Lateral response of nonseismically detailed reinforced concrete flat slab structures.

Abstract

An experimental investigation was conducted to determine the lateral response of older flat slab structures in seismic zones. These structures are assumed to have a probability of catastrophic failure during earthquakes due to discontinuous bottom reinforcing bars. This speculation combined with lack of data leads to extensive and costly seismic retrofits. This study explores the possibility of more economical retrofit. The experimental specimens consisted of a 2 story-2 bay frame and an interior and exterior isolated slab-column connection subjected to quasi static lateral cyclic loads. Contrary to expectations, ductile behavior was observed for all specimens, even after loss of bottom reinforcing bar anchorage. Slight pinching was observed in the hysteretic loops of the frame specimen due to the loss of stiffness at the exterior connection. Comparisons were made between the behavior of isolated connection specimens and connections in a frame. It was concluded that not all behaviors of isolated connection specimens can be extrapolated to full frame behavior. An effective slab width model was developed to predict the behavior of these older flat slabs. This model was successfully tested by modeling a flat slab building which was damaged in an earthquake and comparing the actual damage to the post-predicted damage. Since the behavior of these older flat slab structures was better than expected, the strength and stiffness of the existing frame can contribute to the retrofit design, making the upgrade more economical. Also, it has been established that the unstrengthened bays of the retrofitted structure will respond ductily.