Izuru Takewaki - Academia.edu (original) (raw)

Papers by Izuru Takewaki

Japan architectural review, Jun 30, 2022

Journal of Structural and Construction Engineering (Transactions of AIJ). This paper is based on ... more Journal of Structural and Construction Engineering (Transactions of AIJ). This paper is based on the translation of the Japanese version with some slight modifications.

International journal of earthquake and impact engineering, 2016

An efficient and systematic procedure is proposed for finding an optimal damper placement to mini... more An efficient and systematic procedure is proposed for finding an optimal damper placement to minimise an integrated dynamic compliance of a three-dimensional shear setback building with eccentricity. The integrated dynamic compliance is expressed in terms of an area of a transfer function with respect to frequency. The integrated dynamic compliance is minimised subject to a constraint on the sum of the damping coefficients of added dampers. A sensitivity-based optimisation algorithm is developed and the optimal damper placement is determined. Different types of integrated transfer function are used as the objective function in the algorithm. The proposed algorithm enables one to find an optimal damper placement sequentially with respect to gradually increasing damper capacity level. The main outcomes of this study are summarised as follows. First, the optimisation algorithm proposed in this paper is less affected by characteristics of input ground motions than other optimisation algorithms based on minimisation of transfer function amplitude or maximisation of the lowest-mode damping ratio. Secondly, the optimisation algorithm is applicable to realistic and complex structural models affected by both translational and torsional modes.

Nihon Kenchiku Gakkai kōzō-kei ronbunshū, 2003

Anew Gritical excitation method is developed for a damped linear elastic structure ． In contrast ... more Anew Gritical excitation method is developed for a damped linear elastic structure ． In contrast to the previous studies ， no sp ial constraint is needed on nonstationarity ofinput motiQns ． The input energy to the structure during an earthquake is introduced as a new rneasure ofcriticality ．匸 t is shown that the fbrmulation ofthe earthquake input energy jn 1he ． fヒequenoy domain ． is essentiat fbr solving the cdtlcal excitation proble 卯 and deriving a bound ， on the earthquake input energy 、 It is also olari丘ed that the complex modal analysis is very efflcient fbr computatioll of earthquake input energy to linear elastic struetures yvith vadous damping coef 貨cient distributions and ．ぼ that the real eigenmodes in addjtion tD the complex ． eigenmodes play an itnportant role in the energy cornputation ． Keywbrds ． ' Critica1 exaitation method ． Earthguake input enet9) t ， Non − proportionai damPS ' ng ， Complex eigenvalue ana ！ ysis ， Frequency domain analysis ， Response bound

Nihon Kenchiku Gakkai kōzō-kei ronbunshū, 2007

Frontiers in Built Environment, Aug 18, 2020

Engineering Structures, Nov 1, 2019

Extracting physical parameters for damage identification problems from full-field measurements is... more Extracting physical parameters for damage identification problems from full-field measurements is a promising research because of the recent spread of vision-based measurement techniques in the experimental mechanics. This paper presents a vision-based measurement framework using the camera system for damage identification. The framework is composed of four procedures: camera calibration, image processing, system identification and sensitivity analysis. In contrast to traditional finite-point measurements, the camera system allows considerably greater non-contact measurement flexibility. Such flexibility has two important benefits: first, less number of modes is required for modal-based damage identification problems; and second, more physical parameters could be extracted, taking advantage of the plentiful experimental data. A laboratory test comparing the camera system to traditional accelerometer measurement is conducted to confirm the above advantages. Further statistic analysis shows that the major drawback of this technique is that the camera system presents high levels of noise in small vibration responses at higher frequencies. Suitable strategies to circumvent this disadvantage are developed. Moreover, a technique for practical camera calibration without the requirement that the objective plane should be strictly perpendicular to the camera axis is also demonstrated and verified by the proposed laboratory test.

