Probabilistic design using yield stress as the failure criterion must be accomplished…what minimum safety factor is acceptable?
Cumulative normal distribution is explained, e.g. on web page http://en.wikipedia.org/wiki/Normal_distribution
where mu is the center, sigma is the standard deviation, and x (z in your book) is the deviation from the center.
The value of Phi is the probability of the random quantity it describes to be less or equal …
This provides an example of probabilistic design to determine minimum safety factor.