ROBUST SAFETY FORMATS FOR STRUCTURAL DESIGN.

Design rules in codes of practice have to be formulated in ways that are straightforward for designers to use. It is also commonly assumed that, unless specifically required to the contrary, the level of safety given by structures designed to the code should be as uniform as is compatible with the simplicity requirement. More controversially, this paper assumes that probability of failure is the appropriate way to measure the degree of safety provided by a code. A number of safety formats used by codes of practice are examined, and a new one proposed. In this, one load or element of the resistance takes a value whose probability of being exceeded is the same as the required probability of failure for the resulting structure, while all the others take values corresponding to a specified, less extreme, probability. The performance of this rule is examined in a number of situations and it is shown to give a much narrower range of structural reliabilities than the other rules considered. (A)