EVALUATION OF SEISMIC DESIGN STRENGTH REDUCTION FACTOR CONSIDERING CUMULATIVE DAMAGE AND SITE CONDITIONS

摘要

終局限界状態における，繰り返しに伴う累積損傷および地盤条件を考慮した必要耐力についての検討を行った。また，繰り返しによる劣化を考慮するための履歴則，および適切な劣化度合いを表すパラメータの設定法についての提案を行った。検討の結果，累積損傷を考慮した必要耐力および設計用地震力低減係数は地盤条件の影響が大きく，特に軟弱地盤の場合に顕著であった。%In current seismic design practice, the design yield strength of a structure is typically obtained through the use of strength reduction factor that reduces elastic strength demand to design levels. The strength reduction factor due to the inelastic behavior of structure is usually formulated in terms of target maximum ductility. This conventional approach fails to consider cumulative damage that occurs under cyclic loading. In this study, damage-based strength reduction factor was evaluated from the strength demands computed considering cumulative damage and different site conditions. The results indicate that the spectral shape of damage-based strength reduction factor has similarity with the conventional ductility-based reduction factor. An equivalent limit ductility ratio as a certain percentage of the monotonic ductility capacity may therefore also be used. This reduction depends on the monotonic ductility capacity and while it is not significantly affected by the natural period of the structure, it should be carefully evaluated in the case of soft soil site and where the natural period of the structure is close to the predominant period of ground motion. Simple expressions for estimating the damage-based strength reduction factor are also proposed.