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Application of Adaptive Method in Optimum Seismic Design of Steel Moment Resisting Frames and Dampers

Hosseini Gelekolai, Mojtaba | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50909 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moghaddam, Hassan
  7. Abstract:
  8. The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural systems and earthquake excitations before they can be used in common practice. The aim of this work was to identify the most suitable lateral load patterns for the seismic design of steel moment-resisting frames. To do this, the non-linear seismic behaviour of three-, five-, seven-, ten- and 15-storey frames designed with nine different lateral load patterns were compared under 20 real and synthetic spectrum-compatible earthquakes using performance parameters such as maximum inter-storey drift, maximum plastic hinge rotation and cumulative damage. It was found that, for the same structural weight, structures designed with more efficient load patterns experienced less global damage than their code-based counterparts. In the second part of this study, a practical performance-based optimisation method is introduced for optimal cross-sectional distribution of steel moment resisting frames (SMRFs) under earthquake excitations. The proposed method is based on the concept of uniform distribution of damage, in which the unused material is redistributed from strong to weak parts of a structure by using a novel adaptive optimisation algorithm. To demonstrate the effectiveness of the method, 3, 5, 7, 10 and 15 storey SMRFs are optimised under 15 synthetic design spectrum compatible earthquakes and 5 real strong earthquake ground motions. Using ASCE41 performance criteria, maximum plastic rotations and strength-based demand to capacity ratios are considered as the main design parameters for deformation-controlled and force-controlled members, respectively. The results indicate that the proposed method is very efficient at controlling the selected performance-based design parameters and improving the efficiency of the whole structural system in only a few steps. It is shown that, for the same performance level, the optimally designed frames require less structural weight compared to their code-based design counterparts, leading to a significant reduction in the construction costs. Subsequently, the average storey shear force distributions of the optimum frames under the design spectrum compatible earthquakes are used to obtain more efficient lateral load patterns for seismic design of SMRFs. It is shown that using the proposed load pattern in the design process could considerably improve the seismic performance of the frames compared to those designed in compliance with the conventional seismic design guidelines. In the third part in order to control the inter-storey drift ratios in the optimal frames, the height-wise distribution of viscous dampers obtained by means of adaptive method. The results indicate that proposed method is very efficient at controlling the inter-story drift ratios in a specific limit and optimizing the damping coefficient of viscous dampers only in a few steps
  9. Keywords:
  10. Viscous Damper ; Nonlinear Dynamic Analysis ; Uniform Deformation Theory ; Lateral Load Pattern ; Moment Steel Frames ; Performance-Based Seismic Design ; Adaptive Method

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