近年來，國內推行高強度鋼筋混凝土(New RC)結構系統研發計畫，其中由於鋼筋強度f_y=685 MPa(SD690)已超過現行規範ACI 318-14許多經驗公式之鋼筋上限值規定。因此，本文將研究此類新型鋼筋混凝土梁之耐震設計參數，以有效初始勁度與鋼筋超額強度因子為關注之重點。藉由收集、整理及統計歷年來之反覆載重下梁撓曲破壞之相關試驗，共計約100個試體進行分析與探討，其中SD420普通RC梁其f_c^′介於15至87 MPa與SD690 New RC梁其f_c^′介於30至120 MPa。本研究將比較SD420 與SD690之RC梁差異，探討國內本土混凝土彈性模數Ec，與利用Paulay (1992)方式求取有效初始勁度Ke。再者，亦利用學者Brooke (2011)統計方法，歸納出SD690鋼筋之超額強度係數，以供工程界結構分析作參考。 本研究結果顯示，目前國內預拌混凝土之彈性模數Ec，其中所調查之混凝土強度介於20至90 MPa，有低於ACI 318-14 Ec經驗式值之趨勢，因此建議所計算Ec值應再乘以0.8較符合現況。而在結構梁降伏以前，配置SD690主筋之RC梁構件其有效慣性矩Ie平均為0.25Ig，而傳統SD420鋼筋RC梁為平均0.30Ig；但梁構件尺寸較長者Ie值有高於平均值之現象。最後，鋼筋超額強度因子統計結果顯示，隨著鋼筋強度種類不同而有差異，SD690鋼筋研究結果平均值為1.15，而傳統SD420鋼筋為1.25。;The reinforced concrete with higher steel strength (f_y= 685 MPa) than traditional reinforcement (f_y= 420 MPa) is so called as New Reinforced Concrete (New RC). In recent years, the New RC starts considering the construction materials in Taiwan, but the strength limitation of reinforcing steel specified for design codes (ACI 318, 2014) is only up to 420 MPa. Therefore the objective of the research is to investigate the seismic design parameters of New RC structures for seismic design. Until now, 200 experimental data from many countries were collected to provide the research on the effectively initial stiffness and the overstrength factor. The effectively initial stiffness EcIe was estimated according to the 75% secant method, to obtain the member stiffness at a yield state. In addition, this report also investigates the overstrength using Brooke’s (2001) method and discusses the differences in material and structure properties between the RC beam used for SD420 and SD690 steel reinforcement. The results showed the modulus of elasticity of concrete in Taiwan is lower than the empirical equation provided by ACI 318.A modified factor, for reducing should be 0.8. Meanwhile, the effectively initial stiffness of New RC beams is smaller than the traditional RC members. Thus, the effective moment inertia (I_e) of 0.25I_g for New RC beams is suggested as design. Besides, RC sectional moment inertia I_e varies clearly with the shear span ratio (a/d). This finding implied that the member stiffness varied with the structural length could be considered in seismic rather than assuming a constant value as the traditional design. The overstrength factor of beam flexural reinforcement is different due to the different steel strength. Therefore, the overstrength factor for SD690 rebar is 1.15 in average whereas the factor for SD420 is 1.25 in average.