Nondeterministic analyses of structures with intrinsic uncertainties in their parameters and loading regimes are attracting considerable research attention. Probabilistic model has been used extensively for the representation of system uncertainties when sufficient statistical information is available to form reliable probabilistic feature. Interval models have been increasingly adopted in structural systems for handling uncertain parameters without sufficient statistical data but with precisely known changing ranges. Uncertain problems with mixed random and interval parameters are commonplace in structural analysis and design, especially for large-scale practical-size structures where complete probabilistic features of all structural parameters are not always available. In this study, nondeterministic dynamic characteristics of engineering structures are investigated with allowance for the inevitable random and interval uncertainties in their parameters. Unified stochastic interval analysis is implemented to furnish the complete uncertain spectrum of random interval dynamic characteristics. Bounded mean value, standard deviation, probability density function and cumulative density function of uncertain natural frequencies and mode shapes are constructed by the developed unified stochastic interval method by combining advanced sampling technique with optimization strategy. A practically motivated 3D structure is analyzed to demonstrate the accuracy and effectiveness of the proposed approach by comparing with the reference Monte Carlo simulation method.
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