Apply concentrated force and moment in Abaqus

[edward law]

I added a reference point at the middle of pile cap, and tried to assign to concentrated load at this reference point, the result of the sum of reaction is equal to input load, so the result of reaction of supported piles is a reasonable result. After that, when i only apply a moment on the middle of pile cap in Abaqus, the result of reaction of supported piles are appear up and down distribution, it still is a reasonable result. However, when i apply a concentrated force and moment together at a same point, the reaction of each piles are same, this result should not appear when a moment is applied. Anyone know which step i was wrong in the model.

 

[FEA way]

Here's what comes to my mind:
- is the analysis linear ? If it's linear then you should remember about the principle of superposition.
- about which axis the moment acts ?
- is the reference point applied as part of the geometry (in the Part module) or as separate feature connected with the cap by coupling ?
- is the cap modeled using shell elements ? If yes then did you use shell-to-solid coupling to connect it with piles ?
- do you check reaction moments (RM) too or only reaction forces (RF) ?
- did you try refining your mesh ? Quad/hexa elements will be better and I think that you should use more elements for the piles.