Application of structural damage curve in seismic resistance: a case study of the Türkiye earthquake in February 2023

The degradation of structural stiffness is quantifiable through changes in the natural vibration period of the structure, facilitating the assessment of damage severity. The structural damage curve is defined by the variation in the natural vibration period of a structural system attributable to member stiffness degradation during severe earthquakes. In this study, two representative earthquake records from the February 2023 Mw 7.8 earthquake in Türkiye were selected for the elastoplastic time-history analysis of a standard ten-story reinforced concrete frame structure. Additionally, a method for defining the plastic hinge was employed to derive the structural damage curve. Analysis of varying damage levels under the influence of two seismic waves was conducted using the T-f response spectrum. The analysis results reveal: (a) Structural damage curves effectively reflect the plastic development via natural vibration period variations. (b) The T-f response spectrum encompasses amplitude, spectrum, and duration characteristics of ground motion, which, when integrated with damage curves, more intuitively delineates the structural damage mechanism. (c) Diverse impacts on the structure by seismic waves, even with identical peak values, are attributed to their distinct time-frequency characteristics. Additionally, five seismic records matching the site type of the representative records of the Mw 7.8 earthquake in Türkiye were selected from the Pacific Earthquake Engineering Research Center ground motion database in the United States. Regression analysis was utilized to derive the proposed structural damage curves at peak ground motion accelerations of 125 gal, 220 gal, 400 gal, and 620 gal. The study also includes a validation of the elastoplastic time-history analysis results with experimental data, enhancing the credibility of the findings.