Generalized corrective eccentricities for nonlinear static analysis of buildings with framed or braced structure

Abstract

The nonlinear static method of analysis has become the most popular tool for the seismic assessment of existing buildings. However, seismic codes do not allow its use for in-plan irregular buildings because it does not provide accurate predictions of the deck rotation. To overcome this limitation, the “corrective eccentricity method” evaluates the maximum seismic response as the envelope of the results of two nonlinear static analyses. In these analyses, the lateral force is applied with two different (corrective) eccentricities with respect to the centre of mass of the deck. The corrective eccentricities were calibrated on single-storey systems with unidirectional resisting elements, i.e. with elements that are representative of walls or braced frames. This paper proposes new corrective eccentricities aiming at generalizing and simplifying the previous corrective eccentricity method. In particular, new equations are defined for the corrective eccentricities devoted to predict the displacement demand on the stiff side of the building. These equations are defined based on the response of a set of single-storey systems representative of buildings with uni-directional or bi-directional resisting elements (e.g. moment resisting frames). Further, the displacement demand on the flexible side of the building is determined assuming a null eccentricity of the lateral force. The response of a set of multi-storey buildings is predicted by means of the new and original corrective eccentricities and compared to the maximum response obtained by nonlinear dynamic analysis. This comparison is made in terms of floor displacements, storey drifts and storey shears. The set of the examined structural systems comprises buildings with steel braced structure as well as buildings with r.c. framed structure.