Abstract
A computer algorithm for the computation of discrete age-dependent relaxation spectra of concrete from creep or relaxation test data is presented and a full FORTRAN IV listing is given. The algorithm is base on a previously outlined method, consisting in the expansion of relaxation curves in series of real exponentials on the basis of a least square criterion. This method is refined herein by imposing suitable smoothing conditions upon the spectra in order to reduce spurious sensitivity of results to small changes in given creep data. Two variants are given; in one the spectrum is approximated as a cubic polynomial in the logarithm of age and the logarithm of the relaxation time, while in the other one a cubic polynomial in the logarithm of age alone is used. Numerical examples show that given smooth creep data can be recovered from the spectra with a negligible error, which demonstrates that the spectra fully characterize creep properties. Apart from being a fundamental characteristic of creep, the relaxation spectra convert a hereditary creep law into a history independent rate-type form, which is requisite for creep analysis of large structural systems.
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