報告書番号

N05002

タイトル（和文）

経年化したダム洪水吐きゲートの構造信頼性評価方法の提案

タイトル（英文）

Structural Reliability Evaluation Method for Aged Dam Spillway Gates

概要 （図表や脚注は「報告書全文」に掲載しております）

著者らは、ダム洪水吐きラジアルゲートの開閉時における脚柱基部の座屈問題に着目し、経年を考慮した解析的検討を行い、構造信頼性評価方法を提案した。解析モデルとして日本国内で用いられている設計参考例を対象とし、鋼材の腐食と支承部（トラニオンピン）の摩擦抵抗を考慮した上で、設計洪水位と設計震度に対する解析を行った。腐食については日本国内で取得したデータ、トラニオンピンの摩擦については計測事例が少ないことから専門家アンケートを行って劣化モデルを作成した。パラメータ解析と各劣化要因の起こりやすさを踏まえた評価から、対象構造物の構造信頼性を算出した結果、設計水位に対する破壊確率、設計震度に対する破壊確率ともに10のマイナス５乗レベルとなり、他の一般土木構造物と同等以上の性能があることを確認した。また、維持管理業務に活用するため、破壊確率と許容応力の関係に基づき評価した簡易式を例示した。

概要 （英文）

The authors considered that the phenomenon of greatest concern was the buckling of the support arms during dam spillway radial gate opening operation and discharge, performed analytical investigations that incorporate the aging factor, and proposed a structural reliability assessment method. Corrosion of steel parts and sliding friction of the support bearing (trunnion pin) were considered as factors contributing to aging. On the other hand, the design flood level and design seismic intensity were considered as the loads. Past records in Japan were used for the rust states. Since few survey examples are available for trunnion pin friction, a deterioration model was created based on a questionnaire survey answered by specialists in Japan. In this report, an evaluation method of structural reliability is discussed for aged dam spillway gates. First, we clarify the significance and necessity of evaluating the structural reliability of aged dam gates. Second, the structural reliability evaluation method for radial gates is proposed as follows; (i)The relationship between friction coefficient of support bearings (trunnion pins) and its frequency is evaluated statistically based on expert opinions to be incorporated in the probabilistic model. Also, the relationship between decrease of plate thickness due to corrosion and its frequency is evaluated statistically by using the observed data. (ii) By conducting Finite Element Analyses corresponding to the set of trunnion pin friction and corrosion, the probability density function concerning the stress variable is estimated taking into account the occurrence frequency of deterioration parameters. (iii) Failure probabilities of the target structure are calculated by using information on the structural intensity variable R and the stress variable S. A design reference in Japan is adopted as the analytical model in this report. Investigation results show that the failure probabilities Pf for the design flood level and for the design seismic intensity are both evaluated as 10**{-5}. A comparison with other civil engineering structures indicates that the results obtained from Japanese design standards for dam spillway radial gates stood well above average. In addition, the authors discuss the relation between failure probability and allowable stress for maintenance and operation works.

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