Hirokazu Iemura

A study on interaction control for seismic response of parallel structures

Abstract A structure response control approach which uses controlled interactions between two parallel structures (a primary structure and an auxiliary structure) to reduce the seismic response of the primary structure (P-structure) during earthquake excitation, is proposed. Three strategies of the control approach, including optimal passive control, semi-active control, and active control are examined. The optimum passive-coupling elements between two parallel structures under different circumstances are firstly investigated. Then, emphasis has been placed on the derivation of a simple effective algorithm for semi-active control which guarantees the power absorption of the required control force from the P-structure at every time step. Finally, numerical results in the frequency and time domains are presented to demonstrate the effectiveness of these proposed control strategies. The comparison of the structure response time histories when subjected to El Centro 1940 ground excitation with different control methods also illustrates that the semi-active control based on optimum passive coupling element can achieve improvement in reducing the response of P-structure compared to the passive control and is almost comparable to the active control system with the same degree of magnitude of control force, and that the proposed instantaneous power absorption semi-active control algorithm is always superior to conventional linear control law.

Earthquake and tsunami questionnaires in Banda Aceh and surrounding areas

Purpose – The paper aims to study the effects of the tsunami that affected Banda Aceh in 2004.Design/methodology/approach – During a survey by Japanese researchers in Banda Aceh and surrounding areas in Indonesia after the great Sumatra earthquake, questionnaires were distributed to the people affected by the earthquake and tsunami. The purpose of the questionnaires was to collect information of what happened and what were expected by the affected people to be safe against future earthquake and tsunami. The questionnaires consisted of questions asking their experience during and after the earthquake and tsunami.Findings – One important result of the questionnaires shows that even if people had started running away just after the big earthquake, the percentage of expected survivors would have been less than 100 percent.Originality/value – The paper shows that education, socialization (software) and escape structures, warning system, wave resisting structures (hardware) are important factors for people to b...

The influence of natural hazards on urban housing location

Abstract The effects of natural hazards on urban housing location are investigated, using as an example seismic damage. The seismic damage function is allowed to arbitrarily vary in two-dimensional (r, θ) space rather than the usual one-dimensional models of Mills, Muth, Alonso, etc. Damage is assumed to only affect capital inputs (i.e., the structure), not land. Under the influence of expected damage, the population and CBD (treated as a point) are seen to shift toward lower expected damage. It is found that the relative importance of damage increases as the capital productivity parameter (b) of the Cobb-Douglas production function increases.

Passive and Semi-active Pseudo Negative Stiffness Control of Highway Bridge Benchmark Problem

Active and semi-active control methods for reduction of the dynamic response of structures are emerging and some are being implemented in buildings and bridges. This vast growing technology ows to recent developments of sensing and digital control techniques. Semi-active control is a promising approach for the seismic response reduction in which the control offers the adaptability of active control without requiring the associated large power sources [1-10], since the external energy is only used to modify the dynamic properties (e.g., stiffness, damping, and friction level) of semi-active device during an earthquake attack. Therefore, the semi-active control devices can be considered as controllable passive devices. The problem lies on what algorithm should control this device so that the structural response is favorable under earthquake excitation. Earthquake input energy absorption capability of structural components described by hysteretic loops plays the key role in ensuring proper seismic performance of structures. Members that have stable and large hysteretic loops are considered as ductile have been proved successful in reducing seismic responses. For very important structures, energyabsorbing devices are added to structures so that the hysteretic loops are localized only at the devices. For seismic isolation techniques, for example, hysteretic loops are also employed at the isolation devices to reduce excessive displacement. In this study, passive and semi-active control devices combined with base isolation bearings are used to generate desirable hysteretic loops. The control algorithm is designed so that the combination of the variable damper and isolation bearings yields the desirable hysteretic loops [6-11]. SEMI-ACTIVE SKYHOOK CONTROL SYSTEM

Development of Negative Stiffness Dampers for Seismic Protection

In the first part of this study, theoretical and numerical evaluation of negative stiffness appearing in the skyhook control is conducted. The skyhook control is widely known for the vibration control method in the mechanical engineering field. The skyhook control can also achieve absolute response reduction. In order to realize a negative stiffness, however, the control force that accelerates the deformation should be generated. At present, such a performance is achieved only by using loading actuators or semi-active devices with sophisticated controllers and sensors. In the second part of this research, a new damper realizing a negative stiffness and stable energy dissipation in a passive manner is proposed, and its dynamic performance is investigated through large-scale shaking table tests. It is confirmed that the innovative negative stiffness passive damper reduces both the absolute acceleration and the relative displacement of a bridge model.

FUNDAMENTAL PEFORMANCE EVALUATION OF ENERGY DISSIPATION DEVICE CONSISTING OF MULITIPLE LAMINATED RUBBER ASSEBLIES BY MEANS OF CYCLIC LOADING TESTS

既設の長大鋼斜張橋の耐震補強のために採用が検討されている積層ゴムダンパーの検証のため，４ヶの積層ゴムを対称配置した積層ゴムダンパーの構造を可能な限り模した積層ゴムダンパー試験体を対象とした正負交番載荷試験を行い，ダンパーとしての基本性能を調査した．また，縮小モデルに準静的載荷試験を行い，制震ダンパーとしての性能評価を行った．積層ゴムダンパーの等価剛性および等価減衰定数は，積層ゴムの面圧依存性が小さいことが見出された．また，ダンパーを構成する積層ゴム体各々の単体試験で算出されるエネルギー吸収能に比べて，その後に積層ゴムダンパーの載荷を行った場合では，エネルギー吸収能が低下する結果が得られた．せん断ひずみ300％以上の変形を与えるせん断変形性能試験においても積層ゴムは破断に至らず，十分なエネルギー吸収能力を保持することを確認した．

Dynamic Interaction Effects of Soil-Offshore Structure Systems

The dynamic response analysis plays important roles on the design of an offshore structture subjected to random sea waves and strong earthquake motions. The stationary random sea state is represented with the one-dimensioned Bretschneider type power spectrum. The wave force function is evaluated using the modified Morison equation which is expressed with the small amplitude wave theory. The earthquake motion is also represented with the Tajimi-Kanai’s power spectrum which is utilized for stationary filtered white noise of input ground acceleration. Since it seems that the soil-structure interaction has significant contributions on the dynamic response evaluation, the soil-pile foundation is idealized as system of spring-dashpot elements which can be evaluated with the impedance functions. The governing equation is obtained by substructure method which is most efficient to analyze the dynamic soil structure system. The analysis is carried out in the frequency domain using the mode superposition principle.

Earthquake Failure Mechanism of Hysteretic Structures with Stress-Strain Based Modeling

This paper presents the earthquake response and failure mechanism of inelastic reinforced concrete structures with varying axial forces. Material nonlinearity of an RC element is evaluated by using a so-called “fiber model” based on stress-strain relation. Accuracy of constitutive laws is examined from comparison of analytical and experimental moment-curvature relations. Failure mechanism is then examined with a damage index that includes effects of stiffness degradation and accumulated hysteretic energy absorption. A step-by-step integration of the equation of motion is used to calculate earthquake response of a structure. The method gives a very accurate estimation of inelastic earthquake response and deterioration process of RC structures.