Published papers

To improve the damping models of building structures, the mechanical behavior of exterior walls made of autoclaved lightweight aerated concrete (ALC) is investigated using finite element analysis software, E-Simulator. A specimen of ALC panels and a loading apparatus are modeled using solid elements, rigid beams and multi-point constraints, which reproduce a rocking installation system used in tests of components of a real-scale four-story steel structure for shaking table tests of E-Defense, National Research Institute of Earth Science and Disaster Prevention. Static alternately repeated cyclic loading with incremental deformation amplitude is simulated up to the drift angle of 0.02 rad. It is observed that energy dissipation owing to the plastic deformation of the ALC panels and the friction between an ALC panel and a ruler steel angle becomes remarkably large when the drift angle exceeds 0.015 rad because of the contact.

A design framework is investigated for designing the parameters of a vibration control device installed in a building–equipment coupled system to reduce earthquake damage. An iterative calculation procedure to derive a suboptimal design based on the minimization of damage probability in a certain service period is proposed. The validity of the proposed procedure is examined using a model of a fifteen-storied data-center building that accommodates servers on isolated floors on the second and fifteenth floors and is equipped with a vibration control device on the top floor. The proposed procedure is confirmed to give a suboptimal design within a few calculation iterations.

A robust and decentralized control method for reducing vibration in a building, based on the Lyapunov-control function, is proposed and investigated. A new parameter that gives flexibility to the control design is introduced, and the control law is expressed in terms of dimensionless parameters. In addition, an expression adapted for semiactive control of which feedback gain is finite is proposed for a particular case. Analytical proof of the performance is completely derived for a system in which the control distribution matrix is not singular and a practical performance criterion is obtained. The influence of each parameter, along with the validity of the proposed performance criterion and the robustness to the uncertainties in the structural parameters, is extensively discussed with a single-degree-of-freedom numerical example. The performance of a decentralized system and the controller design in the case where the control distribution matrix is singular are discussed with a two-degree-of-freedom numerical application. A shaking table experiment using a small-scale model of a high-rise building with a vibration control device is conducted to verify the proposed method.

A simultaneous optimal design method of asymmetric large-scale space frames with tuned mass dampers is proposed. The objective function is defined by the maximum absolute acceleration response of the structure to input ground motions of sine waves. Sine waves of periods with the five natural periods having large modal participation factors of the structure are input, and the maximum responses are calculated by time–history response analysis to evaluate the objective function. The shape of the space frame is described by a Bézier surface to reduce the number of design variables. The change from the initial values of the nodal coordinates is constrained to preserve the initial design shape, which is provided by an architect. The method employs a genetic algorithm in optimization. A case study is conducted for an asymmetric steel space frame of a vault-like shape. The results confirm the reduction of maximum absolute acceleration responses in the optimal shapes not only to the five sine waves but also to four scaled ground motion records. Moreover, the presence of tuned mass dampers enables the reduction of the peak response value and maintains similarity to the initial shape.

The mechanical behavior of exterior walls made of autoclaved lightweight aerated concrete (ALC) is investigated using finite element analysis. A specimen of ALC panels and a loading apparatus, which reproduce a rocking installation system, are modeled using solid elements, rigid beam elements and multi-point constraints. The finite element analysis software, E-simulator, is employed to simulate static alternately repeated cyclic loading with incremental deformation amplitude up to the drift angle of 1/50 rad. It is clarified that plastic deformation of the concrete panels, which causes the energy dissipation, is observed in the region around the O bolts and the corners that come into contact with a supporting bottom angle.

Evacuation assistance using a robot is studied. Human subjects experiments of indoor evacuation under robot guidance were conducted and the result showed effectiveness of a robot guidance in the evacuation. Based on the experiment result an agent model for evacuation simulation was conducted. The agent model considers probability distributions of the walking speed and the route decision time of evacuees. Using the constructed agent model, evacuation simulation was carried out for a building with complex hallways. It is demonstrated that effective position of a robot for guidance can be sought through the agent simulation.

This study proposes a scheme to design control parameters for a data center facility with a vibration controller on its top floor and a secondary isolation device with its own vibration controller designed to protect vibration-sensitive computer equipment. The aim is to reduce the effects of acceleration and drift from an earthquake on computer servers placed on the isolation device that must operate during a seismic event. A linear elastic model is constructed and the evaluation function of the linear quadratic Gaussian (LQG) control is formulated. The relationship between the control parameters and the responses is examined, and based on the observations, a control parameter design scheme is constructed to reduce the responses of both the building and the computer server effectively.

