Yoichi Mukai

Investigation of Damage in and Around Kathmandu Valley Related to the 2015 Gorkha, Nepal Earthquake and Beyond

An earthquake with a magnitude of 7.8 (Mw) occurred at 11:56 NST (local time) on 25 April 2015, in the central part of Nepal (Gorkha).We organized a damage survey team and dispatched it to the affected area for several periods following the earthquake (May 26 to June 3: first trip, June 17 to 24: second trip, August 16 to 21: third trip and October 27 to November 2: forth trip) to investigate the damage and collect data. We found traditional construction methods are stronger than imagined. Many traditional earthquake-resistance technologies exist in Nepal. The first and second surveys were to collect timely statistical information on the damage to brick and stone masonry buildings and to confirm the availability of data and their sources for subsequent surveys. We also carried out a first-hand building damage survey in selected areas. The investigation of the strong-motion data set from the USGS Center for Engineering Strong Motion Data includes information from stations in Nepal that continued to function throughout the main shock and the several subsequent strong aftershocks of the 2015 earthquake. The third and fourth surveys were to collect the every building damage survey in selected areas. The motivation behind the survey was to obtain ground truth data for the calibration and improvement of a wide-area damage estimation system that uses satellite data; the system is currently under development by National Research Institute for Earth Science and Disaster Prevention (NEID) and the Japan Aerospace Exploration Agency (JAXA). A survey of the degree of damage was conducted for every house in Sankhu and Khokana by the European Macroseismic Scale (EMS) -98. This report outlines the findings of this investigation team into various aspects of the earthquake disaster in the Kathmandu Valley. The motivation behind the survey was to obtain ground truth data for the calibration and improvement of a wide-area damage estimation system that uses satellite data. Field surveys confirmed that the severely damaged urban area was well detected by the decrease derived from the ALOS-2 satellite SAR data. The higher classification accuracy for non-damaged area helps to detect the damaged urban area using this technique, immediately after a disaster.

Development of Resilient Seismic Response Control with a Semi-active System

An approach to develop resilient structures using seismic response control with a semi-active system is introduced. Actual system performance of control device installing to the practical building structure is evaluated with a RTHS (real-time hybrid simulation) test and an online simulator with the shaking table of Kobe University is used. Specifications of this online simulator system are explained in detail. As one example operating the RTHS tests, performance evaluation for the mid-story isolated building structure controlled by a semi-active device is focused. First, mechanical properties of the testing apparatus of the MR (magneto-rheological) rotary inertia mass damper used for semi-active control are quantified by the device tests, and then numerical simulation model of this damper is provided. Next, the RTHS test studies are operated and the test results are compared with the pure numerical simulation results by the fully modeled analyses. Validity of this online simulator and exactness of numerical model of the semi-active damper are confirmed. Moreover, reproducibility and reliability of the operation for the RTHS tests are evaluated by observing the displacement and the acceleration generated on the shaking table. As a result, it is assured that both the target displacement and acceleration of the shaking table were accurately reproduced under the real-time calculation in this online simulator. And it is confirmed that performance evaluations for the actual test specimen of the semi-active control device were also accurately done through the RTHS test method by using the shaking table.

Response reduction methods for base isolated buildings with collision to retaining walls

This paper proposes a new damper that can change the damping force depending on the response displacement and response velocity. The proposed damper reduces the damage of seismic-isolated structures which undergo excessive deformation during huge earthquakes, without lowering the performance of the seismic-isolation system during medium to small magnitude earthquakes. We investigate the effects of using the proposed attenuator on the responses of a superstructure model to seismic motion that causes collision with retaining walls. An experiment using a shaking table is conducted, and the results from the test are compared with those from numerical analyses. The test results agree approximately with the numerical analysis results except for the absolute acceleration results in collision cases.

DETAILED FEM ANALYSIS FOR FULL SCALE STEEL STRUCTURE CONSIDERING FRACTURE OF BEAM ENDS

Abstract. This paper reports a non-linear analysis of a steel structure using a large-scale and detailed finite element model considering fracture phenomenon. The shaking-table test results of a 3-story full-scale steel frame structure, which were carried out at E-defense in 2013, are evaluated analytically in this paper. The analytical model used in this study is intended to replicate adequately entire shape of target steel frame structure specimen, assembling huge numbers of tiny finite elements. The damage index is introduced as the fracture criterion on steel members model for execution of FE simulations. Elements whose damage index has been reached to 1.0 are eliminated in our way of FEM analyses. The damage index shows a good correlation with the occurrence of the fracture observed in the experimental test. The timing of the first fracture of the beam end in the analysis mostly match well to that of the experiment. In addition, the structural responses obtained by the analysis agree with those of the experiment.