FOSM-based updated consecutive modal pushover procedure (FUCMP) for seismic uncertainty quantification of jacket offshore platforms

Abstract

In this paper, the updated consecutive modal pushover (UCMP) procedure is implemented in the framework of the first-order-second-moment (FOSM) approach, called herein the FUCMP procedure, to propose a simplified and fast method in order to quantify the effects of epistemic (modeling) uncertainties in jacket type offshore platforms (JTOP). The UCMP procedure can take into consideration the progressive changes in the modal characteristics of structures together with the higher mode effects in predicting the seismic demands of JTOPs. The proposed FUCMP procedure is applied to a case study JTOP structure for the ductility level seismic performance evaluation considering the uncertainties in the material mechanical properties, mass and weight, and geotechnical properties. The sensitivity analysis on the seismic drift demands along the platform height to the variability in different random variables is also conducted. To this end, the results of the UCMP procedure for the modified platform models created by different uncertain variables are compared with those of the mean deterministic model. Moreover, the results of the FUCMP procedure are compared with those from the nonlinear response history (NRH) analysis conducted using a suite of far-field earthquake ground motions. These records are scaled to the design abnormal level earthquake (ALE) response spectrum. The results indicate that the FUCMP procedure is successful in predicting the standard deviation of the seismic demands considering various sources of uncertainty. Conceptually, the proposed procedure can be applied for the probabilistic seismic demand evaluation of the other structural systems.