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Izuru Takewaki - One of the best experts on this subject based on the ideXlab platform.
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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 acceleration response
Critical Excitation Methods in Earthquake Engineering (Second edition), 2013Co-Authors: Izuru TakewakiAbstract:This chapter discusses a probabilistic Critical Excitation Method for acceleration responses of nonproportionally damped structural systems to nonstationary inputs. Recently, acceleration responses are considered important from the viewpoint of the protection and maintenance of functionality in buildings. Therefore, it is natural and desirable to develop Critical Excitation Methods for acceleration. In contrast to most of the conventional Critical Excitation Methods, a stochastic acceleration response at a point is treated as the objective function to be maximized. The power and the intensity of the Excitations are fixed, and the Critical Excitation is found under these restrictions. The key to finding the new nonstationary random Critical Excitation for nonproportionally damped structural systems is the order exchange in the double maximization procedure with respect to time and to the power spectral density (PSD) function. Various numerical examples have been incorporated in this chapter. These examples demonstrate the effectiveness and validity of the present Critical Excitation Method. They also reflect that there exist peculiar time-varying characteristics of the generalized nonstationary transfer function multiplied by the envelope function of the input motion model. It is concluded that the damping installation in upper stories is effective in reducing the acceleration.
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Critical Excitation for elastic plastic response
Critical Excitation Methods in Earthquake Engineering (Second edition), 2013Co-Authors: Izuru TakewakiAbstract:This chapter discusses a new probabilistic Critical Excitation Method for single-degree-of-freedom elastic–plastic structures. More specifically, this chapter is aimed at presenting a new measure for describing the degree of Criticality of recorded ground motions. The power and the intensity of the Excitations are fixed, and the Critical Excitation is found under these restrictions. However, the analytical expressions cannot be utilized in elastic–plastic structures. This situation causes difficulties in finding a Critical Excitation for elastic–plastic structures. To overcome such difficulty, a statistical equivalent linearization technique is used. This chapter discusses the concept proposed by Drenick to utilize an equivalent linearization technique in finding a Critical Excitation for nonlinear systems. However, this concept is restricted to deterministic equivalent linearization. In view of the similarity to the theory for linear elastic systems, the shape of the Critical power spectral density (PSD) function is restricted to a rectangular function attaining its upper bound in a certain frequency range. The central frequency of the rectangular PSD function is regarded as a principal parameter and varied in finding the Critical PSD function. The Critical Excitations are obtained for two examples and their responses are compared with those to the corresponding recorded earthquake ground motions.
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Critical envelope function for nonstationary random earthquake input
Critical Excitation Methods in Earthquake Engineering (Second edition), 2013Co-Authors: Izuru TakewakiAbstract:This chapter discusses a new probabilistic Critical Excitation Method for identifying the Critical envelope function of ground motions. It is well known that the envelope shape of ground motions depends on various factors. These factors include an arrival time and an order of various kinds of waves. The maximum structural responses of models with rather shorter natural periods are often induced by the intensive motions existing mostly in the first half portion of ground motions. It is therefore of practical interest to investigate the most Critical envelope shape in ground motions. Time histories of four ground motions have been outlined here to show that a monotonically increasing function may be a candidate for the envelope function in the former half part of the total duration. The chapter assumes the nonstationary ground motion to be expressed as the product of a deterministic envelope function and another probabilistic function representing the frequency content. The former is determined such that the corresponding mean–square drift of a single–degree–of–freedom model attains its maximum under the constraint on mean total energy. The Critical Excitation Method is expected to provide useful information for the design of important structures to which functional and structural damages must be absolutely avoided during severe earthquakes.
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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.
Payam Ashtari - One of the best experts on this subject based on the ideXlab platform.
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seismic design of structures using a modified non stationary Critical Excitation
Earthquakes and Structures, 2013Co-Authors: Payam Ashtari, Seyed Hooman GhasemiAbstract:In earthquake engineering area, the Critical Excitation Method is an approach to find the most severe earthquake subjected to the structure. However, given some earthquake constraints, such as intensity and power, the Critical Excitations have spectral density functions that often resonate with the first modes of the structure. This paper presents a non-stationary Critical Excitation that is capable of exciting the main modes of the structure using a non-uniform power spectral density (PSD) that is similar to natural earthquakes. Thus, this paper proposes a new Method to estimate the power and intensity of earthquakes. Finally, a new Method for the linear seismic design of structures using a modified non-stationary Critical Excitation is proposed.
