Article

Damage-based design earthquake loads for SDOF inelastic structures

Journal of Structural Engineering (ASCE) 01/2011; 137:456-467.

ABSTRACT This paper develops a new framework for modeling design earthquake loads for inelastic structures. Limited information on strong ground motions is assumed to be only available at the given site. The design earthquake acceleration is expressed as a Fourier series, with unknown amplitude and phase angle, modulated by an envelope function. The design earthquake is estimated by solving an inverse dynamic problem, using nonlinear programming techniques, such that the structure performance is minimized. At the same time, the design earthquake is constrained to the available information on past recorded ground motions. New measures of the structure performance that are based on energy concepts and damage indices are introduced in this paper. Specifically, the structural performance is quantified in terms of Park and Ang damage indices. Damage indices imply that the structure is damaged by a combination of repeated stress reversals and high stress excursions. Furthermore, the use of damage indices provides a measure on the structure damage level and thus a decision on necessary repair is possible. The material stress-strain relationship is modeled as either bilinear or elastic-plastic. The formulation is demonstrated by deriving the design earthquake loads for inelastic frame structures at a firm soil site. The damage spectra for the site are also established, which provide upper bounds of damage under possible future earthquakes.

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Available from: Abbas Moustafa, Aug 31, 2015
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    • "Simultaneously, for strong earthquakes, the minimum duration of the strong motion of each accelerogram must be sufficient (about 15s in common cases), whilst, from personal observations, I consider that there should be a minimum number of approximately ten " large " and thirty-five " significant " loading loops, due to the dynamic seismic cyclic loading (i.e. a " large " cycle has an extreme ground acceleration of over 0.75PGA and a " significant " cycle has an extreme ground acceleration of between 0.30PGA and 0.75PGA). However, the subject of the exact definition of the Design Basis Earthquake and the Maximum Capable Earthquake of a seismic hazard area is open to question, while recently, a new framework for the simulation and definition of the seismic action of Design Earthquake Basis for the inelastic single degree of freedom system, using the Park & Ang damage index on the structures, has been developed (Moustafa, 2011 "
    Earthquake-Resistant Structures - Design, Assessment and Rehabilitation, 02/2012; , ISBN: 978-953-51-0123-9
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    • "It was shown that critical repeated acceleration sequences produce larger structural damage compared to single critical earthquakes. Afterwards, Moustafa (2011) developed a new framework to model the design earthquake loads for inelastic structures. New measures of the structure performance that were based on energy concepts and damage indices were introduced in his paper. "
    Advances in Geotechnical Earthquake Engineering - Soil Liquefaction and Seismic Safety of Dams and Monuments, 02/2012; , ISBN: 978-953-51-0025-6
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    • "There have been several recent attempts to avoid such reliability problem in its full form. Moustafa (2011) proposed a framework for deriving optimal earthquake loads expressed as a Fourier series. More widely, critical excitation methodologists propose to identify critical frequency content of ground motions maximizing the mean earthquake energy input rate to structures, for details see e.g. "
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    ABSTRACT: This paper contributes to the structural reliability problem by presenting a novel approach that enables for identification of stochastic oscillatory processes as a critical input for given mechanical models. Identification development follows a transparent image processing paradigm completely independent of state-of-the-art structural dynamics, aiming at delivering a simple and wide purpose method. Validation of the proposed importance sampling strategy is based on multi-scale clusters of realizations of digitally generated non-stationary stochastic processes. Good agreement with the reference pure Monte Carlo results indicates a significant potential in reducing the computational task of first passage probabilities estimation, an important feature in the field of e.g. probabilistic seismic design or risk assessment generally.
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