Sosa, Eduardo M.

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    Computational buckling analysis of cylindrical thin-walled above-ground tanks
    (2005-06) Sosa, Eduardo M.; Godoy, Luis A.; College of Engineering; Zapata, Raúl E.; López, Ricardo R.; Suárez, Luis E.; Department of Civil Engineering; Gutiérrez, Gustavo
    This thesis evaluates the stability of cylindrical above-ground steel tanks under imposed support settlements and wind pressures. The tanks considered are representative of tanks constructed in Puerto Rico and in the Caribbean Islands. Typical tanks are constructed with a cylindrical shell with variable thickness and a conical roof supported by rafters. The behavior of these tanks is evaluated by means of computational experiments performed using finite element models developed with ABAQUS. The influence of support settlements on the out-of-plane displacements in the cylindrical shell is investigated considering an elastic material behavior and using different types of analyses. Results are presented for geometric linear, geometric non-linear and bifurcation buckling analyses. Linear results provide a poor indication of the real displacements in the shell, so that geometric non-linearity is included in the analysis for working loads. Results show that the equilibrium path is highly non-linear and that the shell displays a stable symmetric bifurcation behavior. The lower bound approach for the buckling load of imperfection-sensitive shells is implemented in this thesis. Initially, the formulation is presented in a way to highlight what computations can be done following a reduced energy model. Then, a proposed methodology is used in conjunction with a general purpose finite element program to compute the lower bound buckling load for tanks with different geometric and load configurations. Results show that the proposed reduced energy model can predict the lower bound load for cylindrical shells under uniform pressure distributions, but cannot estimate the lower bound for wind pressures. The dynamic stability of an empty tank under wind pressures is investigated. An assumed space variation of pressures, and a simplified deterministic model of time fluctuating pressures due to wind, are applied. The response is calculated using explicit integration of the equations of motion and the dynamic buckling load is identified through a qualitative criterion. The response is analyzed in the time and in the frequency domain in order to recognize the nature of the problem. Results show that pressure fluctuations do not induce resonance of the structure, so that simpler pressure models may be used in practical analyses.