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Wind energy is a rapidly growing field of renewable energy and as such, intensive scientific and societal interest has been already attracted. Research on wind turbine structures has been mostly focused on the structural analysis, design and/or assessment of wind turbines mainly against normal (environmental) exposures while, so far, only marginal attention has been spent on considering extreme natural hazards that threat the reliability of the lifetime-oriented wind turbine's performance. Especially, recent installations of numerous wind turbines in earthquake prone areas worldwide (e.g., China, USA, India, Southern Europe and East Asia) highlight the necessity for thorough consideration of the seismic implications on these energy harnessing systems. Along these lines, this state-of-the-art paper presents a comparative survey of the published research relevant to the seismic analysis, design and assessment of wind turbines. Based on numerical simulation, either deterministic or probabilistic approaches are reviewed, since they have been adopted to investigate the sensitivity of wind turbines' structural capacity and reliability in earthquake-induced loading. The relevance of seismic hazard for wind turbines is further enlightened by available experimental studies, being also comprehensively reported through this paper. The main contribution of the study presented herein is to identify the key factors for wind turbines' seismic performance while important milestones for ongoing and future advancement are emphasized.

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Summary Period lengthening, exhibited by structures when subjected to strong ground motions, constitutes an implicit proxy of structural inelasticity and associated damage. However, the reliable prediction of the inelastic period is tedious and a multi‐parametric task, which is related to both epistemic and aleatory uncertainty. Along these lines, the objective of this paper is to investigate and quantify the elongated fundamental period of reinforced concrete structures using inelastic response spectra defined on the basis of the period shift ratio (Tin/Tel). Nonlinear oscillators of varying yield strength (expressed by the force reduction factor, Ry), post‐yield stiffness (ay) and hysteretic laws are examined for a large number of strong motions. Constant‐strength, inelastic spectra in terms of Tin/Tel are calculated to assess the extent of period elongation for various levels of structural inelasticity. Moreover, the influence that structural characteristics (Ry, ay and degrading level) and strong‐motion parameters (epicentral distance, frequency content and duration) exert on period lengthening are studied. Determined by regression analyses of the data obtained, simplified equations are proposed for period lengthening as a function of Ry and Tel. These equations may be used in the framework of the earthquake record selection and scaling. Copyright © 2015 John Wiley & Sons, Ltd.

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This article presents a Matlab-based educational software developed at Aristotle University of Thessaloniki in Greece, in order to familiarize students and young engineers with fundamental concepts of structural dynamics and, in particular, soil-structure interaction problems. This user-friendly educational tool aims to assist the students in comprehending the nature of this complex phenomenon and the role played by the physical parameters involved, while increasing their awareness of the potential impact of neglecting soil flexibility during seismic design of reinforced concrete (RC) buildings. This software is also used as a case study for teaching the development of civil engineering-oriented applications in Matlab within a course where all the relevant material is provided online. Two demonstration examples are comparatively assessed to illustrate the applicability of the software and justify the necessity of its implementation in class, while the integration of the software in the curriculum as well as students' feedback is also discussed. ß