Performance of precast concrete floor systems during the 2010/2011 Canterbury earthquake series

The 2010/2011 Canterbury earthquakes have provided an opportunity to further examine the seismic performance of precast concrete floor systems. Extensive research has been performed on precast floor systems throughout the past 10 years, during which many deficiencies have been identified and revisions to current standards have been made. Furthermore, a large number of possible failure modes have been examined and were compared against the damage that was observed during the earthquakes. In general, precast flooring units performed well and only minor damage was observed. Severe damage in several buildings was attributed to either displacement incompatibilities within the structure or a lack of robustness of the floor diaphragm as a whole. There have been significant advances in the design provisions for precast concrete floor systems in recent years and much of the observed damage would not have occurred in buildings constructed following current best practice. However, issues remain with the design of floor diaphragms and it has been recommended by the Structural Engineering Society of New Zealand (SESOC) that a more robust and unified design method is required. In particular, minimum topping thicknesses should be increased, precast units should be required to be supported on low-friction bearing strips and non-ductile mesh should not be permitted.