Civil Engineering Reference
In-Depth Information
Column
loss
Figure 12.4
Sudden column loss. Adapted from Izzudin
et al
., 2007
slabs, (d) Vierendeel action, and (e) compressive arching in the
beams and/or fl oor slabs. For most structures, the redistribu-
tion of load solely through the classical mechanism of catenary
action shown in (a) is not possible and successful redistribu-
tion of load through alternative loadpaths relies on the success-
ful mobilisation of one or more of the mechanisms shown in
(b) to (e). In some types of structure, it may also be possible to
develop compressive strut action in masonry (f) or similar, the
load-bearing capacity of which can be signifi cant.
capacity and must therefore be designed to remain broadly elas-
tic, a dynamic load factor of 2.0 is necessary.
12.9.2.2 Accidental loadcase
Eurocode 0 (BS EN1990) defi nes two loadcases for a typical
offi ce building (BSI, 2002b) as follows, the partial load factors
taken from the UK National Annex (BSI, 2005b) and applica-
ble in the UK:
1.0 G
k
+ (0.5 or 0.0) Q
k
+ 0.0 W
k
+ 1.0 A
k
(12.1)
12.9.2.1 Arrest of collapse
When undertaking an alternative loadpath analysis, the dynamic
effects of the load should be considered. Approved Document A
describes the removal of the column, wall or load-bearing beam
as 'notional', but consideration of the forces involved solely as
static forces will underestimate the problem. Where structures
are designed and detailed so that they can develop signifi cant
ductility post-yield, a dynamic load factor in the range 1.3 to 1.5
may be justifi ed; however, for structures that have little ductile
1.0 G
k
+ (0.3 or 0.0) Q
k
+ 0.2 W
k
+ 1.0 A
k
where
G
k
= dead load
Q
k
= imposed load (partial factor depends on whether action is
adverse or benefi cial)
W
k
= imposed load
A
k
= accidental load.
