论水工建筑物的可靠性设计

主要由于替代惯用的单一安全系数法的分项系数极限状态方法被混同于可靠度分析法,至今特别在水工结构设计业界对其应用都存有争议。单一安全系数法包含了非随机性的工程经验因素和各类随机的不确定性,但不能区别各类随机不确定性的程度。可靠度分析法可以对各类不同程度的随机不确定性综合评价其失效概率,但不能计入目前对水工结构仍相当重要的工程经验因素。本文对若干导致争议的概念上的混淆作了澄清。在分项系数极限状态方法中各分项系数不仅可以区别各类随机不确定性的不同程度,且引入了表征工程经验的结构系数γd。因而显然要比单一安全系数法更为合理。目前为保持规范的连续性,各分项系数的取值总体上仍需和传统的安全系数相适应,因而实质上为多安全系数法,在安全水平的设置上与单一安全系数法并无本质差异。但它完全不同于可靠度设计方法,因为各分项系数独立确定,与目标可靠指标无关,且引入了结构系数。因而并无可靠度设计方法中的复杂理论、术语和统计样本不足等困扰。最后,简述了分项系数极限状态方法在《水工建筑物抗震设计规范》中成功应用的实例。

On the reliability design of hydraulic structures

So far the application of the method of limit state method with partial factors to substitute the conventional single safety factor method has been disputed especially in the design circles of hydraulic structures，mainly because the former to be confused with reliability analysis. The single safety factor method involves both the non-random factor of engineering experience and all random uncertainties but without regard to their degree of uncertainty. The reliability analysis method can evaluate the combined failure probability of random uncertainties with different degrees but is unable to consider the factor of engineering experience which is now still important for design of hydraulic structures.In this paper some confused concepts inducing the debate are clarified. In the limit state method not only the different degrees of all random uncertainties can be distinguished by the partial factors，but also a structural factor γd is introduced to reflect the engineering experience. Obviously，it should be more logical than the conventional single safety factor method. At present，all the partial factors have still to be determined in accordance with the traditional safety factor in order to keep the continuous of the design codes. So，the concerned method is actually a multi-safety factor method having no essential difference with the conventional single safety factor method concerning the setting of safety level as a whole. However，it is entirely different from the reliability analysis method，as a structural factor γd is introduced and all partial factors both of action effects and resistances are determined independently from the reliability index. So，neither complex theory and unfamiliar terms nor insufficient statistical data must be worried about by the designers. Finally，as an example the successful application of the method of limit state method with partial factors in the《Seismic Design Code of Hydraulic Structures》is briefly described.