Concrete Cracking at External Corner

[humanengr]

I'm designing a circular cast-in-place reinf. concrete structure. Special steel doors are required
for safety reasons. The steel door attachment to concrete details must be followed exactly with embed plate as shown in attached detail. A concrete anchor is required near the outside corner as shown exacerbating the problem.
All dimensions in mm.
My concern is the concrete will crack where shown on attached sketch.
My plan is to "build-out" the concrete at the corner and add stirrup-like rebar (shown in blue on sketch) to reinforce the build-out and integrate it into the main structure.
I'm not a concrete detailing person since most of my experience is with steel structures.
Question: Does anyone see anything wrong with this approach? Is this build-out not necessary? Do you
know of a better approach?

Your feedback is appreciated.

 

[Michel60]

Good morning humanengr,

Probably the more compelling reason to add the extension is difficulty in getting good concrete placement in the corner and probably less so for the spalling off at the plate. With that said I think your proposed configuration is reasonable but if you are implying a reinforcing "U" into the extension it might be a bit difficult to build with the wall at just 150mm. You might consider just a horizontal hooked bar with the tail oriented parallel to the door jamb and maybe a vertical jamb bar.

regards,
Michel

 

[Michel60]

....and the form work guys will hate the little extension but if appearance counts it's probably still a good idea.

 

[bpstruct]

Is there any way to shift the door towards the interior of the shaft a bit so that you don't have the anchors so close to the edge?

 

[charliealphabravo]

The head of the stud also comes relatively close to the exterior edge. You might have another failure point there depending on the load from the door.

I think that some neatly trimmed WWR extending into to the corners of the form might go a long way to reinforcing the brittle corners. If you can thicken the edge as shown that can only help I think.

 

[JKW05]

I agree with bpstruct and charlie...the head of the anchor seems close to the outside face. Not sure what restrictions there are aesthetically, but you may consider widening the extension past the length of the stud. You could then also extend the U bars into the wall past the anchor stud.

 

[shobroco]

If you can widen your extension to 200 it would be better, & I'm not so sure your stirrups help; 10M is plenty to put in that small space and could actually cause rather than solve problems. I'd also want to crank the jamb anchor into the wall to get it further from the exterior surface. WWM (WWF/WWR?) would be better than stirrups if carefully bent & placed.

 

[TXStructural]

The forces will be put into the concrete by the anchor (you have a stud shown), but I would consider using a deformed bar anchor instead. This would allow you to extend farther into the concrete, reducing the stresses near the edge of the concrete. This would negate the need for the extension. Also, a bar or mesh outside the anchorage will serve as supplemental/confinement reinforcement under ACI 318 Appendix D.

As far as cracking where you have it shown, the most likely culprit would be shrinkage of the concrete around the plate, if the anchorage is sufficient. I would never recommend relying upon the concrete bearing along the edge of a thin plate like this for shear resistance. If you expect much shear across the axis of the stud, you might want lugs on the back of the embedded plate to transfer the forces. But I don't imagine the loads are high enough to require much shear resistance.

I'm not sure what the smaller post-installed anchor near the top edge is doing.

 

[RHTPE]

As one who has been in concrete construction for far too long, I would suggest extending your embedded plate to the corner and NOT do the concrete extension.

It is a troublesome forming condition that may never get built correctly, or, if it is built correctly, it may not stay that way when the concrete is placed.

JMHO


Ralph
Structures Consulting
Northeast USA

 

[humanengr]

Thank you all for your constructive responses. The diameter of the concrete structure or "tower" is relatively small, therfore, there is not adequate clearance to move the door inwards.
The concrete anchors are specified by the door manufacturer. This is one of a limited number of approved doors for the specific protective requirements.
The door has been tested and must be installed under these specific and precise anchorage requirements. I'll also send the concrete details to the door manufacturer to see if they can concur this is consistent with their tested conditions.
Thanks to all, once again.