1988. Precast prestressed hollow core floors. (PDF)

Prestressed hollow core units are among the most advanced products in the precast concrete industry, especially with regard to their high quality and low material consumption. During the past two decades, they have been widely used for flooring and roofing, and occasionally for walls. Spans of up to 20 m can be achieved due to prestressing and low self-weight. They are produced by slipforming, wet casting, or extrusion on long-line prestressing beds.

The real breakthrough came about 15 years ago with the development of extrusion methods. Since then, hollow core units have gained an important market in many Western countries.

The design of the cross-section allows concrete to be used optimally in both compression and tension zones, while keeping the dead weight very low. However, automated manufacturing methods impose limitations on the placement of secondary reinforcement. On the other hand, extrusion processes in particular result in very high and reliable concrete quality.

Extensive field experience gathered worldwide, together with significant research—especially on extruded hollow core units—justifies taking the tensile stress capacity of concrete into account in design. Consequently, a reduction in conventional reinforcement is justified, leaving only the prestressing strands.

Of course, certain regulations must be imposed with respect to the design and manufacture of these units, and this has been the main task of the Working Party on hollow core units. Over the past nine years, this Working Party has initiated important research on several topics, as substantial knowledge had to be gathered in order to formulate general recommendations. The FIP Technical Report Design Principles for Hollow Core Slabs regarding Shear and Transverse Load-Bearing Capacity, Splitting and Quality Control, published in 1982, reflects part of this work.

The present Recommendations are the outcome of nine years of intensive work. They provide engineers and precasters with guidance for a sound design philosophy and make available calculation methods and examples of good practice for the various aspects of hollow core floor design. In this context, they are intended as a basic document for future codes.

A. van Acker
Chairman
FIP Commission on Prefabrication