CSI SAFE 2016 Punching Shear Tutorial - Example and Practical Theory

In this video, we investigate how to analyze a slab for punching shear, how to design rebar and stud rails, and some theory, tips and tricks. Enjoy!
Punching shear manual calculation Canadian code: • Two Way (Punching) She...
Designing a transfer slab in SAFE 2016: • CSI SAFE 2016 - Slab A...
Immediate Concrete Deflections in SAFE: • CSI SAFE 2016 - Reinfo...
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[@AFMathandEngineering]

Hope you enjoyed the tutorial! Let us know below if you want to see anything specifically! Check the links below: Transfer slab design in SAFE 2016: kzbin.info/www/bejne/pIrIZJ2fqKmbjsk Immediate Concrete Deflections in SAFE 2016: kzbin.info/www/bejne/kILMdXmPiK5gr9k Manual punching shear calculation based on the Canadian concrete code: kzbin.info/www/bejne/g3bMopatdp6phqc

[@vasubhadania]

I have a doubt.... In ETABS if we have used insertion offsets in column......that joint where base reaction are found for column will not be at the center of column...... Obviously we get moments corresponding to insertion offsets but in point load the size of load remains same as size of column.......now this created some douts as that joint is not at the centre of column....

[@genieyas5186]

Hello, i have a question please, it is preferable to release colomn or to keep them fixed sincerly

[@engsam777]

I don't want to import slab from etabs, how to I include seismic and wind load in csi safe for slab design

[@IrfanShaikh-SE]

Please create more videos in detail. I really like your videos

[@walaaeldinmegahed1260]

Thanks bro. for this valuable video, I have a question .. how can I get the distance between the Rebar Sets , Is it the typical Rebar Spacing?

[@user-pc4gm7lf7c]

What does the first and second number mean by renforce the shear, is it possible for a diagram to show the renforce

[@aquibqadirtunio4090]

What is difference between ties and stud reinforcement for punching? Which type is preferred for actual designing and how we have to convert SAFE rebars values into practical drawings

[@AFMathandEngineering]

Great question, in terms of design stud rails are able to resist a higher stress limit than rebar ties as per Canadian code. In addition, you may only use pin ties in a slab that has thickness of 300mm or greater. So for 200mm residential slabs you can use stud rails for punching shear. In reality rebar is preferable normally as it comes with the regular rebar delivery for the pour. Stud rails need.to be ordered from a separate supplier, are expensive and sometimes end up sticking out of the soffit if not placed correctly. Also guys on site are usually more familiar with rebar than stud rails. You can convert safe values by creating a spreadsheet based on your code and take the punching shear forces from SAFE. This is the preferred method for sure.

[@chilotberassagarsamo2340]

Can you please explain the meaning of the reinforcement results? how is it interpreted? For example, what does 4x9-10d@100 mean?

[@xanzem]

Stud rails x studs per rail x stud diameter x distance between each stud. Therefore in your example... 4 stud rails with 9 studs each rail, each stud has 10 mm diameter and they are separated 100 mm from each other (between studs), therefore the length of the rail would be 900 mm, you need 4 rails and 36 studs of 10 mm diameter.

[@anjankuinkel6844]

Are we able to incorporate fibres instead of reinforcement while designing slabs in the software?

[@AFMathandEngineering]

Fibres are not a suitable substitute for reinforcement in a framed slab.

[@sarahfuad4033]

Why i have zero reinforcement after design and check ??

[@engsam777]

can you do one with shear walls

[@jiaweisun8584]

Thanks Fred. Btw do you know why sometimes SAFE doesn’t give you punching shear ratio? Says N/C. And sometime when I use punch shear overwrites, it shows N/C for that column I overwrote.

[@AFMathandEngineering]

Hey Jiawei, hope all is well! Typically it's when you're trying to model a column with a beam, or a condition where punching isn't applicable. I've seen safe be buggy though and n/c regular columns..I think it's just poorly programmed.

[@jiaweisun8584]

@@AFMathandEngineering Appreciated! Happy Holiday!

[@d_soulseeker]

I got into trouble. My analysis results are not showing punching shear. How to correct it?

[@johndfr]

you got it?

[@d_soulseeker]

@@johndfr I remodelled. Then it’s okay.

[@aniliqbal6654]

Very informative. How do you calc. punching shear force. Is it Shear Force?

[@AFMathandEngineering]

Thanks! Depending on the column type, the shear force contributing to punching is a combination of the shear force due to gravity load and the unbalanced moment acting on the column. See our punching shear video in the description for more on how to calculate the shear force (not unbalanced moment) by hand.

[@gustavoalvarez1496]

how can i check the punching shear for wall footing in safe?

[@AFMathandEngineering]

Typically you don't check two way shear.in a strip footing, one way shear governs.

[@gustavoalvarez1496]

@@AFMathandEngineering i gess those calculations have yo be done manually 😅 do You have any video where You explain shear in one direction? Thanks for answering.

