Seismic performance and forensic analysis of a precast concrete hollow-core floor super-assemblage

Abstract

Recent earthquakes and laboratory research has demonstrated the seismic vulnerability of buildings constructed with precast prestressed concrete hollow-core floor systems. However, further investigations have shown that with simple detailing enhancements, significant improvement in the seismic performance of hollow-core floor systems can be expected. The New Zealand Concrete Structures Standard provides two “acceptable solutions” for the connection of hollow-core floor units to concrete supporting beams (Amendments to NZS 3101, 2004). The second of these “acceptable solutions” is currently untested, and the present experimental investigation aims at validating this solution as well as several other new detailing enhancements. Two dimensional sub-assemblage component experiments are conducted utilising a newly developed, more realistic loading configuration. Based on the sub-assemblage research findings, a concrete frame super-assemblage is constructed incorporating a reinforced connection that rigidly ties the floor into the supporting beam and an articulated topping slab cast onto a timber infill solution that bridges between the hollowcore units and parallel longitudinal frame beams. The full-scale structure is cyclically tested in both the longitudinal and transverse directions to inter-storey drifts of ±5%. Visual and instrumental observations from the experiment are presented and discussed. A forensic analysis of the experimental observations is performed. Torsional hinging behaviour that is observed due to a strong floor-to-beam connection and weak support beam is explained and experimentally observed displacements are compared with computational modelling. The lateral load capacity of the super-assemblage is predicted and it is seen that it is necessary to incorporate all sources of strength enhancement. Finally, the results from this present investigation are compared and contrasted with similar previous research investigations and recommendations for the forthcoming revision of the New Zealand Concrete Standard, NZS 3101, are made. The experimental observations demonstrate that with appropriate detailing enhancements there can be significant seismic behaviour improvements whereby a relatively fragile hollow-core flooring system is transformed into a robust frame-floor system where all the damage is transferred into the plastic hinge zones of the supporting moment resisting frame.