Behavior of hollow beams under 4 point loading
I am analyzing RCC beams with longitudinal opening in various positions.
The ultimate load carrying capacity is supposed to reduce when the opening is moved to the compression zone than the solid control beam without opening. But the ultimate load carrying capacity was increased when the hole is provided at Neutral Axis and much more increased when the hole is at compression zone.
can anyone please explain me the correct way and the mistake I made?
I don't know what are the pictures I have to attach, so please tell me and I will attach it.
I have created 3D model in space claim, analyzed in static structural 4 point loading and load was applied as displacement as 0.01mm per step up to 0.8mm ( beam fails within 0.8mm displacement), standard earth gravity is applied.