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 a structure. Previous research has shown that vectorizing scalar IMs leads to a more reliable structural response, particularly in nonlinear regions and near collapse. Furthermore, the nonlinear behavior of ductile structures results in elongation of their /effective period". Therefore, this paper proposes a new approach to selecting ground motion records considering the effect of spectral shape and period elongation. This method contains two disaggregation analyses at the fundamental and elongated periods 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 ensure a better prediction of the vulnerability of structures to collapse.