Conceptual Retrofit Strategy for Existing Hollowcore Seating Connections

D.K. Bull, J.P. Jensen and S. Pampanin

Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand

Presented at New Zealand Society for Earthquake Engineering Annual Conference (NZSEE06), New Zealand, 2006.

Previous research regarding the seismic performance of existing precast hollowcore floor and ductile lateral frame systems has highlighted several behavioural uncertainties. In particular poor seismic performance due to deformation incompatibilities between the floor diaphragm and frame seismic resisting system have become apparent. Significant rotation and displacement demand on the floor systems due to frame beam elongation, seating beam rotation, and longitudinal perimeter vertical displacement have been identified as the main sources of undesirable damage. As a result the structural integrity at hollowcore seating and perimeter connection interfaces can be jeopardised, potentially leading to a partial or even complete floor collapse. In this paper an overview of expected compatibility issues is given while providing suggestions for conceptual low-invasive retrofit strategies. Particular focus will be given to the experimental investigation on the vulnerability of and suggested retrofit solutions for hollow core-seating connections. The Quasi-static experimental testing procedure focusing on a series of as-built and retrofitted specimens, reproducing a hollowcore-to-seating-beam connection with traditionally adopted details will be presented. Both seating rotation due to the imposed lateral drift and beam elongation effects are simulated in the applied testing set-up. Simplified analysis and modelling aspects regarding the connection behaviour are discussed; expected damage and performance criteria associated with the alternative existing or retrofit solution are also tentatively indicated.

Observed post earthquake collapse and extensive experimental investigation have highlighted significant uncertainties in the seismic performance of typical existing precast hollowcore floor diaphragm systems when coupled with ductile seismic resisting frames (Norton et al. 1994; Matthews et al. 2003). A poor combined structural response results from the conflicting intrinsic behaviour of the two individual structural systems; that being seating beam rotation, frame beam elongation, and longitudinal perimeter vertical displacement of the frame systems; and the stiff, brittle nature of hollowcore floor units, in addition to the lack of any transverse reinforcement.

References

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