Earthquake Engineering Research - HKU Libraries - The University ...

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rebuild; which is the state in which the structure is deemed as being preserved.
As for "building users", generally speaking, both the "severity for hazard to human life" and the "loss
in value of property" are given more attention than the other items, in which "no injure" and "slight
injure", "no loss" and "small loss" are deemed as acceptable performances.
As for "building owners", both the "severity of hazard to human life" and the "loss in value of
property" are emphasized, as well as the "required function of the structure", in which "keep limited
function and can be used after repair" and items under it is taken of as acceptable performances, is also
paid greater attention to than "building users"
Structural damage levels
Structural engineers are familiar with structure damage levels, which are distinctly defined in codes for
earthquake-resistant design in lots of countries. The structure damage levels are defined as followed:
Select one of the following levels of damage: 1) no damage 2) slight damage, 3) small scale damage, 4)
middle scale damage, and 5) serious damage and no guarantee for life safety, which is the damage
state.
In the level of serious damage, serious damages in structural members are not able to avoided, and
partial collapse is probable to occur. Consequently, the hazardous damage to human life must be
avoided.
As for structural engineers, clients' demands about structural performance in complex range have to be
clarified and simplified into key definitions and procedures of performance-based design, according to
the principles in design Code, and then detailed criteria for the performance-based design of specific
structural types and performance levels need to be defined. Clarifying and simplifying clients'
demands, and then identifying design criteria are carried out by means of Fuzzy Set Theory.
Fuzzy Set Theory
The Fuzzy Set Theory, which was first introduced by Lotfi A. Zadeh in 1965, is considered as a means
for quantifying the ambiguity and including it in an understandable logic. The most innovating aspect
is the fuzzy reasoning hi which both variables and the relations between them are considered as fuzzy.
The Fuzzy Set Theory can be considered as a complement to the theory of probabilities. There are, in
fact two sources of uncertainties: randomness and fuzziness. The latter describes the vagueness,
imprecision or ambiguity of the information. They are fundamentally different: a random or
probabilistic phenomenon becomes certain after an event occur, whereas the ambiguity in the
definition of a concept persists and is toe-insensitive, hi general, the imprecise or fuzzy information
is replaced for which the membership is a binary notion (Le. yes/no or 0/1), by fuzzy sets, or for which
the transition from membership to non-membership is smooth and not abrupt (i.e. sets whose elements