Problems with connectors 1

[tgab]

Hi everyone, new here and I hope this isn't the same question over and over again, sorry in advance.
I'm having problems with connectors, specifically finding one meeting my needs: I need to model nails with a connector having three different elastic-plastic behavior in the three different directions U1, U2, and U3; I'm not interested in UR. I tried CARTESIAN first, then BUSHING, but I always obtain the same result: when I move the ending point of the connector in the direction the connector develops, let’s say X, I obtain results similar (not exactly the same, and this is another problem) to those I expect, when I do it in Y or Z, I obtain something around zero (10^-9). When I apply the displacement in y, I see in the visualization that the orientation system of the connector, placed in the first point of the connector, rotates at each step of the analysis around the Y axis of about something more than 180° (?).
The first point belongs to a 3D plate with encasters and the second is a reference point constrained to the surface of another 3D plate. The displacement is applied to this second plate.. I also tried with a two point wire alone, same result.
I also get this warning for the first point of the wire, the one belonging the 3D plate: Solver problem. Zero pivot when processing D.O.F. 4 of 1 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_4_1_1_1_1. I get this multiple times, for DOF 5 and 6 too.
When I apply a displacement in 2 and 3 I get the first warning way more times and I also get this: There is zero FORCE everywhere in the model based on the default criterion. please check the value of the average FORCE during the current iteration to verify that the FORCE is small enough to be treated as zero. if not, please use the solution controls to reset the criterion for zero FORCE.
It is evident I’m doing something wrong, but I don’t know what. I hope someone could help me. Thank you very much.

 

[Ron]

It would be helpful if you would describe the use of the connector and the software you are using. We can guess all day, but adequate information will help get you an answer if anyone here is familiar with your application.

 

[LittleInch]

Glad I'm not the only one who doesn't have clue what you're on about.

Drawings, sketches etc make a massive difference

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[tgab]

Really sorry guys, my bad. I'm working on Abaqus CAE. I thought I posted on the abaqus related forum, I didn't.

 

[dhengr]

Tgab:
WE CAN’T SEE IT FROM HERE.
Until you explain your problem sufficiently, with sufficient engineering design info. and provide some sketches, with dimensions, loads, coordinate system, materials properties, etc., etc…., the engineering info. needed to begin to address your problem, why should we waste our time guessing at what you want or need. You want some free help, but won’t spend the time to develop your problem well enough so a real engineer can begin to understand it.

 

[tgab]

It isn't a structural or engineering design problem, it is a matter of the way I'm using (improperly) a tool in a specific FEA software, Abaqus.

In the second line of the first post it is written “I need to model nails with a connector having three different elastic-plastic behavior in the three different directions U1, U2, and U3”. You are not supposed to be a “real engineer” to be able to understand that this means the problem is not a structural or engineering design one, you just need to be able to read to understand this is a modeling problem. Second, I already stated, in the second post I wrote, I wrongly posted the thread in this forum, I thought I was posting it in the DASSAULT: ABAQUS FEA Solver forum. I’ve already apologized for that, there is no need to insult or imply I’m not a “real engineer”.

If one is familiar with CARTESIAN and BUSHING connectors in Abaqus, one should know, at least for the second type of connector, a local coordinate system must be chosen. As I wrote, it was placed in the first point of the two forming the connector. The problem, as written, is to perform a connection with three different elastic-plastic behaviors in the three direction of possible motion (in Abaqus, 1, 2, and 3), regardless the loads, displacements, and elastic-plastic behaviors themselves.
The problems I encountered are expressed, that is a zero force response in the direction orthogonal to the one of the connection. The warnings and the time they appear during the analysis are posted too.
If one is not familiar with Abaqus’ connectors, the post could be difficult to understand, especially since the forum is the wrong one (I repaet, my bad).

As already written, I know the forum is the wrong one, and I already reported it, but the thread has not been moved so far.

 

[r13]

I understand how to design pile cap or deep wall (or beam) as strut and tie under gravity. But how do I design walls as strut & tie for lateral?

I'll help you for that. No need to feel been offended for the miscommunication.

 

[FEA way]

I think that the reason of this problem may lie in the way this connector is attached to plates. Try with a simple model of the connector fixed (Encastre BC) at one end and loaded at the other end.

 

[tgab]

retired13:
Thank you!

FEA way:
Thank you for the hint.
The CARTESIAN connector works fine, I think I tried only the BUSHING in the point-to-point configuration with the ENCASTRE, I thoiught I tried both.
When I try the CARTESIAN in the plate-to-plate configuration, the reaction force in the X direction is OK, the one in the Y and Z directions is around zero. I think the starting point, the one belonging to the first plate, rotates, but I don't get why it's happening as the point should belong to the plate which doesn't rotates. After this, I've tried the BUSHING with rigid rotations, and it "works", the RFY is 270 but the displacement is 100 and the stiffnes 3, so it should be 300, but apart from this it's OK. I plotted the rotations in the base plate for both CARTESIAN and BUSHING connectors, and the highest rotation in the first case is 1.133, in the second is 0.067.

 

[FEA way]

Exactly how did you attach the connector’s end to the plate ?

 

[tgab]

I partitioned the plate in order to highlight the center, than I selected that point.

What I don't understand is that CARTESIAN connectors shouldn't mess with rotations, only with displacements. Rotations are not settable DOFs, so, in my mind, the connector should work as a BUSHING with rigid rotations as long as the point is an ENCASTRE or belongs to a solid element. I don't get why there is such a difference in rotations in the plate, given that the two connectors are attached to the same point in the same way, only the connector assignment varies.

Furthermore, the values I get from the connector in terms of force-displacement don't fit the settings, but that's another story.