Published papers

We propose a new method to evaluate quantitatively the effectiveness of retrofitting of houses for evacuation. A model of evacuation route selection under road blockade is constructed based on a subject experiment and built it into an agent model for evacuation simulation. The priority of houses that should be retrofitted is probabilistically evaluated. Because evacuation behavior is considered, this method can appropriately identify houses that should be retrofitted. An index is newly introduced to evaluate retrofitting priority of houses quantitatively using improvement ratio of number of evacuees in a unit time. The proposed method can show retrofitting priority of houses effectively when the ground motion intensity is assumed as JMA Seismic Intensity 6 upper.

An elevator set up in a high-rise building may cause a problem of elevator rope sway. To solve this problem, the responses of building-elevator systems are examined based on the Complex Complete Quadratic Combination method and damage risk is evaluated with respect to possible earthquakes in Chuetsu district of Niigata Prefecture and the northwestern part of Chiba Prefecture. It is observed that some positions of elevator car can reduce the damage risk of main rope by shifting the natural periods of the rope away from the natural periods of the building.

To solve the problem of elevator rope sway in a high-rise building, the seismic damage risk of a building and suspension rope are examined using the Complex Complete Quadratic Combination method. A building site was assumed at Sinjuku, Tokyo in Japan and possible earthquake source zones were considered in Chuetsu, Niigata and the northwest of Chiba. The following findings were obtained: For the 100-, 150- and 250-meter-high buildings, the damage risk of the rope was high when an elevator car or a counterweight was in a lower floor because the rope was long to cause resonance. However, for the 50-, 100- and 200-meter-high buildings, the damage probability was the highest when in a layer other than the bottom. The distribution of the probability of rope damage varies considerably depending on the building height.

The project of E-Simulator is under way at Hyogo Earthquake Engineering Research Center (E-Defense) of National Research Institute of Earth Science and Disaster Prevention (NIED), Japan, which facilitates the world's largest shaking table. The E-Simulator uses the parallel finite element (FE) analysis software package called ADVENTYRECluster (ADVC) as a platform. In this study, we report the results of high-precision FE-analysis for simulation of collapse behavior of the 4-story steel building frame that is the specimen of the full-scale total collapse shaking-table test conducted in September 2007 at E-Defense. It is shown that elastoplastic dynamic responses can be estimated with good accuracy using a high-precision FE-analysis without resort to macro models such as plastic hinge and composite beam effect.

Introduction: In structural analysis, the iterative substructuring method is a most promising framework, which is to be used on parallel computer systems. But using just the parallel processing does not allow us to obtain the desired level of performance. We need special preconditioning procedures well-suited to the iterative method and the domain decomposition method. The CGCG method [1], which will be described in some detail in this paper, gives high performance to the iterative substructuring method by a precondition technique depending on the domain decomposition. The CGCG method is implemented in a commercial code ADVENTURECluster (ADVC), and ADVC can solve dynamic nonlinear problems with more than 10 million degrees of freedom. Hyogo Earthquake Engineering Research Center (E-Defense) owns the world’s largest shaking table [2]. Also E-Defense is developing E-Simulator code which we hope to act as a virtual shaking table by fully taking advantage of recent development of high-performance computing. E-Simulator uses ADVC as a platform. The paper shows the results of a nonlinear seismic analysis of steel building frames as a test specimen of the virtual shaking table. Numerical Algorithms and Examples: The CGCG method is a fully iterative method based on the domain decomposition method, in which the decomposed subdomains are not considered as substructures, whereas the standard iterative substructuring methods take those as substructures. Recent enhancement of the preconditioning gave the method higher performance than the original CGCG method. The enhanced CGCG method and E-simulator equipped with the enhanced CGCG method are applied to solve nonlinear seismic analyses of steel building frames. Conclusions: The enhanced CGCG method is described, and the E-simulator equipped with the enhanced CGCG method is applied to analyze nonlinear seismic analyses of steel building frames, which will be examples of the virtual shaking test. References: [1] Akiba et al, Proceedings of SC06. [2] http://www.bosai.go.jp/hyogo/ehyogo/.

