The Influence of the Flexural Strength Ratio of Columns to Beams on the Collapse Capacity of RC Frame Structures

Reinforced concrete (RC) frames are designed based on the strong column-weak beam (SCWB) philosophy to reduce structural damage and collapse during earthquakes. The SCWB design philosophy is ensured by the required minimum flexural strength ratio of columns to beams (FSRCB) in the seismic code. Quantifying the relationship between the FSRCB and the collapse capacity of the frames may facilitate the efficient assessment of the seismic performance of the existing or newly designed RC frames. This paper investigates the influence of different FSRCBs on the collapse capacity of three- and nine-story RC frames designed according to Chinese seismic codes. The results show that the collapse capacities of the RC frames can be efficiently improved by increasing the FSRCB, and the collapse capacities of frames with FSRCB = 2.0 are improved by approximately 1.6-2.0 times compared with those of the frames with FSRCB = 1.2. Compared with the middle- or high-rise (nine-story) frames, it is more efficient to improve the collapse capacity for low-rise (three-story) frames by increasing the value of CBFSR. The logarithmic standard deviation of the collapse capacity of the RC frames designed according to the Chinese seismic codes ranges from 0.5-0.9, which is larger than the proposed maximum logarithmic standard deviation (0.4) in FEMA P695.