مقاله انگلیسی رایگان در مورد ارزیابی قابلیت اطمینان سازه های بتن آرمه – تیلور و فرانسیس ۲۰۱۷

In the concrete structural reliability assessment, the material damage and its influence on the response are often of particular concern. Generally, the continuum stress–strain law with random coefficients is adopted in the simulation. However, the concrete material is heterogeneous, non-uniform and random at micro-level. In this context, the non-uniformity and randomness at micro-level may influence the constitutive law of the concrete in a stochastic manner. In addition, this randomness finally affects the structural behaviours and reliability assessment. In this regard, it is more reasonable to consider the stochastic damage of the concrete material at micro-level, and study its effects on the non-linear response and reliability evaluation of structures. The concrete fracture or damage has been widely investigated and a number of models (Beck & Gomes, 2013; Curtin, 1998; Strauss, Zimmermann, Lehký, Novák, & Keršner, 2014) have been proposed. Among these models, the fiber bundle model (Li & Zhang, 2001; Peirce,1926) is the most commonly used, and also effective in practical applications at micro-level. The fiber bundle model research could be traced to the pioneering work of Peirce (1926). Later, Daniels (1945) studied the influence of microscopic randomness to the macro-strength of material, and proposed the primary form of stochastic damage model. In 1986, Krajcinovic and Fanella (1986) established the classic parallel bundle model for concrete damage mechanics analysis, and the degradation of concrete was denoted by the failure probability of the bundle. It should be noted that the damage variable is deterministic in Krajcinovic’s model. Therefore, Kandarpa, Kirkner, and Spencer (1996) improved Krajcinovic’s model by introducing a random field to describe the stochastic damage evolution at micro-level. Li and Zhang (2001) developed a uniaxial stochastic damage model for concrete, and the fracture strains of the micro-elements were also defined as random field. Li and Yang (2009) further modified the classic fiber bundle model by introducing the remnant strain. The fiber bundle model uses a series of fibres to simulate the concrete material, and appears in an extremely simple form. Nonetheless, it can achieve a perfect balance between complexity and comprehensiveness. Furthermore, it can be quite effectively used in the simulation of stochastic fracture and damage of material. At present, the calculation of the stochastic damage is mainly based on two types of methods. One is the moment-based method (Krajcinovic & Fanella, 1986; Kandarpa et al., 1996) and the other is the direct numerical simulation method (Iwan, 1967). The moment-based method, in general, obtains the firstand second-order moments of the stochastic damage while the direct numerical simulation is usually time-consuming in computation, especially when a large number of random variables are required. In this regard, reducing the random variables would be the key issue for the numerical simulation of the problem. In this paper, a stochastic model is developed and used to establish a probabilistic relation between the fibre strain and the concrete damage variable. In this context, the stochastic damage evolution of the concrete can be quantified by two representative random variables.