Punching Shear In Safe Very Important Issue

[mhdhamood]

I have an idea to discuss here related to Punching shear; that is In categorization of columns there are :

1. Interior ,where the distance from each face of a column to the slab edge is at least four times the slab thickness

2. Edge column, where one face of a column in direction of design strip is closer to the slab edge in the same direction by four times the slab thickness .

3. Corner column, where two adjacent faces of a column are closer to their associated slab edges by less than four times the slab thickness. But the issue that is SAFE doesn't consider these definitions so it may give safe results where it may be unsafe .

Please discuss All Regards

Edited June 6, 2017 by UmarMakhzumi
Fixed font formatting

[WR1]

SAFE takes all of the above consideration in its calculations. You can simply select appropriate column type if its not taking it automatically. You can assign the column as interior, corner or edge column. If you are specifying corner or edge column there are further four options to select which corner or edge.

[mhdhamood]

Dear Mr Rana Waseem;
Thank you so much for your response. Exactly I am talking about a case like the following:
1. An edge column has a slab extent less than 4*(depth of slab) of one of it's sides; that mean it shall be taken as edge column and that direction will be    ignored in calculations of parameter of punching except only for a distance of d/2 from that direction will be considered in computing punching perimeter.

2. As ACI papers; wherever the distance from the edge of column to the slab edge is less than 4*(depth of slab), that direction will be ignored in calculating perimeter of  punching except for a distance of d/2.

3. The issue now that : SAFE program for the case mentioned in 1, will not ignore the slab for the direction where distance less than 4*(depth of slab).    Other than it will take that distance in its calculations to the end of slab (Here is the issue, I mean it shall not take that direction because it is neglected as  per  ACI papers except for d/2 distance only........................ why is that? According to any code it works ??? Here to be sure I do the punching  calculations manually but that time consuming).

4. The good news that  SAFE will calculate another case of perimeter as an interior column for the above mentioned case, and takes the case with        smallest perimeter.But still the issue why SAFE take the distance that shall be neglected into its calculations?.

Your involvement is appreciated all.
Regards 
Mohammad

[WR1]

Okay! SAFE is doing it perfectly. See PCA Notes Fig 16-5 "Edge column" (see attachment).
 
Include the marked dotted area also in calculating punching perimeter. Hope that clears your confusions?

[mhdhamood]

Dear Mr Rana waseem;
Thank you. But I am not talking about what you attached. My case is that there is a distance behind an edge column less than 4*depth of slab( I mean not as perfect case which is =0 as you attached). Now this distance shall be taken only = d/2; not all the distance. This is shown in the following topic Figure3 b http://docslide.us/documents/design-for-punching-shear-strength-with-aci-318-95.html. Note that how that he didnt take the whole distance because it shall be ignored.
Please if you all get my point tell me to proceed .
Thank you all.
Regards 
Mohammad

[WR1]

Please attach your specific problem as an image. Its very hard to understand engineering problems through words. Show markups where required for easy understanding!

[sameersaleem]

There is an option in safe that you can input user punching perimter in it. you should try this option.that will take the punching perimeter as you want it to take.hope this will solve your problem.

[mhdhamood]

The problem how can I attach here ???
Itry to attach but the URL apperas... does that mean I need to upload this pic to a website??

[WR1]

Just click on "More reply options" adjacent to "Post" button and attach the images.

[mhdhamood]

Dears;
Please see the attached pic. I wish it is helpfull

[WR1]

There is no pic attached...

[mhdhamood]

Dears;
Now its attached please note the pic

[WR1]

The provision you are talking about is performed in other softwares like ADAPT, but I could not find such definition of edge/corner columns in ACI. Can you please share where it is written in ACI code? I dont think there is such provision in ACI.

 

If you read ACI-318 2008 R11.11.1.2, it says

 

"For edge columns at points where the slab cantilevers

beyond the column, the critical perimeter will either be

three-sided or four-sided."

 

So draw punching perimeter around column and see if it lies inside the slab, then take it as interior column. (SAFE does this, if you keep the column location Auto).

 

If any edge of punching perimeter lies outside the slab footprint, ignore that edge.

 

In your case of example attached above, the column should be taken as interior column.