[@AFMathandEngineering]

@@gustavoalvarez1496 Two way shear calculations don't need to be performed at all for strip footings assuming length to width ratio qualifies them as acting one way. We have two videos, check out links below: kzbin.info/www/bejne/iJO5Z4eNrceWiLs kzbin.info/www/bejne/inTNf4CZjZ5lhKs Please like and subscribe!

[@gustavoalvarez1496]

@@AFMathandEngineering i meant the one direction shear calculations have to be checked manually.

[@AFMathandEngineering]

You could get this information from software, don't necessarily need to hand calculate.

[@mecheil2000]

Many Thanks for this video...really very good... I did many checks for punching on raft foundation with spring support ...i see safe is so much over design ...hope u can share me with some clarification ... as example if I get max reaction from column ...the punching very safe ..but when adding the loads on shell element ( raft ....i see results over design ..why ...i could not understand ...

[@AFMathandEngineering]

Yes, I also find that SAFE is extremely conservative with shear reinforcement for deep concrete members, especially things like raft or mat foundations. It will always say you require shear reinforcement even when the mat is clearly thick enough to resist based on plain concrete strength. You have to either use a different analysis program or do some hand calculation given the applied shear force to see if you actually require shear reinforcement or not.

[@joserolandomonteza1303]

Why i have error n/c?

[@AFMathandEngineering]

Safe won't check certain columns if they're too close to walls, beams, etc. Sometimes safe auto detects the wrong punching condition (edge, corner, interior) and you have to manually change it. This program require alot of checking and engineering judgement to make sure you're getting the right results.

[@mozko0010]

@@AFMathandEngineering you're true, my strap beam just to close to column. i got my problem solve. many thanks!

[@UnmeshBane]

How do I validate the shear force calculated for punching shear??

[@AFMathandEngineering]

The shear force contribution due to slab load is fairly easy, the geometric tributary area of the support is generally equal to that force (SAFE also takes into account stiffness, so not 100% accurate). The shear force contribution based on any misalignment of supports above and below can be approximated based on geometric distance to the support, although again finite element will probably do a better job at this.

[@UnmeshBane]

@@AFMathandEngineering for raft slab analysis, the variation of soil pressure would be different over the area and the tributary area calculations for columns not in grid is very difficult, so for that is there any way to do it manually to verify with safe for a small example

[@AFMathandEngineering]

The geometric tributary calculation of an irregular column grid is easily done on CAD. I agree though in a raft that it's more difficult to validate punching shear due to the soil spring behavior vs a slab.

[@AFMathandEngineering]

For design purposes a raft can be idealized as an upside down two way slab where the loading is the factored soil pressure based on the loads on the columns and walls. Again you can approximate this geometrically but it's difficult to calculate the factored bearing pressures when the grid is irregular (for a simple shape this is easy).

[@UnmeshBane]

@@AFMathandEngineering thanks for quick reply

[@NTC]

I have a question regarding the drop panels. If I have a drop of irregular shape (and probably not symmetrically positioned at the centroid of the column), how does SAFE determine the punching shear perimeter?

[@AFMathandEngineering]

Safe calculates the critical perimeter based on the code you're using, for CSA it will calculate bo from d/2 from the face of the column. If your drop panel intersects the critical perimeter, I'm assuming SAFE will do one of two things: 1. It won't check the column and you'll get an N/C when you're looking at the ratios. 2. It may assume it's a corner or edge column depending on where the perimeter intersects the edge of the drop and analyze it as such.

[@NTC]

@@AFMathandEngineering I am not very clear at that point. The whole point of having a drop is to make the shear area bigger, thus more shear capacity. Thus, I think SAFE should check it. But my question is about once there is a drop, the program should also check the punching shear assuming that the shear occurs at the face of the drop too. and in that case, how the punching shear perimeter is defined is not not clear.

[@AFMathandEngineering]

@@NTC SAFE is a buggy program sometimes, and isn't the best at recognizing where critical perimeters are always. Like any tool you have to understand what programs are good at and use your judgement with the results. Did you try this case in SAFE yet?

[@NTC]

@@AFMathandEngineering yes I've tried a square column drop with an oval shape, SAFE still reported the punching shear perimeter being a square shape

[@AFMathandEngineering]

Safe isn't great for irregular cases, knowing the limitations of the program is important Sometimes it's best to calculate by hand especially if you know that the program isn't likely to give you accurate results.

[@aniliqbal6654]

how do you apply envelope load case In SAFE?

[@AFMathandEngineering]

There are a couple ways to do it, either draw a null beam element where your facade is and apply a line load, you can also create a dummy beam of minimum height and depth allowable by safe and apply a line load to that. Some people don't like using null elements as it can cause errors and problems some times. Both are reasonable options IMO.

[@aniliqbal6654]

I try to add new load combination and there is an option for linear and envelope load combination

[@AFMathandEngineering]

That's up to your building code what load combinations you want to use. It also depends what safe is assigning your envelope load as (SID, dead, etc.) You're the designer, you have to establish what load combos you want to use and what you're going to assign your facade load as.