On the evaluation of seismic response of structures by nonlinear static methods

Abstract

SUMMARYIn the most recent seismic codes, the assessment of the seismic response of structures may be carried out by comparing the displacement capacity, provided by nonlinear static analysis, with the displacement demand. In many cases the code approach is based on the N2 method proposed by Fajfar, which evaluates the displacement demand by defining, as an intermediate step, a single degree-of-freedom (SDOF) system equivalent to the examined structure. Other codes suggest simpler approaches, which do not require equivalent SDOF systems, but they give slightly different estimation of the seismic displacement demand. The paper points out the differences between the methods and suggests an operative approach that provides the same accuracy as the N2 method without requiring the evaluation of an equivalent SDOF system. A wide parametric investigation allows an accurate comparison of the different methods and demonstrates the effectiveness of the proposed operative approach.

Design of steel frames equipped with BRBs in the framework of Eurocode 8

“…The scale factor SF, equal to 0.58, is calculated by means of Eq. (26). The maximum demand of storey drift angle (Δ max ) of the buildings is plotted as a function of the behaviour factor adopted in design and is shown in Fig.…”

“…However, these studies refer to frames designed according to seismic codes different from EC8 (e.g. Iranian Earthquake Resistance Design Code or FEMA 302/303) and are sometimes carried out by means of pushover analysis [25], which is not always accurate in the prediction of the seismic response [26][27][28]. Moreover, the modelling adopted in these research studies for BRBs casts a shadow on the accuracy of the obtained results.…”

Predicting displacement demand of multi-storey asymmetric buildings by nonlinear static analysis and corrective eccentricities

“…This assumption is justified because the present research study is intended to investigate solely the improvement caused by the corrective eccentricities to the prediction of the torsional response. Owing to this, the errors committed by the pushover analysis and regarding the translational response of the structures have been eliminated [10]. In particular, when predicting the floor displacements, the displacements provided by the pushover analysis at each storey of the building are scaled so that the displacement at the centre of mass equals the average of the maximum dynamic displacements of the corresponding planar system.…”

“…Generally, this method provides reasonable results for planar frames [9][10][11]. Instead, in the case of in-plan irregular structures, it is not always effective.…”

The applicability of the N2 method to the estimation of torsional effects in asymmetric base‐isolated buildings

“…Also, in [26] it is suggested that a similar equivalent nonlinear SDOF system for asymmetric multi-storey buildings (mathematically derived by two static pushover analyses of the spatial building) could be used in combination with inelastic design spectra. An interesting recent contribution has been made by Bosco et al [27], who suggested an 'N1 method', which does not require the use of an equivalent SDOF model, and avoids the problems related to the bi-linear idealization of the pushover curve, which is required by the N2 method.…”