EVALUATION OF SEISMIC PERFORMANCE OF STEEL MOMENT FRAMES CONSIDERING DETERIORATION EFFECTS USING IDA

In recent decades several destructive earthquakes resulted in extensive structural and non-structural damage in structures which was produced due to strength and stiffness degradation of structural elements. On the other hand, steel structures are generally modeled considering an elasto-plastic behavior with strain hardening which may be overestimated performance of structure. Therefore, it reveals the necessity for the accurate estimation of deterioration of both the strength and stiffness of elements, affecting the overall structural performance under seismic loading (Ribeiro et al., 2014). The main purpose of this paper is to assess seismic performance factors of steel moment frames with and without deterioration effects, utilizing incremental dynamic analysis (IDA) and FEMA P-695 methodology accurately. At least, the authors would like to present precise compare of modified Ibarra and Krawinkler (2005) model and an elasto-plastic model with strain hardening to simulate beam behavior of steel structures. For this purpose, two-dimensional models of 3, 9, and 20-story of SAC steel moment frames are implemented in the OpenSees framework. All models included a leaning column with no lateral stiffness to account for P-Delta effects. In this study 2% Rayleigh damping has been used. Columns are modeled using fiber elements, which effectively simulate interaction between axial force and moment. The behavior of the fiber elements is represented by a bilinear model with a 3% strain hardening. The columns in the 3-story are assumed to be fixed at the ground floor level, and the columns in the 9- and 20-story are assumed to be pinned at the basement level. Beams are modeled to behave in an elastic range. Nonlinear behavior of beams, as shown in Figure 1, is represented by zero-length plastic hinge springs placed at the ends of each beam,considering elasto-plastic behavior with strain hardening and a bilinear model with deterioration where My and Mc are the yield and capping moment strengths, respectively, while qp and qc are the plastic and capping rotation capacity, which can be calculated using the regression equations proposed by Lignos and Krawinkler (2011).

Keywords:

Moment resisting frame , Incremental dynamic analysis , CMR , Deterioration , FEMA P-695