Determination of a unique aftershock spectra
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TECHNICAL NOTE
Determination of a unique aftershock spectra Fatemeh Soleiman Meigooni1 · Mohsen Tehranizadeh1 Received: 18 April 2020 / Accepted: 15 June 2020 © Springer Nature Switzerland AG 2020
Abstract Aftershock seismic hazard analysis depends on both mainshock magnitude and elapsed time after the main earthquake. Aftershocks can result in an increment in the seismic demand of the structures. The objective of the current study is to determine a final aftershock spectrum as an applicable outcome in seismic design and assessment of buildings. As a numerical example, aftershock probabilistic hazard analysis (APSHA) was calculated at a location in southern California. The proposed method was applied for four different periods. Furthermore, a three-story existing concrete building was selected and analyzed regarding aftershock spectrum. It was shown that the amount of spectrum follows an upward trend by increasing the amount of main shock magnitude. The second finding was that the spectral value decreases with growth in elapsed time after the mainshock. While both beams and columns did not have enough strength, by applying aftershock to the building, 20% of the columns were required to be retrofitted again, and the figure for strengthened column experienced a rise of about 38%. However, the number of retrofitted beams did not change considerably. Keywords Aftershock · Main shock · Spectrum · Rehabilitation · Probabilistic seismic hazard analysis · Concrete building
Introduction Preliminary studies on APSHA were undertaken by Yeo (2005). They introduced a procedure in which APSHA was calculated for specific elapsed time and mainshock magnitude. Khanmiri reported a new procedure to consider aftershock impacts in performance-based design and assessment Nazari Khanmiri (2015). Many other investigations have been done in which main shock was used as an aftershock. Garcia and Aguilar claimed that repetitive mainshock records could not be acceptable indicators of aftershocks (Ruiz-García and Aguilar 2014), while Li and Ellingwood defined probability density function of aftershock by Gutenberg–Richter relationship and introduced a factor for converting the primary shock spectrum to an aftershock one (Li and Ellingwood 2007). This new spectrum depended on mainshock magnitude, and its return * Mohsen Tehranizadeh [email protected] Fatemeh Soleiman Meigooni [email protected] 1
Department of Civil and Environmental Engineering, Amirkabir University of Technology, Hafez Ave., 1591634311 Tehran, Iran
period was different from that of the primary vibration. Several studies have attempted to employ synthetic records to consider aftershock influences. In research by (Goda et al. 2015), aftershocks were extracted from a pool of earthquake records according to a defined time-place window. Hatzigeorgiou and Beskos reported a new synthetic procedure to obtain two or three following shocks. An attenuation relationship as well as Gutenberg-Richter law was applied to obtain the ratio of aftershock PGA on mainshock PGA (Hatzigeo
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