Hisanori Otsuka

Structural damage detection method using uncertain frequency response functions

A structural damage detection method using uncertain frequency response functions (FRFs) is presented in this article. Structural damage is detected from the changes in FRFs from the original intact state. The measurements are always contaminated by noise, and sufficient data are often difficult to obtain; making it difficult to detect damage with a finite number of data. To surmount this, we introduce hypothesis testing based on the bootstrap method to statistically prevent detection errors due to measurement noise. The proposed method iteratively zooms in on the damaged elements by excluding the elements which were assessed as undamaged from among the damage candidates, step by step. The proposed approach was applied to numerical simulations using a 2D frame structure and its efficiency was confirmed.

Optimal yield level of bilinear seismic isolation devices

The yield level of an insulator is one of the important parameters which are related to responses and absorbing energy under seismic input energy in isolated structures. The purpose of this paper is to determine the optimal ratios of yield force of the isolator (Qy) to the total weight of the structures (W). To obtain the optimal ratio, 1044 two-degree-of-freedom isolated bridge models, which have bilinear isolators, were selected. These 2-DOF isolated bridge models with superstructure isolation can consider pier flexibility and various parameters of the isolator. Two formulas for determining the optimal yield ratio are proposed and compared with the previous researches. RAE (the ratio of absorbed energy by the isolator to the total input energy) is related directly to structural responses, and Optimal Yield Ratio (OYR), defined as a yield ratio at maximum RAE, can be obtained from the relationship between RAE and Qy/W. Here, we found that RAE is a reliable factor to evaluate OYR, and it is proportional to earthquake amplitudes under the same kinds of earthquake loadings. Using the proposed formulas, OYR is determined and the optimal yield force of the isolator can be obtained easily and reliably at a seismic isolation design stage. Copyright

SIMPLE ESTIMATING METHOD OF MAXIMUM AXIAL STRAIN OF IRREGULARLY-SHAPED GROUND DURING EARTHQUAKE ASSUMING CONSERVATION OF ENERGY

本研究では，基盤面および地表面段差型不整形地盤の地震時最大軸ひずみを簡易に推定する手法に関して検討を行った．まず，最大軸ひずみの特徴を調べるために，層厚·傾斜幅·せん断波速度の様々に異なる53通りの不整形地盤の有限要素解析を行った．最大軸ひずみの推定式は，不整形性によって生じる速度差が生む運動エネルギーが，地盤がひずむことによるひずみエネルギーで受け持たれるとの仮定の下，段差部両端の水平地盤の最大速度応答差の1次式として得られた．推定式に必要な速度応答差を算定する手法として，1自由度モデルと成層地盤モデルを用いた1次元地震応答解析を採用した．有限要素解析結果と推定式による簡易推定結果の比較を行い，簡易推定手法の有用性を検討した．

INVESTIGATION OF THE CAUSE OF DAMAGE AND THE REINFORCEMENT OF A STEEL TOWER FOUNDATION COLLAPSED IN 1999 CHI-CHI EARTHQUAKE

1999年に発生した台湾集集地震により, 我国では例の無い送電鉄塔の地震被害が発生した. 本研究では, まず超高圧送電鉄塔に関する最新の被害調査結果をまとめた. 次に, 架渉線-連成系の影響を簡易に考慮した鉄塔の単体モデルを提案した. 更に, 台湾で最大の345kV鉄塔で唯一完全倒壊した#203鉄塔が片継脚鉄塔であることに着目し, 地震時の振動により倒壊した可能性を解析的に検討した. その結果, 付近で観測された地震波を入力した場合, #203鉄塔は脚部に全体座屈が発生する可能性が高いとの知見が得られた. 最後に, #203鉄塔の復旧時において基礎形式がつなぎばり基礎に変更されたことを受けて, 基礎の不同沈下時の鉄塔の耐震性向上策として, つなぎばり基礎の有効性を示した.

Construction of generalized neural network system for recognizing several non-linear behaviors

Generally, in formulating a spring-mass model for hysteric behavior of materials and members with inelastic characteristic, a mathematical model based on load-deformation experimental results is considered. The model must approximate the inelastic hysteresis of the material. However, assumption of material’s behavior using mathematical models is crucial, since it may cause serious errors if inappropriate model is applied for a particular situation. This paper describes multiple layered neural network to simulate the non-linear hysteretic behavior like Ramberg-Osgood model, modified bilinear model and Takeda model. In this study, based on the pattern recognition ability of neural network, non-linear hysteretic behavior was modeled by the network directly without replacing it with a mathematical model. The effectiveness and applicability of the network in numerical analysis were evaluated. Generalized multiple layered neural network to evaluate non-linear hysteretic curve was constructed. The network can recognize well the three types of hysteretic curve. The network is available as a subroutine of non-linear spring in dynamic response analysis.Copyright

APPLICATION OF NEURAL NETWORKS TO THE DYNAMIC ANALYSIS OF NONLINEAR HYSTERETIC BEHAVIOR OF HIGH DAMPING RUBBER BEARINGS

本研究ではニューラルネットワークの有する関数近似能力に着目し, 高減衰積層ゴムの非線形履歴挙動を対象として学習済みのニューラルネットワークが動的解析を行う際の数値演算サブルーチンとして利用可能であること示した. 有限な教師データに基づき学習を行った階層型ニューラルネットワークが非線形履歴挙動に対して十分な模擬精度を有することを高減衰積層ゴムの動的載荷実験結果との比較により確認した. また, 動的載荷実験より得られた有限な教師データに基づき学習を行った階層型ニューラルネットワークが未学習の挙動を対象とした動的解析を行う際の数値演算サブルーチンとして利用可能であることを, 実地震波を用いた高減衰積層ゴムの振動台実験結果との比較により検証した.

Study On The Seismic Isolation Of High-elevatedRigid Frame Bridge With Double Deck

The purpose of this paper is to investigate dynamic characteristics of a base isolated bridge for transverse direction and to study the effectiveness of base isolation. This bridge is rigid frame with double deck and its center of gravity is relatively high compared to its pier distance in transverse direction. It indicates that tensile reaction would occur at the isolator during strong earthquake. As a result of 3-dimensional time history analysis of a non-isolated bridge, this kind of bridge is unstable for an overturning in the transverse direction and must be prepared for overturning. But according to the survey of the suitable characteristics of the isolator, tensile reaction at the isolator can be reduced in practical terms, and other seismic responses such as bending moments and shear forces are also reduced remarkably.