Mechanical Anchor Supplementary Shear Reinforcing as a Retrofit Technique for Hollowcore Floors

Hollowcore floor systems have been prevalent in New Zealand construction since the 1980s. The susceptibility of these elements to fail under seismic action has been highlighted through numerous post-earthquake observations, particularly those made after the 2016 Kaikoura earthquake. Recent full-scale testing of hollowcore floor panels has revealed previously undocumented failure mechanisms that render commonly adopted retrofit techniques inadequate. As a result, the engineering industry requires new, verified, retrofit techniques for the effective seismic strengthening of hollowcore floors to assist structural engineers with developing and maintaining a safe, seismically resilient building stock. This paper presents a proof-of-concept testing regime with supporting finite element (FE) analysis of a new, purpose-built mechanical fixing for use as supplementary shear reinforcing in hollowcore floors. This retrofit technique offers a practical and costeffective alternative to other currently proposed techniques. Subsequently, the availability of this retrofit technique has the potential to increase the accessibility of hollowcore retrofits to building owners across New Zealand, thereby facilitating a safer and more seismically resilient national building stock.