Retrofit testing on hollowcore floors

Abstract

c While the details for these floor systems have been improved in new buildings, support conditions for units in existing buildings designed before 2006 are likely to lead to significant damage and potentially collapse in design level ground motions.

Buildings with precast floors comprise a large percentage of the commercial building stock in all New Zealand cities, with likely over 60% of commercial buildings in Wellington falling in this category. There are increasingly more residential buildings with older precast floor details as more buildings are being converted from commercial to residential in Wellington CBD. A Wellington Fault event will undoubtedly lead to multiple floor collapses in numerous buildings throughout Wellington.

Assessing the likely performance of these floors in an earthquake is a challenge for engineers. While guidance has recently been developed for the seismic assessment of buildings with precast floors (so-called Yellow Chapter), engineers will urgently need direction on retrofit approaches to address vulnerable buildings. In particular, concern has been raised that seat angles, already provided as a retrofit for several buildings, could potentially lead to unintended negative moment failures and collapse of hollowcore floors. This research identifies under what conditions such unintended failure modes may be triggered and provides a retrofit solution where vulnerability to negative moment failure is identified.