Introduction: The project of E-Simulator is under way at Hyogo Earthquake Engineering Research Center (E-Defense) of National Research Institute of Earth Science and Disaster Prevention (NIED), Japan, which facilitates the world's largest shaking table (Hori et al. 2007).The E-Simulator uses ADVENTYRECluster (ADVC)/ADVENTURE as a platform (Akiba et al. 2006, Ohsaki et al. 2009). ADVC is a commercial software package of parallel finite element (FE) analysis that uses the domain decomposition technique for parallel implementation. ADVENTURE is an open source version, which is a prototype of ADVC. ADVC can solve dynamic nonlinear problems with more than 10 million DOFs for a structure discretized by three-dimensional solid elements. The E-Simulator is conceived as a virtual shaking table, and its final form is a software environment to simulate global and local seismic responses of a city, as assemblage of buildings and infrastructures, by fully taking advantage of recent development of computer science and high-performance computing in computational mechanics. Analyses of Steel Building Frames: As a part of this project, the purpose of this study is to show that the global and local elastoplastic behaviors of steel frames under severe seismic motions can be simultaneously simulated by a high-precision FE-analysis software, E-Simulator. Elastoplastic dynamic analyses are carried out for a 31-story high-rise steel building model and for the 4-story frame model that models the specimen of full-scale shaking-table test conducted at E-Defense shaking-table facility. The whole structures are discretized using hexahedral solid elements without resort to macro models such as plastic hinge and composite beam effect. Conclusion: It is shown that E-Simulator can simulate the large-strain elastoplastic dynamic behaviors of the steel building frames. Both global and local behaviors of the structures are estimated accurately by the simulation using fine meshes with the solid elements. References: Hori et al., Journal of Earthquake Engineering 29, 1420-1425, 2007 (in Japanese) Akiba et al., Proc. of SC06, 2006 Ohsaki et al., EESD, 38, 635-654, 200.

This study proposed a multistable structure using snap-through behavior as an adaptable structure, which can change its size and transform its configuration easily. To know the stable configuration and stress of the structure, the form finding analysis method of the structure is formulated. Then, a design support system is proposed based on a calculation method of required forces to transform its configuration. Finally, several configurations are demonstrated with a small scale model to show the adaptability and feasibility of the proposed structure.

This paper first clarifies the vibration characteristics of elevator rope in a high-rise building with a response control system such as active mass damper and linked structures. When a cost function for optimal control is formulated to reduce distance between a building and rope, response of the building deteriorates especially in high frequency range. In order to overcome this drawback, a control method is proposed based on frequency shaping linear quadratic Gaussian and variable gain feedback. Time history analysis is carried out using simulated ground motion and it is verified that the proposed method can reduce the response of both a building and rope effectively.

A simultaneous optimization method is proposed for a structural system controlled by a least quadratic regulator (LQR) under seismic excitation. An LQR-controlled system is converted into an equivalent uncontrolled structural system and the natural period and the damping factor are derived. A design response spectrum is used to consider input earthquake motion and the maximum response and control force of the system are calculated based on the spectrum. Simultaneous optimization consists of the following two stages: 1) feasible region of design variables are evaluated; 2) the objective function of the cost of the total system is minimized. A single mass structure with LQR controller is simultaneously optimized as a numerical example.

The results of high-precision FE-analysis is presented for simulation of collapse behavior of the 4-story steel building frame that is the specimen of the full-scale total collapse shaking-table test conducted in September 2007 at E-Defense. The computation is carried out using the E-Simulator, which is under development at Hyogo Earthquake Engineering Research Center (E-Defense) of National Research Institute of Earth Science and Disaster Prevention (NIED), Japan. The E-Simulator uses the parallel finite element (FE) analysis software package called ADVENTYRECluster (ADVC) as a platform. It is shown through numerical examples that elastoplastic dynamic responses can be estimated with good accuracy using a high-precision FE-analysis without resort to macro models such as plastic hinge and composite beam effect.

Elevator rope-sway is a serious problem for a high-rise building under seismic excitation. Vibration control of the rope-sway using active mass damper (AMD) is investigated, which is usually designed simply for control of building response. The linear quadratic regulator (LQR) is employed as the AMD control system. Numerical simulations are conducted and the responses are analyzed in both frequency and time domains. The relative displacement between the building and the rope is evaluated as well as the story drift and the absolute acceleration of the building. It is observed that the control method considering the rope-sway can effectively decrease response of the rope after seismic excitations.

This paper studies the effect of spatially random ground motions on the seismic response of a one-story multi-span wooden building considering the stiffness of the horizontal diaphragms. The deformation angles at columns and horizontal diaphragms are examined using time history response analyses with simulated input motions. It is shown that stiffness increase of the horizontal diaphragms and dimensions increase of the building make responses large to damage, and that large responses at the horizontal diaphragms are much more serious than at columns.

This study investigates equivalent linear models which can assess occurrence of building damage with high accuracy for several threshold values. The accuracy of the following three equivalent linear models are examined: 1) the conventional model of which stiffness of all the story is determined based on seismic story shear force, 2) the shear-force-equivalent model of which equivalent stiffness of the first story is determined based on seismic story shear force, and 3) the energy-equivalent model of which equivalent stiffness of the first story is determined based on earthquake input energy. The equivalent damping is obtained from input energy of earthquake motion using nonlinear models. As a result, the most accurate equivalent linear model is the shear-force-equivalent model.

