OFFSET INQUIRY

[TSOFA]

Hi,

I would like to ask how the offset works (I thought I knew until I did the below test). I run the attached simple example but the shear forces were not as expected. I have a project that I must use offset a lot in both directions X,Y and I want to be sure that the program will give me the right forces due to eccentricity. Thanks

[t.sautierr]

It seems you applied your loads right above supports so it normal you don't get any effort in the beam. With excentricity, you will be able to have moment due to axial forces but don't use just this  that to simulate a composite section, It is not made for this purpose, it has to be combined with other tricks.

You can find some topic in the forum about composite section

[TSOFA]

So Robot doesn't understand that the force of 1000kn is offset by 1m because is applied to the one node of the offset column. 

For which reason the offset command should be used?

How I can model the attached foundation? I thought of adding a node for the eccentricity of ex, but what I can do for the eccentricity of ey? Rigid links? How the moments due to eccentricities will be taken to account?

[Artur.Kosakowski · Accepted solution]

I'd define bars as they are in 'reality' and use rigid links instead.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[t.sautierr]

As Artur proposed, I'd do the same.

Offset is useful for horizontal loads or lods is the same plane or along the same axis than the element.

[TSOFA]

i did a test for membrane rigid links and I didn't have the results that I was expecting. Why the edge of the slabs do not have the same displacements as the bar?  when we have a rigid link with all the directions fixed, the nodes that we fix together shouldn't have the same displacement?

[jivkomitev2]

rigid links do not make the displacements in the nodes the same. Rigid links limits the displacements in the nodes relative to each other

[TSOFA]

what do you mean by saying 'limits the displacement' but not 'make them same'? what do you ensure by using rigid links? transfering of loads? that the two nodes/ elements will move in the same way?

[TSOFA]

In my case I have a foundation beam 60x80 connected to a raft slab 50cm thick. How I will model this in order their interface to be connected properly? In the attached file i use nodes 2 and 3 to create the contour of the slab. It will be better to use nodes 1 and 3 for the contour? then I will have a part of the slab 'inside' the width of the beam. How I can connect the two elements? in reality, node 1 and 2 will have the same displacement.

[jivkomitev2]

"what do you mean by saying 'limits the displacement' but not 'make them same'?" - Points 1 and 2 have different displacements in terms of global coordinate system, but point 2 have displacements zero with respect to point 1. Rigid links make distance a=const (and  rotations and other directions )

[jivkomitev2 · Accepted solution]

I prefer model 1. The best model (closest to reality) is model 3. Difference between model 1 and model 2 - in model 1 you need more reinforcement in plate, in model 2 you need more reinforcement in beams. When beams become weak  (they realy are), plate takes more of the loads.