Published papers

Effectiveness of probability-based explanation of seismic capacity was investigated based on a questionnaire survey. Dynamic analysis using a two-degree-of-freedom model of a wooden house was conducted to formulate a fragility curve. Then, probability of damage in a certain period was evaluated based on the fragility curve and a seismic hazard curve. An empirical formula of relation between JMA intensity and peak ground velocity was used to evaluate probability of damage under a certain seismic intensity. About 55% of the respondents answered that probability of damage under a certain seismic intensity was the easiest among presented explanations of seismic capacity, and less than 10% of the respondents chose probability of damage within a certain period as the easiest explanation. In explaining several seismic capacities for comparison, showing only ratio or difference of the probabilities of damage was not as easy to understand as showing each probability value. The respondents had bias of overrated seismic risk first. But a house with high seismic capacity was preferred even after information on proper risk of seismic damage and additional cost to improve seismic capacity were provided. These results suggest that probability of damage is useful to explain seismic capacity of house.

The questionnaire survey was conducted to clarify effective explanation of seismic capacity of houses. The respondents were people who lived in Yokohama City, Kawasaki City or 23 Wards of Tokyo, who wanted home ownership for 20 to 30 years in future, and who were 30 to 49 years old, and 759 valid answers were obtained. Questions regarding seismic risk perception and preference of seismic capacity of a house were asked through a Web page from November 1 to 2, 2006. It was observed that the respondents overrated seismic risk; about 60% of the respondents thought that they would experience strong ground motion of JMA intensity 7 in future and 85% thought a damaging earthquake would occur within 30 years in their or nearby town. In addition, the respondents underrated performance of a house with higher earthquake resistance grades. Risk of building collapse could be reduced to 1/5 by upgrading from Grade 1 to Grade 2 (1.25 times larger resisting force) and 1/10 from Grade 1 to Grade 3 (1.5 times larger resisting force). However, about 70% of the respondents did not think that the risk could be reduced to the above ratios. These results suggest that preference of seismic performance of a house can be changed by providing reliable risk information.

本論文は，大都市圏の地震防災性の向上に資する従来よりも効率的で，かつ，より説得力のある提言を行うことを目的として，提言の施策への反映状況や既往の提言の文章表現や構造を分析した。具体的には，既往の提言の文章の表現や構造を詳細に分析し，提言の各文章を主語，述語，目的語に分類し検討を行った。また提言を社会に発信するまでの手続き(体制)についても，関連する学会を対象に調査した。最終的に，今後，学会が提言を行う際に参考となるポイントについてとりまとめ，地震防災性向上に資する提言のあるべき姿を示した。

本論文は，大都市圏の地震防災性の向上に資する従来よりも効率的で，かつ，より説得力のある提言のあり方を検討することを目的として，土木学会や建築学会が兵庫県南部地震の後に行った提言の分析と提言を取り巻く環境の分析を行った。具体的には，地震被害や地震防災対策の全体像に対する既往の関連学会の提言の位置づけと，対象としてきた課題の分野を明らかにし，これらの提言が社会に及ぼした影響や提言を取り巻く環境の変化を，研究発表，科学技術研究費補助金，国の防災関連予算，及び関連新聞記事等の変化から定量的に分析した。

Regarding damage detection of reinforced concrete (RC) structure using an impact hammer and a piezoelectric acceleration sensor, experiment and analysis were carried out to propose a reliable index to assess severity of damage to a member of RC structure. A test piece of a RC beam was used. First, the test piece was simply supported and two vertical downward forces were loaded monotonically to damage it. At some stage of damage severity, the test piece was moved out from the loading apparatus, and then was supported by urethane bearings. After that with an impact hammer, an impulse wave was given on the surface of the test piece in which downward forces were applied. The vibration (acceleration) of the normal direction of the surface was measured by the six accelerometers that were placed on the loaded and impact excited surface. Impact excitation was conducted at seven points. The above set of processes of loading (damaging) and measuring response to impact excitation was repeated until the test piece exhibited multiple visible cracks from the bottom to the top of the beam. The accelerograms were analyzed by the Fourier transform and some indices using not only the Fourier amplitude spectrum but also the Fourier phase spectrum were examined on the applicability for detecting damage.

For programs of earthquake disaster reduction, past studies have revealed that it is quite important not only to provide reliable risk information, but also to promote the communication with others for information exchange. The result of a questionnaire survey to homeowners supported this neighbors’ positive influence to retrofitting and also identified importance to provide engineering information on retrofitting plainly and to improve credibility of contractors of retrofitting work. Hence, interactive risk communication among homeowners, engineers and government officials is desired to assist comprehensive seismic risk management of homeowners. Based on the findings, programs to promote seismic risk management of houses are proposed from a viewpoint of effectiveness of risk communication.

Strong motion indices are analyzed on relevance to damage of two-story wooden structures. After nonlinear time history analyses of models with various stiffnesses for nine hundred input motions, a rank correlation coefficient are evaluated with respect to the relevance between intensity of an index and structural damage defined by a certain threshold of maximum story drift. It is clarified that the responses of linear single-degree-of-freedom systems with a particular elongated period and 20% damping ratio show fairly good correlation with the damages. It is observed that specific combinations of stiffnesses tend to disperse the damage, and consequently reduce the relevance.

