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Selected AbstractsSimplified inelastic seismic analysis of base-isolated structures using the N2 methodEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2010Vojko Kilar Abstract In the paper a simplified nonlinear method has been applied to the analysis of base-isolated structures. In the first part, a three-linear idealization of the capacity curve is proposed. The initial stiffness is defined based on the first yielding point in the superstructure, whereas the secondary slope depends on the failure mechanism of the superstructure. A consequence is a much more pronounced secondary slope, which does not correspond to the presumptions used in the originally proposed N2 method. A parametric nonlinear dynamic study of single degree of freedom systems with different hardening slopes and damping has been performed for an ensemble of seven EC8 spectrum-compatible artificial accelerograms. It was concluded that, in the long-period range, the equal displacement rule could be assumed also for the proposed systems with non-zero post-yield stiffness. In the second part, the proposed idealization was used for the analysis of isolated RC frame buildings that were isolated with different (lead) rubber-bearing isolation systems. The stiffness of the isolators was selected for three different protection levels and for three different ground motion intensities, which have resulted in elastic as well as moderately and fully damaged superstructure performance levels. Three different lateral load distributions were investigated. It was observed that a triangular distribution, with an additional force at the base, works best in the majority of practical cases. It was concluded that the N2 method can, in general, provide a reasonably accurate prediction of the actual top displacement, as well as of the expected damage to the superstructure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Probabilistic estimate of seismic response design values of RC framesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2009Angelo D'Ambrisi Abstract Probabilistically controlled design values of the nonlinear seismic response of reinforced concrete frames are obtained using a method previously proposed by the authors. The method allows to calculate conservative design values characterized by a predefined non-exceedance probability, using a limited number of spectrum-fitting generated accelerograms. Herein the method is applied to elastic-strain hardening single degree of freedom systems representative of RC framed structures and is then assessed with reference to four reinforced concrete model frames designed according to EC8. The frames are characterized by different natural periods and aspect ratios. The results, compared with those obtained applying current EC8 recommendations, show the effectiveness of the proposed method. EC8 provides for design values of the seismic response of a structure with a nonlinear behavior computed as the mean value of the responses to seven accelerograms or as the maximum value of the responses to three accelerograms. These two criteria lead to design values characterized by very different and uncontrolled non-exceedance probability levels, while the proposed method allows the analyst to directly control the non-exceedance probability level of the calculated design values. Copyright © 2009 John Wiley & Sons, Ltd. [source] The effect of foundation embedment on inelastic response of structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2009Mojtaba Mahsuli Abstract In this research, a parametric study is carried out on the effect of soil,structure interaction on the ductility and strength demand of buildings with embedded foundation. Both kinematic interaction (KI) and inertial interaction effects are considered. The sub-structure method is used in which the structure is modeled by a simplified single degree of freedom system with idealized bilinear behavior. Besides, the soil sub-structure is considered as a homogeneous half-space and is modeled by a discrete model based on the concept of cone models. The foundation is modeled as a rigid cylinder embedded in the soil with different embedment ratios. The soil,structure system is then analyzed subjected to a suit of 24 selected accelerograms recorded on alluvium deposits. An extensive parametric study is performed for a wide range of the introduced non-dimensional key parameters, which control the problem. It is concluded that foundation embedment may increase the structural demands for slender buildings especially for the case of relatively soft soils. However, the increase in ductility demands may not be significant for shallow foundations with embedment depth to radius of foundation ratios up to one. Comparing the results with and without inclusion of KI reveals that the rocking input motion due to KI plays the main role in this phenomenon. Copyright © 2008 John Wiley & Sons, Ltd. [source] Stability analysis for real-time pseudodynamic and hybrid pseudodynamic testing with multiple sources of delayEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2008Oya Mercan Abstract Real-time pseudodynamic (PSD) and hybrid PSD test methods are experimental techniques to obtain the response of structures, where restoring force feedback is used by an integration algorithm to generate command displacements. Time delays in the restoring force feedback from the physical test structure and/or the analytical substructure cause inaccuracies and can potentially destabilize the system. In this paper a method for investigating the stability of structural systems involved in real-time PSD and hybrid PSD tests with multiple sources of delay is presented. The method involves the use of the pseudodelay technique to perform an exact mapping of fixed delay terms to determine the stability boundary. The approach described here is intended to be a practical one that enables the requirements for a real-time testing system to be established in terms of system parameters when multiple sources of delay exist. Several real-time testing scenarios with delay that include single degree of freedom (SDOF) and multi-degree of freedom (MDOF) real-time PSD/hybrid PSD tests are analyzed to illustrate the method. From the stability analysis of the real-time hybrid testing of an SDOF test structure, delay-independent stability with respect to either experimental or analytical substructure delay is shown to exist. The conditions that the structural properties must satisfy in order for delay-independent stability to exist are derived. Real-time hybrid PSD testing of an MDOF structure equipped with a passive damper is also investigated, where observations from six different cases related to the stability plane behavior are summarized. Throughout this study, root locus plots are used to provide insight and explanation of the behavior of the stability boundaries. