The Experts below are selected from a list of 189 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 earthquake input energy to connected building structures using impulse input
Earthquakes and Structures, 2015Co-Authors: Yoshiyuki Fukumoto, Izuru TakewakiAbstract:A frequency-domain method is developed for evaluating the earthquake input energy to two building structures connected by viscous dampers. It is shown that the earthquake input energies to respective building structures and viscous connecting dampers can be defined as works done by the boundary forces between the subsystems on their corresponding displacements. It is demonstrated that the proposed energy transfer function is very useful for clear understanding of dependence of energy consumption ratios in respective buildings and connecting viscous dampers on their properties. It can be shown that the area of the energy transfer function for the total system is constant regardless of natural period and damping ratio because the constant Fourier amplitude of the input acceleration, relating directly the area of the energy transfer function to the input energy, indicates the Dirac delta function and only an initial velocity (kinetic energy) is given in this case. Owing to the constant area property of the energy transfer functions, the total input energy to the overall system including both buildings and connecting viscous dampers is approximately constant regardless of the quantity of connecting viscous dampers. This property leads to an advantageous feature that, if the energy consumption in the connecting viscous dampers increases, the input energies to the buildings can be reduced drastically. For the worst case analysis, Critical Excitation problems with respect to the impulse interval for double impulse (simplification of pulse-type impulsive ground motion) and multiple impulses (simplification of long-duration ground motion) are considered and their solutions are provided.
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Critical earthquake response of elastic plastic structures under near fault ground motions part 2 forward directivity input
Frontiers in Built Environment, 2015Co-Authors: Kotaro Kojima, Izuru TakewakiAbstract:The triple impulse input is used as a simplified version of the forward-directivity near-fault ground motion and a closed-form solution of the elastic-plastic response of a structure by this triple input is obtained. It is noteworthy that only the free-vibration appears under such triple impulse input. An almost Critical Excitation is defined and its response is derived. The energy approach plays an important role in the derivation of the closed-form solution of a complicated elastic-plastic response. It is shown that the maximum inelastic deformation can occur after the second impulse or the third impulse depending on the input level. The validity and accuracy of the proposed theory are discussed through the comparison with the response analysis result to the corresponding three wavelets of sinusoidal waves as a representative of the forward-directivity near-fault ground motion.
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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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toward greater building earthquake resilience using concept of Critical Excitation a review
Sustainable Cities and Society, 2013Co-Authors: Izuru TakewakiAbstract:Abstract The words of ‘unexpected issue’ and ‘earthquake resilience’ are frequently used after the 2011 off the Pacific coast of Tohoku earthquake which occurred March 11, 2011. Although the unexpected issues are hard to include in the structural design stage of civil structures, those certainly decrease the earthquake resilience of those civil structures. Once these unexpected issues are taken into account in the structural design, those issues become expected issues. However these repetitions of cycles, i.e. experiences of unexpected issues during earthquakes and incorporation into design codes, never resolve the essential problems in structural earthquake engineering. In this paper, a historical review is made on the development of Critical Excitation methods as worst-scenario analysis and some possibilities of application of this concept to upgrading of building earthquake resilience are discussed.
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uncertainties in long period ground motion and its impact on building structural design case study of the 2011 tohoku japan earthquake
Engineering Structures, 2013Co-Authors: Izuru Takewaki, Kohei Fujita, Shinta YoshitomiAbstract:Abstract On March 11, 2011, Japan was shaken by the 2011 off the Pacific coast of Tohoku earthquake (the Great East Japan Earthquake). This paper reports some aspects of this earthquake related to long-period ground motions and its impact on building structural design. It was reported that long-period ground motions were induced extensively in Tokyo, Nagoya and Osaka. The response of high-rise buildings to the recorded ground motions during this earthquake and the simulated ground motions provided by the Japanese Government is discussed from the viewpoint of resonance and Critical Excitation. The main topics of this paper are (i) the investigations on uncertainties in long-period ground motions (uncertainty in predominant frequency, duration and amplitude) and (ii) its impact on structural design of super high-rise buildings. It is shown finally that the earthquake input energy and its bound analysis lead to clearer understanding of the effect of long-period ground motion on building structural design.
Robert A Nyman - One of the best experts on this subject based on the ideXlab platform.
