In view of the multiple-crack characteristics of ordinary concrete members,the current theory based on the single crack model only reflects the ultimate crack resistance of the member,but does not re-flect the harmful crack development inside the member before the ultimate load.A crack-system model was proposed to study the subcritical crack propagation process.For simplicity,the axial tension member was selected as the research object.First,a wedge-shaped model of single crack was established based on the micro-crack zone model of crack tip.Then,a crack-system model consisting of single crack arranged in string was established based on the geometric distribution parameters:average crack spacing,initial crack length and its number percentage.The results of simulating tensile test and fracture test of axial tension members show that the crack-system model can accurately reflect the macro fracture process and micro crack growth with appropriate parameters.For the specimen with prefabricated cracks,the results of the crack system model with the total number of cracks being the actual number are consistent with the results of the existing single-crack model.The further analysis using this model indicates that the subcritical crack propagation of concrete should be due to the progressive development of initial cracks in sequence from long to short;and the real crack initiation point is much earlier than that observed by normal tests,and the instability toughness can be improved by reducing the minimum length of the initial cracks.
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