Soil Dynamics and Earthquake Engineering, Mar 1, 2019

Fluid viscous dampers (FVDs) are well-established supplemental energy dissipation devices that ha... more Fluid viscous dampers (FVDs) are well-established supplemental energy dissipation devices that have been widely used for earthquake protection of structures. Optimal design, placement and sizing of FVDs have been extensively investigated in the last four decades. In this review paper, an overview of the most popular methodologies from the abundant literature in the field is presented. Key aspects and main characteristics of the different strategies to identify the optimal damping coefficients and the optimal placement of FVDs are scrutinized in a comparative manner. The optimal design problem is often solved through a numerical approach to a constrained optimization problem, by minimizing some performance criteria that are representative measures of the system response. With reference to two simple benchmark six-story shear-type structures subject to both a stochastic earthquake excitation and 44 natural ground motions extracted from the FEMA P695 record set, comparison of the seismic performance is carried out considering FVDs designed according to different methods an overall number of 138 different design scenarios are incorporated in this comparative study. These methods are based either on a desired (target) damping ratio constraint or on a fixed total cost, here roughly related to the sum of the damping coefficients of the added FVDs. Some energy-based perspectives are also given in this review paper in order to interpret the seismic performance in terms of the amount of energy dissipated by the FVDs, out of the total input energy from the earthquake excitation.

Japan architectural review, 2023

CRC Press eBooks, Aug 25, 2017

Near-fault ground motions and long-period, long-duration ground motions possess special character... more Near-fault ground motions and long-period, long-duration ground motions possess special characteristics. The essential aspect of the near-fault ground motions can be characterized by one-cycle or a few-cycle sinusoidal waves (e.g. Ricker wavelet) which are well represented by double or triple impulses. Furthermore, the principal part of the long-period, long-duration ground motions can be characterized by many-cycle sinusoidal waves which are well described by multiple impulses. In this paper, it is shown that good approximate elasticplastic responses of various structural models to the near-fault ground motions and long-period, long-duration ground motions can be derived by using the responses to the double, triple and multiple impulses. The energy approach plays an important and critical role in the derivation of such good approximate responses in closed form.

Summaries of technical papers of annual meeting, Sep 12, 2014

Journal of Engineering Mechanics-asce, 2005

Chief Research Engineer, Technical Research Institute, Obayashi Corporation, Kiyose, Tokyo 204-85... more Chief Research Engineer, Technical Research Institute, Obayashi Corporation, Kiyose, Tokyo 204-8558, Japan, e-mail: nakamura.mitsuru@obayashi.co.jp The authors would like to thank the discusser for his interest in the paper (Takewaki and Nakamura 2005). The discusser raised two points : (i) the validity to take the limit of the spectral functions as ω→ 0 , (ii) the clarification of the procedure to evaluate the spectral functions. As for the first point, it is important to note that the authors clearly stated that the limit of the spectral functions as ω→ 0 can be estimated via the fitting of the spectral function around the zero point with the parabolic function. This procedure had been actually implemented in identifying the stiffness and damping in the original paper. In other words, the stiffness was estimated through the extrapolation with the fitted parabolic function in the frequency range between 0.3Hz and 0.6Hz. Figs.1 and 2 in this closure show examples of that procedure. As for the second point the discusser raised, the discusser states that the periodogram as an estimator of the spectral density function is characterized by a large variance (i.e. coefficient of variation exceeding 1). It appears that the simple explanation of the proposed procedure in the original paper, especially the implementation of the ensemble mean, may cause some difficulty of understanding. The authors would like to explain this procedure (ensemble mean) in detail. First of all, the overall duration

International journal of earthquake and impact engineering, 2017

Two severe ground shakings attacked some specific regions in Kumamoto Prefecture in Japan on Apri... more Two severe ground shakings attacked some specific regions in Kumamoto Prefecture in Japan on April 14 and April 16 of 2016 with the seismic intensity 7 (the highest level in Japan Metheorological Agency (JMA) scale, approximately X-XII in Mercalli scale). In the seismic design codes of many countries, it is usually supposed that a building experiences severe earthquake ground shaking with such level once in its working period. In this paper, a general method is proposed on the evaluation of the seismic resistance of damaged residential houses under multiple consecutive severe ground motions with high intensity. The method can be used for the analysis and design of buildings under multiple consecutive severe ground motions. As in the previous paper, the present paper adopts an impulse as a representative of near-fault ground motion and multiple separated impulses are used as the repetition of intensive ground shakings with high seismic intensity. A building collapse scenario (collapse limit in terms of zero restoring force with P-delta effect) under multiple repeated severe ground shakings is provided and an energy balance law is used for the response evaluation. The reliability of the proposed theories is examined through numerical analysis using recorded ground motions.

