I have used two different shaped rebars (circular c/s & Hexagonal c/s, Helically twisted) for pullout tests as shown in the figure. The parameters for both the cases are the same, but the results of simulations are quite different ( stress almost a variation of 10e12 is observed )for both the case for almost similar displacements. Circular is giving correct results( matching with experimental ). How what kind of changes do I have to to get almost similar results with Helical.

Please help me out. Thanks for the reply.