Earthquake Response Analysis Research Articles

構造物のARXモデルとアクティブマスダンパの運動方程式に基づく振動制御

Structural control and system identification are integrated to directly utilize the results of system identification of an objective structure for its active control. After the structure is expressed as ARX models and an active mass damper (AMD) is expressed as the motion of equation, a state equation and an output equation for the AMD-structure system are introduced in the discrete-time space. By considering the zero-th terms for input signals in the ARX models, the formulation and the optimal regulator problem can be generally applied to building structures. As the measurements, the feedback control law requires the AMD's velocity and stroke and the structure's acceleration at least. Numerical examples indicate high applicability of the proposed control strategy to MDOF structures. The earthquake response analysis and the poles of the AMD-structure system confirm the control effectiveness.

空間の確保と損傷の防止を目的とした既存ピロティ建築物の地震応答制御

Collapse or severe damage has been observed in many RC residential buildings with soft story at the previous earthquake disasters. Hence development of an effective structural control technology is one of the urgent tasks for residential apartments in the urban area. However, most of the conventional structural control methods for soft story buildings stuff a space with structural elements such as RC walls or response control dampers. This paper proposes a new technique for structural control of RC buildings with soft story by using ductile short columns as response control devices placed beside the existing columns at the soft story. The objective of the response control is upgrading safety as well as reparability for damage mitigation without partitioning off the spaces at the soft story. The main role of these devices are to increase story shear capacity to reduce response drift of the soft story, and to support axial force due to overturning moment in order to reduce axial force acting on the soft story columns. Results of the inelastic earthquake response analysis indicate that yielding of the soft story column can be successfully prevented since the response control devices work effectively.

セル式岸壁の最適断面設定方法に関する研究

When designing the cellular-bulkhead quay wall, designers should determine the embedded length and the width of the cellular-bulkhead quay wall. As there are plural design alternatives for these parameters, designers should also calculate the construction costs and find the optimal profiles. In this study, authors present the general rule for the determination of the optimal design for the cellular-bulkhead quay wall. Authors then discuss the effects of these parameters on the earthquake resistant performance of the cellular-bulkhead quay wall by conducting the earthquake response analyses.

エネルギーの釣合に基づく履歴型ダンパー付鉄骨造骨組の地震応答予測

This paper presents a seismic response prediction method for steel frames with hysteretic dampers. This method is based on energy balance and is able to predict the seismic response of frames with dampers yielding under an earthquake to occur several times during the life of buildings. In this method, the number (_dn_l) of eauivalent cycles of plastic deformation in hysteretic dampers is utilized to predict earthquake response of frames with hysteretic dampers. In order to grasp the _dn_l values, earthquake response analysis of analytical frames with hysteretic dampers is carried out. And, the adequacy of seismic response prediction by this method is verified through a comoarison with results of earthquake response analysis of three different story frames.

羽田空港における地震動増幅特性と表層地盤Ｓ波速度構造の関係

Amplification characteristic of earthquake motion at Haneda Airport is ascertained with strong-motion array observation records and linear earthquake response analyses. It is shown that correlation between amplitude ratio and mean S-wave velocity is low, whereas amplitude ratio with 0.5-1 Hz band pass filter is highly correlated with mean S-wave velocity of 30m thick surface ground.

Earthquake response analysis in the time domain for 2D soil–structure systems using analytical frequency‐dependent infinite elements

AbstractThis paper presents a time domain method for soil–structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating analytical frequency‐dependent infinite elements for the far‐field soil region. Equivalent earthquake input forces are calculated based on the free‐field responses along the interface between the near‐ and far‐field soil regions using the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far‐field soil region formulated using the analytical frequency‐dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil–structure system in the time domain. Earthquake response analyses have been carried out on a multi‐layered half‐space and a tunnel embedded in a layered half‐space, and results are compared with those obtained by the conventional method in the frequency domain. Copyright © 2003 John Wiley & Sons, Ltd.

Input and system identification of the Hualien soil–structure interaction system using earthquake response data

AbstractThis paper presents an input and system identification technique for a soil–structure interaction system using earthquake response data. Identification is carried out on the Hualien large‐scale seismic test structure, which was built in Taiwan for international joint research. The identified quantities are the input ground acceleration as well as the shear wave velocities of the near‐field soil regions and Young's moduli of the shell sections of the structure. The earthquake response analysis on the soil–structure interaction system is carried out using the finite element method incorporating the infinite element formulation for the unbounded layered soil medium and the substructured wave input technique. The criterion function for the parameter estimation is constructed using the frequency response amplitude ratios of the earthquake responses measured at several points of the structure, so that the information on the input motion may be excluded. The constrained steepest descent method is employed to obtain the revised parameters. The simulated earthquake responses using the identified parameters and input ground motion show excellent agreement with the measured responses. Copyright © 2003 John Wiley & Sons, Ltd.

