Since several years, the trends to
designing structures are towards probabilistic design more than deterministic
design. This is based on the fact that a null risk does not exist. Engineers now
prefer to speak in terms of probability of failure. This means that a given risk
of failure is accepted. In counterpart, a cheaper structure is expected.
The problem is in determining the
pertinent failure criterion and the corresponding random input variables. If the
laws of distribution of mechanical properties are generally well known, it is
more difficult to have those representing the type and size of defects, or
loading. Some experiments should be done to obtain the desired data.
There are several reliability indexes
that are presented in this work. We will focus with the following on the Hasofer
and Lind’s index, that exhibits some theoretical advantages in conjunction with
easiness of computation.
Four methods of computation are
presented: a “black box”, associated with finite elements software, a numerical
method implemented with the help of symbolic computation software, the same but
operating with a spreadsheet and the well-known Monte-Carlo method. A
calibration test and an example have been treated with these methods and the
results are compared in terms of precision, speed, easiness of programming and
Keywords: structures, reliability, reliability indexes, numerical
methods, probability of failure, Hasofer-Lind’s index