Sosokan, a building at the Yagami Campus of Keio University, has a semi-active control system that include 8 semi-active dampers and 24 passive dampers installed in the base-isolation layer. The parameters of the semi-active controller were designed using the initially assumed design values of the building. However, these parameters may not be identical to its present actual condition and can be updated on basis of observation records. This paper aims to improve the performance of the controller through identification of the building properties by updating the control parameters on basis of the records of seismic responses during the main shock and aftershocks of the 2011 Great East Japan Earthquake. In the identification, errors between the time history responses of the main shock records and simulation results are minimized by an optimization scheme. Thereafter, structural properties of the updated building model is applied to improve the performance of the semi-active controller.

The inability of equipment and instruments in a building to function is one of the serious effects of seismic ground motion. We discuss the situation of computer servers in a data center and the required linear optimum control of a building to reduce the damage. We construct a mass–shear spring model of a building that con-tains computer servers on a seismic isolation floor and that is equipped with an active vibration controller on the top floor. Simulated ground motions are input to the model, and the maximum responses are examined to evaluate the fragility curve of the server. Finally, we propose a technique that can be used to design parame-ters of a controller, enabling a reduction in damage to the servers.

A method for predicting the maximum control force of a proportional-derivative controlled system is pro-posed based on a response spectrum method. In designing structural control devices for the reduction of seis-mic response, it is important to choose an actuator with an adequate control force capacity in order to achieve a satisfactory control effect. To accomplish this, the maximum control force under assumed seismic ground motions has to be estimated. To verify the proposed method, the predicted maximum forces are compared with the results of a time-history analysis using white noise and design ground motions. With respect to the analysis models, three-story and 25-story building models with active bracing for each story are used. It is found that the differences between the predicted values of the maximum response and control force and the time-history analysis results are sufficiently small, and thus the proposed method is reliable to use in design.

We propose a new quantitative method to evaluate the effectiveness of seismic retrofitting of houses for evacuation safety. The priority of houses that need retrofitting is evaluated on the basis of the probability of evacuees becoming isolated owing to road blockades caused by the debris of collapsed houses after an earthquake. We improve the method to extract samples by using the Markov chain Monte Carlo method. A new index is introduced to evaluate the difference of total expected numbers of isolated evacuees before and after the retrofitting.

The loss of a building function is one of the serious effects of seismic ground motion. We discuss the situation of computer servers in a data center and the required linear optimum control of a building to reduce the damage. We construct a model of a building that contains computer servers on a seismic isolation floor and that is equipped with an active vibration controller on the top floor. Simulated ground motions are input to the model, and the maximum responses are examined to evaluate the fragility curve of the server. Finally, we investigate design parameters of a controller which enable a reduction in damage risk of the servers placed on different floors.

A method to determine a control scheme and parameters is proposed for a data center facility with a vibration controller on its top floor and a secondary isolation device with its own vibration controller designed to protect delicate computer equipment. The aim is to reduce acceleration and drift from an earthquake for computer servers placed on the isolation device that must operate during a seismic event. A linear elastic model was constructed and the evaluation function of the linear quadratic Gaussian control was formulated. The relationship between control parameters and responses was examined, and it was confirmed that the proposed scheme properly defined system parameters to minimize the responses of both the building and computer server.

設備や非構造部材の被害を低減するためには設計者・技術者間のコミュニケーションが不可欠である。人命保護などの要求性能にはサブ性能のヒエラルキーが存在しており、役割分担と協調のため、性能というコンセプトで展開される技術コミュニケーションが作り手側に求められる。また、構造設計者は、利害関係者の要望を吸い上げ、安全性能を具体化し実現するプロセスにより積極的に関わるべきである。従来の耐震設計などの性能チェックにとどまらず、多分野と連携し、居住性や事業継続性など建築主や社会のニーズに応えた建物を実現する性能設計の普及を期待する。

This paper formulates a response prediction formula based on complex modal superposition and frequency response functions of single-degree-of-freedom systems for both storey drift and floor acceleration of a mid-storey-isolated building under the assumption of white noise input. This study verifies that the proposed formula can estimate the seismic response of a building accurately, even if a system includes the overdamped mode, by comparing the same with the results of a time-history analysis. To support the structural design of a mid-storey-isolated building, the proposed formula is applied to an optimal design problem, which considers the objective function of acceleration response in a superstructure and constraints on storey drifts. A genetic algorithm is employed to obtain the optimal stiffness distribution and damping coefficient of the isolation layer. This study confirms that the acceleration response of the optimal design is successfully reduced, with other responses remaining within acceptable ranges.

