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Improvment of Nonlinear Static Analysis of Moment Resisting Frame Structures

Mirjalili, Mohammad Reza | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50300 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Rahimzadeh Rofouie, Fayyaz
  7. Abstract:
  8. The dynamic response of the structural systems are influenced by various parameters such as the effect of higher and torsional modes, the change in frequency or inertial loads caused by the structural softening, frequency content of earthquake records, etc.. Therefore, any method that is only based on static procedure without considering the dynamic characteristics of the structural system may lead to erroneous output. The enhanced pushover procedures have been developed to minimize the inaccuracies of the nonlinear static analyses in predicting the real nonlinear response of structures while maintaining their simplicity. In this research the innovative methods are proposed individually for the symmetric tall structures (2-D frames) and also plan-asymmetric buildings. For the symmetric structures, a modified dynamic-based pushover analysis (MDP) is proposed to properly consider the effects of higher modes and the nonlinear behavior of the structural systems. For this purpose, first a dynamic-based load pattern is constructed using a linear dynamic analysis, either time history (THA) or response spectrum (RSA). Performing an initial pushover analysis with the load pattern, a nonlinearity modification factor (NMF) is calculated to modify the load pattern. The target displacement for the pushover analyses can be calculated using the available codes such as ASCE 41-13 with a suggested modification factor. The efficiency of the proposed MDP procedure is investigated using the results of nonlinear time history analysis besides some existing pushover procedures. For this purpose the two-dimensional 9, 15 and 20-story, SAC steel frame building models are considered for parametric studies using OpenSees program. The results indicate that the proposed MDP method can significantly improve the performance of the pushover analysis. For plan-asymmetric buildings, a simple Dynamic-based Pushover analysis for Plan Asymmetric buildings (DPPA) is proposed with the aim of properly considering the effects of torsional behavior as well as the higher modes in the applied lateral load pattern. According to the proposed method, the peak story drifts obtained from the response spectrum analysis (RSA) can be resolved into their translational and rotational components, and the related equivalent static lateral forces and torsional moments can be calculated. Consequently, for accurate estimation of the maximum drift demands of plan-asymmetric buildings, it is proposed that the drift responses obtained from the RSA for the stiff and flexible edges of the building be utilized to construct two lateral-torsional load patterns for nonlinear static analyses. The envelope of the results of two pushover analyses using the constructed load patterns is considered as the seismic demands of the building structure. The target displacement for the pushover analyses can be calculated using the available codes such as ASCE 41-13 with a suggested modification factor. Using a number of structural models, the versatility of the proposed DPPA procedure in estimating their local and global seismic demands is demonstrated by comparison of the obtained results with those calculated from other approaches such as nonlinear time history analysis (NL-THA) and the practical modal pushover analysis (PMPA) or the extended-N2 methods as two well-known pushover procedures. The comparison of the results clearly demonstrates the efficiency of the proposed DPPA procedure in accurately capturing the response parameters, especially in shear-building structures while is more applicable and much easier to use in practical structural designs with respect to other available enhanced pushover procedures
  9. Keywords:
  10. Pushover Analysis ; Higher Mode Effect ; Nonlinear Response ; Asymmetric Concrete Buildings ; Torsion ; Unsymmetric-Plan Buildings ; Moment Resistance Frame

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