We study long-time strength of fiberglass-plastic reinforcing members experimentally. We carried out tests for fiberglass-plastic reinforcing members under tension and buckling. It is shown that the test procedure and data treatment in the tension tests results in understated estimates for the values of long-time strength of reinforcing members. We propose a procedure for durability test of reinforcing members under buckling that allows us to test a great number of samples simultaneously. Using the results of treatment of a great body of experimental data, we have an opportunity to make more exact prognosis for the long-time strength of fiberglass-plastic reinforcing members. We propose empirical formulas for calculation long-time strength valid for useful time of one hundred years and more. The data obtained under buckling are in good agreement with the results published earlier.