The Experts below are selected from a list of 2019 Experts worldwide ranked by ideXlab platform
Izuru Takewaki - One of the best experts on this subject based on the ideXlab platform.
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Critical double impulse input and bound of earthquake input energy to building structure
Frontiers in Built Environment, 2015Co-Authors: Kotaro Kojima, Kohei Fujita, Izuru TakewakiAbstract:A theory of earthquake input energy to building structures under single impulse is useful for disclosing the property of energy transfer function. This property shows that the area of the energy transfer function is constant irrespective of natural period and damping of building structures. However single impulse may be unrealistic from a certain viewpoint because the frequency characteristic of input cannot be expressed by this input. In order to resolve such issue, a double impulse is introduced in this paper. The frequency characteristic of the Fourier amplitude of the double impulse is found in an explicit manner and a Critical Excitation Problem is formulated with an interval of two impulses as a variable. The solution to that Critical Excitation Problem is derived. An upper bound of the earthquake input energy is then derived by taking full advantage of the property of the energy transfer function that the area of the energy transfer function is constant. The relation of the double impulse to the corresponding one-cycle sinusoidal wave as a representative of near-fault pulse-type waves is also investigated.
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Critical Excitation for Elastic-Plastic Response Using Deterministic Approach
Critical Excitation Methods in Earthquake Engineering, 2013Co-Authors: Izuru TakewakiAbstract:A Critical Excitation Problem of elastic-plastic structures is an interesting Problem of significant difficulty. Although statistical equivalent linearization is useful because of its nature to be able to include probabilistic properties of inputs and responses, it is also meaningful to treat an earthquake ground motion as a deterministic time series since it simulates actual recorded seismographs. The earthquake load is modeled as a deterministic time history expressed in terms of a Fourier series that is modulated by an enveloping function. The resulting nonlinear optimization Problem is tackled by using the sequential quadratic programming method. A Critical Excitation Problem for elastic-plastic structures under a ground motion consisting of a body wave and a surface wave can be solved by this method using sensitivity analysis. The elastic-plastic structure damaged by the first attack of the body wave may experience further significant damage by the surface wave with longer frequency contents. This scenario is confirmed by numerical examples exploring various types of seismic waves (body and surface waves) and their influence on damage of the structure under worst-case earthquake inputs.
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Critical Excitation for Earthquake Energy Input Rate
Critical Excitation Methods in Earthquake Engineering, 2013Co-Authors: Izuru TakewakiAbstract:This chapter discusses a Critical Excitation method for earthquake energy input rate. It explores a new probabilistic Critical Excitation method for identifying the Critical frequency content of ground motions maximizing the mean earthquake energy input rate to structures. The Critical Excitation Problem includes a double maximization procedure with respect to time and to the power spectral density (PSD) function. The key to finding the Critical frequency content is the order exchange in the double maximization procedure. No mathematical programming technique is required in the proposed method. It is shown that the proposed technique is systematic and the Critical Excitation can be found extremely efficiently within a reasonable accuracy. Extension of the proposed method is discussed for a more general ground motion model. The chapter discusses the process to derive a new expression on the probabilistic earthquake input energy and its rate in terms of uniformly modulated and nonuniformly modulated ground motion models. The process to formulate a new Critical Excitation Problem with the probabilistic earthquake energy input rate as the Criticality measure is mentioned. A deterministic expression of earthquake energy input rate to a base-isolated building model is also presented in order to capture the properties of earthquake energy input rate in more detail.
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Critical Excitation for Multi-Component Inputs
Critical Excitation Methods in Earthquake Engineering, 2013Co-Authors: Izuru TakewakiAbstract:Abstract Critical Excitation for multi-component inputs is explained in this chapter. In the Problem under horizontal and vertical ground motions, the input directions coincide with the building principal axes in most cases. On the other hand, in the Problem under two horizontal inputs, the input directions do not necessarily coincide with the building principal axes. This situation brings a further Problem of great significance. The Critical Excitation Problem under horizontal and vertical ground motion inputs is to find the worst cross-spectrum and the corresponding cross-correlation function of the horizontal and vertical inputs that produce the maximum mean squares response of the uplift. An algorithm is devised such that the order of the maximizations with respect to time and the cross-spectrum is exchanged. The Critical Excitation Problem under two horizontal ground motions is to find the worst cross-spectrum and the corresponding cross-correlation function of the two horizontal inputs that produce the maximum mean squares response. The coherence function between two horizontal ground motions is a function of the ratio of power spectra of two horizontal ground motions and the angle of input to the building. For each angle of input to the building and the ratio of power spectra of two horizontal ground motions, the coherence function between two horizontal ground motions is computed. Then a technique similar to that for the Problem under horizontal and vertical ground motion inputs can be used. The solution algorithm both for the Problem under horizontal and vertical ground motions and that under two horizontal ground motions can be interpreted and characterized by an inner product of the response quantities and the cross spectrum of multi-component inputs.
