報告書番号

U88061

タイトル（和文）

フィルダムの動的解析における地下逸散減衰の評価

タイトル（英文）

ESTIMATION OF RADIATION DAMPING IN DYNAMIC ANALYSIS OF FILL DAMS

概要 （図表や脚注は「報告書全文」に掲載しております）

フィルダム等の土構造物の地震応答解析にあたって応答に大きな影響を与える地下逸散減衰の評価法として，材料減衰に逸散減衰分を上乗せする“等価逸散減衰定数”による方法が従来用いられている。本研究では解析精度の向上を図る目的で，モデル境界で逸散波を吸収する機能を取り入れた地震応答解析プログラム“ＮＯＤＡＬ－２”を開発し，同プログラムを用いたパラメーターサーベイ等から，等価逸散減衰定数の適用性，フィルダムー地盤間の動的相互作用特性に関する諸検討を実施した。等価逸散減衰定数については，ダムー地盤間のインピーダンス比が０．５程度以下の場合にはその適用性が示されたものの解析精度の向上を期するためには，波動逸散が考慮できる解析手法を用いることが望ましいこと，また，フィルダム－地盤間の動的相互作用特性については，地下逸散減衰に及ぼす入力の周波数特性，ダム－地盤間のインピーダンス比等の影響を明らかにした。

概要 （英文）

IN THE SEISMIC RESOPONSE ANALYSIS OF SOIL STRUCTURE SUCH AS ROCK FILL DAM RADIATION DAMPING IS A FACTOR THAT IS CONSIDERED TO BE INFLUENTIAL. SO FAR,IN MANY CASES THE EFFET OF RADIATION DAMPING HAS BEEN TAKE INTO ACCOUNT USING EQUIVALENT RADIATION DAMPINGIN WHICH RADIATION DAMPING IS EVALUATED AS INCREMENT OF MATERIAL DAMPING. HOWEVER,AS TO THE ESTIMATION OF EQUIVALENT RADIATION DAMPING A THOROUGH INVESTIGATION HAS NOT BEEN MADE YET. IN THIS REPORT,AT FIRST GENERAL CHARACTERISTICS OF RADIAATION DAMPING IS INVESTIGATED FROM THE RESPONSE ANALYSIS OF SIMPLE 1-D SHEAR WEDGE AND SHEAR BEAM MODEL FOR DAM-GROUND SYSTEM. AND 2-D FEM PROGRAM ORIGNALLY DEVELOPED FOR SEISMIC RESPONSE ANALYSIS OF SOIL STRUCTURE IS IMPROVED SO THAT IT CAN TAKE INTO ACCOUNT THE EFFECT OF RADIATION DAMPING. FROM PARAMETER STUDY USING THIS PROGRAM,EQUIVALENT RADIATION DAMPING IS ESTIMATED ACCORDING TO IMPEDANCE RATIO BETWEEN THE DAM AND THE GROUND AND ALSO THE APPLICABILITY OF THE EQUIVALENT RADIATION DAMPING IS INVESTIGATED. AS A RESULT OF THIS STUDY,THE FOLLOWINGS ARE MADE CLEARE: (1) FROM THE ANALYTICAL RESULTS WITH 1-D MODEL,EQUIVALENT RADIATION DAMPING INCREASES MONOTONICALLY WITH FREQUENCY, AND IS PROPORTIONAL TO THE RECIPROCAL OF IMPEDANCE RATIO AND THEEFFECT OF MATERIAL DAMPING OF THE DAM IS SMALL. (2) RESULTS OF RESPONSE ANALYSIS WITH 2-D FEM USING EQUIVALENT DAMPING WITH BOUNDARY CONDITION OF RIGID BASE AGREE WELL WITH THAT USING VISCOUS DAMPERS AT THE BOTTOM WHERE THE IMPEDANCE RATIO IS SMALLER THAN 0.5 OR SO. AND THE VALUE OFEQUIVALENT RADIATION DAMPING OF 5% PROVED TO BE CONSERVATIVE FOR ROCKFILL DAMS CONSTRUCTED ON USUAL BEDROCK. (3) RESULT OF RESPONSE ANALYSIS USING THE NEWLY DEVELOPED COMPUTING CODE AGREED WELL WITH THE OBVESEVATION OF THE ACTUAL DAM DURING EARTHQUAKE,AND THE AVAILABILITY OF THE CODE IS PROVED.

報告者

キーワード