Trough bolt on concrete wall 2

[Jandra11]

In this kind of connection where the bolt goes trough the wall and bolted at the other side of the wall.Should I only check concrete edge failure and ignore the pry out failure.because when i try to model it to hilti. it is failing in pry out categor. Thank you in advance

 

[Mjkkb2]

you cannot really check it adequately in Hilti (Profis software I assume) since it does not do thru-bolted anchors. You are also out of the scope of ACI appendix D provisions. You basically have a 2-sided bearing plate condition at edge. The pryout will not govern, most likely the side face blowout or breakout (depending on loads you have on this connection) will be your failure mode.
IF I was to check it, I would do a base plate design/check and then try to apply appendix D ignoring the back plate.

 

[Jandra11]

@mjkkb2 thank you for feedback. I agree that HILTI cant compute it exactly but i just assume same embedment of anchor to the thickness of the concrete.The governing load here is vertical force that leads to concrete edge failure. and due to some reason its failing in pry out but with the presence of the plate at the other side of the concrete is enough to bypass the pry out checking. And i dont have any problem on the thickness of the plate because its only compression and downward force. is there any other way to increase the concrete edge capacity other than increasing the number of bolts from top and bottom?.

 

[WARose]

I'd still check it as per Appendix D because (in my opinion) a lot of the failure modes are still applicable. (Probably even (for example) side face blow out. That is if the bearing stress on the bolt head is high enough and the edge distance is close enough. And that is ignoring the stiffness of the back plate, which I think is appropriately conservative.)

I'd definitely limit how much of the anchor embedment I'd consider using for shear. Probably about 8*diameter (of the bolt) or the minimum edge distance. (Whichever is less.)

 

[Jandra11]

@warose thank you for the feedback. Is side face blow out different on concrete edge failure? I actually using ETAG annex C and I havent seen any section telling we should limit the anchor embedment considering shear failure. But I notice in HILTI they are limiting le to maximum 12d not 8d? is hef or 12d.

 

[WARose]

Is side face blow out different on concrete edge failure?

It is caused (in part) by being close to an edge.

 

[KootK]

and due to some reason its failing in pry out but with the presence of the plate at the other side of the concrete is enough to bypass the pry out checking.

I disagree with this and believe that you still need to contend with pryout. Pryout arises from the eccentricity between where the shear is delivered and where it is resisted. And you still have that here. If HILTI says you've got a pryout problem with the anchors modelled at full thickness, then I'd still be worried about it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[canwesteng]

The limit on load bearing length of an anchor in shear is codified at 8*d in ACI and CSA codes, it will likely be limited in your code as well somewhere. Unintuitively, the limit is the definitions portion in the CSA annex for example. If you're code allows 12d I'd take it.
For pryout, I think you can make the case the back side plate adds some resistance but I have no idea how to quantify it.

 

[WARose]

The limit on load bearing length of an anchor in shear is codified at 8*d in ACI and CSA codes, it will likely be limited in your code as well somewhere. Unintuitively, the limit is the definitions portion in the CSA annex for example. If you're code allows 12d I'd take it.

Good point. But I am now wondering if the "le" to use in the shear breakout equations in Appendix D shouldn't be something more conservative than 8d or 12d. Maybe closer to the value called out in Sect. D.6.2.2 (for "torque-controlled expansion anchors"): le= 2d[sub]a[/sub]?

My reasoning would be: if it is a post-installed anchor (with a oversized hole).....you'd think that would cut down on how much would be in bearing.

(Kootk, if you are reading this....what do you think?)

 

[KootK]

For pryout, I think you can make the case the back side plate adds some resistance but I have no idea how to quantify it.

Some ideas:

1) Look at the usual app D frustum but consider the depth of it to be the full concrete depth. And remove the back side resistance as there's no concrete to concrete boundary there upon which to exert tension.

2) Seriously eccentric punching shear.

I like the punching shear as I can tie that back to codified stuff more cleanly.

Kootk, if you are reading this....what do you think?

I think the same and probably for the same reasons. In an oversized, ungrouted hole, you're not going to get that spiffy laterally loaded pile stress distribution that we simplify with 6d/8d. Instead, you're just going to lean up against the edge of the hole in a way that concentrates all of the force there. This is part of why I rarely do through bolt connections unless:

1) It's straight axial load and I deal with it as punching shear or;
2) I treat is as a pretensioned friction connection which has it's own issues.

For something like this, if it can't be done with anchor theory, I consider that to mean that it can't be done. Sure, the back side plate feels good mechanically. But we aren't able to quantify that rigorously and, conspicuously, there doesn't seem to be much testing on these kinds of connections. And if I learned one thing from appD, it's this: our instincts suck when it comes to concrete anchorage. Can't. Trust. Self.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Jandra11]

@warose yeah I thinks its almost the same as the concrete edge failure.

 

[Jandra11]

@kootk this connection is failing due to pry out but it is the same with this one its a through bolt and has base plate at the end

its failing because the hilti is considering the pry out due to individual bolt which i think it should by group because of the presence of the base plate at the back? does it make sense?

 

[KootK]

It may well be that pryout would occur in groups >1 but I'm not sure that all of the fasteners would be forced to pry out in unison. You've got a pretty good lateral spread on your anchors and the plates have little torsional stiffness.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JLNJ]

Do you have just axial force in the connected member - no tension?

 

[Jandra11]

@kootk any advise to improve this connection? Btw im really grateful for all the feedback guys all your comments are very much appreciated.

@jlnj yup compression and vertical force to be exact

 

[KootK]

@kootk any advise to improve this connection?

I'll try.

1) What are your loads?

2) What direction do your loads act? Are they reversible?

3) Where abouts are any concrete edges located that might affect the design?

4) What size is the steel member?

5) How thick is the concrete wall?

6) In general, what is this thing?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

OK, I am certainly no expert in App. D, but how can pry-out be an issue with a plate on the backside?
This is a fancy picture of a pry-out failure that I found.

 

[KootK]

7) Is the concrete new or existing?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Jandra11]

@KOOTK
1) What are your loads?850KN COMPRESSION 600KN VERTICAL LOAD

2) What direction do your loads act? Are they reversible?NO

3) Where abouts are any concrete edges located that might affect the design? ITS CONNECTED TO 400X400MM COLUMN (FC=50MPA)

4) What size is the steel member?UB203X203X60

5) How thick is the concrete wall? 400MM

6) In general, what is this thing? ITS A BRACING END PLATE SUPPORT

7) Is the concrete new or existing? YES EXISTING

thank you

 

[Jandra11]

@xr250 thank you for the reference. yup im thinking the same way but i dont have any solid reference to back that up.