RC梁、柱剪力增大系数取值的有效性

抗震混凝土框架结构的梁、柱剪力增大系数是保证结构抗震安全性的关键指标之一。中国结构设计规范对各抗震等级的剪力增大系数取值作了规定，但却未见有关实际控制效果的研究成果发表。按照现行设计规范设计了3个规则空间框架结构算例，分别位于设防烈度7度（0.15g）区、8度（0.20g）区和9度（0.40g）区。对每个算例进行罕遇地震作用下的非弹性动力反应分析，以不少于90%的梁、柱满足“罕遇地震作用剪力”小于“平均强度抗震抗剪能力”为标准，判断剪力增大系数取值的有效性。当不满足该标准时，调整剪力增大系数取值，直到满足上述标准。结果表明，现行结构设计规范对框架梁取用的剪力增大系数有效，可继续使用；框架柱剪力增大系数取值，在一级抗震等级时过大，在二、三级抗震等级时不满足上述标准。建议了两套柱剪力增大系数的取值方案。

Shear overstrength factors for RC frame members in Chinese code

Using shear overstrength factors is one of key earthquake resisting measures for reinforced concrete (RC) frame members,which aims to ensure the safety of structures under rare earthquakes. The shear overstrengh factors for different seismic grades have been provided in Chinese code,while little research has been conducted up to date which focused on the actual effect of shear overstrength factors. Three regular RC frame structures were designed according to the current code,which respectively located in intensity region 7(0.15g),8(0.20g) and 9(0.40g). Nonlinear dynamic analyses under rare earthquakes were finished.The ratio of the shear demand under rare earthquakes to the average shear capacity for beams and columns was calculated to identify the effectiveness of the shear overstrength factor. The rule is that the ratio of more than 90% components are less than 1.0. The adjustments were made in the case when the shear overstrength factor did not meet to the rule,which continued until that the factor is up to grade. The result proves that shear overstrengh factors for RC frame beams can keep on; the shear overstrength factors for first seismic grade is oversized,while that for second and third seismic grades can not satisfy the shear demand. Two sets of schemes for column shear overstrengh factors are proposed based on further analysis.