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Critical Excitation for Earthquake Energy Input in MDOF System
Critical Excitation Methods in Earthquake Engineering, 2013Co-Authors: Izuru TakewakiAbstract:This chapter explores a new general Critical Excitation method for a damped linear elastic single-degree-of-freedom (SDOF) system. It introduces the input energy to the SDOF system during an earthquake as a new measure of Criticality. It is shown that the formulation of the earthquake input energy in the frequency domain is essential for solving the Critical Excitation Problem. It is also essential for deriving a bound on the earthquake input energy for a class of ground motions. The Criticality is expressed in terms of degree of concentration of input motion components on the maximum portion of the characteristic function defining the earthquake input energy. It is remarkable that no mathematical programming technique is required in the solution procedure. The constancy of earthquake input energy for various natural periods and damping ratios is discussed from a new point of view based on an original sophisticated mathematical treatment. It is shown that the constancy of earthquake input energy is directly related to the uniformity of “the Fourier amplitude spectrum” of ground motion acceleration. It is not directly related to the uniformity of the velocity response spectrum. The bounds under acceleration and velocity constraints are clarified through numerical examinations for recorded ground motions.
Kohei Fujita - One of the best experts on this subject based on the ideXlab platform.
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Critical double impulse input and bound of earthquake input energy to building structure
Frontiers in Built Environment, 2015Co-Authors: Kotaro Kojima, Kohei Fujita, Izuru TakewakiAbstract:A theory of earthquake input energy to building structures under single impulse is useful for disclosing the property of energy transfer function. This property shows that the area of the energy transfer function is constant irrespective of natural period and damping of building structures. However single impulse may be unrealistic from a certain viewpoint because the frequency characteristic of input cannot be expressed by this input. In order to resolve such issue, a double impulse is introduced in this paper. The frequency characteristic of the Fourier amplitude of the double impulse is found in an explicit manner and a Critical Excitation Problem is formulated with an interval of two impulses as a variable. The solution to that Critical Excitation Problem is derived. An upper bound of the earthquake input energy is then derived by taking full advantage of the property of the energy transfer function that the area of the energy transfer function is constant. The relation of the double impulse to the corresponding one-cycle sinusoidal wave as a representative of near-fault pulse-type waves is also investigated.
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Critical correlation of bi-directional horizontal ground motions
Engineering Structures, 2010Co-Authors: Kohei Fujita, Izuru TakewakiAbstract:Abstract A stochastic model is treated of bi-directional horizontal ground motions (2DGM). It is shown that, in comparison with the Penzien–Watabe model (1975) [3] , the cross power spectral density (PSD) function between 2DGM along the building structural axes can be treated in a more general manner by using an extended Penzien–Watabe model introduced in this paper. The auto PSD functions of 2DGM along the building structural axes are assumed to be given and the cross PSD function between these 2DGM is treated as a complex unknown function. A Critical Excitation Problem is then considered for a one-story one-span moment resisting three-dimensional frame. The corner-fiber stress at the column-end is taken as the objective function and the worst cross PSD function of the 2DGM is determined so that the maximum corner-fiber stress at the column-end is maximized. It is shown that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross PSD function can be obtained by a devised algorithm including the interchange of the double maximization procedure in the time and frequency domains.
