Susceptibility of mid-rise and high-rise steel moment resisting frame buildings to the nonlinear behavior of beam-column connections

Bayraktar, Murat
Moment resistinting steel frames provide significant energy dissipation capacity in the event of a major seismic excitation. In order to ensure this, one of the most critical regions to pay attention is the beam-column connections, where their behavior is greatly simplified and idealized for the purpose of design in practice. In this thesis, the variables inherent in steel connections are taken into account through a parametric study by considering both static push-over analysis and nonlinear time history analysis. There has been research on this topic especially for low-rise buildings, but for mid-rise and particularly high-rise buildings, the effects of connection nonlinearity, such as strength loss and pinching in response, as well as the design approach of structural system, is not investigated in detail through a parametric nonlinear time history analysis. In order to undertake this effort, OpenSees structural analysis program is considered, where force-based frame element with fiber discretization is adopted to capture spread of inelasticity along element length and section depth. Connection behavior is introduced through a hysteretic model that can consider strength loss and pinching effects. The selected mid-rise and high-rise buildings have perimeter moment resisting frames, where these are analyzed in the plane. The effects of internal gravity frames are taken into account through the use of lean-on-columns. vi Nonlinear geometric effects on all columns are considered through the use of corotational transformation. For the time history analysis 2 set of 20 ground motions that are scaled for 10% and 2% probability of exceedance in 50 years are imposed on the structure. Inter-story drift ratio profiles and base shear versus rooft drift ratio responses of the structures are examined. Limit states considered in the specifications are taken into account in order to assess the significance of connection nonlinearity on overall structural system response. It is concluded that the influence of nonlinear behavior at beam-column connections yields less increase in structural drift demands on mid-rise to high-rise structures than those observed in low-rise structures. Furthermore, as long as ductility of connections is ensured, semi-rigid behavior of connections provide energy dissipation, and still maintain the structural response of mid-rise and high-rise steel moment resisting frame structures within limits.