Question

The probability of failure implied in limit state design is of the order of

• A. ${10}^{-2}$
• B. ${10}^{-3}$
• C. ${10}^{-4}$
• D. ${10}^{-5}$

Answer 1

The correct option is A ${10}^{-2}$

The structure may fail when
(i) the load exceeds the design load
(ii) the strength is less than the characteristic strength
(iii) both the load exceeds the design load and strength is less than the characteristic strength. The probability of load exceeding design load = 5%
The probability of strength less than characteristic strength =5%.
The probability of failure is = $0.05\times 0.95+0.05\times 0.95+0.05\times 0.05$
= $0.0975$
Thus the order of failure is ${10}^{-2}$.