Connection and meshing 1

[remimarin]

Hello,

I am currently doing an internship, where I am asked to used SAP2000 V16 to make a simple container, put some loads and get results.

I am not really getting on how the connection between frame and shell elements are made. I have been searching on the web, readng manuals and CSI website.
The thing is that if I got it right, it depends on the joints, and options where you are meshing, but it is not really clear for me. for exemple, I would like a connection between the edge of my shell element and the beam, as you can see on the picture.




Also, would you mind clariying a bit how meshing works on SAP ? I am currently using automesh, is there a way to see the mesh on my part ? And I have been reading things about manual meshing, but I didn't find how to do it.

Thanks a lot for the help, I know that it is some really basics questions but I am a bit stuck.

 

[SteeliestFire55]

A couple of suggestions regarding the meshing. Frames can only connect with area elements at node points. Your SAP model only has nodes at the end of some frames (transverse and vertical frames which are parallel to your meshing direction) where it connects to area elements and no nodes in between. Hence there is no force transfer between the frames and the shells except at the ends.

So you have a couple of alternatives here (instructions and menus per SAP2000 v14)
1) EDIT>EDIT AREAS
[Pre-Analysis]. Manually mesh the frames and areas before running analysis. Verify that the nodes are common to both the frames and the areas
2) ASSIGN>FRAME>AUTOMATIC FRAME MESH, ASSIGN>AREA>AUTOMATIC AREA MESH
[During Analysis] Assign automesh to the frames and areas such that SAP2000 automatically generates intermediate nodes. Manually verify that the area mesh coincides with the frame nodes.

Some additional advice you'll need further on: If you look carefully into the extruded model, you'll notice that the frames are shells are connected at the centroids which is not true for beams with a slab poured on top. I suggest you research cardinal/insertion points and joint offsets if you wish to accurately model composite stiffness.

 

[remimarin]

Thanks for everything, it really helped me ! I also took care of the insertions points.

my next question is that I have some superimpostion where one part of the frame meets another one, is it really a problem ? It looks like it is a bit complicated to make a clean connection between beams, but those the software take account of the extruded beam connection ? Or the calculcation is based only on what you can see on the non extruded view ?

 

[SteeliestFire55]

An image of would help visualizing your issue. As for connections between frames, I do not believe that SAP2000 can directly take into account extruded beam connections. I recommend looking into member offsets and panel zones. You can specify clear spans for your beams (or have SAP2000 attempt to auto calculate it). This has an impact on analysis if you specify rigid panel zones, and on design by ignoring demands in the offset length and only designing for demands in the clear span.

TLDR: SAP2000 does not directly account for extruded connections. However, you can implement member offsets to account for joints and connections.

 

[remimarin]

thanks for the explaination.

I think I have an issue of connection between my roof shell element and the side walls shell elements. I have a high stress concentatrion on the edge between theses shell elements, located on the roof, And it is only loaded by his own weight. Units are newton and millimeters, so it would be 1400MPa, a bit more than what I was expecting ! Do I have to do something to let the stress being able to spead trough shell connections ?

 

[SteeliestFire55]

A list of items that are worth looking into:


1. What stress were you expecting? What's the span, material, thickness? Can you dig deeper into which stress is 1400 MPa? How does it compare to the principal out-of-plane bending directions? (S11,S22 for stresses and M11,M22 for bending)
2. Are any other load patterns assigned with a self-weight modifier (Define>Load Pattern)
3. In your latest screenshot, visual inspection shows multiple nodes along the stress concentration area. Verify the node connectivity.
4. Is there a chamfer or fillet at these ends that isn't modeled?
5. Try generating Area edge constraints
6. If this slab is part of the joint at the beam, look into joint constraints.

In regards to #1 - How does this stress compare if you didn't model the longitudinal beams with insertion points? There is a difference in bending distribution when you change the insertion point. The primary reason is the shift in the geometric centroid (Read

https://wiki.csiamerica.com/display/kb/Insertion+point

)

 

[remimarin]

First Steeliestfire55, thanks for everything it really helps me.

Material is A36 steel, thickness is 5 mil bending / 5 mil membrane.

I displayed the maximum von mises stress on the picture.

I have been doing a test on a simple case, and the stress actually spread into the side wall, I just don't get why on my model it doesn't

 

[remimarin]

the test case is a simple box, loaded with a vertical uniform shell load on the roof

 

[remimarin]

I have another question : as you an see on the attached picture, I would like to put some weight only on one part of a beam. I am currently using distributed loads , in the table :

for 0 (% of the beam) -> 1700N
for 0,5 -> 1700
for 0,50001 -> 0
for 1 -> 0

the thing is that I want a load for a total of 1700N, I don't know how loading is workng on the distributed case, and how to get the proper total value

 

[SteeliestFire55]

Okay, so let's see if I interpret this correctly, you've applied 1700 N/m on half the frame length in the model.
However you'd like the total load to be 1700N? Is that per frame?

First of all it's good practice to assign the load you are applying as a different load pattern + load case. After you run the model you can always check the reactions for each load case. Dispay>Show Tables> Analysis> Structure Output> Base Reactions

If you want to see how SAP2000 is distributing the load. Display> show forces> Frames > Axial. I recommend right clicking on the frame you're interested in and scroll through the different orientations (axial, Major, Minor directions) and that should show the external loads and the internal force in each direction.

 

[remimarin]

Thanks for everything.

Another question, it is pretty easy to plot the stress, but I don't know how to get the displacement and the deformations, could you help me ? thanks

 

[WiQi]

after analysis go to Display>Show forces/stresses>frames

the pop down appears select the load combination, and direction in which you require displacement and select show values at the end, scrolling pointer will show you the displacements.

 

[AP92]

Hello every one ...sorry for interrupting you ... I am facing a problem , when I am modelling a steel cantilever beam using shell element then it gives correct natural frequency.. but when i model it using rectangular beam element then it doesnt give correct result???? Please help me out ..please , i am in a fix.... Thank you