Resistance deterioration which is purely a time function such as typified by simple corrosion problems is considered herein for structural systems subjected to one or more stochastic load processes. The resistances are modelled as Gaussian random variables and the loads as Gaussian random processes. Deterioration is considered by either of two simple models -exponential or parabolic functions of time. Both an upcrossing and an outcrossing formulation is used to estimate the up (out) crossing rate through linear domain boundaries. Numerical integration is employed to evaluate the resulting integrals, although significant simplifications are occasioned through the use of Gaussian random variables and processes. Results are given for two simple structural examples and compared to purely simulation results both for the outcrossing rate and for various sensitivity results. Good agreements is found. The results suggest that results for failure probability based on mean values of the deterioration models may be satisfactory in some cases.
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