This paper reviews several measures of structural redundancy, deterministic and probabilistic, which may be thought to be acceptable to quantity the redundancy level of a complex structural system such as offshore platforms. The present author has developed a reasonable theory and method for this throughout the paper. From the previous results of the system reliability analysis of tension leg platforms (TLPs) the reserve strength characteristic of such structures has been drawn and it has been found that TLP structures possess surprisingly high reserve strength. A simple procedure of correlating the structural safety and redundancy (reserve strength) is also introduced for use in design of steel structures to achieve a balanced design with adequate redundancy and still safety, and the results show a rough correlation between low component reliability and high reserve strength. This is an attempt to link the structural safety with the structural redundancy.


It has been much emphasised that the structural redundancy should be considered in design and the system reliability analysis is important for verification of the reserve and the residual strength (Faulkner,1984). The classic definition of the structural redundancy is the number of additional members or support reactions in excess of those required to calculate member forces by Static equilibrium. However even for discrete structures redundancy is more usefully measured by the role played by individual members in a structural system. This then identifies and allows for the existence of weak link members in an otherwise highly redundant (and mainly parallel) system. In principle each member should be systematically removed and the consequences on the residual strength of the system assesses in terms of the load at which progressive collapse occurs. A hierarchy of member importance can then be established.

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