Assessment of hollow-core floors for seismic performance

Abstract

The objective in writing this report is to provide a guide to structural engineers on how to assess the potential seismic performance of existing hollow-core floors in buildings and the steps involved in the design of new floors.Hollow-core units in New Zealand do not contain stirrups within the precast concrete section.This is due to the way that they are manufactured.The only reinforcement in the great majority of hollow-core units consists of pretensioned strands that are located close to the soffit.A consequence of this is that hollow-core units have a number of potential brittle failure modes that can occur when adverse structural actions are induced in the units.These adverse actions can be induced in a major earthquake due to the relative vertical, horizontal and rotational displacements that occur between hollow-core units and adjacent structural elements, such as beams or structural walls.A number of large scale structural tests backed up by analytical research has shown that extensive interaction occurs between floors containing prestressed precast units and other structural elements, such as walls and beams.The constraint that prestressed units in a floor can apply to adjacent beams can result in an increase in strength of the beams to a considerably greater strength than that indicated in editions of the New Zealand Structural Concrete Standard published prior to 2006.The extent of this increase is such that it could in some cases result in the development of a non-ductile failure mechanism instead of the ductile failure mechanism assumed in the design.