本研究主要目的是探討高拉力鋼筋(SD690)混凝土梁(New RC梁)構件受疲勞荷載作用下，對於橋梁等需承受高週次疲勞之行為，探討New RC梁與一般RC梁疲勞行為是否有差異。 故本研究主要以鋼筋混凝土梁進行單向覆載之疲勞實驗，探討SD690鋼筋於不同應力差幅(fr)之反覆載重作用下，所對應之疲勞壽命。並於各疲勞週次，記錄梁中點撓度、混凝土應變及裂縫變化，探討New RC梁受覆載時在梁勁度變化情形。 統計至目前New RC梁疲勞試驗結果[30, 31]，發現SD690高拉力鋼筋之疲勞特性與Helgason等人[5]所提出之一般鋼筋疲勞壽命經驗公式之計算結果相近。另外，對於鋼筋竹節尺寸(r/h)的研究結果顯示，r/h值越大鋼筋之疲勞壽命亦越大。而SD690鋼筋在發生疲勞破壞後，其疲勞裂紋面積所佔比例相對較小，不同於SD420W鋼筋之疲勞特性。實驗結果顯示，配置壓力鋼筋之RC梁可以有效抑制混凝土潛變應變的增長及斷面勁度之衰減。 ;The main purpose of this research is to investigate the fatigue behavior of high-strength steel (SD690) concrete beams (New RC beams) subjected to fatigue loads and find the difference of the fatigue behavior between New RC beams and general RC beams. The fatigue loading test is performed to observe the fatigue behavior of RC beams with SD690 steel reinforcement. In the test, the mid-span deflection, concrete strain, the maximum width of the concrete crack, and the compressive strain of top sectional concrete are measured for studying the fatigue characteristics of the New RC beams. The statistics on the current fatigue test results of New RC beams [30, 31] has shown that the fatigue characteristics of SD690 high tensile steel bars is similar to the calculation results of the general fatigue life empirical formula proposed by Helgason et al. [5]. In addition, the results for the steel bars of the ratio of the radius of the lug curve (r) to the height of the lug(r/h) showed that the greater the r/h value had, the greater the fatigue life of the steel obtained. The fatigue crack area of the SD690 steel bar is relatively small after fatigue failure, which is different from the fatigue characteristics of the SD420W steel bar. Experimental results also show that RC beams with compression steel bars can effectively restrain the growth of concrete creep strain and the degradation of the sectional stiffness.
