Civil Engineering Reference
In-Depth Information
value of the action (F
d
). The design effects of the action then depend on the limit state under considera-
tion but could be, for example, a sliding force or a moment.
The sequence is thus:
Characteristic action
(F
k
)
representative action
(F
rep
)
design action
(F
d
)
design effects of action
(E
d
)
Correlation
factor,
ψ
Partial factor
of safety,
γ
F
i.e.
F
= ×
F
ψ
(
ψ
≤
1 0
.
;
ψ
=
1 0
.
for persistent actions
)
rep
F
=
F
×
γ
d
rep
F
Note 1: Characteristic self-weights are calculated from characteristic weight density values (e.g. see
Example
5.3)
.
Note 2: In geotechnical design work an assumption may be made that any structural action has already
been combined with the correlation factor,
ψ
. This makes sense as a structural action coming onto a
geotechnical structure will almost certainly be the result of a structural design process.
Example 5.1:
Design value of action
A representative action has magnitude 200kN. Considering a partial factor of safety,
γ
F
=
1.35, determine the design value of the action.
Solution:
F
=
F
× =
γ
200 1 35
×
.
=
270
kN
d
rep
F
5.4.4 Design values of geotechnical parameters
Defining characteristic values of geotechnical parameters has already been discussed in Section
5.4.1
. To
reach the design value of the geotechnical parameter, the characteristic value is divided by the appropri-
ate partial factor of safety.
Characteristic geotechnical
parameter
(M
k
)
Design geotechnical
parameter
(M
d
)
Partial factor
of safety,
γ
M
i.e.
M
k
M
=
γ
d
M