衛星リモートセンシングを用いた被害把握技術の概要と中解像度画像を活用した被害推定技術の解説，ならびに近年日本により打ち上げられた陸域観測技術衛星による自然災害モニタリングの事例を紹介。

耐震性能を詳細に考慮した都市・建物の地震被害推定技術，ならびに衛星リモートセンシングを用いた被害把握技術について解説。

To propose more useful strong motion indices and to improve estimation accuracy of building damage, some strong motion indices (peak ground velocity, spectrum intensity, Japan Meteorological Agency seismic intensity, spectral displacement, etc.) are investigated with respect to correlation with damage of wooden structures. A nonparametric correlation coefficient, Spearman’s , is employed as an indicator of accuracy of damage estimation. Multiple input motions are used for nonlinear time history analysis of two-degree-of-freedom models of wooden structures, which have various combinations of story stiffnesses. As a damage model, maximum story drift angle is considered and three levels of threshold, 1/60, 1/30 and 1/15 rad are examined, which approximately correspond to minor, moderate, and major damage of a structure. Distributions of Spearman’s  of the strong motion indices are compared, and it is revealed that displacement response of a linear single-degree-of-freedom system with a damping ratio of 20% and with the elongated period that is determined by a damage threshold, shows fairly good correlation with the structural damage.

It is important to maintain functions of a building such as providing medical services, performing production operations, and dwelling during and after an earthquake. Until now, vibration control devices have been devised and installed in many buildings. To maximize the control effects under the limited capacity of a control force, a method for constructing an evaluation function on the basis of the prescribed control objectives is proposed, in which the control objectives are expressed as dimensionless numbers using the required performance levels. The effectiveness of the proposed method is verified by a time-history analysis.

近年報告されているエレベータロープの地震被害を低減するため、アクティブマスダンパー(AMD)や連結制振などの建物用の制振装置を用いた制御手法を提案した。提案手法は建物とロープの両方の安全確保を目標とした線形二次ガウシアン制御に基づいている。提案手法の有効性を実証するため、超高層建物の縮小モデルであるアルミ製の4層試験体を用いた実験を行った。エレベータロープは銅の薄板でモデル化し、AMDを試験体の最上層に設置した。震動台実験を行った結果、提案手法はエレベータロープの応答を低減することを確認した。

屋内ガス配管用機械式継手の数値解析モデルを曲げ実験・震動台実験の結果に基づき2種類構築した。まず，硬化型特性を持つバイリニアばね・線形弾性ばね複合モデルを構築した。次に，Ozdemirモデル・線形ばね・ギャップクロージングばねに基づき非線形のヒステリシス特性を持つばねを構築した。震動台実験を再現する時刻歴応答解析を行い，モデルの妥当性の評価を行ったところ，後者のモデルは応答レベルが小さい場合に良好に実験を再現することを確認した。

An optimization method is developed for the structural and control systems of a multi-story building equipped with proportional-derivative (PD) controlled active braces. The method uses design response spectra to consider ground motions and employs the complex complete quadratic combination method to estimate the maximum response and the maximum control force. Both structural and control costs are minimized under the constraints of the maximum inter-story drift and the absolute acceleration responses. The proposed method is applied to the simultaneous optimization of a three-story building with PD-controlled active braces and it is demonstrated that the method can efficiently provide Pareto optimal solutions.

As a first step to establishing a reliable numerical simulation model for interior city-gas piping, some cases of shake-table tests for a partial-piping specimen were conducted. Static bending tests using almost the same supporting apparatus as the shake-table test were also conducted to obtain the mechanical characteristics of the clamp, the hanging bolt and the mechanical coupling, and simplified analytical models were investigated for the non-coupling specimen and for the with-coupling specimen. Finite element analyses (FEA) were then carried out for these models. The experimental data regarding the seismic response during the shake-table tests generally agreed with the FEA results. It was therefore inferred that the major structure of the analytical models proposed in this study is adequate to evaluate seismic safety for interior city-gas piping.

The 2011 off the Pacific coast of Tohoku Earthquake triggered liquefaction of soil in wide areas of Japan. In particular, a number of damaged houses were found in the land reclamation areas of the Kanto region. Some residents who lived in houses that were tilted by liquefaction complained of health disorders. We report on the results of a questionnaire survey of residents in Mihama Ward, Chiba City, about the characteristics of their houses, earthquake damage, health disturbances, and so on. Probability models of health disturbance with respect to house tilt angle due to liquefaction are constructed based on the survey data. The probability that a respondent experienced health disturbance was found to be considerably higher when the tilt angle exceeded 0.013 rad.

When both a building and its equipment have a vibration controller, the controller of the equipment should consider the behaviour of the building and vice versa. First, we classified control schemes according to the amount of state variables communicated between the controllers and the type of control objectives. Then, a high-rise building with an elevator system is analysed under seismic excitation to compare the performance of the classified control schemes that use a linear quadratic regulator. It is observed that the story drift and the response of the elevator rope are best reduced when all the state variables are communicated, but they can be sufficiently reduced even if not all the state variables are communicated.

To maximize the control effects under the limited capacity of a control force, a control method based on variable gain feedback control for a coupled model of a building and an elevator is proposed. In this method, a controller selects a proper control objective and prevents the saturation of the control force considering the intensity of the ground motion and the associated building response level. For preventing saturation, the maximum required control force is estimated on the basis of the square root of sum of squares (SRSS) method using the input ground acceleration. The effectiveness of the proposed method is verified by a time-history analysis. The analysis is performed using the long-period ground motion record of the 2011 off the Pacific coast of Tohoku Earthquake, 100 simulated waves with the peak ground velocity of about 25 cm/s2 and 300 waves obtained by scaling the simulated waves.

Global and local responses of steel frames are simultaneously simulated using a high-precision finite element (FE) analysis considering composite beam effects. A detailed analysis is first carried out for a 4-story building frame subjected to seismic motion. The steel material is modeled using a piecewise linear isotropic-kinematic hardening that can incorporate a yield plateau. Static cyclic response analysis is then carried out for a compo-site beam supported by a column. It is demonstrated that the experimental results, which show asymmetric behaviors due to contact of the slab to the column, can be simulated accurately using the high-precision FE-analysis.