“…Since the development of Rice's formula, amounts of improvements have been made. For example, Vanmarcke proposed a commonly used improved formula, accounting for the dependence between the crossing events and the time that the process spends above the barrier in application to normal stationary random process model 2 Mathematical Problems in Engineering [18]; Madsen and Krenk developed an integral equation method for solving the first-passage problems [19]; a timedependent reliability analysis method with joint upcrossing rates, inspired by [19], was further developed by Hu and Du [20] for more general cases of the limit-state functions that involve time, random variables, and stochastic processes; by combination of the ideas of outcrossing and system reliability, Wang et al [13] presented an improved subset simulation with splitting approach by partitioning the original high dimensional random process into a series of correlated, short duration, low dimensional random processes; several improved formulations for calculating the outcrossing rate based on the Poisson assumption were, respectively, extended by Schall et al [21], Engelund et al [22], Streicher and Rackwitz [23], and so forth. Recently, additional correlational researches have been also suggested by [24,25].…”