Second-Moment Combination of Stochastic Loads

A practical method for specification and evaluation of stationary stochastic loads and their combinations is developed. A set of descriptor functions for stationary processes is introduced that describes the mean and variance of the extreme over given intervals of time, in terms of the random-point-in-time mean and variance of the process. For linear combinations of stationary loads, the mean and variance of the combined extreme are obtained in terms of the random-point-in-time means and variances of individual loads and their respective descriptor functions. Computed values of the extreme may be used in conjunction with the second-moment theory to evaluate structural reliabilities or required safety margins. Applications of the method to several load models are presented. Computed results for various combinations are shown to be in good agreement with Monte Carlo simulations.