Time domain earthquake response analysis method for 2-D soil-structure interaction systems

A time domain method is presented for soil-structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating infinite elements for the far field soil region. Equivalent earthquake input forces are calculated based on the free field responses along the interface between the near and far field soil regions utilizing the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil-structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space with the assumption of the linearity of the near and far field soil region, and results are compared with those obtained by the conventional method in the frequency domain.

A seismic free field input model for FE-SBFE coupling in time domain

A seismic free field input formulation of the coupling procedure of the finite element (FE) and the scaled boundary finite-element (SBFE) is proposed to perform the unbounded soil-structure interaction analysis in time domain. Based on the substructure technique, seismic excitation of the soil-structure system is represented by the free-field motion of an elastic half-space. To reduce the computational effort, the acceleration unit-impulse response function of the unbounded soil is decomposed into two functions; linear and residual. The latter converges to zero and can be truncated as required. With the prescribed tolerance parameter, the balance between accuracy and efficiency of the procedure can be controlled. The validity of the model is verified by the scattering analysis of a hemi-spherical canyon subjected to plane harmonic P, SV and SH wave incidence. Numerical results show that the new procedure is very efficient for seismic problems within a normal range of frequency. The coupling procedure presented herein can be applied to linear and nonlinear earthquake response analysis of practical structures which are built on unbounded soil.

地盤インピーダンスの時間領域変換による成層地盤に埋込まれた構造物の地震応答解析 : その2 変換法の改良及び離散的地盤解析モデルに基づく応答解析

The author has studied the time domain evaluation of soil impedance and has proposed a transform method. In a previous paper, structures deeply embedded in layered soil were investigated based on the embedded SR model. However, actual soil often has inhomogeous conditions that can not be expressed by theoretical impedance like that used in the paper. For estimating such soil conditions, discrete soil analysis models like FEM are employed. In this paper, a modified transform method was proposed to improve the convergence characteristics, first. Then, full-matrix soil impedance of structures embedded in inhomogeous soil was calculated by axi-symmetric FEM models. The full-matrix impulse response was evaluated by the modified method, and earthquake response analyses were carried out. The efficacy of the proposed method was confirmed through these studies.

改正建築基準法の解放工学的基盤波を想定した表層地盤増幅特性の簡便評価法

We proposed a simplified method to evaluate strong ground motions response spectra at ground surface considering the inelastic amplification characteristics of surface layers. We assume that input motions on the engineering bedrock are given by the reviesed Enforcement Order of the Building Standard Law of Japaa This method is far simple and easy to calculate compared to the limit strength method in the revised Building Standard Law of Japan, because this method requires only the 30m depth soil layer data from the surface and substitution from these data to several equations. Despite of simplicity, this method predicts the results of equivalent elastic earthquake response analyses more adequately than the limit strength method in the revised Building Standard Law of Japan.

Nonlinear earthquake response analysis and energy calculation for seismic slit shear wall structures

Based on the concept of structural passive control, a new type of slit shear wall, with improved seismic performance when compared to an ordinary solid shear wall, was proposed by the authors in 1996. The idea has been verified by a series of pseudo-static and dynamic tests. In this paper a macro numerical model is developed for the wall element and the energy dissipation device. Then, nonlinear time history analysis is carried out for a 10-story slit shear wall model tested on a shaking table. Furthermore, the seismic input energy and the individual energy dissipated by the components are calculated by a method based on Newmark-β assumptions for this shear wall model, and the advantages of this shear wall are further demonstrated by the calculation results from the viewpoint of energy. Finally, according to the seismic damage criterion on the basis of plastic accumulative energy and maximum response, the optimal analysis is carried out to select design parameters for the energy dissipation device.

Seismic analysis of base-isolated liquid storage tanks using the BE–FE–BE coupling technique

A three-dimensional soil–structure–liquid interaction problem is numerically simulated in order to analyze the dynamic behavior of a base-isolated liquid storage tank subjected to seismic ground motion. A dynamic analysis of a liquid storage tank is carried out using a hybrid formulation, which combines the finite shell elements for structures and the boundary elements for liquid and soil. The system is composed of three parts: the liquid–structure interaction part, the soil–foundation interaction part, and the base-isolation part. In the liquid–structure interaction part, the tank structure is modeled using the finite elements and the liquid is modeled using the internal boundary elements, which satisfy the free surface boundary condition. In the soil–foundation interaction part, the foundation is modeled using the finite elements and the half-space soil media are modeled using the external boundary elements, which satisfy the radiation condition in the infinite domain. Finally, above two parts are connected with the base-isolation system to solve the system's behavior. Numerical examples are presented to demonstrate the accuracy of the developed method, and an earthquake response analysis is carried out to demonstrate the applicability of the developed technique. The properties of a real LNG tank located in the west coast of Korea are used. The effects of the ground and the base-isolation system on the behavior of the tank are analyzed.

Fluid-structure-soil interaction analysis of cylindrical liquid storage tanks subjected to horizontal earthquake loading

This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.

