I have modeled bridge pier. I have assigned plastic hinges to circular piles and oblong column. I am getting error only in oblong column hinge as PMM surface is not convex. I am not taking any error regarding circular pile hinges. I am using mander confined concrete and unconfined concrete with proper material properties in section designer. I am utilizing concentrated hinge. I am assigning elastic perfectly plastic caltrans hinge. When column reaches plastic state, moment in hinge state display tab is higher than what it should be at that axial load. I think while program is adjusting surface of PMM, it is enlarging PMM surface. Do you know any solution?