On the choice of creep function for standard recommendations on practical analysis of structures

In the proposed revision of the C.E.B. International Recommendations, the unit creep curves for various ages t′ at loading are approximated in the form f(t-t')+g(t)-g(t') where t = time. Using optimization techniques to find functions f and g which give optimum fits of experimental data, it is shown that, by contrast with the present form, the proposed from of the C.E.B. creep function cannot reasonably approximate experimental creep curves over the full range of t′ of interest. In addition, the simplification of creep structural analysis intended by this formulation of creep function can be achieved, even to a greater extent, by another recent method. Therefore, the creep function of form φ{symbol}(t')F(t-t'), which is presently used by C.E.B., should be retained, although improvement in the definition of functions φ{symbol} and F is in order.