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Finite element modeling and parametric studies of a chevron braced frame with a vertical slotted connection detail Seeton, Andrew

Abstract

This thesis presents the findings of comprehensive parametric sensitivity studies of a series of three-dimensional finite element models. The models considered relate to a steel chevron braced frame system with an innovative vertical slotted connection (VSC) detail that ideally improves the seismic performance of the system by precluding the application of an unbalanced load to the mid-span of the beam upon buckling of either brace. Since simplified models of a prototype specimen of the system were unsuccessful in predicting the experimentally observed behaviour, a sophisticated three-dimensional modeling investigation was undertaken. The primary lateral load resistance and energy dissipation qualities of the chevron braced frame system are provided by the bracing elements. Therefore, these members constituted the initial focus of the modeling investigation. Stub column simulations were undertaken to determine the sensitivity of the predicted local buckling behaviour to an extensive set of modeling-related parameters. Next, a single brace model was developed, to investigate the sensitivity of global buckling predictions to the modeling parameters. The results from the parametric studies of the stub column and single brace models enabled a well-informed approach to the modeling of the full chevron braced frame system with the VSC detail, which itself was also subjected to parametric study. Refined three-dimensional modeling of the VSC detail including material, geometric, and contact nonlinearities enabled the kinematic behaviour of the system to be carefully scrutinized. The general purpose finite element program LS-DYNA was used to conduct the investigation. Five analysis methods were used, including: eigenvalue vibration analysis, eigenvalue buckling analysis, implicit static analysis, implicit dynamic analysis, and explicit dynamic analysis. The capabilities of the analysis methods were tested, and particular focus was placed on the use of the explicit method. While stability considerations limit the maximum allowable time step size for explicit time stepping methods, it was determined that quasi-static solutions could be obtained, so long as a sensitivity study was paired with the analysis in order to quantify the extent to which time scaling procedures affect the results. Although an exact match between the experimental and analytical results was ultimately not achieved, the finite element model was able to capture the key characteristics of the lateral loading response of the proposed chevron braced frame system with a VSC detail.

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