Kohju Ikago

Modal Response Characteristics of a Multiple-Degree-Of-Freedom Structure Incorporated with Tuned Viscous Mass Dampers

Abstract A new seismic control device using a ball screw mechanism as an apparent mass amplifier has been developed, which is referred to as the tuned viscous mass damper (TVMD). This device enables effective seismic control using a tuned mass. For a multiple-degree-of-freedom (MDOF) seismic control system incorporated with the TVMD, a design method based on numerical optimization has been previously presented by the authors. However, simpler design methods that are suitable for a practical design have not yet been presented. At the preliminary design stage, it is essential for structural designers to understand the seismic response characteristics of the structure in terms of modal responses. However, a complex-valued eigenvalue analysis, which most structural designers are unfamiliar with, is required for accurate seismic response estimation. This is because the seismic control system incorporated with TVMDs is nonproportionally damped. In this paper, the authors propose a seismic response estimation method that does not require a complex valued analysis. An analysis example illustrates that the square root of the sum of the square (SRSS) of the maximum modal responses derived from the undamped real eigenvalue analysis gives a good approximation in practical terms.

Causal Realization of Rate-Independent Linear Damping for the Protection of Low-Frequency Structures

AbstractThe devastating low-frequency ground motions of the 2011 Great East Japan Earthquake produced large displacements in low-frequency structures previously thought to be safe, including base-i...

A STUDY ON INVERSE CONVERSION FROM LINEAR MODEL FOR DESIGN TO NON-LINEAR MODEL FOR THE TUNED VISCOUS MASS DAMPER

*1 (株)免制震ディバイス技術部 博士(工学) (〒 102-0075 東京都千代田区三番町 6番 26 号) *2 (株)免制震ディバイス技術部 *3 THK(株) ACE 事業部 *4 東北大学災害科学国際研究所 教授・博士(工学) *5 東北大学 名誉教授・工博 *1 Technical Dept., Aseismic Devices, CO., LTD., Dr. Eng. *2 Technical Dept., Aseismic Devices, CO., LTD. *3 Amenity Creation Engineering Division, THK CO., LTD. *4 Prof., International Research Institute of Disaster Science, Tohoku Univ., Dr. Eng. *5 Emeritus Prof., Tohoku Univ., Dr. Eng. 本稿は文献 9) における既発表内容を改めてまとめたものである。 ON INVERSE CONVERSION FROM LINEAR MODEL FOR DESIGN TO NON-LINEAR MODEL FOR THE TUNED VISCOUS MASS DAMPER

RECONNAISSANCE OF DAMAGED STEEL SCHOOL BUILDINGS DUE TO THE 2011 TOHOKU EARTHQUAKE

An outline of a reconnaissance of steel school buildings damaged by the 2011 Tohoku earthquake is presented. In this reconnaissance, a total of 216 facilities have been investigated by the Steel Structure Working Group of the Subcommittee on Seismic Performance of School Buildings, Architectural Institute of Japan. The damage to structural elements, connections, non-structural elements, foundation and surrounding soil, as well as the details including building history and seismic retrofit have been recorded and the overall damage has been evaluated based on the “Standard for Post-earthquake Damage Evaluation of Damaged Buildings” published by the Japan Building Disaster Prevention Association. Not only seismic damage but damage caused by the devastating tsunami are also covered. Detailed analysis of the damage to individual structural and non-structural components are presented in following papers.