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]
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