1982. Design principles for hollow-core slabs regarding shear and transverse load bearing capacity, splitting and quality control. (PDF)

The prestressed hollow-core slab has, during the 1970s, become an increasingly important component within precast concrete construction. It is being used worldwide, essentially for flooring but also for roofing and walling purposes.

The reason for this development is, firstly, that hollow-core slabs may be designed to meet varying load-carrying requirements very efficiently, using a limited material input. Joints, supports and ties can, by grouting and complementary local concreting, be made such that reliable composite action between adjacent slabs is achieved without using concrete topping over the whole floor.

Secondly, the appropriate choice of hollow-core slab sections may satisfy a set of important functional requirements for a building, such as sound insulation, fire rating, ducts for piping and ventilation, thermal capacity, ready-made false ceilings, durability, etc.

Thirdly, a number of efficient manufacturing methods exist, based either on moulding wet or dry concrete mixes, slipforming or extrusion. The latter two methods, and some wet casting procedures, apply the long-line pretensioning principle, which facilitates the manufacture of slabs of any suitable length. The qualities of the hollow-core slab mentioned above make it applicable to a very wide range of building types, often at lower cost than alternative comparable solutions.

Manufacturing methods such as slipforming and extrusion, however, limit the possibilities of placing secondary reinforcement. On the other hand, extrusion processes in particular, if properly handled, result in a very high and reliable quality of concrete. The above facts have led to a limitation, and even the omission, of secondary reinforcement normally required according to conventional specifications. Current design practice, where such departures are permitted, makes use of the observed load-bearing capacity of the hollow-core slab, in some countries in accordance with their specifications, in others in accordance with special agreements. Due to different assumptions, however, the optimum design and limitations in use vary considerably. A synthesis of research work and experience available from various countries would therefore be of great value.

Within the FIP Commission on Prefabrication, it was agreed that design recommendations for hollow-core slabs should be prepared, and a working party was formed in 1978. One aim was that such documentation would provide a basis for proposing revisions to the FIP–CEB Model Code on the subject. During the ensuing period, it was found that the knowledge and research work available on the matter was not a sufficient basis for the preparation of general recommendations. Instead, work was initiated on the most important issues in order to establish the necessary background.

As regards the design of hollow-core slabs with respect to shear strength, two different approaches are presented. This technical paper thus deals with documentation which, by being published now, will not only inform on recent developments but is also expected to result in contributions and criticism from readers. Further work on a Guide to Good Practice or recommendations, planned to be presented at the FIP Symposium in Calgary 1984, would greatly benefit from such a broad input.