Aspects affecting the nonlinear behavior of precast prestressed hollow‐core units failing in shear

Due to the extrusion manufacturing process, hollow‐core units in New Zealand do not have transverse shear reinforcement. The prestressing strands will not be fully developed near the ends of the hollow‐core units, which significantly affects the shear capacity and makes them prone to transverse and web cracking under deformation demands. In addition, initial end slip of the strands caused during cutting of the units in the production process may exacerbate this effect. This vulnerability of hollow‐core slabs was remarked during the 2016 Kaikōura earthquake, where an estimated 22% of the damaged buildings presented transverse cracking to hollow‐core units, sometimes accompanied by evident web cracking. The observed damaged, produced by earthquake‐imposed deformations, highlighted the urgency to advance the understanding of the behavior of hollow‐core floors. Subsequently, an experimental testing program was initiated to investigate the properties of extruded concrete and the shear strength of hollow‐core units under different shear span‐to‐depth or aspect ratios. The 200 mm deep specimens were loaded well beyond the peak shear force to study the postpeak behavior of the hollow‐core units. Additionally, the present study evaluates the effect of initial end slip of the prestressing strands on the pre and postpeak capacity of the units. The results obtained are compared against the formulations provided by commonly used design standards such as the New Zealand concrete standard NZS3101:2006, the ACI 318‐19, as well as the fib Model Code 2010 and the BS EN 1168:2005.