A general procedure for ®rst/second-order reliability method (FORM/SORM)

First/second-order reliability method (FORM/SORM) is considered to be one of the most reliable computational methods for structural reliability. Its accuracy is generally dependent on three parameters, i.e. the curvature radius at the design point, the number of random variables and the ®rst-order reliability index. In the present paper, the ranges of the three parameters for which FORM/SORM is accurate enough are investigated. The results can help us to judge when FORM is accurate enough, when SORM is required and when an accurate method such as the inverse fast Fourier transformation (IFFT) method is required. A general procedure for FORM/SORM is proposed which includes three steps: i.e. point ®tting limit state surface, computation of the sum of the principal curvatures Ks and failure probability computation according to the range of Ks. The procedure is demonstrated by several examples. # 1999 Elsevier Science Ltd. All rights reserved.