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Volume Title: ICASGE2015

DOI: ICASGE-RCS

A.E. Abdelnaby

This paper aims at studying the effect of multiple strong earthquakes on reinforced concrete (RC) frames as a consequence of the exceptionally rich set of records obtained from the earthquake sequence of Tohoku (Japan) that started on March 11, 2011. The Tohoku earthquake sequence is unique since it is characterized by a large (Mw 9.0) magnitude mainshock followed by thousands of smaller magnitude aftershocks (Mw < 7.4). Ground motion records measured at two hundred and forty stations are selected to represent a set of sites subjected to mainshockaftershocks sequences of varying source-to-site distance, soil conditions, aftershocks magnitudes, and ground motions order of sequence. Inelastic nonlinear dynamic response history analyses are carried out on a special RC frame system designed based on ACI code. The frame system is modeled using the Mid-America Earthquake Center open source fiber-based finite element analysis tool, Zeus-NL. The finite element model used in this study contains salient damage features on the material level that are essential to capture the stiffness degradation and strength deterioration in concrete and steel as a result of repeated shaking. Based on the structural response results obtained from the dynamic analyses, fragility relationships are developed for the cases of (1) mainshock only, (2) aftershocks only, and (3) mainshock-aftershocks ground motion sequences. The results provided in this study indicate that damage induced in reinforced concrete structures as a result of the main earthquake event (mainshock) can significantly increase the vulnerability of these structures when subjected to subsequent events (smaller magnitude aftershocks).

Tohoku mainshock-aftershocks sequence; damage accumulation; fragility relationships; multiple earthquake effects