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non stationary statistics and formation jitter in transient photon condensation
Nature Communications, 2020Co-Authors: Benjamin T Walker, Joao D Rodrigues, Himadri Shekhar Dhar, Rupert F Oulton, Florian Mintert, Robert A NymanAbstract:While equilibrium phase transitions are easily described by order parameters and free-energy landscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. We quench the system to a far-from-equilibrium state and find delayed condensation close to a Critical Excitation energy, a transient equivalent of Critical slowing down. Besides number fluctuations near the Critical Excitation energy, we show that transient phase transitions exhibit timing jitter in the condensate formation. This jitter is a manifestation of the randomness associated with spontaneous emission, showing that condensation is a stochastic, rather than deterministic process. Despite the non-equilibrium character of this phase transition, we construct an effective free-energy landscape that describes the formation jitter and allows, in principle, its generalization to a wider class of processes. Description of non-equilibrium phase transitions is problematic, due to the absence of suitable free energy landscapes. Here, the authors experimentally show delayed photon condensation and timing jitter in a dye-filled microcavity, modelled by a non-equilibrium extension of the free-energy landscape.
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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uncertainties in long period ground motion and its impact on building structural design case study of the 2011 tohoku japan earthquake
Engineering Structures, 2013Co-Authors: Izuru Takewaki, Kohei Fujita, Shinta YoshitomiAbstract:Abstract On March 11, 2011, Japan was shaken by the 2011 off the Pacific coast of Tohoku earthquake (the Great East Japan Earthquake). This paper reports some aspects of this earthquake related to long-period ground motions and its impact on building structural design. It was reported that long-period ground motions were induced extensively in Tokyo, Nagoya and Osaka. The response of high-rise buildings to the recorded ground motions during this earthquake and the simulated ground motions provided by the Japanese Government is discussed from the viewpoint of resonance and Critical Excitation. The main topics of this paper are (i) the investigations on uncertainties in long-period ground motions (uncertainty in predominant frequency, duration and amplitude) and (ii) its impact on structural design of super high-rise buildings. It is shown finally that the earthquake input energy and its bound analysis lead to clearer understanding of the effect of long-period ground motion on building structural design.
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the 2011 off the pacific coast of tohoku earthquake and response of high rise buildings under long period ground motions
Soil Dynamics and Earthquake Engineering, 2011Co-Authors: Izuru Takewaki, Kohei Fujita, S Murakami, Shinta Yoshitomi, Masaaki TsujiAbstract:Abstract In the afternoon of March 11, 2011, the eastern Japan was severely attacked by the 2011 off the Pacific coast of Tohoku earthquake (the Great East Japan earthquake). Nearly 30,000 people were killed or are still missing by that earthquake and the ensuing monster tsunami as of April 11, 2011. This paper reports some aspects of this devastating earthquake which hit an advanced country in seismic resistant design. It has been reported that long-period ground motions were induced in Tokyo, Nagoya and Osaka. The properties of these long-period ground motions are discussed from the viewpoint of Critical Excitation and the seismic behavior of two steel buildings of 40 and 60 stories subjected to the long-period ground motion recorded at Shinjuku, Tokyo is determined and discussed. This paper also reports the effectiveness of visco-elastic dampers like high-hardness rubber dampers in the reduction of responses of super high-rise buildings subjected to such long-period ground motions. The response reduction rate is investigated in detail in addition to the maximum response reduction. In December 2010 before this earthquake, simulated long-period ground motions for earthquake resistant design of high-rise buildings were provided in three large cities in Japan (Tokyo, Nagoya and Osaka) and nine areas were classified. Two 40-story steel buildings (slightly flexible and stiff) are subjected to these long-period ground motions in those nine areas for the detailed investigation of response characteristics of super high-rise buildings in various areas.
