Seismic enforced-displacement pushover procedure on multistorey R/C buildings

Abstract

This paper proposes a new direct Displacement-based procedure of nonlinear static (pushover) analysis on multi-storey reinforced concrete (R/C) buildings designed to exclude floor plastic mechanism formation. The proposed procedure can be easily applied with safety on all asymmetric multi-storey R/C buildings with the necessary regularity in elevation required by the seismic codes, irrespective of torsional sensitivity or high asymmetry. The proposed methodology places under full control by the designer of both the seismic inelastic angular deformation demands of the building floors in elevation and the actual seismic floor inelastic displacement demands that develop at the Near Collapse state of the building. The proposed procedure takes full account of the following: (a) the coupling between translational and rotational degrees of freedom at the floor-diaphragms, (b) the contributions resulting from the action of higher modes in the linear area of response, and (c) the P- Delta effects. According to the proposed procedure, a vector of enforced-displacements is applied on the floor-diaphragms and a set of sixteen final nonlinear static analysis cases coming from all possible sign combinations is performed having as action the previous floor enforced-displacements, without the use of any other floor force or moment information. Suitable drift-based values for floor enforced-displacements are proposed, following an extensive parametric analysis. These floor enforced-displacements are combined in such a way that the spatial action of the two seismic horizontal components of the ground motion is fully considered, avoiding at the same time the various superposition techniques recommended by the seismic codes within the nonlinear area. The envelope of the abovementioned sixteen final nonlinear static analyses can adequately approximate the seismic demand resulting from nonlinear response history analyses.