本研究主旨在探討SD420W竹節鋼筋與SD690螺紋節鋼筋之疲勞行為，以及驗證疲勞累積損傷定理，故以鋼筋混凝土梁進行疲勞試驗。 試驗以反覆載重實驗方式，在不同應力差幅(fr)之作用下，對應之疲勞壽命，並記錄梁中點撓度及混凝土應變，且參考試驗記錄普通強度與高強度鋼筋混凝土梁之數據，探討SD420W竹節鋼筋與SD690螺紋節鋼筋之疲勞行為。 疲勞累積損傷之試驗乃利用S-N曲線，規劃數個應力差幅fr，並給定循環周次(Ni)，疲勞損傷值(D)為循環周次(Ni)與S-N曲線上對應之(Nfi)之比值。從Miner線性累積損傷理論可得知，當疲勞累積損傷值D=1時，試體將發生破壞，故以此理論可推測試體之剩餘壽命，透過此試驗驗證疲勞累積損傷定理。 根據先前高強度鋼筋混凝土梁疲勞實驗〔13、14〕與本次實驗結果發現SD420W竹節鋼筋與SD690螺紋節鋼筋之S-N曲線近似Helgason提出之經驗公式。而SD420W竹節鋼筋與SD690螺紋節鋼筋於疲勞斷裂時，兩者之疲勞裂紋面積，前者大約為80%，後者大約為6%；兩者之斷裂面，前者有受拉斷裂的現象，後者較為平整。 此次疲勞累積損傷試驗之結果，疲勞累積損傷值皆未達Miner線性累積損傷理論值D=1，然而根據Hashin修正之非線性Miner’s rule所得之疲勞累積損傷值與本實驗之結果有相當好的一致性。 ;The main purpose of this study is to investigate the fatigue behavior of SD420W deformed reinforcement and SD690 thread deformed reinforcement, and to verify the fatigue cumulative damage theorem, by means of the fatigue test testing on the reinforced concrete beams. The test is based on the repeated load test method, under the action of different stress differences (fr), corresponding fatigue life, and the measurement at the beam midpoint deflection and concrete strain. The testing will be performed to the normal strength and high strength reinforced concrete beams to mainly explore the fatigue behavior of SD420W and SD690 steel bars. The fatigue cumulative damage test is also carried out through the S-N curve to plan several stress difference amplitudes (fr). It was then given few limited cycle numbers(Ni) to evaluate the fatigue damage value(D), being defined as the ratio of the cycle(Ni) to the corresponding(Nfi). According to Miner’s linear cumulative damage theory when the fatigue cumulative damage value D=1, the tested beam will be destroyed. By such a experimental study, a proper fatigue cumulative damage theorem can be verified. According to the previous high-strength reinforced concrete beam fatigue test 〔13、14〕 and the results obtained from this research, the S-N curves of SD420W deformed reinforcement and SD690 thread deformed reinforcement are similar to the empirical formula proposed by Helgason. The fatigue fractural area is also measured to SD420W deformed steel bar and the SD690 thread deformed steel bar after fatigue fracture occurred, the fatigue crack area of the two types of bars is about 80% for SD420W bars, and about 6% for SD690 bars. The fracture surface of the SD690 bar is very flat in comparison with the SD420W bar. The result of the fatigue cumulative damage test showed the fatigue cumulative damage values did not match the Miner rule, which is linearly cumulated damage value to the theoretical D=1. However, the fatigue cumulative damage values obtained according to the Minin′s rule modified by Hashin were pleasantly consistent with the experimental results.
