Reinforced concrete (RC) hollow core slabs beam work with cracks in service, however there is no accurate mechanical properties calculation method for this type beam. The Extended finite element method has many advantages in the study of crack problems, such as less calculation, no need to formulate crack propagation path, and so on. In this paper, the extended finite element model of RC hollow core slab is built on ABAQUS, in which the material constitutive model and the modeling method are based on the relevant scholars' achievements. The author simulates the initial damage of concrete by prefabricating cracks of different numbers and depths. Then the equivalent vehicle load is loaded at the most disadvantageous position. And the effects of the number, depth and location of cracks on the crack width, crack growth path, mid-span deflection and relative depth of crack (crack depth/beam depth) of RC hollow core slabs are studied. The results show that the number of initial cracks has little effect on the bearing capacity, but the RC hollow core slabs' stiffness decreases with the increase of the number of cracks. The method of judging whether the RC hollow core slabs have been subjected to steel yield load by relative depth of crack (Crack depth/Beam depth =0.456) is given through the correlation calculation. Keywords: RC hollow core slab, Extended finite element method, Crack, Midspan deflection

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