14. 7/05/13'
14'
Bolted connections
• Type 1 – shear in the bolt
• Type 2 – tension in the bolt
Capacity of Type 1 Bolted connections
AS1720.1 4.4.3.2
• φ - capacity factor Table 2.2
! type of structure, element
! different for small and larger diameter bolts
• k1- duration of load factor Table 2.3
! given by shortest duration load in the combination
• k16- side plate factor
! stiff side-plates and close-fitting holes can
prevent rotation of bolt
• n - total number of bolts in joint
Nd,j = φk1k16k17nQsk
15. 7/05/13'
15'
k17 Multiple bolt factor
AS1720.1 Table 4.12
• Large difference in k17 for bolts in seasoned and
unseasoned timber
• Seasoned timber dimensionally stable
! no shrinkage hence k17 = 1
• Unseasoned timber used in dry conditions becomes
partially seasoned
! leads to shrinkage perpendicular to grain
! where restrained, can cause cracking, k17 = 0.5
! where unrestrained, k17 depends on number of rows
- e.g. one bolt per row
Nd,j = φ k1k16k17nQsk
Capacity of Type 1 Bolted connections
Qsk – characteristic system capacity of a single joint
• Joint strength group from species of timber
• Different capacities for angle between load and
grain
! Qskl – system capacity parallel to grain – sum of all Qkl for the
shear planes on one bolt in the connection Table 4.9
! Qskp – system capacity perpendicular to grain – sum of all
Qkp (load to grain) for the shear planes on one bolt in the
connection Table 4.10
Nd,j = φ k1k16k17nQsk
Q
Q Q
Q Qsk
skl skp
skl skp
θ
θ θ
=
+sin cos2 2
17. 7/05/13'
17'
Detailing bolted connections
Distances measured centre-to-centre
• Minimum end distances – measured parallel to
grain
• Minimum edge distances – measured
perpendicular to grain
• Spacing parallel to grain
• Spacing perpendicular to grain
Washers
• Minimum size and thickness
Variations
• Coach screws
• Dowels
• Dowelled fin plates
18. 7/05/13'
18'
Fire
• Timber burns, but slowly and from outside in.
! Charring on outside protects timber inside
! Wood acts as an insulator
• Timber member fire design philosophies
! Sacrificial timber – oversized members char – leave residual
section that can carry fire limit states loads
! Protect timber structural elements with
Plasterboard
Other non-structural timber
• Connections
! Steel as a conductor if part exposed to fire
Connections in fire
19. 7/05/13'
19'
Problems for timber connections
• Steel fasteners
! soften with temperature and become more flexible
! transfer heat into the members
! potential for premature failure and loss of structural integrity
• Glues
! may deteriorate at high temperatures
Strategies
Ensure connections are not weakest link
• Make sure connections have higher fire ratings than
members
• Alternatives
! protect connections behind plasterboard
! place sacrificial timber between connections and the potential
fire – either plugs or plates
! use 100% timber connections eg timber dowels
20. 7/05/13'
20'
Plasterboard
Plasterboard
• Connections are part of tested system
• Cover and protect the connection as though it is
timber
• Care at corners, penetrations and junctions (use
fire-resistant sealant – fire-grade flexible material
filling gaps)
• Extra layers at connections ensure fasteners are not
the weakest link
21. 7/05/13'
21'
Plasterboard
Fire protection coverings:
! 13 mm fire-grade plasterboard
! 12 mm cellulose fire-reinforced cement sheeting complying with
AS2908.2
! 12 mm fibrous plaster reinforced with
13 mm x 13 mm x 0.7 mm galvanised steel with mesh located not
more than 6 mm from the exposed face
! Other material equivalent to 13 mm fire-grade plasterboard
!
• Protection by:
o surface
protection or
o embed fixings
under plugs
• Other protection
measures need test
data to support their
use
Plugs
23. 7/05/13'
23'
Plates
• Thickness of the plate is sacrificial depth of timber
for charring
• Cover the connection as though it is timber
• Care at corners, penetrations and junctions (use
fire-resistant sealant – fire-grade flexible material
filling gaps)
• Extra layers at connections ensure fasteners are not
the weakest link
Timber dowels
24. 7/05/13'
24'
Timber dowels
• Substitute for steel (steel may soften in fire)
• Dowels char in same way and rate as member
Conclusions
• Timber can be used for large, interesting
commercial and iconic structures
• Many different types of timber systems can be used
for elegant structural solutions
• Connections are important in the realisation of the
structural scheme and are often part of the early
concept designs
• A lot can be achieved with the standard bolt if
used sensibly
• Fire protection by sacrificial timber or oversizing
25. 7/05/13'
25'
Other information
• Handbook 108-2013 (Standards Australia)
• Wood Solutions website
www.woodsolutions.com.au
• Two-day UTas Masterclass
Perth, 2 and 3 May, 2013
AS1720 Timber Engineering Master Class April/May 2013
