General Methods For Reliability-based Design & Assessment Of Engineering Structures

In the civil engineering field, the method of approximate probability limit state design is an advanced method known at domestic and overseas. The method for measure and control structural reliability is implemented by reliability index related to failure probability, overcoming the defect of the previous empirical method basically. But in practical application, partial factor was determined by predetermined probability characteristics of basic variable, design working life and target reliability index were also set beforehand. The method will not suit for reliability-based design when real probability characteristics of basic variable are different form predetermined probability characteristics, or owner's demand of design working life and target reliability index are different form setting value. Because of a lack of flexibility, this method cannot satisfy the need of design of new structures and new material structures, and can't be used in the assessment of existing structures. At the same time, the current design method only considers the randomness of things, but did not consider the uncertainty of human's recognition.Aiming at defective in limit state design method of approximate probability, the dissertation establish general method for re liability-based design and assessment of engineering structures, and also take into account of the affections of subjective to the analysis result of structural reliability. The research contents and result includes:1. Mathematical treatment method for subjective uncertainty and reliability analysis method based on subjective uncertainty are proposed. The dissertation induces all kinds of uncertainty in human's recognition as subjective uncertainty; to establish general mathematical treatment method for subjective uncertainty by uncertain variables and belief function. Based on be lief analysis of structural failure probability, the paper creates structural reliability analysis method considering subjective uncertainty, further to establish reliability measures and control methods with combing probability and belief. 2. General expression for the design and assessment of reliability of engineering structures are proposed. At present, there are plenty of shortcomings about reflecting the impact of the random variables in the practical design expression. In the paper, according to the JC method recommended by the international organization JCSS, functional relationships among partial factor and probabilistic characteristic of basic variable, design working life, target reliability index are founded. At last, the general expression for the design and assessment of reliability of engineering structures are proposed. Based on the solid theoretical basis, the expression can be use to design the new structure and new material structure, to assess the existing structures. So it can satisfy the different needs on the design working life and target reliability index.3. The paper proposes determination method of standard sensitivity coefficient. The standard sensitivity coefficient is critical to establish general method of the reliability-based design and assessment of engineering structures. But current enumeration method and fitting method are not only tedious but may also to miss the adverse cases. Therefore, the boundary vector and center vector are set up for the sensitivity coefficient. Aiming at the ultimate limit states and serviceability limit states, the paper makes use of the analytical vector method to determine the optimal sensitivity coefficient and standard sensitivity coefficient of reliability-based design. At last, the general expression for the design and assessment of reliability of engineering structures are founded. At the same time, analytical method is derived to design and assessment the reliability of engineering structures.4. The paper proposes inference rules for probability characteristics of basic variables, material strength and resistance.The research on the number characteristics of basic variables, material strength and resistance are essential to engineering practice, especially the general method of reliability-based design and assessment. The material strength and resistance at any time for the existing structures are determined objectively but uncertain and unknown variables also existing subjectively. The current methods of probability and statistics are not entirely suitable for their inference. According to the characteristics of the existing structures, the reliability inference method for the number characteristics of basic variables and material strength and resistance are proposed. The method considers the impact by subjective uncertainty reasonably and the information of the measured member. Considering the deficiency of inference method on the variation coefficient at present, new inference method is proposed. Comparing with present approximate inference method including the national standard GB/T11891-89 approximate inference method, it also has higher accuracy and widely applied.