The Seismic Performance of Hollow-Core Flooring:The Significance of Negative Bending Moments

Abstract eng:
Precast, prestressed hollow-core flooring is used extensively around the world. Comprehensive research has been completed on its performance under gravity loads; the same degree of research has not been completed into its seismic performance. Over the last 15 years, research has been taking place at the University of Canterbury investigating the seismic performance of hollow-core floors used in New Zealand. Typical units contain prestressing strands in the bottom of each web and no shear reinforcement. Unit depths range from 150 to 400 mm deep with a 50 to 75 mm steel reinforced insitu concrete topping. A suite of possible failure mechanisms have been compiled along with a preferred hierarchy of failure. Of particular concern is the potential for brittle failure mechanisms due to the non-ductile characteristics of hollow-core flooring, which could lead to floor collapse. This paper presents two failure mechanisms that have been identified, and demonstrated using theory. One of the mechanisms has also been verified by a sub-assembly test. The failure mechanisms discussed are caused by shear and flexure in negative bending moment regions. Hollow-core flooring is generally not designed for negative bending moments but can be exposed to them. Starter bars linking the insitu topping concrete to the supporting beams can induce negative moments and axial tension into the floor. These actions are induced by the relative rotation between the supporting beam and the hollow-core unit, and by plastic elongation of reinforced concrete beams parallel to the hollow-core units. The tension in the starter bars, together with bending moments due to vertical ground motion, can induce brittle negative moment failure of the hollow-core units and insitu topping.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket