Structural resistance R refers to the ability of the whole structure or structural members to bear the action effects (i.e. internal force and deformation), such as the bearing capacity and stiffness of the members. After the section size, concrete strength grade, steel bar type, quantity and reinforcement method of concrete structural members are determined, the section of the members will have certain resistance. The resistance can be determined according to a certain calculation model. The main factors affecting resistance are material properties (strength, deformation modulus, etc.). ), geometric parameters (component size) and the accuracy of calculation model (the basic assumptions and calculation formulas used in resistance calculation are not accurate enough), etc. These factors are random variables, so the structural resistance synthesized by these factors is also random variables.