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modified non stationary Critical input Excitation by a design oriented objective function
2008Co-Authors: Payam Ashtari, Gholamreza Ghodrati AmiriAbstract:Abstract– Nowadays, seismic design of structures performed by any seismic code is based on resisting previous natural earthquakes. Therefore, the Critical Excitation Method has been proposed in recent years to consider probable future earthquakes that may be more destructive. Nonstationary Critical Excitation for a structure is found under specified constraints to resonate the structure. In this paper, the objective function of non-stationary Critical Excitation is taken as the maximization of all the inter-storey drifts at different times, separately. The power (area under power spectral density function) and the intensity (magnitude of PSD function) are limited, and Critical Excitation is found according to these constraints. Three techniques of finding nonstationary Critical Excitation are proposed, optimum line, simple and modified techniques. Then, the proposed techniques are used in many MDOF models and the results are investigated.
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optimization technique for finding probabilistic Critical Excitation
2004Co-Authors: Gholamreza Ghodrati Amiri, Payam AshtariAbstract:Because of earthquake uncertainty, the worst-case analysis is needed for the earthquake resistant design of structures. The probabilistic Critical Excitation Method proposes an input Excitation with Critical and largest responses in the structure. An optimization problem is introduced that is solved easier in frequency domain. In this research, a stationary input Excitation is found for shear model of buildings in frequency domain to maximize drift as a design criterion. The input power (area of power spectral density function) and the intensity (magnitude of PSD function) are fixed and the optimal Critical Excitation is found under these constraints by solving an optimization problem using Simpson integration. This Method is presented for structures with different natural frequencies. In addition, the effect of the first mode relative to higher modes is investigated.
Gholamreza Ghodrati Amiri - One of the best experts on this subject based on the ideXlab platform.
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modified non stationary Critical input Excitation by a design oriented objective function
2008Co-Authors: Payam Ashtari, Gholamreza Ghodrati AmiriAbstract:Abstract– Nowadays, seismic design of structures performed by any seismic code is based on resisting previous natural earthquakes. Therefore, the Critical Excitation Method has been proposed in recent years to consider probable future earthquakes that may be more destructive. Nonstationary Critical Excitation for a structure is found under specified constraints to resonate the structure. In this paper, the objective function of non-stationary Critical Excitation is taken as the maximization of all the inter-storey drifts at different times, separately. The power (area under power spectral density function) and the intensity (magnitude of PSD function) are limited, and Critical Excitation is found according to these constraints. Three techniques of finding nonstationary Critical Excitation are proposed, optimum line, simple and modified techniques. Then, the proposed techniques are used in many MDOF models and the results are investigated.
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optimization technique for finding probabilistic Critical Excitation
2004Co-Authors: Gholamreza Ghodrati Amiri, Payam AshtariAbstract:Because of earthquake uncertainty, the worst-case analysis is needed for the earthquake resistant design of structures. The probabilistic Critical Excitation Method proposes an input Excitation with Critical and largest responses in the structure. An optimization problem is introduced that is solved easier in frequency domain. In this research, a stationary input Excitation is found for shear model of buildings in frequency domain to maximize drift as a design criterion. The input power (area of power spectral density function) and the intensity (magnitude of PSD function) are fixed and the optimal Critical Excitation is found under these constraints by solving an optimization problem using Simpson integration. This Method is presented for structures with different natural frequencies. In addition, the effect of the first mode relative to higher modes is investigated.
Seyed Hooman Ghasemi - One of the best experts on this subject based on the ideXlab platform.
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seismic design of structures using a modified non stationary Critical Excitation
Earthquakes and Structures, 2013Co-Authors: Payam Ashtari, Seyed Hooman GhasemiAbstract:In earthquake engineering area, the Critical Excitation Method is an approach to find the most severe earthquake subjected to the structure. However, given some earthquake constraints, such as intensity and power, the Critical Excitations have spectral density functions that often resonate with the first modes of the structure. This paper presents a non-stationary Critical Excitation that is capable of exciting the main modes of the structure using a non-uniform power spectral density (PSD) that is similar to natural earthquakes. Thus, this paper proposes a new Method to estimate the power and intensity of earthquakes. Finally, a new Method for the linear seismic design of structures using a modified non-stationary Critical Excitation is proposed.
Abbas Moustafa - One of the best experts on this subject based on the ideXlab platform.
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characterization and modeling of near fault pulse like strong ground motion via damage based Critical Excitation Method
Structural Engineering and Mechanics, 2010Co-Authors: Abbas MoustafaAbstract:Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.