前人研究結果顯示，RC構件在承受反覆載重下，隨著位移增加會使混凝土抗剪能力漸漸失效，同時產生強度的衰減，並且剪力強度衰減程度較撓曲強度衰減劇烈。因此為了預防結構產生不預期的剪力破壞，目前ACI318耐震設計規範與NZS規範在剪力設計上，則規定可忽略混凝土抗剪的貢獻。本實驗研究目的是探討RC梁在反覆載重下的剪力衰減行為，以求得RC梁在不同層間變位角下，其混凝土強度抗剪的貢獻，以討論ACI318耐震規範之剪力設計可不考慮混凝土抗剪貢獻之疑問。再者，本研究亦引用Priestley學者建議的混凝土剪力衰減模式，藉以驗證該模式的準確性。 經由實驗結果，可以整理出普通強度與New RC的混凝土剪力衰減模式。從模式中可發現，ACI318規範混凝土設計抗剪貢獻0.17√(f_c^′ )之規定，對本研究試體而言是為保守。故同樣以0.17√(f_c^′ )作為New RC梁之混凝土剪力強度，則更為保守，值得再進一步作調查。而觀察本實驗結果建立的剪力衰減模式得知，ACI318耐震規範在梁剪力設計上，忽略混凝土的抗剪貢獻，顯然是較於保守，尤其是New RC梁，故值得商確。最後，Priestley所建議的混凝土剪力衰減模式，應可作為評估耐震區RC梁混凝土抗剪強度。 ;According to previous research results, when reinforced concrete (RC) members subjected to cyclic loading, the shear resistance of concrete degrades with increasing ductility demand, and the shear strength degradation is faster than the flexural strength. Therefore, in order to prevent shear failure of RC structures, the seismic specification in ACI318 and NZS code assumed the contribution of the concrete shear strength to be zero. The purpose of this experiment is to investigate the flexure-shear degradation behavior of RC beams under the cyclic loading, and to find the contribution of concrete shear strength. Meanwhile, the discussion on shear design of ACI318 seismic code assuming zero concrete shear strength will be performed. The concrete shear degradation model created by Priestley is also verified. In this study, the shear degradation mode of Normal RC and New RC can be obtained from experiment results. The results showed that ACI318 adopting 0.17√(f_c^′ ) as the designed nominal shear stress is too conservative for both Normal RC and New RC beams. From the test results, Priestley’s concrete shear degradation model can be used as the assessment of RC beam shear under seismic region.
