1982. Shear at the interface of precast and in situ concrete. (PDF)

Composite structures are often built up from concretes of different ages and, even with cast in situ concrete, the monolithic structure is often composed of parts cast in varying stages. If the units are prefabricated, they interact with in situ concrete or with each other via the in situ concrete. Indeed, composite action is of vital importance in utilising all structural possibilities. When making use of composite action, the transfer of forces—especially shear at the interface—between continuous concretes must be considered in both design and construction.

As composite design has been applied to various types of structure in many different countries, it is not surprising that specifications have come to vary considerably. For instance, in many countries it is common practice to make use of composite action in low shear situations, although no reinforcement crossing the interface is provided, whereas in other countries this is not permitted.

One aim in the preparation of this publication was that it should serve as a guideline when corresponding codes or specifications are being prepared or revised. Another is to give the designer a tool, and an understanding of the conditions necessary, to achieve composite action safely.

The intention has been to keep the design rules simple, in spite of the complexity of influencing factors and different applications. Thus, it will not always be possible to utilise the full intrinsic strength capacity at the interface unless further studies are made with a specific case in mind. However, the design rules require that the execution of interface surfaces and concrete toppings be taken into account, this being recognised as the only way to avoid excessive reinforcement crossing the interface.

This Guide to Good Practice has been prepared by a Working Group of the FIP Commission on Prefabrication consisting of: Mr K. Gustavsson (Sweden), Chairman; Dr G. Somerville (UK); Mr M. Vesa (Finland); Mr E. Witta (Switzerland); Mr K.-G. Bernander (Sweden); Mr J. Calavera (Spain); and Mr R. Piñeiro (Spain). The main editing work has been carried out by Dr G. Somerville, and valuable contributions and comments have been received from Dr Ing. Thode (West Germany), Mr A. J. Threfall and Dr J. L. Clarke (UK), Mr J. Dardare (France), Mr J. Walraven and Prof. H. W. Reinhardt (Netherlands).