N° 156. 1983. Concrete under Multiaxial States of Stress - Constitutive Equations for Practical Design

This publication is intended for the practical design engineer. It is not written for scientists engaged in experiment al or theoretical research in the multiaxial behaviour of concrete. 

Practical engineers need information in this area for their work in two fields: 

- Multiaxial stress states often determine the behaviour of simple structures, such as plates, walls, anchorage zones of beams, hinges etc. Therefore the design engineer in his daily work has to know at east qualitatively their effect.

- As numerical method s are used more and more in the investigation of complicated reinforced concrete structures, the responsible design engineer has to know the two and three-dimensional constitutive formulations which represent one of the most important inputs into this type of investigation.

For these reasons our Task Group attempted to acquaint the practical engineer with the triaxial behaviour of concrete as understood by the experimentalists. Simultanously a short guide through the more theoretical concepts of stress space, failure surface and constitutive laws (Appendix B, D ) including the necessary nomenclature, are given. Nevertheless competing with excellent text books on this subject [40 , 56] is not the aim of the CEB Task Group .

The Task Group felt that guidelines should be qiven to design engineers for a check of the underlying constitutive basis in their FE-programs. Some of the available formulations - an excellent state of the art report is given in reference [19] - are determined more by the needs of the user than by the secured state of experimental knowledge . 

Therefore, it seemed judicieus to express the boundaries of current knowledge. This is not meant to hinder rational extrapolation but to distinguish between proved facts and hypothesis. This tendency was also promoted by the fact that experimentalists working in this field, such as Aschl, Gerstle, Hilsdorf, Kotsovos and Schickert, were members or in close co-operation with the Task Group. We also thought that it could be helpful to give recommendations for cases where the design engineer is still free to choose a constitutive law of his preference. 

Safety considerations and partia l safety coefficients, which are of special importance when treating stress combinations shall be considered by a new Task Group consisting of members more competent in this particular area.