“…The random variable Nf
is independent in the principle of probability theory, and its approximate limit state function is as follows (Liu et al ., 2016, 2022b; Koyluoglu and Nielsen, 1994):where the mean value μX={μx1,μx2,⋯,μxn}T
, the standard deviation σX=(σX1,σX2,...,σXn)T
, ∇g(μX)
represents the gradient of g
at point μX
, ∇g(μX)={∂g(μX)∂x1,∂g(μX)∂x2,⋯,∂g(μX)∂xn...…”