Response Spectra of RC Rocking Structures on Inelastic Base Floor Support

Abstract eng:
Single degree of freedom inelastic response spectra are re-evaluated for a class of simplified reinforced concrete (RC) building oscillator models that exhibit both rocking and lateral response and behave as rigid blocks above the ground story; rocking and lateral deformation at the ground level are resisted through RC columns with axial – rocking resistance interaction. This type of building oscillators are encountered in a wide variety of irregular RC building systems, either intentionally discontinuous (open ground floor for shops and parking) or, unintentionally discontinuous, due to the inclusion of stiff infill panels above the base floor. The inelastic response spectra of the simplified rocking models are evaluated using code OpenSees (developed at PEER) and are compared to lateral only inelastic spectra as traditionally assumed in design. Comparisons of lateral ductility and inelastic demand at the base columns are presented, as a function of the system’s parameters, namely: natural periods TL, Tθ and normalized resistances ηL, ηθ (yield strength normalized by the corresponding peak inertial force). It is shown that for a certain period range, the presence of rocking, coupled with the inelastic lateral response, increases both the transverse ductility demand as well as the axial resisting forces at the ground floor, compared to those obtained from conventional elastic analysis procedures.

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