Application Study Of Reliability Theory In Some Aspects Of Structural Design

Since the1980s, the application of reliability theory in structural design has been developed greatly and reliability-based design method has been adopted by design specifications of many countries, such as building code and bridge design specification of America, Eurocode, some structural design specifications in Japan and China etc. However, whether domestic or abroad, the application of reliability theory is not perfect in many aspects which still need further extensive research. In China, reliability theory was early applied in the field of building structures and developed much faster, while the application of reliability theory in power engineering started later and developed slowly. Combining with three research projects, this paper focuses on some issues of the application of reliability theory in design of building structures, port engineering structures and transmission lines. The details are listed as follows:1. Aiming at the problem that for different cases there are great differences between reliability indices of structure designed by the method of partial safety factor specified in the current design code, reliability index-based design method of building structures was proposed in this paper. The sensitive coefficients of load effects and resistances were optimized and analyzed and the sensitive coefficients were described by linear function of load effect ratio. Accordingly, the relationship between partial safety factors and load effect ratio was presented. The results show that the reliability index of structure designed by the method proposed in this paper has a good agreement with target reliability index.2. Aiming at the problem that the factors for determining frequent value and quasi-permanent value in serviceability limit states design of the current standard are determined based on engineering empirical judgment, the factors of frequent value and quasi-permanent value for live loads on floor and wind loads were determined according to the statistical analysis in this study. With regard to the new revisions about load combination adopted by crack width checking computation of serviceability limit states in "Code for Design of Concrete Structures", the reliability of RC flexural members in cracking width limit states was analyzed respectively based on factors of quasi-permanent value specified in code and determined in the present paper. The results show that the reliability of crack width limit states under the new revised quasi-permanent combination satisfies the requirements of unified standard.3. According to the operating features of RC structures in marine environments, probabilistic models for corrosion percentage of reinforcing steel were developed for three different states, i.e., no corrosion, ongoing corrosion but no cover concrete cracking and concrete cover cracking. Statistical analysis fof corrosion percentage of reinforcing steel was conducted using Monte-Carlo simulation, in which the occurrence probabilities of above three different states were also determined. Based on the probabilistic model for corrosion percentage, time-dependent reliability analysis of RC flexural members meeting the minimum durability requirements was performed. The statistical results show that corrosion percentage of reinforcing steel can be described by a bimodal normal distribution; the occurrence probabilities of no corrosion and no concrete cracking decrease with time; the reliability of RC members in marine environments significantly decreases with time.4. Based on the statistical data of relevant load effects and resistances of general transmission line as well as the acceptance criteria specified in standards, statistical parameters and probabilistic models for load effects and resistances of tower member, insulator, fitting and wire of transmission line were determined. To provide foundation for determination of target reliability indices of transmission line across high-speed railway, reliability calibrations of tower member, insulator, fitting and wire of transmission line were conducted by using JC method.5. Based on the results of reliability calibration of general transmission line, target reliability indices of relevant members of overhead transmission line were presented. The relationships between the reliability indices and the important factors of tower members as well as safety factors of insulator, fitting and wire were developed, thereby performing the reliability-based design of the transmission line directly by the important factors or safety factors.