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Nonlinear Performance of 3-D Steel Structures by Scaled Nonlinear Dynamic Procedure

Hashemian, Behdad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39926 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Mofid, Masoud
  7. Abstract:
  8. It is well known that the most rigorous method to assess the performance and to predict the seismic demands of a structure subjected to earthquake is nonlinear time history analysis. However, this technique is accompanied by complexities and difficulties in evaluating the seismic demands of structures and requires superior knowledge and skill. As a result, in recent years, nonlinear static analysis has been proposed in performance based design procedures. One of the primary assumptions of nonlinear static procedures is that the behavior of a structure with multiple degrees of freedom (MDOF) subjected to seismic ground motion can be estimated from the response of an oscillator with a single degree of freedom (SDOF). The actual maximum global displacement for the MDOF system can differ from the equivalent SDOF approximation. The deviations of the actual distribution of forces and deformations from those associated with the equivalent SDOF system are termed MDOF effects. Recent studies have shown that none of the current nonlinear static procedures can properly account for the contribution of higher modes to the response of structures. To consider MDOF effects, a new analytical procedure, called the scaled nonlinear dynamic procedure (Scaled NDP), has been developed. In this procedure response quantities are determined by nonlinear dynamic analysis using ground motion records that are scaled so that the peak roof displacement observed in the nonlinear dynamic analysis matches the target displacement determined by a nonlinear static procedure. In this investigation, the ability of the proposed procedure in considering higher mode effects and evaluating seismic demands of 3-D steel structures has been examined by comparing with nonlinear time history analysis. In order to compare these procedures, various 3-D steel structures including structures with mass irregularities in plan and structures with mass, stiffness and geometric irregularities in elevation are analyzed. Comparison of the results reveals that the Scaled NDP properly considers MDOF effects in evaluating seismic demands of structures.
  9. Keywords:
  10. Nonlinear Time History Analysis ; Scaled Nonlinear Dynamic Procedure ; Multi Degrees of Freedom Effects ; Three Dimentional Irregular Steel Structures

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