[mhdhamood]

Thank you Mr Rana Waseem . I say about you you are like an ocean. You introduce a nice discussion.
But let me say that : What is the definition of edge column ?. I guess from your paragraph that it is the one when you draw the perimeter which has three edges.
But as this paper says http://docslide.us/d...aci-318-95.html. that the edge columns is the one has a free edge od less than 4* thickness of slab.

[WR1]

Have your really read the paper you are mentioning? 

 

This paper talking about distance < 4d is only applicable to "Prestressed slabs".

[WR1]

Moreover, SAFE methods are based on Amin Ghalis book for deflection and punching. You can read his book for insight. (Author of this technical article as well)

[mhdhamood]

I have read dear. He says that this is applicable for also non prestressed.
Also please read this for definition of columns :  

https://www.scribd.com/doc/36838507/Punching-Shear-ACI-Code

[WR1]

The document section I have quoted clearly says the clause you were mentioning is for prestressed sections. 

 

Now you have attached the summary that explains the intent of the document that the clauses in this document are written for the design of prestressed and non-prestressed concrete sections (same like ACI). Based on this you cannot say that all what is written inside is applicable to both. Each one of them is treated separately. The section I quoted above is for "Prestressed".

 

Instead of putting links and reference to other items, why don't you show me directly where it is written in ACI the definition of edge column with distance less than d/2?

 

So that we can talk directly on the specific point instead of loop referencing!

 

I have not read the documents you attached the link for, in your last post. Please take a screenshot where it says specifically, and attach it here. 

[WR1]

And before that, make sure the document is really from ACI? (I also dont know about this clause, so please let me know, I am learning from you).

 

Because the document you are referring says "ADAPT Technical Notes", its does not look like official document of ACI.

 

And remember ADAPT program is used for PT slabs. ( I mentioned this in post#14 as well).

 

Also you still have the option to overwrite punching perimeter (as he said in post#7).

 

 

Show me the edge column definition from some standard ACI paper or code in next post. (Not from the documents you have already mentioned).

 

Thanks.

[WR1]

If you really want to go in details, then see RISA explanation what it does in finding critical parameter;

 

https://risa.com/risahelp/risafoundation/Content/Common_Design/Punching%20Shear%20-%20Design.htm

 

Goto " Finding the Controlling Case (Interior, Edge or Corner) " section and see how many options are there to find punching perimeter; you can do this manually if the column is very critical.

[UmarMakhzumi]

The provision you are talking about is performed in other softwares like ADAPT, but I could not find such definition of edge/corner columns in ACI. Can you please share where it is written in ACI code? I dont think there is such provision in ACI.

 

If you read ACI-318 2008 R11.11.1.2, it says

 

"For edge columns at points where the slab cantilevers

beyond the column, the critical perimeter will either be

three-sided or four-sided."

 

So draw punching perimeter around column and see if it lies inside the slab, then take it as interior column. (SAFE does this, if you keep the column location Auto).

 

If any edge of punching perimeter lies outside the slab footprint, ignore that edge.

 

In your case of example attached above, the column should be taken as interior column.

Good discussion. I will just add that Canadian Code CSA A23.3-09 allows a max distance 'dv' to be considered as part of punching shear perimeter where the slab cantilevers off column/ pile.

Thanks.

[mhdhamood]

Dear,
You have introduced a very nice discussion that reveal your excellent knowledge. Thank you so much. You made a big favor to me and I learned from you. Now I would like to say that I was wrong in:
1. I was very conservative in my estimations to perimeter of punching  because I was ignoring the distance after d/2 when the edge is less than 4*h. 2. I thought that I have to recheck after SAFE program checks for columns near periphery.

But I would like to mention that SAFE define the column according to 5*thickness of slab. Try to overwrite a column location type for a column having a free edge greater than 5*h( which should be treated as interior column) as edge column, then it will give NC (not calculated). 
Best Regards 

[mhdhamood]

Mr Umar Makhzumi;
I would like to thank you to enter the discussion. Your discussion  is appreciated.
Regrads

[WR1]

But I would like to mention that SAFE define the column according to 5*thickness of slab. Try to overwrite a column location type for a column having a free edge greater than 5*h( which should be treated as interior column) as edge column, then it will give NC (not calculated). 

Best Regards 

 

I am not sure about 5h provision in SAFE. I will check. Thank a lot!