本計畫因應目前國家推動節能減碳政策，傳統土木工程研究朝向新材料新工法創新研究開發。亦美國鋼筋混凝土新規範ACI318-19已將鋼筋強度提高至SD690級數，故本計畫新型高強度鋼筋材料(SD690/SD550鋼筋)之高強度鋼筋混凝土(New RC)研究相關課題甚為急切性。其中，此類新型高強度鋼筋混凝土耐震行為與裂縫之使用性能研究，已經過一系列整合型研究中告一段落，故目前將持續研究這一系列新型高強度鋼筋混凝土使用性能中之梁疲勞特性，以應目前New RC開始採用在橋梁、精密廠房、大型風機RC基礎等，其中這新材料鋼筋混凝土疲勞性能設計參數尤其需要。本研究所需鋼筋混凝土梁疲勞測試系統已先前在中央大學力學館建置完成，故本計畫主要以鋼筋混凝土梁疲勞實驗方式進行，用以討論新型鋼筋混凝土梁疲勞設計參數。2019年申請之計畫未獲准，先行由國家地震中心提供之材料，進行螺紋節SD690 鋼筋混凝土T形斷面梁受單向反覆力之疲勞測試，用以觀察高強度鋼筋混凝土梁之疲勞特性。目前結論為，公路橋梁在一般竹節鋼筋疲勞設計所引用之S-N經驗式，可適用於SD 690鋼筋之RC結構作疲勞壽命預測。然而從中發現，竹節凹點半徑與竹節高度之比值(r/hr )、應力差幅(fr)、高強度混凝土等對疲勞週次有明顯影響，有待進一步研究。今年申請內容，則主要規劃執行SD550/SD420 竹節鋼筋混凝土疲勞特性研究，配合先前SD690 螺紋節鋼筋之New RC疲勞測試結果，探討r/hr值、fr、高強度與一般強度混凝土等對RC結構疲勞壽命影響。本計畫亦規劃往後年度內容，則將研究New RC疲勞設計參數，如高拉力螺紋節鋼筋r/hr值規定、S-N設計經驗式、最大鋼筋應力限制、合理疲勞壽命週次、應力範圍限制值等設計參數。 ;Nowadays, the new-type steel reinforcement, in which the yield strength of the steel rebar is raised up to SD 690 grade, has been adopted into the new version design code of reinforced concrete structures, ACI 318-19. Such a rapid revolution in the new construction materials forms the research. The author has been involved in a series of researches on the seismic design of the New RC beams with SD 690 reinforcement since years ago. Then the new project is further to extend the study on the behavior of the new-type SD550/SD690 reinforced concrete (so called as “New RC”) at the ultimate stage to the behavior at the service load stage, specially focusing on the fatigue behavior of the New RC beams. Thus the results can be applied to the recent need for the design of New RC bridges, New RC high-tech manufacture plants, and the New RC foundation of the giant draught fans located around the Taiwan seashore. The project is proposed for a period of three years to investigate the fatigue design of New RC structures using SD690/SD550 screw bars. In the first and second year, several specimens of SD690/SD550 New RC T-beams will be tested under the cyclic fatigue loading. In the third year, the fatigue design parameters for the New RC beams will be found in accordance with the previous test results. These parameters include the S-N curves, the limit of the maximum bar stresses and stress ranges, and a rational fatigue life cycle of the New RC beams. Some specimens will also be tested to verify the Minor’s rule for finding the fatigue cycles subjected to multiple stress ranges. Meanwhile, the possibility of concrete fatigue, the degradation of concrete elastic modulus, and the effective stiffness of the New RC beams will be discussed.
