Research On Seismic Design Method Of RC Category Ⅱ Framework Based On Nonlinear Dynamic Analysis

National standard—《Standard for classification of seismic protection of buildings》(GB50223-95) adopts the method of upgrading the seismic-measures to upgrade category Ⅱ structure's earthquake-resistance level. It is different from some foreign codes (such as US,New Zealand) which adopt the method of upgrading the earthquake-design-level. The main topic of this dissertation is to study which method is more effective. The author firstly designs three representative reinforced concrete frames in 8 region according to new codes—《Code for seismic design of buildings》(GB50011-2001) and 《Code for design of concrete structures》(GB50010-2002). The three frames are category Ⅲ frame without upgrading seismic-measures and earthquake-design-level, category Ⅱ frame of higher seismic-measures and category Ⅱ frame of higher earthquake-design-level. Then, the author carries out nonlinear dynamic analysis on three frames under intermediate earthquake action and rare earthquake action. The results show as follows:(a) The performance of the two category Ⅱ frames of higher seismic-measures or higher earthquake-design-level are much better than that of category Ⅲ frame; (b) The earthquake-design-level of higher earthquake-design-level category Ⅱ frame is upgraded by 50 percent, which is a high limit that is adopted by foreign codes. But its performance under earthquake is still worse than higher seismic-measures frame. On the other hand, the higher seismic-measure frame is upgraded from grade 2 to grade 1. In Chinese codes, the disparity between grade 1 seismic-measures and grade 2 seismic-measures is eminent and is much greater than the disparity between any other two grades. So, we can draw some conclusions as follows: The method of upgrading the seismic-measures which is adopted by GB50223-95 is effective and is more effective than the method of upgrading the earthquake-design-level for those category Ⅱ frames of which seismic-measures are needed to be upgraded from grade 2 to grade 1. But for those category Ⅱ frames of which seismic-measures are not upgraded from grade 2 to grade 1 (e.g. those frame of which seismic-measures are needed to be upgraded from grade 3 to grade 2 or from grade 4 to grade 3), whether the method of upgrading seismic-measure is more effective than the method of upgrading earthquake-design-level needs further research. Moreover, the author gains the charts of storey shears and equivalent lateral loadsof three frames under rare earthquake actions. These charts are useful references for research on lateral load profile in push-over analysis. From the charts we can get some information as follows: The distribution of inertial forces has some relationship with structure's characters under earthquake. The fixed lateral load profile which is not variable during the whole push-over course may be not appropriate and adaptable lateral load profile which can consider the re-distributing of inertial forces may be more appropriate.