End Distance

Spacing Minimum distance

End distance 10D
Edge distance 5D
Between screws
- along grain 10D
- across grain 3D

D = shank diameter of screws

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Pre-drilling

SPAX screws can be driven into radiata pine and other softwoods with or without pre-drilling . We recommend
pre-drilling in hardwood and LVL according to the below diameters:

Drill Hole Diameter (mm)

Outer Thread Diameter
Softwood Hardwood
4.0 2.5 3.0
4.5 3.0 3.0
5.0 3.0 3.5
6.0 4.0 4.0
8.0 5.0 6.0
10.0 6.0 7.0
12.0 7.0 8.0

How to Specify SPAX

When specifying SPAX screws, the following items should be included:

• Screw diameter and length

• Head type
• Thread type i.e. full thread or partial thread
• Material / corrosion protection
• Edge distances and spacings on drawing
e.g. SPAX 8 x 240 DELTA-SEAL cylinder head full thread.

Contacts
Head Office
PO Box 975
Gordonvale
QLD 4865
Phone: 07 4056 2009
Email: info@spaxpacific.com
Website: www.spaxpacific.com

Technical Consultant
Phone: 0499 887895
Email: greg.pankhurst@spaxpacific.com

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Example 1

Cut through Purlin Cut through Chord

60 60 60
a4,t a2 a4,t

180 x 280

240
p

h
a
α
80 x 160
160
p

α
60 40 40
a1 a4,c a4,c

Selected fastener: SPAX 8.0x400 countersunk head, full thread with CUT point, w/o predrilling subject to
shear and withdrawal. Timber is radiata pine (JD4).
Minimum dimensions
Min. thickness t1 = 10 x D = 10 x 5.7 = 57< 160mm OK
tp = 7 x D = 7 x 5.7 = 40< 280mm OK
Edge distance = 5 x D = 5 x 5.7 = 28.5 OK
No end distance
Spacing (along grain) = 10 x d1 = 10 x 5.7 = 57 OK
Shear resistance – per screw
1. Characteristic resistance Qk = 2079 N Table 1

Nd,j = φ k1 k13 k14 k16 k17 n Qk

Nd,j = 0.8 x 0.86 x 1 x 1 x 1 x 2x 2079 = 2860 N

Withdrawal resistance – per screw

1. Withdrawal of threaded part
Qk = 108 x lp = 108 x 240 = 25920 N Table 2
Nd,j = ф k13Qk = 0.8 x 1.0 x 25920 = 20736 N
2. Tensile steel resistance
Nd,tc = 13600 N Table 3
3. Head pull-through
Nd,j = max (3.1 head pull-through
(3.2 withdrawal of thread headside
3.1 Head pull-through
Nd,j = φ k1 n Qb= 0.8 x 1 x 1920 = 1536 N Table 4
3.2 Withdrawal of thread headside
Nd,j = ф k13 lp Qk = 0.8 x 1.0 x 160 x 108 = 13824 N (max) Table 2

Governing resistance is tensile steel resistance Nd,tc=13600 N per screw

For joint Nd,tc =2 x13600 = 27200 N

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Example 2

ϱϬ ϴϬ ϱϬ
ϰϱ

ϵϬ
90Σ

΀Ϯ΁ ΀Ϯ΁

ϴϬ
180Σ
ϭϴϬ

ϭϬϬ
΀ϭ΁
ϭϴϬ ϳϱ ΀ϭ΁
F F

^ĐƌĞǁƐ ĂůŝŐŶĞĚ ;ŶŽƚ ƐƚĂŐŐĞƌĞĚͿ ΀ŵŵ΁

Selected fastener: SPAX 8x120 washer head, partial thread, w/o predrilling subject to shear.

Minimum dimensions
Min. thickness t1 = 10 x D = 10 x 5.7 = 57 > 45mm Reduce capacity by 45/57 = 0.79
tp = 7 x D = 7 x 5.7 = 40 < 90mm OK
Edge distance = 5 x D = 5 x 5.7 = 28.5 OK
End distance = 10 x D = 10 x 5.7 = 57 OK
Spacing (along grain) = 10 x D = 10 x 5.7 = 57 OK
Spacing (across grain) = 3 x D = 3 x 5.7 = 15 OK

Shear resistance – per screw

1. Characteristic resistance Qk = 2630 N Table 1
Reduction for thickness 2630 x 0.79 = 2077

Nd,j= φ k1 k13 k14 k16 k17 n Qk

Nd,j = 0.8 x 0.86 x 1 x 1 x 1 x 2 x 2077 = 2858 N

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Title: ©kodobist, iStockphoto · Back: ©MicroOne, fotolia
SPAX is not only called
“International” – it actually is!
Production is carried out at our site in Ennepetal
and we export SPAX products to more than 40
countries across all continents.
Image credits:

SPAX SPAX Pacific Pty. Ltd. You can also find us at:
ALTENLOH, BRINCK & CO - GROUP youtube.com/user/SPAXglobal
linkedin.com/company/spax-pacific-pty-ltd
facebook.com/spaxpacific
PO Box 975 Gordonvale Qld 4865 Australia instagram.com/spaxpacific
Phone: 07 4056 2009
info@spaxpacific.com · www.spaxpacific.com