Civil Engineering Reference
In-Depth Information
perfectly elastic material with a constant shear modulus for
a given temperature and stress duration. Equations for critical
load, maximum defl ection and maximum surface stress are
available in Haldimann
et al.
(2008). For long-term loads and/
or high temperature environments, it is sensible to ignore the
contribution of the interlayer altogether. The initial imperfec-
tions in laminated glass are the same as those for the constitu-
ent glass plates.
concentrations at the connections particularly when point con-
nections, such as the frameless glazing connections like those
described in Section 21. 2.1.3, are used.
Bolted connections
Determining the state of stress around bolt holes is analytically
complex and often involves nonlinear fi nite element analysis.
Guidelines on this are beyond the scope of this chapter, but
it is important to model the connection as faithfully as pos-
sible by, for example, (a) introducing contact elements around
the bolt hole to simulate the bearing of the bolt; (b) assigning
the appropriate characteristics to the various materials used in
the connection; and (c) specifying the correct boundary condi-
tions, particularly where semi-rigid restraints are present.
Given that there is a suffi cient end distance
c
, edge distance
(
d
-
H
)/2, and an adequate intermediate liner is placed between
the steel bolt and the glass to reduce hard spots, the strength of
bolted connection is governed by the tensile stresses generated
by the elongation of the hole. This peak stress occurs at the rim
of the hole approximately perpendicular to the direction of the
force. Stress concentration factor charts such as those provided
in Pilkey (1997) are useful for determining the peak tensile
stresses around the hole, particularly at early design stages.
The peak tensile stress concentration
K
t
around a bolt hole
may also be determined from empirical formulae such as that
provided by Duerr (1986). For a loading confi guration shown
in
Figure 21.19
this is given by:
21.5.2.2 Lateral torsional and local buckling
Slender glass members such as fi ns subjected to bending about
their major axis are particularly susceptible to lateral torsional
buckling and local buckling (
Figure 21.18
).
For rectangular fi ns with a cross-section width
b
and depth
d
subjected to pure bending
M
x
, with torsional restraints
M
z
located
l
ey
apart: the critical elastic bending moment is given by:
hd
hd
EG
hd
h
πhd
π
hd
(21.16)
M
EG
10
− 63
=
EG
10
cr LT
.
6
l
d
,
ey
For fi ns with torsional restraints
M
z
and rotational restraints
M
y
located
l
ey
apart, the critical elastic bending moment is
given by:
hd
hd
EG
hd
l
h
πhd
π
hd
(21.17)
M
EG
10
− 63
=
EG
10
cr LT
.
3
d
,
ey
Guidelines for fi ns subjected to non-uniform bending moments
are provided in AS 1288.
Local buckling often governs the sizing of a glass fi n; this
can be determined approximately from:
2
t
=
+
−
H
H
(21.19)
K
1=+
1
= 125
H
H
−
1
0
0675
−1
−
−
0
0675
−
1=+
1
=+
.
=+
1
= 12
.
=+
12
.
.
1
.
d
d
where the stress concentration factor
K
t
is defi ned as:
3
Eh
H
(
)
(21.18)
Hdt
M
σ
ma
σ
m
σ
x
Hd
cr
=
(21.20)
+
( )
K
6
6
(
ν
ν
)
t
=
P
Equations (21.16), (21.17) and (21.18) ignore initial imper-
fections and the presence of the PVB interlayer that are nor-
mally encountered in glass fi ns. They should therefore be
regarded as approximate and used for preliminary design pur-
poses only. Further details on the performance of laminated
glass under compressive loads are provided in Haldimann
et al.
(2008).
P
21.5.2.3 Connections
The inherent brittle nature of glass means that the load-bearing
capacity of glass members is often governed by the stress
y
z
x
l
ey
l
ey
H
Figure 21.18
Sign convention for lateral torsional buckling
Figure 21.19
Pin and lug notation
