Validation of the Extended N2 Method and the Combination Rules for Pushover Analyses of Reinforced Concrete Asymmetric Structures

Nonlinear Time History Analyses (NTHAs) are considered the most precise and realistic analytical methods available. However, due to their simplicity, reduced computational demands, and fewer output data requirements, Pushover (PO) analyses are frequently favoured in design practices. According to European and Italian seismic standards, the seismic demand derived from Pushover (PO) analyses must be calculated using the “original” N2 method. Initially designed for planar frames with responses dominated by the fundamental mode of vibration, the N2 method is now also applied to 3D structural analyses. The building is analysed along the two reference axes, and the results are then combined using established rules. This study assesses the accuracy and effectiveness of the original N2 method and the combination rules in predicting seismic demands in Pushover (PO) analyses. Additionally, this paper evaluates the “extended” N2 method (N2ext) in order to address the limitations of the original method. To achieve this, a series of case-study buildings, typical of older Italian RC structures, are analysed. The seismic demands from these nonlinear static analyses are calculated for three levels of seismic hazard and then compared with the results from Nonlinear Time History Analyses (NTHAs), which serve as the benchmark.