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Property of Critical Excitation for moment-resisting frames subjected to horizontal and vertical simultaneous ground motions
Journal of Zhejiang University-SCIENCE A, 2009Co-Authors: Kohei Fujita, Izuru TakewakiAbstract:It has often been reported that, when building structures are subjected to near-fault earthquake ground motions, horizontal and vertical impulsive inputs may cause Critical damage during the first few seconds. In practical design of building structures, however, the safety check, taking into account the effect of multi-component ground motions, is hardly conducted except the design of important structures such as high-rise buildings and nuclear power plants. Furthermore, it is not clear how the correlation of multi-component ground motions influences the actual safety of structures. In this paper, the detailed property of Critical Excitation is discussed in association with the relationship between the characteristics of ground motions and those of structures. The properties of various auto power spectral density (PSD) functions of the horizontal and vertical ground motions are investigated, and those of the Critical cross PSD function of these two-directional ground motions are found by a devised algorithm in a feasible complex plane. A closed-form expression is derived from the Critical relation of the auto PSD functions of the simultaneous inputs. This Critical Excitation method provides us with a new approach for earthquake-resistant design against the possible future earthquake which causes the Critical damages to buildings.
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Critical disturbance for stress resultant in long span moment resisting frames subjected to horizontal and vertical simultaneous ground inputs
Journal of Structural and Construction Engineering (transactions of Aij), 2008Co-Authors: Kohei Fujita, Izuru Takewaki, Naohiro NakamuraAbstract:A Critical Excitation problem is formulated for a long-span moment-resisting frame subjected to a multi-component base input. The horizontal and vertical ground motions are characterized by a non-stationary model consisting of a given deterministic envelope function and a stochastic function, to be found, obeying a zero-mean Gaussian process. The Critical Excitation problem is such that, given the power spectra of the horizontal and vertical ground motions, find the worst cross spectrum of the horizontal and vertical inputs which maximizes the mean-squares of the sum of bending moments at the end of the beam under horizontal and vertical inputs. It is shown that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross spectrum can be obtained by an algorithm including the order interchange of the double maximization procedure for the time and cross-spectrum domains. Numerical examples indicate that the proposed algorithm can work very well. The physical meaning of the Critical cross-correlation function is also discussed.
Benjamin T Walker - One of the best experts on this subject based on the ideXlab platform.
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non stationary statistics and formation jitter in transient photon condensation
Nature Communications, 2020Co-Authors: Benjamin T Walker, Joao D Rodrigues, Himadri Shekhar Dhar, Rupert F Oulton, Florian Mintert, Robert A NymanAbstract:While equilibrium phase transitions are easily described by order parameters and free-energy landscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. We quench the system to a far-from-equilibrium state and find delayed condensation close to a Critical Excitation energy, a transient equivalent of Critical slowing down. Besides number fluctuations near the Critical Excitation energy, we show that transient phase transitions exhibit timing jitter in the condensate formation. This jitter is a manifestation of the randomness associated with spontaneous emission, showing that condensation is a stochastic, rather than deterministic process. Despite the non-equilibrium character of this phase transition, we construct an effective free-energy landscape that describes the formation jitter and allows, in principle, its generalization to a wider class of processes. Description of non-equilibrium phase transitions is problematic, due to the absence of suitable free energy landscapes. Here, the authors experimentally show delayed photon condensation and timing jitter in a dye-filled microcavity, modelled by a non-equilibrium extension of the free-energy landscape.
Joao D Rodrigues - One of the best experts on this subject based on the ideXlab platform.
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non stationary statistics and formation jitter in transient photon condensation
Nature Communications, 2020Co-Authors: Benjamin T Walker, Joao D Rodrigues, Himadri Shekhar Dhar, Rupert F Oulton, Florian Mintert, Robert A NymanAbstract:While equilibrium phase transitions are easily described by order parameters and free-energy landscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. We quench the system to a far-from-equilibrium state and find delayed condensation close to a Critical Excitation energy, a transient equivalent of Critical slowing down. Besides number fluctuations near the Critical Excitation energy, we show that transient phase transitions exhibit timing jitter in the condensate formation. This jitter is a manifestation of the randomness associated with spontaneous emission, showing that condensation is a stochastic, rather than deterministic process. Despite the non-equilibrium character of this phase transition, we construct an effective free-energy landscape that describes the formation jitter and allows, in principle, its generalization to a wider class of processes. Description of non-equilibrium phase transitions is problematic, due to the absence of suitable free energy landscapes. Here, the authors experimentally show delayed photon condensation and timing jitter in a dye-filled microcavity, modelled by a non-equilibrium extension of the free-energy landscape.