Abstract:
The use of precast concrete floor systems is widespread within New Zealand. Support connections for precast concrete floor units are subjected to earthquake induced deformations, including a relative rotation between the unit and support beam and a pull-off effect caused by beam elongation. Additionally, beam elongation can contribute to the failure of joints between precast units where the connection consists of a lightly reinforced insitu concrete topping. Damage to both support connections and connections between precast units were observed during the 2010/2011 Canterbury earthquakes in New Zealand and a testing programme was initiated to investigate these damage modes. Precast hollow-core units with a depth of 400 mm (400HC) were tested to investigate the seismic performance of the support connection details recommended in NZS 3101:2006. The hollowcore support connection was subjected to deformations simulating seismic and gravitational actions. Preliminary test results suggest that the existing support connection details recommended in NZS3101:2006 are suitable for 400HC units. Damage to precast ribs used in rib and timber infill floors can occur when the rib is locked into the support beam. An initial test has been conducted to investigate the reinforcement details at the rib support using the same test setup as the 400HC tests. The test indicates that a satisfactory seismic performance can be achieved when the ribs are seated on low-friction bearing strips with additional stirrups placed in the ends of the precast ribs. Lastly, tests were completed to investigate the seismic performance of the connection between precast units provided by the insitu concrete topping. The cyclic tests of topped units highlighted the poor performance of cold drawn steel mesh in comparison to ductile steel mesh and standard deformed reinforcing steel.