There are different levels of reliability analysis, which can be used in any design methodology depending on the importance of the structure. The term ‘level’ is characterized by the extent of information about the problem that is used and provided. The methods of safety analysis proposed currently for the attainment of a given limit state can be grouped under four basic “levels” (namely levels IV, III, II, and I ) depending upon the degree of sophistication applied to the treatment of the various problems.

Space of State Variables