3.2 Uncertainties in reliability assessment 。Random variables(随机变量) Loads(作用)，material strength,geometry of section, Location of rebars,calculating methods,human errors Design use the concept of probability and apply the methods of statisticsl Random variables (随机变量) Loads(作用), material strength, geometry of section, Location of rebars, calculating methods, human errors Design use the concept of probability and apply the methods of statistics