Hi guys,
I am modelling a slab supported on piles, the piles are actually tension piles to support upheave beneath the slab. I model the slab using plate elements and use vertical restraint node support at where the piles are located. The issue I am facing here is that, the out-of-plane shear will be very high, especially at those localized area and also closer to the edge of slab. I think that those shear is not realistic. I have read somewhere that, modelling some dummy members might help but I am not sure how to do it or if there is other methods to resolve this issue. There is no beams in the structure, only slab and piles. I have included a few snap shots of the loading conditions and out-of-plane shear results. I am pleased to attach my staad file here too. 1261.Launch chamber.STD
Best regards,
Ze Yang Lee
Check a 2nd point in this Wiki: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/29385/avoiding-stress-concentrationsAs it suggests, you may connect the support node with adjacent nodes by using the dummy members, which would have a material with high E value and low density. This would spread the stresses and reduce it.
Dear sir,
Yes, I have read about that previously. However, my load is now applied as a plate load instead of a concentrated point load. Do I need to create dummy beams around the perimeter of the slab as my supports are mainly at the 2 sides of the perimeter to help on this situation in this case?
Please attach the model where dummy members were added.
1106.Launch chamber.STD
Hi sir, the model attached here is without the dummy members in it, I have removed them and did not save the model when I realize the edge (not at the support location) still has high stresses. However, the way I have added the dummy members is by creating it a the support, forming a T shape around the support. The support stresses are fine, but at the edges shown in the photos in the previous post is still there (not shown in SAFE model.)
I still have my dummy materials created in the model and appreciate if you can provide some advice.
I have been cracking head on this.
I have attached my model with the dummy members. From the results, you can see there is no much difference. I am not sure how should I resolve the edge high stresses.
1581.Launch chamber.STD
The stress value I see from your plot are 1284 kPA which is only 1.284 N/mm2. When you say high stresses, what stresses are you expecting ? On a side note, the DUMMY material you defined has a very low E value ( should be 1000 times that of the material you used for the other entities). However it may not make much of a difference in your case as I do not see high stress anyway.
Dear Sye,
Really appreciate your reply sir. I have included dummy elements (high stiffness) now at the support location (one side only to allow us to see if the dummy beams help).
As you said, there is no much of a difference there. When I run this in SAFE, I do not see such a high shear at the edge of the slab like what is showing here. I would expect the stress will be high at the support position but not along the edges. The out of plane shear stresses is still 1.27MPa ish , with 600mm thickness, it is about 770kN ( a lot larger than all other points at the supports), and this makes my slab really thick >1m thick. Not sure I am interpreting the stress correctly?
I have tried different mesh size (refine it further but does not help).
Appreciate if you can advice sir.
0081.Launch chamber.STD