LVL Handbook EUROPE

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5. STRUCTURAL DESIGN OF CONNECTIONS
5.5.2 Axially loaded screws
For connections in softwood timber or LVL/GLVL with ε ≥ 15°
of screws in accordance with EN 14592 with:
• 6 mm ≤ d ≤ 12 mm
• 0,6 ≤ d1 /d ≤ 0,75
where
d is the outer thread diameter; and
d1 is the inner thread diameter
The characteristic withdrawal capacity should be taken as 32:
F_(ax,ε,Rk)=(n_ef ∙ k_(ax )∙ f_(ax,90,k) ∙ d ∙ l
(5.28)
where
k_ax={█(0,5+(0,5∙ε)/(45°) for 15°≤ε45°≤ε≤90°)┤
(5.29)
k_β=1,5∙cos^2 β+sin^2 β (5.30)
Fax,ε,Rk is the characteristic withdrawal capacity of the
connection at an angle ε to the grain [N];
fax,90,k is the characteristic withdrawal strength perpendicular
to the grain determined in accordance with EN 14592
for the associated density ρa [N/mm²];
nef is the effective number of screws, n ef = n0,9 where n is
the number of screws acting together in a connection;
kax is a factor to consider the influence of the angle ε
between screw axis and grain direction and the
long-term behavior;
lef is the penetration length of the threaded part [mm];
ρk is the characteristic density [kg/m³];
ρa is the associated density for fax,k [kg/m³];
kβ is a factor considering the influence of the angle β
between the screw axis and the LVL’s wide face;
ε is the angle between the screw axis and the grain
direction, with ε ≥ 15°, see Figure 5.7; and
β is the angle between the screw axis and the LVL’s wide
face, with 0°≤ β ≤ 90°, see figure 5.7.
Note: Failure modes in the steel or in the timber around the screw
are brittle, i.e. with minimal ultimate deformation and therefore
have a limited possibility for stress redistribution.
For screws in LVL, the characteristic withdrawal parameter
may be assumed as fax,90,k =15 N/mm², when ρa = 500 kg/m³
and screws 6 mm ≤ d ≤ 12 mm in softwood LVL/GLVL.
The characteristic pull-through resistance of connections
with axially loaded screws should be taken as:
F_(ax,ε,Rk)=n_ef∙f_(head,k)∙d_h^2 (ρ_k/ρ_a )^0,8 (5.31)
where
Fax,ε,Rk is the characteristic pull-through capacity of the
connection at an angle ε to the grain [N], with ε ≥ 30°
fhead,k is the characteristic pull-through parameter of the
screw determined in accordance with EN 14592 for
the associated density ρa
dh is the diameter of the screw head [mm]
5.5.3 Inclined screw connections
Inclined screwing is an efficient way to connect LVL members
together or to other types of timber members. Although the
connections transfer shear forces, the fasteners are axially load-
ed. The instructions in this subsection are based on the Finnish
Handbook RIL205-1:2017 for Eurocode 5, Chapter 8.7.4S 31.
These rules concern the design of single shear connections
according to Figure 5.11, where the screw inclination angle α
should be between 30°…60° in regard to the shear plane. The
screws are axially loaded. The head side timber member ( t1)
may be replaced with a steel plate if the screw head has a full
bearing area on the steel plate for a Figure 5.12 (b) tension
screw connection. The screws should be self-drilling and fully
threaded or partly threaded with a smooth part diameter of
ds ≤ 0.8d, where d is the outer thread diameter.
Different or supplementary connection types and screw
specifications differing from eurocode 5 may be used accord-
ing to their ETA.
