Methods for reliability of structures under multiple time varying loads

Current probabilistic studies on load combination have been concentrating on the modeling and linear combination of loads and load effects. Herein, a methodology for the assessment of life-time reliability of structural systems under multiple time varying loads is proposed. The method is based on considerations of load occurrences (including coincidence) and conditional probability of failure given occurrence whereby current methods of structural reliability and random vibration analysis can be incorporated. It has a wide range of applications. The emphasis is on the time domain load behavior, structural capacity uncertainty and non-linear dynamic load effects. The accuracy and computational advantage of this method as compared with other methods are examined by a numerical example of a simple frame under loads modeled as Poisson renewal pulse processes. Also, the errors implied in the widely used 'Turkstra' rule, a recently proposed modification of this rule, the load reduction factor method, and a SRSS (square root of sum of squares) rule for load combinations are quantified for linear combination and the implication in risk evaluation mentioned. (orig.)