Assessing the seismic response of existing RC buildings using the extended N2 method

Abstract

Extensive studies have confirmed the good performance of the N2 method, recommended by Eurocode8, when performing pushover analyses in regular structures. However, this procedure shows lack of accuracy in predicting the torsional motion of planasymmetric buildings. In order to overcome this problem, Peter Fajfar and his team have proposed an extension of the method based on a combination of a pushover analysis and of an elastic response spectrum analysis. Since definitive answers about this topic have not yet been reached, this paper intends to proceed the study applying the extended N2 method to real existing RC buildings. Three real plan-asymmetric buildings with three, five and eight storeys were assessed. The results obtained with the extended N2 method were compared with the ones evaluated by means of the original N2 and with the nonlinear dynamic analysis through the use of semi-artificial ground motions. The analyses were performed for different seismic intensities in order to evaluate the torsional response of the building through different stages of structural inelasticity. The results obtained show that the extended N2 method generally reproduces in a very good fashion the real torsional behavior of the analyzed buildings. The conclusions herein outlined, added to the ones already published by the aforementioned authors, seem to confirm that the extended N2 method can be introduced in the next version of Eurocode8 as a nonlinear static procedure capable of accurately predicting the torsional response of plan-asymmetric buildings.Keywords Seismic assessment · 3D pushover analysis · Extended N2 method · Real plan-asymmetric buildings · Torsion

Performance assessment of irregular RC buildings with shear walls after Earthquake

“…As mentioned before, preceding studies showed that plan-wise irregular buildings require 3-D modeling due to the torsional behavior under seismic excitation [13][14][15][16][17][18][19][20][21][22][23][24][25]. Structural schemes of Figure 3 provide evidence that one of the RC structures is irregular in plan.…”

“…In the case where irregularities are dominant, those procedures are flawed, since they do not have a robust background. To overcome those deficiencies scientists developed 3D pushover techniques to take into account the torsional effects [13][14][15][16][17][18][19][20][21][22][23][24][25]. In their study Fajfar et al [16] stated that with an increase of plastic deformations the torsional effects tend to decrease.…”

N2 building design method

“…The application of the N2 method was extended to bridges [11] and base-isolated structures [24][25][26]. In addition, the extended N2 method for asymmetric buildings was rigorously tested on a set of existing real-life buildings [10,27]. Key results obtained in these studies are summarized in later sections of this paper.…”

“…The N2 method has been used to this day for almost every type of building (eg. [5,[9][10][11][12]). However, some limitations still exist, as will be shown later on in this paper.…”

The extended N2 method considering higher mode effects in both plan and elevation

“…Antoniou and Pinho 2004;Chopra and Goel 2002;Elnashai 2001;Kunnath 2006, 2007;Moghadam and Tso 2002;Poursha et al 2009;Sucuoglu and Günay 2010), in plan (e.g. Bento and Pinho 2008;Bento et al 2010;Bhatt and Bento 2011;Erduran 2008;Lin and Tsai 2008), and in both plan and elevation (e.g. Aydınoglu 2003Aydınoglu , 2004Fujii 2011;Chopra 2010, 2011).…”