Using springs to measure twisting of foundations

[PaulMcNulty]

hi,

I am trying to model how a 3D foundation for a bridge twists under loading. It is prevented from displacing in the vertical direction, but can twist in the other direction. I initially tried to put 4 springs in at the four corners of the end face of the foundation. In this way, one end of the foundation could displace more if it had a greater force. However, I cant get this to work. I am doing an explicit analysis and I am having trouble connecting the other end of the spring to a fixed point in the part. I was able to use a reference point for this, but I can only seem to create one per reference point per part, and I need four reference points. Anyone have any suggestions on how I can model this?

 

[burningDiesel]

Are you using rigid bodies or something?
If not, just use connectors with spring behavior, or the *spring option (maybe the spring is only for standard, idk)

 

[PaulMcNulty]

Hi,

Yeah I have tried to use the connectors now, they seem much easier. However, it asks me for a D value, when I choose elastic behaviour for the connector. I have checked through the manual, but I dont know what D is. I was expecting a stiffness (E) value instead. Do you know anything about this?

 

[burningDiesel]

Just do per component:

Data lines to define linear uncoupled elastic behavior (the COMPONENT parameter is included and the NONLINEAR parameter is omitted):

First line:

Elastic stiffness (force or moment per relative displacement or rotation; force for SLIPRING).


see:
31.2.2 Connector elastic behavior

the D (21 value matrix) is for coupled unsymmetric linear stiffness, which you probably don't need.

 

[PaulMcNulty]

I have attached a screenshot of the connector section that I have developed. I think I have to put in a D11 value that represents the elastic stiffness. I have run this model but even for a very low stiffness value, the foundation did not move much, which makes me think something is not correct. Is that connector section okay?

 

[burningDiesel]

an axial connector is exactly what it says it is, a connection that only allows movement in the axial direction (for the value 1 this is 1 force per length).
Are you sure you don't want e.g. a cartesian connector (with 3 stiffness values for each of the 3 directions)?
Also check your units for consistency.
Other than that, we will need more info (e.g. an input file)

 

[PaulMcNulty]

Well I have put the axial connectors in the two directions that I want the foundation to twist (see the screenshot attached). I am still a bit confused about the D11 value. It is a stiffness value yes? Is 1 a very low value or not?

 

[burningDiesel]

by twist you mean rotate? Then you should use a rotational connector and rotational stiffness.
And D11 is a stiffness value, abaqus is unitless so I don't know if 1 is low or not.

 

[PaulMcNulty]

I am currently running the axial connectors I had before, but going for the non-linear option. I am only putting in one line in the data so its actually behaving linearly (I just put in a force and displacement). I tried changing the D11 value in the linear model but it didnt seem to make any difference. I would use the rotational connector, but im not sure which moment (M1, M2 or M3) to use?