Prediction of long-term extreme load effects due to wave and wind actions for cable-supported bridges with floating pylons

The characteristic values of the extreme environmental load effects should correspond to a specified annual probability of exceedance. These load effects can be calculated using short-term or long-term methods. The full long-term method is considered the most accurate approach, but it requires tremendous computational effort for complicated structures, especially when nonlinearities must be considered. In a case study of the dynamic behavior of a three-span suspension bridge with two floating pylons, these nonlinearities are found to have a significant effect on the extreme values of some of the load effects. It is thus recommended to determine these responses in the time domain. However, time-domain simulations can be very time consuming even by using simplified approaches such as the environmental contour method (ECM) and the inverse first-order reliability method (IFORM). Therefore, this paper introduces a computationally efficient approach utilizing the ECM and the IFORM to determine long-term extreme values based on responses from combined frequency- and time-domain simulations.