様々な工業製品の設計解析において，大規模構造計算は重要で現実的なツールになりつつある。有限要素解析における解析の並列化の困難は克服されつつあり，近年の高性能計算機を有効活用できるようになってきている。兵庫耐震工学研究センターの数値震動台（E-シミュレーター）は，解析コードADVENTUREClusterをプラットフォームとしており，コースグリッド共役勾配法を用いた並列解析により陰解法による大規模構造解析を可能にした。これを用いた31層超高層建物の地震応答解析の事例を報告した。

Vulnerability functions for wooden buildings are proposed, which employ a probability distribution model of seismic performance. An acceleration response spectrum is used as input to the functions. The probability distribution model is formulated based on two indices of seismic diagnosis data: stiffness and resistance force, and it is clarified that the bivariate normal distribution is a reliable model. Regarding estimation accuracy, the proposed functions are compared with experience-based vulnerability functions in past literature for three earthquake disasters. The proposed functions indicate fairly good accuracy when proper parameters of stiffness increase and resistance force increase due to non-structural walls are used.

A new framework is presented for analysis of dynamic collapse behavior of steel frames using large-scale parallel finite element method based on the domain decomposition method. The analysis software is based on ADVC as a part of the E-Simulator that takes advantage of recent development of computer science and high-performance parallel computing in computational mechanics. By making an analysis model with fine meshing, a complicated sequence of local buckling of columns and beams can be simulated. Numerical results are shown for dynamic collapse analysis of single-story and 5-story frame models to show that the global and local behaviors are simultaneously simulated by a high-precision finite element analysis. Eigenvalue analysis is also carried out for a 31-story frame to demonstrate that dynamic analysis can be carried out for a structure discretized to solid elements with more than 70 million DOFs.

We propose a new method to evaluate the effectiveness of seismic retrofitting of houses for evacuation quantitatively. The priority of houses that should be retrofitted is evaluated based on a probability to yield isolated evacuees due to road blockade caused by debris of collapsed houses after a severe earthquake. We improve the method to extract samples using the Markov chain Monte Carlo method. An index is newly introduced to evaluate the retrofitting priority, which is difference of expected numbers of isolated evacuees in a target area between before and after the retrofitting. The proposed method can show retrofitting priority of houses effectively when the ground motion intensity is assumed to be JMA Seismic Intensity 6 upper.

Strong earthquake ground motions hinder the use of seismic vibration control systems in buildings because they may damage the sensors or cables connected to controllers. To maximize the vibration control of the building even during large earthquakes, we designed a redundant vibration control system that tolerates errors in sensing instruments and the accuracy deterioration in the estimated state variables. To monitor the accuracy of each sensor, we introduced a reliability parameter that quantifies the accuracy of the estimated state variables. Using this, we designed a new algorithm based on linear-quadratic Gaussian control theory to reduce the building seismic response and obtain a redundant and robust building vibration control system.

Modeling and numerical simulation techniques for performing a detailed finite element analysis of a composite beam are presented. The finite element analysis is performed using E-Simulator, which is under development at the Hyogo Earthquake Engineering Research Center (E-Defense) of the National Research Institute for Earth Science and Disaster Prevention (NIED). A piecewise linear isotropic-kinematic hardening law is used for the steel material, and heuristic and implicit rules are incorporated to simulate its complex cyclic elastoplastic behavior. The extended Drucker-Prager model is used for the concrete material. The steel beam, steel column and reinforced concrete slab are discretized into solid elements. The wire mesh consisting of steel bars in the slab is also modeled using solid elements and rigid beams are used for the stud bolts. Detailed analyses are carried out for both a steel beam and a composite beam subjected to static cyclic loading. Good agreement is found with experimental results such as strength degradation due to local buckling of the flange, and asymmetric behaviors resulting from contact between the slab and the column.

This study focuses on the scheduling in public real estate management (PREM) and derives the optimal scheduling using real option approach considering seismic risk. This study defines a seismic risk as the uncertainty in PREM and proposes a method to derive the optimal scheduling of seismic retrofitting of facilities managed by a municipality using real option considering seismic risk. To verify the effectiveness of the proposed method, this study conducts a case study. A retrofitting problem of school facilities in Kawasaki City, Japan is selected as a case study subject. Through the case study, it is confirmed that the proposed method can derive the optimal retrofit schedule with a reduced cost and a reduced risk of damage due to earthquakes.