Nonlinear behaviour of RC frames under repeated strong ground motions

This paper presents an extensive parametric study on the inelastic response of eight reinforced concrete (RC) planar frames which are subjected to forty five sequential ground motions. Two families of regular and vertically irregular (with setbacks) frames are examined. The first family has been designed for seismic and vertical loads according to European codes while the second one only for vertical loads, to study structures which have been constructed before the introduction of adequate seismic design code provisions. The whole range of frames is subjected to five real seismic sequences which are recorded by the same station, in the same direction and in a short period of time, up to three days. In such cases, there is a significant damage accumulation as a result of multiplicity of earthquakes, and due to lack of time, any rehabilitation action is impractical. Furthermore, the examined frames are also subjected to forty artificial seismic sequences. Comprehensive analysis of the created response databank is employed in order to derive important conclusions. It is found that the sequences of ground motions have a significant effect on the response and, hence, on the design of reinforced concrete frames. Furthermore, it is concluded that the ductility demands of the sequential ground motions can be accurately estimated using appropriate combinations of the corresponding demands of single ground motions.