Aiko Furukawa

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.

VULNERABILITY ASSESSMENT OF NON ENGINEERED HOUSES BASED ON DAMAGE DATA OF THE 2009 PADANG EARTHQUAKE IN PADANG CITY, INDONESIA

Several powerful earthquakes have struck Padang during recent years, one of the largest earthquake event was an M 7.6 that occurred on September 30, 2009 and caused more than 1000 casualties. Following the event, A 12-site microtremor array investigation to gain a representative determination of the soil condition of subsurface structures in Padang has been conducted. From the dispersion curve from the array observations, the central business district of Padang corresponds to relatively soft soil condition with Vs30 less than 400 m/s. Because only one accelerometer was existing, the 2009 Padang earthquake was simulated to obtain peak ground acceleration for all sites in Padang city. By considering the damaging data of the 2009 Padang earthquake for engineered houses, Seismic risk vulnerability estimation of non-engineered houses for rock, medium and soft soil condition can be obtained, and also estimate the loss ratio based on the ground response, seismic hazard of Padang and the existing damaged to non-engineered structure houses due to Padang earthquake in 2009 data for 500 return periods of earthquake events.

Evaluation of Damage to a Historic Masonry Building in Nepal through Comparison of Dynamic Characteristics before and after the 2015 Gorkha Earthquake

On April 25, 2015, a Mw 7.8 earthquake struck the Gorkha district of Kathmandu, Nepal. In Patan, vibrational characteristics of a 300-year-old two-story masonry building near Patan Durbar Square had been measured prior the Gorkha earthquake. In the inspection of the building after the Gorkha earthquake, several new cracks were found. The vibrational characteristics of the building were measured again, and it was found that the natural frequencies after the earthquake were smaller than those before the earthquake, indicating the reduction of the stiffness. Finite element models of the structure representing pre- and post-earthquake conditions are established so that the natural frequencies match the pre- and post-earthquake measurements and the structural damage is identified based on the stiffness reduction. Finally, the dynamic analysis of the finite element model of the building in the pre-earthquake condition using the observed ground motion record during the Gorkha earthquake as the input is conducted, and the structural response of the building during the Gorkha earthquake is discussed.

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．