Hollow-core units are frequently used to form floors in multi-storey buildings as they are economic, have good sound and thermal properties and long spans can be achieved economically. The poor performance of buildings with hollow-core floors, backed up by the premature failure of a floor in a structural test, has demonstrated the vulnerability of these buildings.
Hollow-core flooring units, as described in the technical literature, are intended to be used as simply supported members. However, in construction continuity is often established between the units and supporting structure by the addition of insitu topping concrete and reinforcement. This change in structural form can result in negative moments and axial forces being induced in the floor by gravity loads, wind and seismic actions. Vertical seismic ground motion in particular can make a significant contribution to negative moments induced in the floor. It is shown that, with the detailing in common use prior to the release of the Structural Concrete Standard, NZS 3101-2006, there is a potential for brittle negative moment failure to occur under seismic conditions. Analytical work indicates that under some conditions a diagonal tension (shear) failure may also occur. As the failure of a floor may lead to progressive collapse it is important that these two aspects are considered along with a number of other potential failure modes in the retrofit or design of buildings.
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The other issue with hollow core structure is the lack of anchor options capable of securing into this type of concrete structure. The options are to anchor into the web between the hollow cores which gives limited concrete embedment depth because of the steel tendon running through the web or you anchor into the hollow core itself. This process required a mechanical anchor to be epoxied into the concrete which is very time consuming.