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Abstract
Structures with concrete-filled steel tubular (CFST) sections have been widely accepted and rapidly used owing to its advantageous structural style. However, a notable drawback of CFST members is the time-dependent deformation caused by the creep of the inner concrete. In order to maintain a structure in proper working order and to ensure more efficient usage of CFST members, it is necessary to correctly predict the effects of creep and shrinkage of the concrete core on the long-term behavior of CFST members. Considering the intrinsic uncertainties in geometric and material properties, the non-deterministic analysis of time-dependent behavior, local buckling, buckling and post buckling of concrete-filled steel tubular members under sustained load are systematically investigated. Interval analysis framework is implemented to assess effects of system uncertainties on structural responses.
Interval analytical models based on the algebraically tractable age-adjusted effective modulus method are developed for the interval analysis of CFST structures with bounded parameters. The virtual work method is used to establish the differential equations of equilibrium for the time-dependent behavior of CFST members as well as the age-adjusted effective modulus method is adopted to model the creep behavior of the concrete core. By implementing the interval arithmetic and the concept of monotonic interval function, the interval analyses of CFST structures accounting for the uncertainties of creep and shrinkage of the concrete core are investigated. The interval exact solutions provide useful benchmark results for interval numerical analyses of CFST structures.
Interval numerical analyses of CFST structures under sustained load are attempted through the combination of finite element method and perturbation method. Both upper and lower bounds of displacements are determined. Existing experimental results are performed to validate the results obtained by the developed methods. Extensive parametric studies are carried out to examine the effects of system parameters on the responses of CFST structures under sustained loading. The methodology developed in this dissertation provides a new tool to address uncertainties in the predication of structural long-term behavior and assessment of structural safety.