Report - PEER - University of California, Berkeley

EXTENSIONS OF THE N2 METHOD — ASYMMETRIC BUILDINGS,INFILLED FRAMES AND INCREMENTAL N2Peter FAJFAR, Matjaž DOLŠEK, Damjan MARUŠIĆ and Iztok PERUŠ 1ABSTRACTThe N2 method is a relatively simple seismic analysis technique based on pushover analysisand inelastic response spectrum approach. Its basic variant is based on a number ofassumptions, which impose restrictions to its applicability to general structural systems. Recentresearch has been aimed to extending the applicability of the method to plan-asymmetricbuildings and to infilled reinforced concrete frames. Moreover, the incremental N2 (IN2)method has been developed as a simple alternative to incremental dynamic analysis (IDA). Inthe paper, the basic N2 method and the three extensions are summarised.Keywords: Simplified non-linear analysis; Inelastic spectra; Reduction factors; Torsion;Infilled frames.1. INTRODUCTIONIn recent years, a breakthrough of simplified inelastic analysis and performanceevaluation methods has occurred. Such methods combine the non-linear static(pushover) analysis of a multi degree-of-freedom (MDOF) model and the responsespectrum analysis of an equivalent single-degree-of-freedom (SDOF) model. Theycan be used for a variety of purposes such as design verification for new buildingsand bridges, damage assessment for existing structures, determination of basicstructural characteristics in direct displacement based design, and rapid evaluation ofglobal structural response to seismic ground motion of different intensities. Anexample is the capacity spectrum method (CSM), developed by Freeman (1998) andimplemented in different variants in different regulatory documents in the USA and inJapan. Another example is the N2 method, which has been implemented into the finalversion of the Eurocode 8 standard (CEN 2003).The simple basic variant of the N2 method cannot be applied to some structuralsystems with specific structural behaviour, e.g., to infilled reinforced concrete (RC)frames. Moreover, the basic variant of the N2 method is, like other simplified non-1 University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1000, Slovenia357