Springer eBooks, 2019

For calculation models to examine the exactness of the extended rod theory proposed here, we cons... more For calculation models to examine the exactness of the extended rod theory proposed here, we consider a doubly symmetric high-rise building, as shown in Fig. 5.1. This model is created based on an existing high-rise building in Japan. The structural plan is shown in Fig. 5.1a. The frame elevations in the y-direction corresponding to the longitudinal direction of the building is represented in Figs. 5.1b, c. The x-, yand z-axes are defined as the vertical, longitudinal, and span directions, respectively. This building consists of 35 floors and the total height is 150.5 m. Each story plan is 72 m × 36 m, and the height of each story is 4.3 m. On the frames 2 and 10, the beams stationed in the z-direction (span direction) are absent, and only the columns exist. The weight per unit floor area of each story including the structural members is assumed to be 8 kN/m 2. The cross sections of the columns and beams are represented in Table 5.1. The load for the dynamic calculation per story is w = 8 kN/m 2 × 72 m × 36 m = 20736 kN. The mass M for each story is given by M = w g = 20736 kN 9.8 m/s 2 = 2.12 × 10 6 kg/story We consider the case where earthquake ground motion acts in the y direction. (2) Natural period The natural period of the current building is shown in Table 5.2. Here, SNAP and SS3 are structure calculation software platforms. SNAP is based on the three-dimensional frame analysis produced by Kozo System, Inc. SS3 is based on lumped mass analysis in the dynamic calculation produced by Union System, Inc. In order to examine the exactness of the extended rod theory, we compare the numerical results obtained

Soil Dynamics and Earthquake Engineering, Nov 1, 2021

Abstract A pseudo-double impulse (PDI) is proposed as an extension of the ordinary double impulse... more Abstract A pseudo-double impulse (PDI) is proposed as an extension of the ordinary double impulse (DI) as a substitute of a one-cycle sine wave. PDI is treated as a set of impulsive lateral forces while the ordinary DI was introduced as an impulsive ground acceleration. The deformation and acceleration responses of multi-degree-of-freedom (MDOF) models under DI largely exceed those under the corresponding one-cycle sine wave as a main part of a near-fault ground motion. This is because DI has multiple frequency components and the higher-mode responses are excited. While the influence coefficient vector of the ordinary DI consists of 1 at every component, the influence coefficient vector of PDI is set to be proportional to the undamped fundamental natural mode. Therefore, the fundamental-mode response is mainly excited and the higher-mode responses are hardly excited by PDI. The displacement responses, the velocity responses and the input energy under DI and those under PDI are derived here for both elastic proportionally and non-proportionally damped MDOF models. The critical timing under PDI is also derived. The critical timing can be obtained by the time-history response analysis without repetition. It is demonstrated through the time-history response analysis that the distributions of interstory drifts and floor accelerations under the critical PDI correspond well to those under the critical one-cycle sine wave. Moreover, it is shown that, as far as the input level is large, the critical input period of PDI and that of the one-cycle sine wave correspond well. Since this procedure is not limited to elastic models, the proposed procedure helps to efficiently estimate the critical responses under the one-cycle sine wave for elastic-plastic MDOF models. Finally, the responses under recorded near-fault ground motions are compared with those under PDI. It is shown that the correspondence of the response under PDI and that under the recorded ground motions is fairly good although recorded ground motions are not always critical inputs for elastic-plastic MDOF models.

Elsevier eBooks, 2013

This chapter explores a new general critical excitation method for a damped linear elastic single... more 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.

Frontiers research topics, 2019

This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics... more This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac

CRC Press eBooks, Feb 17, 2021