Seismic Fragility of Low-Rise RC Frames with Construction Deficiencies Subjected to Mainshock-Aftershock Sequences

The accuracy of local contractors in constructing Low-rise RC structures located in small towns is subjected to substantial fluctuations that increase the vulnerability of these structures, especially when sequential excitations are under consideration. Four major construction deficiencies are identified in this study by an initial field survey and are then considered in numerical modeling of a ۳-story RC moment frame. The median collapse capacity (MCC) of Low-rise RC moment frames under sequential excitations is evaluated in presence of construction faults identified in a field study. Various mainshock levels represented by their maximum inter-story drifts are then imposed on the as-designed and the deficient structures. Following each mainshock, the median collapse capacities (MCCs) of the structures under the aftershock are computed using the IDA method. Investigating the obtained MCCs showed that unintended increase of the beams’ width can help in reducing structure’s vulnerability against sequential excitations. Despite this, the comparison of the residual drifts imposed by the mainshocks showed the decreased ductility caused by this construction deficiency. Ranking the MCC reductions caused by the other deficient models, the highest vulnerabilities were posed by the models that caused larger column plasticities at the collapse state and prevented effective yielding of the beams.

Keywords:

collapse fragility curves , mainshock-aftershock effects , low-rise RC frames , construction deficiency , Modeling method evaluation