Titel_SS06

(^5) Q factor between 0 and 1, modelling the relative fraction of wind load
The corresponding design equation is written:
zRac m/ 6 ( (1 56 ) G caG 556 ( QQ CQ 1 (1 5 6QQ QQ) 2 Q 2 C) ) 0 (11.14)
Variable Distribution type Coefficient of variation Quantile
G Permanent load N 0.10 50 %
Q Variable load G 0.40 98 %
R Resistance LN 0.05 5 %
XR Model LN 0.03 50 %
Table 11.3: Stochastic model. N : Normal, G : Gumbel, LN : Lognormal.
The number of repetitions of the variable loads in a Ferry-Borges-Castanheta load model is
assumed to be:
 Wind: 360 times per year
 Snow: 10 times in the 5 month period where snow load is assumed to occur
 Imposed load: 1 time per 10 years.
The target annual reliability index is chosen to t=4.2. Further one partial safety factor can be
chosen freely. Here (^6) G=1 is chosen.
First, the case with only one variable load is considered. 5 -values between 0.1 and 0.8 are
assumed to represent typical values. Using CodeCal (2003) the partial safety factors (^6) Q and
(^6) m are determined by solving the optimization problem in Equation (11.5). The result is
(^6) Q=1.65 and (^6) m=1.15.
The reliability index as function of 5 using the optimal values of the partial safety factors is
shown in Figure 11.3.
3.5
3.6
3.7
3.8
3.9
4
4.1
4.2
4.3
4.4
4.5
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
5
 Achieved 
Target 
3.5
3.6
3.7
3.8
3.9
4
4.1
4.2
4.3
4.4
4.5
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
5
 Achieved 
Target 
Figure 11.2: Reliability index as function of 5.
Next, load combination factors Q are determined for the following cases such that the target
reliability index is t=4.2:
 Environmental load and non-dominating imposed load: QIE,