Issue 37

Z. Hongping et alii, Frattura ed Integrità Strutturale, 37 (2016) 352-359; DOI: 10.3221/IGF-ESIS.37.46 353 In recent years, scholars in China and abroad have made a large number of experiments on the factors influencing durability of structure and obtained many durability degeneration models of concrete structure [7]. Traditional structural reliability calculation model does not vary along with time and the characteristics of existing structure determines that the calculation of structural reliability using time-invariant model cannot consider the degeneration performance of structure. But this study considered the variation characteristics of structural resistance and load along with time and calculated the reliability based on time-dependent concept. In addition, we find that, most scholars focus on the construction of degeneration model and concern little about degeneration parameters. Actually, degeneration parameter is an important component of degeneration model. Analysis of durability degeneration model and time-dependent reliability of structure is of significance only when correct parameters are used. As to another innovation point, this study gave uncertainty statistical parameters of reinforced concrete structure resistance based on the detailed introduction of degenerated reinforced concrete resistance decrease model and made an analysis on the rules of resistance decrease of corroded bending element. D EVELOPMENT AND STATUS OF STRUCTURAL RELIABILITY ANALYSIS METHOD he concept of reliability originated from America. In 1939, National Advisory Committee for Aeronautics proposed the concept of airplane accident rate; then the concept was extensively applied in the field of civil engineering. In 1940s, Pugsley and Freudenthal published a paper titled Safety Degree of Structure. They integrated the theory of structural safety degree and the concept of mathematical statistics and proposed a reliability analysis calculation model. Then earliest reliability calculation model was extensively recognized and studied by other scholars [9]. In 1969, Cornell, an American expert, proposed the concept of reliability index, integrated it with structural failure rate and put forward the conversion formula with regard to reliability index and structural failure rate [10]. Then Cornell and Ang proposed first-order second-moment method for the calculation of structural reliability, which was extensively applied in engineering. Since then, many scholars kept innovating structural reliability analysis and calculation and proposed many structural reliability calculation methods. Currently, researches on time-invariant theory have been relatively mature. However, time-dependent reliability theory involving multiple factors and more complex calculation remains to be further studied. On account of this, many scholars carried out a series of researches on time-dependent reliability of reinforced concrete structure. In 2008, Czarnecki et al. [11] proposed a time-dependent reliability model of reinforced concrete structure after finding the significant changes of reinforced concrete structure resistance along with the extension of time under corrosion environment and then applied the model for predicting the service time of structure. In 2012, Frangopol [2] applied structural health monitoring information obtained after integrating structure related priori knowledge and using Bayes updating probability to make a quantitative analysis on degeneration performance of structure. In 2014, Madsen [13] proposed a new structural time- dependent reliability and sensitivity analysis method. Similarly, many Chinese scholars are also dedicated to promoting the development of structural time-dependent reliability analysis. Through analyzing structural resistance decrease process induced by steel reinforcement corrosion, Chen Shoushan et al. [14] designed a method for evaluating and predicting reliability of structure. By investigating the existing resistance information of a structure and using a large number of measured data, Zhou Yan et al. [15] established a resistance time-independent reliability analysis model. Resistance Decrease Model of Reinforced Concrete structure The resistance of reinforced concrete structure depends on calculation model, geometrical parameters and material performance of structure. During the whole service process of structure, concrete carbonization and steel reinforcement corrosion can result in decline of strength of steel reinforcement and concrete, narrowing of cross section of steel reinforcement and deterioration of coordination between reinforced concrete and those adverse effects gradually accumulates as time goes on. Therefore, geometrical parameters and material performance of structure would both be degenerated as time goes on, which can weaken the resistance of structure. On account of this, when we consider the degeneration of resistance of reinforced concrete structure, the resistance decrease model can be expressed as: ( ) [ ( ), ( ), ( )] r aj j sj P t P f t d t k t  (1) Where ( ) r P t stands for resistance of reinforced concrete structure, [ ] P X stands for expression equation of reinforced concrete structure resistance, ( ) aj f t and ( ) j d t stands for performance and geometrical parameter of jth material and they T