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Critical cross-correlation function of horizontal and vertical ground motions for uplift of rigid block
Engineering Structures, 2008Co-Authors: Kohei Fujita, Shinta Yoshitomi, Masaaki Tsuji, Izuru TakewakiAbstract:Abstract A Critical Excitation Problem for a rigid block is considered subjected to horizontal and vertical simultaneous base inputs. The rigid block is supported by a set of a horizontal spring and a dashpot and another set of two vertical springs and dashpots. These springs and dashpots represent the stiffness and damping of ground. The motion of the block consists of a horizontal–rotational (swaying–rocking) motion under a horizontal base input and a vertical motion under a vertical base input. Both the horizontal–rotational motion and the vertical motion contribute to the uplift of the edge of the block. Both the horizontal and vertical base inputs are to be described by two different non-stationary random processes with prescribed power spectra. A Critical Excitation Problem is formulated in which the worst cross-spectrum and the corresponding cross-correlation function of the horizontal and vertical inputs are searched for the maximum mean squares response of the uplift. It is found that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross-spectrum can be obtained by a devised algorithm including the interchange of the double maximization procedure for the time and cross-spectrum ( functional : function of frequency) domains.
Kotaro Kojima - One of the best experts on this subject based on the ideXlab platform.
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Critical double impulse input and bound of earthquake input energy to building structure
Frontiers in Built Environment, 2015Co-Authors: Kotaro Kojima, Kohei Fujita, Izuru TakewakiAbstract:A theory of earthquake input energy to building structures under single impulse is useful for disclosing the property of energy transfer function. This property shows that the area of the energy transfer function is constant irrespective of natural period and damping of building structures. However single impulse may be unrealistic from a certain viewpoint because the frequency characteristic of input cannot be expressed by this input. In order to resolve such issue, a double impulse is introduced in this paper. The frequency characteristic of the Fourier amplitude of the double impulse is found in an explicit manner and a Critical Excitation Problem is formulated with an interval of two impulses as a variable. The solution to that Critical Excitation Problem is derived. An upper bound of the earthquake input energy is then derived by taking full advantage of the property of the energy transfer function that the area of the energy transfer function is constant. The relation of the double impulse to the corresponding one-cycle sinusoidal wave as a representative of near-fault pulse-type waves is also investigated.
Shinta Yoshitomi - One of the best experts on this subject based on the ideXlab platform.
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Critical cross-correlation function of horizontal and vertical ground motions for uplift of rigid block
Engineering Structures, 2008Co-Authors: Kohei Fujita, Shinta Yoshitomi, Masaaki Tsuji, Izuru TakewakiAbstract:Abstract A Critical Excitation Problem for a rigid block is considered subjected to horizontal and vertical simultaneous base inputs. The rigid block is supported by a set of a horizontal spring and a dashpot and another set of two vertical springs and dashpots. These springs and dashpots represent the stiffness and damping of ground. The motion of the block consists of a horizontal–rotational (swaying–rocking) motion under a horizontal base input and a vertical motion under a vertical base input. Both the horizontal–rotational motion and the vertical motion contribute to the uplift of the edge of the block. Both the horizontal and vertical base inputs are to be described by two different non-stationary random processes with prescribed power spectra. A Critical Excitation Problem is formulated in which the worst cross-spectrum and the corresponding cross-correlation function of the horizontal and vertical inputs are searched for the maximum mean squares response of the uplift. It is found that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross-spectrum can be obtained by a devised algorithm including the interchange of the double maximization procedure for the time and cross-spectrum ( functional : function of frequency) domains.
Masaaki Tsuji - One of the best experts on this subject based on the ideXlab platform.
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Critical cross-correlation function of horizontal and vertical ground motions for uplift of rigid block
Engineering Structures, 2008Co-Authors: Kohei Fujita, Shinta Yoshitomi, Masaaki Tsuji, Izuru TakewakiAbstract:Abstract A Critical Excitation Problem for a rigid block is considered subjected to horizontal and vertical simultaneous base inputs. The rigid block is supported by a set of a horizontal spring and a dashpot and another set of two vertical springs and dashpots. These springs and dashpots represent the stiffness and damping of ground. The motion of the block consists of a horizontal–rotational (swaying–rocking) motion under a horizontal base input and a vertical motion under a vertical base input. Both the horizontal–rotational motion and the vertical motion contribute to the uplift of the edge of the block. Both the horizontal and vertical base inputs are to be described by two different non-stationary random processes with prescribed power spectra. A Critical Excitation Problem is formulated in which the worst cross-spectrum and the corresponding cross-correlation function of the horizontal and vertical inputs are searched for the maximum mean squares response of the uplift. It is found that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross-spectrum can be obtained by a devised algorithm including the interchange of the double maximization procedure for the time and cross-spectrum ( functional : function of frequency) domains.