A Method for Evaluating Material Performance Parameters in Long-Life Structural Design under Random Degradation from Freeze–Thaw Cycles

In long-life design of structures, material parameter values should be determined reasonably based on the design working life of the bridge and considering the degradation of the material properties during service. In this study, firstly, according to the relationship between concrete compressive strength and dynamic modulus of elasticity, the degradation data of dynamic modulus of elasticity of concrete under the action of freeze–thaw cycles are processed, and the degradation curve of concrete compressive strength is obtained, and it is intuitively determined that the degradation process of compressive strength can be modeled by the Gamma process. Then, based on the definition of the Gamma process, a program is developed to identify whether the material degradation data conform to the Gamma process. Theoretical verification shows that the degradation process of concrete compressive strength under freeze–thaw cycles obeys the Gamma process. Subsequently, a method is proposed to determine the amount of compressive strength degradation of concrete based on the quantile values of the probability distribution at different time points. Finally, taking into account the stochastic nature of material performance degradation over the design working life, a method is proposed for determining the material parameter values based on the Gamma process, which is used to characterize the degradation process of material performance. This method takes into consideration the different design working lives and can provide guidance for determining material parameter values in the long-life design of bridges.