Gang-Nail Connectors

- How They Work

A Gang-Nail connector is a steel plate with a
collection of spikes or nails projecting from one
face (See diagram). The spikes, or teeth, are
formed by punching slots in steel but leaving one
end of the plug connected to the sheet. The teeth
are then formed so they project at right angles to
the plate. During this process the teeth are shaped
to produce a rigid projection. When the teeth of a
connector plate are pressed into timber laid end-to-
end, the plate welds them together by forming a
Gang-Nail joint. Connectors are always used in
pairs with identical plates pressed into both faces of
the joint.
The concept is simple but the design of efficient
Gang-Nail connectors requires careful balancing of
tooth shape and density, connector plate thickness
and ductility. An ongoing commitment to research
and development ensures that MiTeks licensed
truss fabricators have the most efficient truss
system at their disposal.
Performance criteria for Gang-Nail connectors
It is not economical to have a single connector that
gives optimum performance under all loading
conditions, for all of Australias wide range of
commercial timbers. MiTek Australia Ltd. has
developed a complementary range of connector
plates of varying plate thickness (gauge), tooth
layout and tooth profile. These are:
GQ 20 gauge (1.0 mm thick) galvanised
steel. General purpose connector. Many
short, sharp teeth 128 teeth in a 100 mm x
100 mm area.
GE - 18 gauge (1.2mm thick) galvanized
steel. Similar to GQ. For use when
additional steel strength is required.
G8S 18 gauge (1.2 mm thick) stainless
steel. This connector is only used when the
environment is highly corrosive. 70 teeth in a
100 mm x 100 mm area.
GS 16 gauge (1.6 mm thick) galvanised
steel. Heavy duty connector. 144 teeth in a
100 mm x 190 mm area.
Engineering Data
Gang-Nail connector properties have been
established in accordance with Australian Standard
AS1649 Timber - methods of test for mechanical
fasteners and connectors - Basic working loads
and characteristic strengths. As well as testing new
plate designs, MiTek Australia Ltd. conducts
regular tests on their existing connector range and
monitors the long term behaviour of joints
subjected to constant loading. The CSIRO Division
of Forest Products and the NSW Forestry
Commission Division of Wood Technology have
also done considerable research work on toothed
metal plate connectors.
Full scale truss testing programs have been carried
out at the Universities of Western Australia and
Adelaide, Australian National University and the
Cyclone Testing Station at Capricornia Institute of
Advanced Education.
Connector properties can be divided into two parts:
properties dependent on connector plate
strength, and
properties dependent on the characteristics of
the timber and the teeth.
Gang-Nail Truss System
Table 1.1 Characteristic Capacity for Steel, Q
s
Table 1.2 Characteristic Capacity for Tooth Q
k
,
(N/effective tooth)
The characteristic load capacities are modified to
determine the design capacities. These
modification factors allow for tooth strength
variation due to:
capacity factor
duration of load
angle between load direction and plate axis
angle between load direction and grain
whether plates are pressed into the timber or
rolled in.
Capacity Factor
Values of the capacity factor, f, are listed in Table
2.6 of AS1720.1.
Duration of load
Duration of load factor k
1
is specified in Table 2.7 of
AS 1720.1.
Angle between load direction and plate axis.
Where the connector plate is loaded at right angles
to its main axis, the design capacities for the tooth
should be reduced to 75% for GQ, GS and GE
plates, and 60% for G8S plates. For intermediate
orientations the reduction factor can be calculated
using Hankinsons formula, or the simpler equation:
Angle between load direction and grain
Where the timber is loaded at right angles to the
direction of the grain, the design capacities for the
tooth should be reduced to 80% in addition to any
modification due to load direction/plate axis. For
intermediate orientations, the reduction factor can
be calculated using Hankinsons formula:
Nt = Design Capacity at angle q to grain.
Pt = Design Capacity parallel to grain.
Qt = Design Capacity perpendicular to grain.
Gang-Nail Joints
The basis of joint design is to ensure that there are
enough teeth in each member meeting at the joint
to resist all member forces and that there is enough
plate area to prevent the steel of the connector
failing in tension or shear.
When determining the number of teeth that are
required to connect any member to the joint, there
are parts of the web or chord where the teeth are
considered to be ineffective a 6 mm wide strip
along the edges and a 12 mm long strip across the
end. Allowance is also made for the connector to
be out-of-position by 6 mm in any direction.
. s e t a l p f o r i a p a r o f m m / N n i h t g n e r t S e t a l P r o t c e n n o C
S S E R T S F O E P Y T Q G E G S G S 8 G
n o i s n e T l a n i d u t i g n o L 3 6 2 7 8 3 8 7 5 5 3 5
n o i s n e T l a r e t a L 7 8 1 6 2 2 2 7 2 2 7 2
r a e h S l a n i d u t i g n o L 7 9 1 7 9 2 8 0 4 0 8 2
r a e h S l a r e t a L 8 7 1 5 1 2 3 2 3 6 4 2
: s e t o N
. s t o l s e h t h t i w l e l l a r a p s i s i x a l a n i d u t i g n o l e h T . 1
. r o t c a f y t i c a p a c e h t e d u l c n i t o n o d s e l b a t n i s e u l a V . 2
T N I O J
P U O R G
Q G
H T O O T
E G
H T O O T
S G
H T O O T
S 8 G
H T O O T
2 J
3 J
4 J
2 D J
3 D J
4 D J
5 D J
6 D J
1 0 5
2 4 4
5 9 2
1 3 5
1 3 5
3 8 3
9 3 3
5 9 2
1 0 5
6 8 4
5 9 2
8 7 6
8 7 6
3 8 3
9 3 3
5 9 2
0 6 5
0 6 5
3 1 4
7 6 7
7 6 7
2 4 4
2 9 3
9 3 3
0 9 5
0 9 5
0 3 4
7 3 7
7 3 7
0 3 4
8 6 3
A N
: s e t o N
. s t o l s e h t h t i w l e l l a r a p s i s i x a l a n i d u t i g n o l e h T . 1
. r o t c a f y t i c a p a c e h t e d u l c n i t o n o d s e l b a t n i s e u l a V . 2
360
1
G
F
G G
2 2
QtCos PtSin
Qt Pt
Nt

