Hi,

I am modelling a simple pullout experiment consisting of a 16mm diameter bar embedded at the centre of a 100x100x100mm concrete block (100mm embedment of the bar). I analysed two models; one with a 1D bar with perfect connection, and another model with a 3D square steel bar (having the perimeter of the square cross-section equal to that of a 16mm diameter circle), also perfectly connected to the surrounding concrete. 1D 8mm diameter bars, forming two stirrups confining the concrete around the main bar being pulled out, are also included in both models. The concrete model is based on the Cementitious2 model with a cylinder strength of 25MPa, and other parameters generated automatically with a mean safety format. Load is applied axially to the end of the bar at the top of the block, while the top face of the block is supported. Both models are being meshed with hexaherdral elements of the same size (about 6mm side).

The issue is that in the case with the 1D bar, I am getting a maximum load in the bar of about 28kN, while in the case of the 3D bar, the maximum load is reaching about 89kN. In both cases, after the peak load is reached, the displacement still increases as the load drops.

I think that the load reached in the 3D case is more realistic for the case of perfect connection, and I am not sure why the case of a 1D bar is not reaching a similar maximum load.

I would appreciate any help on this matter.

Thanks.