Cross screw connection
The cross screw connection is built up from symmetrical screw
pairs, see Figure 5.12 (a), in which one screw is under compres-
sion and the other under tension. The characteristic load-car-
rying capacity of the cross screw connection is calculated by
the equation:
R_k=n_p^0,9 (R_(C,k)+R_(T,k) )cos ε (5.32)
where
n p is the number of screw pairs in the joint; and
α is the angle between screw axis and the shear plane
(30° ≤ α ≤ 60°), see Figure 5.12 (a)
The characteristic compression capacity of the screw is calcu-
lated by the equation:
R_(C,k)=min{█(f_(ax,ε,1,k) d l_(g,1)@f_(ax
(g,2)@0,8〖 f〗_(tens,k) )┤ (5.33)
The characteristic withdrawal capacity of the screw is calculat-
ed by the equation:
R_(T,k)=min{█(f_(ax,ε,1,k) d l_(g,1)+f_(head,k)
ρ_a )^0,8@f_(ax,ε,2,k) d〖 l〗_(g,2)@f_(tens,k) )┤ (5.34)
C = � min �( −2)3 or LVL − C and GLVL − C (5.23)
ax,ε,Rk = ef ∙ ax ∙ ax,90,k ∙ ∙ ef
β � k a�0,8 (5.24)
ax = � 0,5 + 0,5∙ 45° for 15° ≤ < 45°
1 for 45° ≤ ≤ 90° (5.25)
= 1,5 ∙ cos2 + sin2 (5.26)
ax,ε,Rk = ef ∙ head,k ∙ h2� k a�0,8 (5.27)
Cross screw connection
The cross screw connection is built up from symmetrical screw pairs, s
which one screw is under compression and the other under tension. T
carrying capacity of the cross screw connection is calculated by the eq
k = p0,9( C,k + T,k )cos (5.2
Where
is the number of screw pairs i the joint; and
α is the angle between screw axis and the shear plane (30°
5.11 (a)
The characteristic compression capacity of the screw is calculated by t
C,k = min { ax,ε,1,k g,1
ax,ε,2,k g,2 0,8 tens,k
The characteristic withdrawal capacity of the screw is calculated by the
T,k = min{ ax,ε,1,k g,1 + head,k h2( a)0,8
ax,ε,2,k g,2
tens,k
where
fax,ε,1,k is the characteristic withdrawal strength parameter for a s
member of the connection at an angle ε to the grain direct
fax,ε,2,k is the characteristic withdrawal strength parameter for a s
member of the connection at an angle ε to the grain direct
d is the outer threaded diameter [mm];
Cross screw connection
The cross screw connection is built up from symmetrical screw pairs, s
which one screw is under compression and the other under tension. Th
carrying capacity of the cross screw connection is calculated by the eq
k = p0,9( C,k + T,k)cos (5.2
Where
np i e number of screw pairs in the joint; and
α is the angle between screw axis and the shear plane (30°
5.11 (a)
Th characteristic compression capacity of the screw is calculated by t
C,k = min { ax,ε,1,k g,1
ax ε,2,k g,2 0,8 tens,k
The characteristic withdrawal capacity of the screw is calculated by the
T,k = min{ ax,ε,1,k g,1 + head,k h2( a)0,8
ax,ε,2,k g,2
tens,k
where
fax,ε,1,k is the characteristic withdrawal strength parameter for a s
member of th connection at n angle ε to the grain direct
fax,ε,2,k is the characteristic withdrawal strength parameter for a s
member of the connection a an angle ε to the grain direct
Cross scr w c nnection
The cross screw connection is built up from symmetrical screw pairs, s
which one screw is under compression and the other under tension. Th
carrying capacity of the cross screw connection is calculated by the eq
k = p0,9( C,k + T,k)cos (5.2
Where
np is the number of screw pairs in the joint; and
α i the angl between screw axi and the shear plane (30°
5.11 (a)
The characteristic compression capacity of the screw is calculated by t
C,k = min { , 1 1
ax,ε,2,k g,2 0,8 tens,k
The characteristic withdrawal capacity of the screw is calculated by the
T,k = min{ ,ε,1,k g,1 + head,k h2( a)0,8
ax,ε,2,k g,2
tens,k
where
fax,ε,1,k is the charact ristic withdra al strength parameter for a s
member of the connection at an angle ε to the grain direct
fax,ε,2,k is the charact ristic withdrawal strength parameter for a s
member of the connection at an angle ε to the grain direct
185 (255)
ax,ε,Rk = ef ∙ ax ∙ ax,90,k ∙ ∙ ef
β ( k a)0,8
(5.28)
where
ax = { 0,5 + 0,5∙ 45° for 15° ≤ < 45°
1 for 45° ≤ ≤ 90° (5.29)
= 1,5 ∙ cos2 + sin2 (5.30)
Fax,ε,Rk is the characteristic withdrawal capacity of the connection at a angle ε to the
grain [N];
fax,90,k is the characteristic withdrawal strength perpendicular to the grain determined in
accordance with EN 14592 for the associated density ρa [N/mm²];
nef is the effective number of screws, nef = n0,9 where n is the number f screws
acting together in a connection;
kax is a factor to consider th influe ce of the angle ε between screw axis and grain
direction and the long-term behavior;
lef is the penetration length of the threaded part [mm];
k is the characteristic density [kg/m³];
i the associa ed density for fax,k [kg/m³];
β is a factor considering the influence of the angle β between the screw axis and
the LVL’s wide face;
ε is the angle between the screw axis and the grain direction, with ε ≥ 15°, see
Figure 5.7; and
β is the angle between the screw axis and the LVL’s wide face, with 0°≤ β ≤ 90°,
see figure 5.7.
ote: Failure modes in the steel or in the timber around the screw are brittle, i.e. with minimal
ultimate deformation and therefore have a limited possibility for stress redistribution.
For screws in LVL, the characteristic withdrawal parameter may be assumed a fax,90,k =15
N/mm², when ρa = 500 kg/m³ and screws 6 mm ≤ d ≤ 12 mm in softwood LVL/GLVL.
The characteristic pull-through resistance of connections with axially loaded screws should
be taken as:
ax,ε,Rk = ef ∙ head,k ∙ h2( k a)0,8 (5.31)
where
Fax,ε,Rk is the characteristic pull-through capacity of the connection at an angle ε to the
grain [N], with ε ≥ 30°
fhead,k is the characteristic p ll-through parameter of the screw determined in
accordance with EN 14592 for the associated density ρa
dh is the diameter of the screw head [mm]
5.5.3 Inclined screw connections 154 LVL Handbook Europe