1. K. William and E. Warnke, in Proceedings of the Seminar of Concrete Structures Subjected to Triaxial Stresses, Bergamo, Italy, 19 May 1974, Vol. 19 (Bergamo, 1975) Paper III-7.
2. J. Wastiels, Report of the Working Commission, Vol. 29 (Technical University of Denmark, 1978–1979).
3. Idem, International Report (Vrije University Brussels, 1981).
4. M. D.Kotsovos, Mag. Conc. Res. 31 (108) (1979) 151.
5. G. F.Smith and R. S.Rivlin, Trans. Amer. Math. Soc. 88 (1958) 175.