Issue 35

W. Xu et alii, Frattura ed Integrità Strutturale, 35 (2016) 481-491; DOI: 10.3221/IGF-ESIS.35.54 485   1 1 1 1 tg e K K         (6) where tg K refers to slope of unit force of spring - relative displacement (Figure 4). Unit grid generation is an important step in modeling which can transform geometrical model into finite element model composed of joints and units. Result of grid generation directly determines preciseness of computation result and computation time [9, 10]. In the study, we adjust grid density for many times during computation process. Dense grids cannot ensure calculation convegence, especially when beam is severely fractured; and discrete grids will result in poor computational accuracy. Figure 5 shows grid generation of concrete unit. Figure 5: Grid generation of concrete unit. Parameters of Model The analytical model uses parameters including axial compression ratio (ratio of design value of axial pressure of column (wall) to product of full sectional area of column (wall) and design value of compressive strength of concrete column) and corrosion rate of steel reinforcement [11]. C30 concrete is used as model; longitudinal steel used is HRB335; stirrup used is HPB235. Corrosion rate of longitudinal steel is 0, 2%, 5%, 10% and 15%; axial compression ratio is 0.2, 0.4 and 0.6. L OADING MEANS AND BOUNDARY CONDITIONS orrosion expansion of steel reinforcement is stimulated by exerting radial displacement on holes of concrete. Assume that the steel reinforcement is evenly eroded, 1 R refers to initial radius of steel reinforcement, 2 R refers to external radius of corrosion product; 3 R is radius of remaining steel reinforcement section. Corrosion rate of steel reinforcement  is: 2 3 1 1 R R          (7) Assume corrosion product is  times as large as original steel reinforcement and 0  is the space between non-corroded steel reinforcement and concrete, then the relationship between corrosion rate of steel reinforcement  and radial expansion displacement of concrete  can be expressed as: C