A new ground motion record selection procedure based on the effects of spectral share and period elongation

One of the most prevalent ground motion Intensity Measures (IMs) is the spectral acceleration at the fundamental period of the structure. Previous research has shown that vectorizing scalar IMs leads to a more reliable structural response, particularly in the nonlinear region and near collapse. Furthermore, nonlinear behavior of ductile structures results in an elongation in the "effective period" of the structure. Therefore, this paper proposes a new approach for selecting ground motion records considering the effect of spectral shape and period elongation. This method contains two disaggregation analyses at the fundamental and elongated period of the structure. Nonlinear dynamic analysis is conducted on a set of reinforced concrete moment resisting frames designed based on ACI 318-05 as representatives of modern structures. Results show a considerable decrease in the median collapse prediction, margin against collapse and dispersion of the structural response. The presented approach can give a better prediction for the vulnerability of the structure toward collapse.