Civil Engineering Reference
In-Depth Information
glazing, but the energy imparted on impact will depend on the
angle that the glass subtends to the vertical.
causes widespread damage to light cladding and glazing. The
response of glazing in blast loading is generally assessed by
means of dynamic analysis and verifi ed by mounting the glass
onto a test cubicle and performing a blast test in a secure range
testing site. The aim of these tests is to determine the hazard
levels by measuring how far glass fragments are projected into
the test cubicle. Alternatively testing can take place in shock
tubes. Pressure impulse charts are useful for initial sizing of
simply supported laminated glass panels, but novel boundary
conditions require testing. Further guidelines on testing for
blast resistance are available in BS EN 13541 and GSA 2003.
21.4.1.7 Intrusion
The degree of security provided by glazing is tested in terms of
the resistance to manual attack. Two tests are described in BS
EN356: (a) hard body drop tests consisting of a 100 mm diam-
eter steel sphere dropped onto a horizontal glass panel from
heights ranging from 1.5 m to 9 m; (b) mechanised swinging
axe tests on a vertical glass panel. In both tests the glazing is
classifi ed in terms of its ability of the glass to resist penetration
by the impactor.
21.4.2 Limit state design with glass
As with other materials, glass structures must be designed and
constructed to minimise injury and loss of property/business.
This is achieved by satisfying the following limit states:
21.4.1.8 Maintenance-related impact on horizontal glazing
The maintenance loads on glazed roofs are a function of the
degree of access afforded to maintenance personnel. This
ranges from glazed roofs that can be walked on for occasional
maintenance to roofs onto which people are physically pre-
vented from walking, falling or dropping tools. The procedure
therefore consists of a sequence of tests involving a soft body
impact test with a 45 kg impactor dropped from a 1.2 m height
onto the glass panel to simulate a person falling onto the roof
from a standing position [13]; a hard body impact test with a
100 mm diameter steel sphere dropped onto a horizontal glass
panel from a 1.2 m height to simulate the effect of tools being
dropped on the roof [15]; a 180 kg static load for a duration of
30 minutes with all plies broken to simulate one person falling
onto the glass and becoming injured and another person giving
assistance. The test is successful if the glass unit does not fall
out, the impact body does not penetrate the glass and no dan-
gerous glass fragments fall out [25]. In addition, roofs that can
be walked on by maintenance personnel will require adequate
slip resistance, which in some instances can be provided by
special footwear.
Ultimate limit state for normal use: adequate strength and stabil-
■
ity for service life loads including superimposed live loads, loads
arising from temperature variations, loads during the construction
stage, and maintenance loads.
Serviceability limit state for normal use: limiting defl ections and
■
vibrations to ensure adequate functioning and appearance of the
structure including comfort of users.
Ultimate limit state for exceptional actions: limit and/or delay the
■
damage to a structure from the exceptional actions such as fi re,
impact, blast and earthquakes. Any damage in the structure shall
not be disproportionate to the cause.
21.4.2.1 Action combinations for ULS (normal use)
The design loads
F
d
for ULS arising from normal use may be
determined from:
∑
(21.9)
F
G
Q
""
""
∑
Q
F G
=
F F G
d
F G
=
γ
F F G
d
F G
F G
F G
""
""
+
+
+
+
""
γ
+
+
""
γ
ψ
∑
∑
γ ψ
γ
ψ
+
d
F G
d
F G
Q
Q
F G
d
F G Q
F G
d
F G
γ
F G
d
F G
F G
d
F G Q
F G
d
F G
Qk
γ
γ
Qk
Q
Q
+
Q
Q
Q
γ ψ
γ ψ
∑
∑
∑
γ ψ
γ ψ
∑
∑
γ ψ
γ ψ
γ ψ
γ ψ
γ ψ
0
0
0
i
Q
ki
d
γ
d
F G
d
F G
γ
F G
,
1
1
γ ψ
γ ψ
γ ψ
Q
Q
Q
Q
Q
Q
γ ψ
Q
γ ψ
Q
γ ψ
Q
γ ψ
Q
γ ψ
Q
γ ψ
Q
Q
Q
∑
∑
∑
∑
∑
∑
∑
∑
γ ψ
γ ψ
γ ψ
γ ψ
γ ψ
γ ψ
∑
γ ψ
γ ψ
γ ψ
γ ψ
0
0
0
0
,
,
,
i
i
i
k
ki
Q
∑
∑
i
21.4.1.9 Public access impact on horizontal glazing
In addition to the standard superimposed live loads specifi ed in
EN1991-1-1, glazing with unrestricted access to foot traffi c such
as glass fl oors and glass staircases must have an adequate impact
and post-fracture capacity. Hard body and soft body impact
tests similar to those described for maintenance loads (Section
21.4.1.8) should be performed, but the glass pane should be pre-
loaded to half the working load for the impact tests. The post-
fracture capacity is assessed by maintaining half the working
load on the glass unit with all plies broken for a duration of 30
minutes. It is also advisable to ensure that the unloaded unit with
all plies broken does not collapse within 24 hours.
where
γ
G
is the partial factor for permanent actions,
G
is the
value of permanent actions (e.g. self-weight load, permanent
equipment),
γ
Q
is the partial factor for variable actions,
Q
k,1
is the characteristic value of the leading variable action (e.g.
imposed load on fl oor, wind, snow) and
ψ
0,i
is the combination
factor for accompanying variable actions.
This includes self-weight, static imposed, wind, snow and
temperature. It excludes impact and blast loads as well as com-
binations that involve simultaneous static and impact loads e.g.
maintenance impact (cf. Section 21.4.1.8) and public access
impact (cf. Section 21.4.1.9) that are assessed separately.
There are no statistics to predict the likelihood of horizontal
static (barrier) loads and wind loads occurring simultaneously.
For buildings where people may congregate it is common prac-
tice to consider the combined action of full wind load plus half
the horizontal barrier load or half the wind load plus the full
horizontal barrier load whichever is greater. For other build-
ings (e.g. residential and offi ce buildings) the wind load and
the barrier load should be considered separately.
21.4.1.10 Blast
The shock wave from an explosion creates a positive high
pressure at its leading edge known as the positive phase that
decays rapidly to ambient pressure; this is followed by a much
longer negative pressure known as the suction phase. The latter
does not normally lead to major structural damage, but often
