Civil Engineering Reference
In-Depth Information
In buildings predominantly used for storage or where the
imposed load is otherwise of a permanent nature, the full
imposed load Q
k
should be used.
The above compares with accidental loadcases in the British
Standards typically defi ned:
load. If the fl oor slab is of continuous construction, it is rea-
sonable to assume that only a proportion of the fl oor slab will
collapse. The extent is for the engineer to determine on an indi-
vidual basis, but if 50% of the weight of the fl oor is applied
with a dynamic load factor of 3.0 and a partial factor of 1.05,
the loadcase will often be less onerous than the loadcase for
the design of the fl oor slab at the ultimate limit state.
In load-bearing wall construction, the Approved Document
requires the removal of a length of load-bearing wall equal to
2.25 times the storey height H. Where columns are close-centred
there is no such requirement; however, it is good practice to
10510
1
.(
1051
.(
.
51.
.
0
0
G
(
0
33
00
)
Q
03
03 W
03
.
03
033
3
W
1
0
1
W
0 A)
+
(
(
0
0
33
33
00
)
Q
Q
+
W
W
+
or
k
+
(
(
(
(
0
0.
0.
0 33
33
or
00
00)
)
Q
Q
Q
k
k
k
W
W
k
W
W
+
1
1
W
0
W
W
A)
k
.
33
or
00
.
k
k
(
(
0
0 33
.
33
33
or
00
00
00)
)
Q
k
k
k
1
1 0
Q
Q
k
(12.2)
The accidental load A
k
in a column removal scenario is the
load that was carried by the column prior to its removal under
an accidental loadcase, multiplied by the relevant dynamic
load factor described above. This is the load that must be
transferred through alternative loadpaths if the structure is to
remain stable.
It is good practice to design the structural slab for the debris
load associated with the area of collapse of the slab(s) above,
in order to ensure successive fl oor collapse does not occur. If
simply supported, the full mass of the structural slab and any
supported fi nishes should be applied assuming a dynamic load
factor of 3.0 and a partial factor of 1.05 for accidental dead
Compression ring
Tension
membrane
Load from
structural bays
Catenary
force
PLAN
Figure 12.5(c) Mechanisms to resist collapse. Tensile membrane
developed in a fl at slab after the removal of the central column.
© Arup
Additional
reaction
forces
SECTION
Figure 12.5(a) Mechanisms to resist collapse. Catenary action in
structural beam/column frame of an internal column after removal of
a supporting column. © Arup
Load from structural
bays above
Additional
reaction
forces
SECTION
Shear
stiffening
SECTION
Figure 12.5(d) Mechanisms to resist collapse. Vierendeel action due
to moment capacity in beam/column connections following loss of
two columns (of which one is lost over two storeys) and the fi rst fl oor
beam over two structural bays. © Arup
Figure 12.5(b) Mechanisms to resist collapse. Shear deformation of
deep transfer/spandrel beams. © Arup
