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Title:Multiple earthquake effects on degrading reinforced concrete structures
Author(s):Abdelnaby, Adel
Director of Research:Elnashai, Amr S.
Doctoral Committee Chair(s):Elnashai, Amr S.
Doctoral Committee Member(s):Spencer, Billie F., Jr.; Kuchma, Daniel A.; Mondal, Paramita
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Multiple Earthquakes
Damage Accumulation
Degrading Structures
Abstract:Multiple earthquakes occur at many regions around the world where complex fault systems exist. These fault systems usually do not relieve all accumulated strains at once when the first rupture takes place. Therefore high stresses form at different locations causing sequential ruptures until the fault system is completely stabilized. The sequential ruptures along the fault segment(s) lead to multiple earthquakes which are often hard to distinguish them as fore-, main- and after-shocks, or a sequence of earthquakes from proximate fault segments. Field investigations reported failure of structural systems under repeated earthquakes, especially where structural retrofitting was not provided due to the short time frames between the successive shaking. In most failure cases the reported damage is mainly due to dramatic loss of stiffness and strength of structural elements as a result of material deterioration under repeated earthquake loadings. Deterioration effects are obvious in structures that experienced main-shock aftershock earthquake sequence and were able to withstand the main-shock however they collapsed in the smaller aftershock. Limited research has addressed the seismic behavior of structures subjected to multiple earthquakes. Repeated shaking induces accumulated damage to structures that affects their level of stiffness and strength and hence their response. Given the complexity of depicting the degrading behavior of structures using the current numerical tools, previous researchers used simplified approaches to compensate for the absence of important numerical model features of stiffness and strength degradation, alongside pinching of load-displacement loops. Moreover ground motion sequences used in previous studies were randomized and hence the characteristics of ground motions effects on the response were not accurately accounted for. Findings from previous research indicated that repeated shaking has a minimal effect on the response of structures in terms of peak displacements, maximum base shear and period elongation and hence it can be neglected for seismic evaluation of structures if the most damaging earthquake is to be considered. This research re-investigates the behavior of reinforced concrete frame systems under multiple earthquakes. The aforementioned damage features are modeled on the material level by using a plastic energy-based degrading concrete model and a steel model that considers reinforcing bars deterioration under large cyclic amplitude plastic excursions. Structural models of reinforced concrete degrading systems are subjected to selected earthquake sequence scenarios. Ground motion characteristics of individual records within the sequence, such as peak ground accelerations, predominant periods, and durations as well as the order of records application in the sequence, are parameterized and their effect on the response is monitored. Finally the effect of multiple earthquakes on current design guidelines is investigated and modifications are proposed accordingly. The case for developing design and assessment methodologies for structures to more than one earthquake is emphasized. The results presented in this study clearly indicate that the response of degrading structural systems is appreciably influenced by strong-motion sequences in a manner that cannot be predicted from simple analysis. It also confirmed that previous research that dismissed the effect of multiple earthquakes lacked the salient modeling features, and that including appropriate degrading constitutive relationships leads to reversing previous recommendations. The effect of multiple earthquakes on earthquake safety can be very considerable.
Issue Date:2012-09-18
Rights Information:Copyright 2012 Adel Abdelnaby
Date Available in IDEALS:2012-09-18
Date Deposited:2012-08

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