本研究主要是承先前研究[17-19]，繼續執行New RC梁高週次疲勞試驗，以利探討出適合高拉力鋼筋之疲勞S-N曲線經驗式，藉此討論高拉力鋼筋之設計疲勞強度(f_(r,limit))，以供New RC橋梁結構在疲勞設計之參考。 目前SD690 New RC梁疲勞試驗結果顯示，大於D25直徑之大號數鋼筋S-N曲線有明顯的鋼筋直徑效應，直徑愈大，疲勞壽命愈短，可設計之疲勞強度則愈小；因此，提出一適合New RC梁之S-N曲線經驗式。 本研究亦探討New RC梁與一般RC梁在疲勞行為差異。比較鋼筋等級(f_y)、鋼筋表面形狀(r⁄h)、鋼筋直徑效應、鋼筋疲勞裂紋面積等差異。當中，亦觀察New RC梁EcIe值變化與高強度混凝土裂紋發展。最後探討設計之疲勞強度應為何，藉此評論疲勞設計規範如我國現行公路橋梁設計規範[1-2]及2020年版AASHTO LRFD橋梁設計規範[3]，是否合適用於New RC梁疲勞設計。 ;This study aims to continue the research conducted in previous studies [17-19] by performing high-cycle fatigue tests on New RC beams. The main objective is to establish an empirical S-N curve suitable for high-strength steel bar and subsequently discuss the design fatigue limit strength (f_(r,limit)) of high-strength steel bars. The results obtained from this study will provide valuable insights for fatigue design of New RC bridge structures. The current fatigue test results of SD690 New RC beams reveal a significant diameter effect on the S-N curve for larger-sized rebars (>D25). It is observed that as the diameter increases, the fatigue life decreases, leading to a lower design fatigue limit strength. Therefore, we propose an empirical S-N curve suitable for New RC beams. This study also investigates the differences in fatigue behavior between New RC beams and conventional RC beams. The comparisons include factors such as steel grade (f_y), rebar geometry (r⁄h), rebar diameter effect, and fatigue crack area. Additionally, the study observes the variation of the EcIe value and crack development in New RC beams. Finally, it explores the appropriate design fatigue limit strength, aiming to assess the suitability of current fatigue design specifications, such as the 2002 edition of the AASHTO LRFD Bridge Design Specifications [1-2], and the 2020 edition of the AASHTO LRFD Bridge Design Specifications [3], for fatigue design of New RC beams.
