Summary: This paper presents the study on non-deterministic problems of structures with a mixture of random field and interval material properties under uncertain-but-bounded forces. Probabilistic framework is extended to handle the mixed uncertainties from structural parameters and loads by incorporating interval algorithms into spectral stochastic finite element method. Random interval formulations are developed based on K-L expansion and polynomial chaos accommodating the random field Young’s modulus, interval Poisson’s ratios and bounded applied forces. Numerical characteristics including mean value and standard deviation of the interval random structural responses are consequently obtained as intervals rather than deterministic values. The randomised low-discrepancy sequences initialized particles and high-order nonlinear inertia weight with multi-dimensional parameters are employed to determine the change ranges of statistical moments of the random interval structural responses. The bounded probability density and cumulative distribution of the interval random response are then visualised. The feasibility, efficiency and usefulness of the proposed interval spectral stochastic finite element method are illustrated by three numerical examples.
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