In general, large-scale space frames, such as stadiums and gymnasiums, have a role as an evacuation facility. However, some accidental falls of a ceiling and equipment during an earthquake have been reported, and these accidents might cause human injury or casualty. On the other hand, these structures often have an aesthetically elaborated design, but they do not always have high performances from a structural point of view. This research proposes a method to support designing a large-scale space frame, which implements: 1) a design elaborated by an architect and 2) structural and control performances, which can reduce damage or fall of a ceiling, on the basis of simultaneous optimization of structural and control systems. The number of design parameters in the optimization problem is reduced by describing the roof shape with a Bézier surface. The genetic algorithm is used for the optimization.

Dynamic collapse analyses of a 4-story steel building frame modeled by solid elements are performed using the E-Simulator, which is a parallel finite element analysis software package for civil and building structures. Code verification, calculation verification, and validation of the numerical codes (V&V) are conducted by comparing the results obtained by the E-Simulator, those obtained by a beam element analysis code, and the experimental results obtained by the 3-D full-scale earthquake testing facility, the E-Defense at NIED. The seismic response analyses under 60% or 100% of the JR Takatori seismic wave of the 1995 Hyogoken-Nanbu earthquake are performed. The shear forces and interstory drift angles of the 1st story obtained by the E-Simulator simulation and the E-Defense full-scale test have good agreement. Both response of the whole frame and local deformation due to plastic buckling are simulated in the analysis using the E-Simulator.

Seismic response analysis is carried out for a base-isolated frame. The RC-frame members as well as the rubber bearings are discretized into hexahedral finite elements. The material properties of rubber are represented by the Ogden model, and the frame is assumed to remain in elastic range. The seismic response analysis of the frame, which has more than 3 million degrees of freedom is carried out using the E-Simulator, which is under development at E-Defense, Japan, based on a software package called ADVENTURECluster. It is shown that the global and local responses can be simultaneously evaluated through a high-precision finite element analysis.

The vulnerability function of wooden-frame houses using the results of seismic diagnosis and a response spectrum was proposed. It employs a probability density function of seismic performance indices of wooden houses, which are separated into an index of horizontal resistance force and other indices. The input seismic motion is evaluated based on an acceleration response spectrum and natural periods determined by indices of horizontal resistance force. The application results to the 1995 Hyogo-ken Nanbu earthquake are compared with the damage statistics at the five sites, which have seismic records. Though the proposed vulnerability function is not based on the damage statistics, the estimated ratios for minor and more damages coincide fairly well with the actual damage surveyed by local governments.

The Nishinomiya Built Environment Database, which can be used to analyze the disaster process of the 1995 Hanshin-Awaji Earthquake Disaster in Nishinomiya City, has been expanded with new data entries. The database contains the following very detailed datasets: (1) the urbanization area base map, (2) casualty data, (3) three sets of building damage data surveyed by the Nishinomiya City, the Architectural Institute of Japan and the City Planning Institute of Japan, and the Kobe University, (4) building property data based on the real estate tax roll, (5) photographs of the damaged buildings with the information on the place and orientation of the picture, and (6) the estimated distribution of the seismic ground motion. The seismic ground motion was simulated for the southern part of Nishinomiya City and two verification sites in Kobe City and Amagasaki City. In the simulation, the borehole data of public facilities were used to model the surface soils as one-dimensional layers, taking into consideration the fact that the spatial distribution of the sediment/basement interface forms a slope. The model of the fault rupture process simulated the characteristics of the seismic motion at basement level, and amplification effects of the surface layers were evaluated based on multiple reflection theory. The distribution of peak ground acceleration and peak ground velocity was estimated from acceleration response spectra at each borehole point. In addition, the relationship between simulated seismic ground motion and building damage was studied based on newly proposed band-passed spectrum intensity using the expanded database. This confirmed that detailed categorization is necessary in order to evaluate the fragility functions, especially for reinforced concrete structures. The database should provide fundamental information for identifying the relationship between the ground motions and the extent and pattern of building damage, or the pattern of the occurrence of casualties.