Experimental verification of creep analyses for prestressed concrete reactor vessels

The purpose of this study was to clarify which of the various analytical methods to evaluate the effect of creep on the behaviour of prestressed concrete reactor vessels is most suitable, in view of the comparison with experimental creep data based on the tests of prestressed and reinforced concrete members subjected to long term temperature gradients. The main conclusions within the limit of experiments are as follows: (1) First, experiments were made to determine the properties of concrete under the environmental conditions similar in a operating PCRV. (2) Experimental investigations were carried out in which prestressed concrete beams, hollow cylinders and a full scale model (outside diameter 3 m, external height 4 m, and wall thickness 0.5 m) were subjected to long term temperature gradients under the similar restraining conditions as in the walls of PCRV. (3) Various analytical methods such as effective modulus, rate of creep, superposition etc., have been used to calculate creep strains in prestressed concrete members for PCRV. It was made clear, however, that these methods could not always give a realistic prediction for creep behaviours of concrete members especially in such stage as initial heatup of PCRV, when concrete undergoes fairly wide variation of temperature. The authors proposed a new method of creep analysis based on the theory of strain hardening, which assumes that accumulated creep at a given time influences the creep after that. The experimental and calculated results agreed fairly well. Further, this method was incorporated in the finite element creep analysis for the prestressed concrete hollow cylinder and the full scale model. (Auth.)