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Investigation of the Nature of Earthquake Lateral Force and its Influencing Factors with Regard To Seismic Behavior of Steel Frames in Elastic and Non-Elastic Domain

Bagheri, Mohammad | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53634 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moghaddam, Hassan
  7. Abstract:
  8. In the conventional design of buildings, seismic loading codes consider the base shear as an earthquake-induced load, and by distributing this base shear along the height of the structure, members are designed to withstand lateral loads (i.e. earthquake force). The most common form of earthquake force distribution is based on the response of the main mode (first mode) of the elastic structure. But this lateral distribution has two major problems. First, it does not take into account the impact of higher modes on the structural response; and second, the entry of the structure to its inelastic domain in severe earthquakes and the difference resulting from this structural behavior change in lateral force distribution are not considered. In fact, in the inelastic domain, the ultimate strength will be a determinative factor in the amount of members force. In this study, considering structural models of steel frame with shear and flexural behaviors, as well as considering the effect of presence or absence of gravity load on frame design for lateral load-bearing, by performing nonlinear dynamic time-history analyses, factors affecting the amount of stories force generated by the earthquake excitation in comparison to code-based lateral load are investigated. Among the factors affecting the difference in shear rates of stories identified in this study, the different distribution of force at the height of the structure at the moment of peak shear than to the code-based distribution of the force, the generation of secondary moments different from those in the elastic design of the structure (due to a large number of inelastic deformations), and the error of the design interaction formula in estimating member strength can be mentioned. Structural lateral force distribution at the peak moment of the story response can cause changes in the axial force level (and hence the bending strength of the member), the buckling strength of the member and the moment ratio of the two ends of the member, which all influence the amount of shear force of the member. The impact of the above factors may be low or high depending on the type of structural model. The lateral force distribution of some models is roughly dependent on their design strength and thus will be similar to the structural design force distribution; others experience a different force distribution than the force distribution used in the design due to the difference in strength and seismic behavior with the design assumptions. Finally, it can be concluded that different models can expect similar results when considering a well-distributed force distribution for structural design
  9. Keywords:
  10. Nonlinear Analysis ; Seismic Forces ; Seismic Behavior ; Steel Frames ; Earthquake Lateral Force Distribution ; Force-Moment Interaction ; Dynamic Time History Analysis

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