The theory for the estimation of the reliability of a structural syste
m which is subject to one or more load processes requires knowledge of
the surface defining the mechanical response of the system. For many
systems this surface may be known only implicitly and defined through
a method of structural analysis. In the formulation presented herein,
the surface is obtained using an established probabilistic structural
analysis technique. The reliability estimation is formulated in the lo
ad process space. In this space, directional simulation is employed to
estimate the outcrossing rate and the initial (zero time) probability
of failure and hence to estimate the probability of failure at any su
bsequent time. Two examples using discrete rectangular pulse (Poisson)
processes are described.