Environmental Engineering Reference
In-Depth Information
Figure 4.13 distinguishes between imposed loads and environmental actions:
- For imposed loads, the partial safety factor related to the 95% quantile for a
reference period of 50 years is taken as the characteristic value:
E
imp
;
d
E
imp
;
k
;
0
:
95
;
N
¼
50
g
imp
¼
- For environmental actions, on the other hand, it is customary to specify the 98%
quantile related to one year as the characteristic value:
E
env
;
d
E
env
;
k
;
0
:
98
;
N
¼
1
¼
E
env
;
d
E
env
;
k
;
0
:
364
;
N
¼
50
g
env
¼
Converting this value to the reference period of 50 years results in the 36.4% quantile
(0.98
50
¼
0.364). This leads to higher partial safety factors for environmental actions
than for imposed loads for the same coefficient of variation!
Furthermore, the combination factors
c
0,i
depend on the basic time interval (T
1
), that is
the period of time during which a constant value for the action may be assumed in the
model [58,25]. The number of basic time intervals during the design working life
(50 years) is
50
T
1
N
1
¼
Values for basic time intervals are specified in [59,60,61].
Combination factors
c
0,i
for variable actions (Q) depending on the coefficient of
variation (V
Q
¼s
Q
/m
Q
) and various basic time intervals (N
1
) are given in Figure 4.14.
Fig. 4.14 Combination factors for variable actions and various basic time intervals [25]