Hysteretic Modeling of Thin-Walled Circular Steel Columns under Biaxial Bending

To ensure the safety of elevated highway bridges under major earthquakes, it is important to predict the ultimate behavior of columns used as bridge piers. After the Kobe earthquake, many analytical and experimental studies have been conducted to examine the ultimate seismic behavior of thin-walled steel columns. However, these studies are mostly restricted to the in-plane behavior of the columns. As observed in the Kobe earthquake, the damages to the columns are usually influenced by the two-dimensional horizontal seismic excitations. Therefore, it is more desirable to consider the effect of biaxial bending at the ultimate stage of earthquake response in the design of steel columns. Herein, we propose a hysteretic model of thin-walled circular steel columns under biaxial bending to predict the ultimate seismic behavior of cantilever-type thin-walled circular steel columns with constant axial load. The proposed column model consists of a concentrated mass and a rigid column with multiple nonlinear springs located at the column base. As the hysteretic constitutive relation for each spring, we adopt the Dafalias and Popov’s bounding-line model by modifying the original model in order to take into account the local buckling behavior. The material constants of the modified bounding-line model can be determined, based on the in-plane hysteretic behavior of the column obtained either by FEM shell analyses or by experiments. The validity of the proposed model is examined by comparing it with results of the two-dimensional horizontal earthquake-response analyses, using the FEM shell model.

ファイバーモデルを用いた系の地震応答解析における直接収斂解法

In this paper, the authors propose a new earthquake response analysis method applying Newmark's β-method and using Fiber-Model. In general, the tangential stiffness of every structural member is necessary for earthquake response analyses, however in the case Fiber-Model is applied to the columns subject to bi-directional moments or variable axial forces, it is impossible to calculate the stiffness. In the proposed method, the equation of equilibrium in Fiber-Model is directly solved by giving the equation of motion as a restricted condition without calculating the tangential stiffness. The authors show its propriety by applying it to a RC column of a single-mass and three-degree-of-freedom system and a 1-span 1-story plane frame.

鉄骨造建物群の被害予測モデルの構築

In previous studies we have established a set of dynamic models of reinforced concrete (RC) buildings and wooden houses for damage evaluation based on the damage statistics in Kobe surveyed after the 1995 Hyogo-ken Nanbu earthquake and nonlinear response analyses for synthetic waveforms simulated by Matsushima and Kawase (2000). In this paper, we proceed to construct a set of dynamic models of steel buildings for damage evaluation. In the process of establishing models we found that strengths of steel buildings are not so much different from those considered in the building code. This implies that the strengths of steel buildings are not influenced strongly by other factors not considered in design such as non-structural partitioning walls. Damage ratio distributions derived from established models show similar pattern to the observed ones though calculated damage ratios are distributed wider than the observed. By using steel building models established here with the models for reinforced concrete buildings and wooden houses already established, we can predict the whole picture of urban seismic disasters.

鋼構造ラーメン骨組の梁と接合部パネルに要求される変形性能

This paper presents the method for the prediction of seismic damage on beams and joint panels in steel moment frame. In this method, the maximum and cumulative plastic deformation of beams and joint panels are estimated on condition that input energy into the system is known. The earthquake response analyses of fishbone-shaped frame are carried in order to evaluate the applicability of the proposed method. Comparing the results of the prediction and the analysis, it is found that the results of the prediction are in good agreement with the average of the results of the analysis.

高層RC建物の地震応答シミュレーション解析と深部地盤構造の影響

This study investigates earthquake response characteristics of a high-rise reinforced concrete building constructed within the damage belt of Kobe City during the 1995 Kobe earthquake. Weak nonlinearity is inferred from the top and base records of the building during the 2000 Tottori-ken Seibu earthquake. After dynamic parameters of the building are tuned up, the records in the building are well simulated in nonlinear earthquake response analyses. Then, the ground motions in the neighboring area are evaluated taking into account the deep subsurface structure. The seismograms obtained at GL-300m beneath the building and at the mountain area are well simulated from records on ground surface adjacent to the building. Finally, the effects of the deep subsurface structure on the seismic response of the building are studied, which is not negligible because of ground motion amplification in the basin-edge structure.

Time history nonlinear earthquake response analysis considering materials and geometrical nonlinearity

A time history nonlinear earthquake response analysis method was proposed and applied to earthquake response prediction analysis for a Large Scale Seismic Test (LSST) Program in Hualien, Taiwan, in which a 1/4 scale model of a nuclear reactor containment structure was constructed on sandy gravel layer. In the analysis both of strain-dependent material nonlinearity, and geometrical nonlinearity by base mat uplift, were considered. The ‘Lattice Model’ for the soil–structure interaction model was employed. An earthquake record on soil surface at the site was used as control motion, and deconvoluted to the input motion of the analysis model at GL-52 m with 300 Gal of maximum acceleration. The following two analyses were considered: (A) time history nonlinear, (B) equivalent linear, and the advantage of time history nonlinear earthquake response analysis method is discussed.