Introduction - The Behaviour and Design of Steel Structures to EC3 - page 29

Resistance

Total load
effect

Shaded area illustrates
probability of failure

Total load effect or resistance

Figure 1.16 Limit states design.

6

5

4

3

2

1

0

-8 -6 -4 -2

10 10 10 10

Probability of failure p F

Figure 1.17 Relationship between safety index and probability of failure.

that an increase in β of 0.5 implies a decrease in the probability of failure by
approximately an order of magnitude.
The concept of the safety index was used to derive the partial factors for EC3.
This was done with reference to previous national codes such as BS 5950 [50]
to obtain comparable values of the probability of failure p F , although much of
the detailed calibration treated the load and resistance sides of equations 1.8
separately.