混凝土强度的标准质量水平,可用其平均强度和标准差来描述。对全国混凝土强度进行典型调查,可以得出不同时期混凝土的全国质量水平。质量水平可分为极限质量水平和合格质量水平。极限质量水平即为保证结构设计的预期安全等级的最低质量水平,可用低于特征强度的概率值(或分位值)来表示,如图2所示。与极限质量水平对应,一般取保证结构设计的预期安全等级的质量上限为合格质量水平。在确定抽样检验方案时,一般要求对合格质量水平的产品,应以大概率接收,但也允许以小概率(α)被拒收。对极限质量水 The standard quality level of concrete strength can be described by its average intensity and standard deviation. A typical survey of the national concrete strength can be used to determine the national quality level of concrete in different periods. The quality level can be divided into the limit quality level and the qualified quality level. The limit quality level is the lowest quality level that guarantees the expected safety level of structural design, and can be expressed by the probability value (or quantile) that is lower than the characteristic strength, as shown in FIG. 2 . Corresponding to the limit quality level, generally, the upper quality limit of the expected safety level of the design of the guarantee structure is the qualified quality level. When determining the sampling inspection scheme, it is generally required that products with acceptable quality levels should be accepted with a high probability, but they are also allowed to be rejected with a small probability (α). To the limit quality water