For GQ, GS & GE

For G8S
225
1
G

F
Gang-Nail Joint Design Example
Consider the joint as in Figure 1, assuming the
truss is manufactured from Pinus Radiata. Member
actions are, as indicated in Figure 1, adjacent to the
joint detail. Note that the cutting details employ
single cuts, with the location point, denoted LP,
common to one face of each intersecting member.
We shall assume DL and LL is the only load case
for this exercise.
Timber is Radiata, i.e. JD4. Consider GQ150125
plate. Note the connector plate axis is at 90
0
to the
bottom chord, and the actual connector plate size is
152.4 x 125.
Figure 1 - Sample Joint
Steel Check
By inspection, connector plate shear horizontally
above bottom chord will be most critical.
Design Capacity
= f x Shear Length x Q
s
= 0.9 x 152.4 x 178
= 24414 N
Applied Shear
= 25177 - 16746
= 8431 N therefore OK
Figure 2 - Web 2 effective connector plate area.
Figure 2 shows the effective connector plate
contact area to Web 2. Note the allowance for
6 mm ineffective edge distance and 12 mm
ineffective end distance. The connector plate has
also been shifted to the limits of connector plate
tolerance as discussed previously.
Using a transparent template, the number of
effective nails in the shaded area has been counted
as 50/side.
Design Capacity
= 2 x n x f x k
1
x F x Q
k
= 2 x 50 x 0.85 x 0.77 x 0.83 x 383
= 20805 > 6750 N therefore OK.
Figure 3 - Web 1
Gang-Nail Truss System
83 . 0
360
60
1 F
Figure 3 shows the effective plate contact on
Web 1. We find 14 teeth to be effective.
Design Capacity
= 2 x n x f x k
1
x F x Q
k
= 2 x 14 x 0.85 x 0.77 x 0.86 x 383
= 6036 > 3375
Note that the member is in compression, and the
angle of bearing as defined in Figure 3 is greater
than 60. The member will, therefore, be self
locking, and nominal plate contact will suffice.
Figure 4 - Bottom Chord
The bottom chord plate area is subject to both axial
and shear forces. The resultant force:
R = 8517 N
Angle between load and plate axis.
Using the transparent template, we find 96 teeth to
be effective.
Design Capacity
= 2 x n x f x k
1
x F x Q
k
= 2 x 96 x 0.85 x 0.77 x 0.77 x 383
= 37060 > 8517 therefore OK.
Adopt GQ150125 Standard Location.
Figure 5
The bottom chord is subject to shear forces
perpendicular to the grain. Generally these are not
critical, but should be checked where heavy loads
are applied to bottom chords such as on girder
trusses or where low density timber is used.
Values for shear at joint details are as given in
AS 1720.
Shear at joint = 1206N
Design Capacity
= f k
1
f
sj
A
s
= 0.8 x 0.77 x 5 x 56.5 x 35 x 2
= 12181N
> 1206 N is therefore OK
Self-locking joints
Some joints are self-locking and do not rely on
the connector to resist all the forces in the joint. For
example, where the angle between a chord and an
intersecting web exceeds 60 degrees and the web
is in compression, the web locks against the chord
and the connector teeth and are only lightly loaded.
All joints need to be designed to resist any tension
loads that occur in service or during manufacture,
handling and installation.
86 . 0
360
50
1 F
2 2
1206 8431 R

= 90 -
=
= 82
o
77 . 0
360
82
1 F
Splice Joints
Truss bottom chords will nearly always require end-
to-end splicing of relatively short pieces of timber to
achieve the desired chord length.
When these splices are acting in compression,
the forces are transferred by direct end bearing
between the pieces and only a nominal connector
would be required to hold the pieces in place and
resist the stresses of manufacture, handling and
installation. However, the normal design
procedures apply when the splice is subject to
tension loads.
The width of splice plates should be at least
20 mm less than the timber width. This minimises
any tendency for the edges of the timber to split
around the connector. In trusses made from green
timber, keeping the plate away from the edge of the
member will also avoid bumps occurring in the
ceiling or roof line as the connector can locally
restrain the timber from its natural tendency to
shrink as it dries.
Gang-Nail Truss System