Experimental and numerical investigation of the seismic behavior of reinforced concrete frames with restricted ductility

In recent decades, the concept of special ductility has been commonly used to design reinforced concrete frames to resist strong earthquakes. There are numerous situations where strong earthquakes impose restricted ductility demands, e.g., structures governed by gravity loads or wind loads rather than seismic loads, and frames with geometric properties such that the dimensions prevent formation of plastic hinges at the ends of beams. To evaluate performance of such structures, this study has been conducted and emphasis is placed on intermediate reinforced concrete frames with code-conforming details. Shake table tests are conducted on a 3-story intermediate frame under a sequence of 9 incremental excitation records varying from 0.10 g to 0.60 g, representing minor to severe ground motions. A relatively satisfactory performance is observed: the maximum interstory drift ratio does not exceed 1.57 %, cracks are not localized at the ends of members but distributed along the spans of both beams and columns, and joints remain almost uncracked. To examine the effects of different parameters, a numerical model is developed and verified against the test results. Three essential parameters are considered: seismic event profile, span-to-depth ratio of the beam, and joint aspect ratio. The results show that the effects of different factors may be ranked from highest to lowest as follows: seismic event profile, aspect ratio of the beam-column joint, and span-to-depth ratio of the beam. The numerical analyses show that the frame will not exceed life safety limit under far field excitations and for joint aspect ratios larger than 0.9, but it may reach the threshold of collapse prevention limit under near fault earthquakes. Overall, the study sheds some light on seismic response of RC frames with restricted ductility and provides some indications of their feasibility as well as their limits in high seismic zones.