Learning Forum

[andres.baeza]

Hello everyone, I have a model of a piece of mechanical equipment on a pile, and I've entered a response spectrum into the "response spectrum" analysis system. I'd like to obtain the shear force and bending moments at the contact surface between the pile and the mechanical equipment, but when defining a "force reaction" or "moment reaction," it only gives me the options to do so in a boundary condition or spring.

 

1) How can I obtain the moments and forces of the structure in a zone other than the fixed support at the base of the pile in "Response Spectrum"?

 

2) I've noticed that moment and force reactions can be obtained in transient structural analysis on any surface (not necessarily in a boundary condition or spring). Would these be the actual bending moment and shear forces experienced by the structure?

[Dennis Chen]

I feel like I am having a hard time pinpoint the actual nature of the question.    What does it mean for a contact pair to have reaction forces?   Reaction forces imply there's an action and this is why it makes sense for reaction forces to exist only on supports because supports are constraints and when there's an action applied on the structure, then there's a reaction on the support.

When it comes to contact, what makes sense is contact forces/pressure.    For example, a penalty based contact has springs which has a very high stiffness (say for bonded contact).   When we probe contact behavior using contact tool, we are looking at the responses of the elements that prevents sliding/separation and thus we get pressure in normal and shear direction. 

Perhaps think more critically about what questions you are really asking and how contact works and then try to formulate a more precise model based question such that it answers your high level program-related questions.

[peteroznewman]

Hello Andres,

I expect there are a limited number of fasteners, between 3 and 6, in holes in the mechanical equipment base plate and matching holes in the pile.  I would typically use a Fixed Joint to represent each bolt that connects each matching hole pair, then in the Solution branch, add a Probe for each joint to extract the forces going through the Joint. Pay attention to the Joint coordinate system, then you can combine the X and Y joint force components into a single shear force for each bolt and use the Z axis for the axial tensile/compressive force for each bolt.

That would work if your pile was modeled using shell elements so the profile is modeled with surfaces and you made bolt holes on the appropriate faces of the pile. This doesn’t work so well if you model the pile using beam elements.

As Dennis mentioned, Reaction Forces are for the Fixed Support of the pile and not useful for extracting forces between components in the model.

I suggest you insert some images that show what your model looks like.