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ground motion duration effects on nonlinear seismic responseEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2006Iunio Iervolino Abstract The study presented in this paper addresses the question of which nonlinear demand measures are sensitive to ground motion duration by statistical analyses of several case studies. A number of single degree of freedom (SDOF) structures were selected considering: (1) four oscillation periods; (2) three evolutionary and non-evolutionary hysteretic behaviours; (3) two target ductility levels. Effects of duration are investigated, by nonlinear dynamic analysis, with respect to six different demand indices ranging from displacement ductility ratio to equivalent number of cycles. Input is made of six real accelerogram sets representing three specific duration scenarios (small, moderate and large duration). For all considered demand quantities time-history results are formally compared by statistical hypothesis test to asses the difference, if any, in the demand concerning different scenarios. Incremental dynamic analysis curves are used to evaluate duration effect as function of ground motion intensity (e.g. spectral acceleration corresponding to the SDOF's oscillation period). Duration impact on structural failure probability is evaluated by fragility curves. The results lead to the conclusion that duration content of ground motion is statistically insignificant to displacement ductility and cyclic ductility demand. The conclusions hold regardless of SDOF's period and hysteretic relationship investigated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Estimate of input energy for elasto-plastic SDOF systems during earthquakes based on discrete wavelet coefficientsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2005Jun Iyama Abstract The response of an elasto-plastic single degree of freedom (SDOF) system to ground motion is estimated based on wavelet coefficients calculated by discrete wavelet transform. Wavelet coefficients represent both the time and frequency characteristics of input ground motion, and thus can be considered to be directly related to the dynamic response of a non-linear system. This relationship between the energy input into an elastic SDOF system and wavelet coefficients is derived based on the assumption that wavelets deliver energy to the structure instantaneously and the quantity of energy is constant regardless of yielding. These assumptions are shown to be valid when the natural period of the system is in the predominant period range of the wavelet, the most common scenario for real structures, through dynamic response analysis of a single wavelet. The wavelet-based estimation of elastic and plastic energy transferred by earthquake ground motion is thus shown to be in good agreement with the dynamic response analysis when the natural period is in the predominant range of the input. Copyright © 2005 John Wiley & Sons, Ltd. [source] Predictive instantaneous optimal control of elastic structures during earthquakesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2003Kevin K. F. Wong Abstract A predictive instantaneous optimal control (PIOC) algorithm is proposed for controlling the seismic responses of elastic structures. This algorithm compensates for the time delay that happens in practical control applications by predicting the structural response over a period that equals the time delay, and by substituting the predicted response in the instantaneous optimal control (IOC) algorithm. The unique feature of this proposed PIOC algorithm is that it is simple and at the same time compensates for the time delay very effectively. Numerical examples of single degree of freedom structures are presented to compare the performance of PIOC and IOC systems for various time delay magnitudes. Results show that a time delay always causes degradation of control efficiency, but PIOC can greatly reduce this degradation compared to IOC. The effects of the structure's natural periods and the choice of control gains on the degradation induced by the time delay are also analyzed. Results show that shorter natural periods and larger control gains are both more sensitive and more serious to the degradation of control efficiency. Finally, a practical application of PIOC is performed on a six-story moment-resisting steel frame. It is demonstrated that PIOC contributes significantly to maintain stability in multiple degree of freedom structures, and at the same time PIOC has a satisfactory control performance. Copyright © 2003 John Wiley & Sons, Ltd. [source] Optimum design of cyclone separatorAICHE JOURNAL, Issue 9 2009Prabhata K. Swamee Abstract Cyclone separators are one of the most widely used gas-solid separators. Although the optimal design of cyclone separators has been suggested earlier, the earlier works do not include all the critical parameters responsible for minimizing the pressure drop which is quite decisive to obtain a correct optimal design. In this article, the optimal design of the cyclone separator has been formulated as a geometric programming with a single degree of difficulty. The solution of the problem yields the optimum values of the number of cyclones to be used in parallel, and the inside diameter of cyclone shell and exit pipe, when a specified flow rate of gas is to be separated from solid particles, when the cut diameter is already specified. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Identification of chaos in a regenerative cutting process by the 0-1 testPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Grzegorz Litak We examine the regenerative cutting process by using a single degree of freedom non-smooth model with a friction component and a time delay term. Instead of the standard Lyapunov exponent calculations, we propose a statistical 0-1 test for chaos. This approach reveals the nature of the cutting process signaling regular or chaotic dynamics. We are able to show that regular or chaotic motion occur in the investigated model depending on the delay time. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||