PSI - Issue 20

D. Reznikov / Procedia Structural Integrity 20 (2019) 17–23 D. Reznikov / Structural Integrity Procedia 00 (2019) 000–000

21

5

If the maintenance program ζ * is implemented the deterministic (standard based) criterion for securing the system's structural integrity may be written down as follows:

n



( ) [ ] t n 

k  .

*

[0; ],     t T i

1, 2, ,

i

i

d

3. Probabilistic approach to securing structural integrity Starting from the second half of the XX centaury a probabilistic approach to ensuring structural integrity is being developed. According to this approach the system's structural integrity is secured if the following condition holds:

[0; ] d t T   ,

P t

( ) { ( ) P C t 

D t  

( )} [ ] P

(6)

f

f

where C ( t ) and D ( t ) are capacity and demand parameters, P f is the estimated value of the system’s failure probability, [ P f ] is the so called tolerable value of the system’s failure probability. This value is determined by the state of the economy, available technologies and wiliness of the industry, supervising agencies and/or society to pay for implementation for protection measures. According to CIRIA-Construction Industry Research and information association (1977) the value of [ P f ] can be determined as follows, by Elishakoff (2004):

4 M   T

[ ] 10 P 

d

,

(7)

f

where χ is a societal criterion factor (Table 2), T d is the design service life of the structure in years, M is the number of people within or near the TS. Similar to the case of deterministic approach, two strategies for securing structural integrity may be defined (Fig.1): - Strategy 1 implies the implementation of a significant set of protection measures including maintenance, routine repair, and overhaul at moments t 1 , t 2 , and t 3 respectively to keep the failure probability below the tolerable value (the maintenance program ζ 1 ). - Strategy 2 implies the selection of the design variables in such a way that the system failure probability will stay below the tolerable value without implementation of protection measures throughout the design service life of the structure (the maintenance program ζ 2 ).

b

a

Fig. 1. Securing structural integrity of TS in case of (a) traditional deterministic and (b) probabilistic approaches: the light gray signed the area where the structural integrity is secured, and dark gray - where is not secured.