Cracked or uncracked concrete

[Arun238]

Hi,

Is it common to consider cracked concrete while designing post installed anchors for a portal frame supported on foundation edge beam ? or the cracked concept is generally for suspended concrete where flexural cracks occur ?

 

[Greenalleycat]

You're opening a can of worms you may regret....
Design of post installed anchors for portals is a hot topic in the office

I normally consider cracked concrete - I think there is a separate certification for anchors rated into flexural tension zones?

 

[DaveAtkins]

I am not in a seismic area (Wisconsin), so I normally assume uncracked concrete. It is difficult sometimes to make things work using the cracked concrete values.

DaveAtkins

 

[Arun238]

@greenalleycat - same here. It's not the anchor itself. Pullout strength in concrete will be very less for cracked concrete. I thought it's more for the installation of anchors on suspended concrete member because of the formation of cracks due to bending.

@DaveAtkins - sorry, did you mean that it's only relevant for seismic zones? What if the anchor is installed to the soffit of concrete beam where flexural cracks might have occurred from service loads? Sorry, I might be missing something.

 

[EZBuilding]

I lean towards cracked concrete for all post-installed anchor designs.

If I need to dig further into the numbers, I tend to consider uncracked conditions for compression elements only.

 

[DaveAtkins]

Arun238, I do not disagree with you. I meant in a seismic zone, I believe it is prudent to assume any concrete member is cracked.

I should probably be a little more careful about what I assume in the future. I agree that if something is likely to be cracked (like the tension side of a flexural member), it should be assumed to be cracked.

DaveAtkins

 

[Greenalleycat]

Going off memory here and not cross-referencing with ETAG blah blah

- I assume cracked concrete for almost any anchor design, particularly if it's primary structure
A portal frame base will always be a high load area and therefore high risk of cracking the concrete around it

- I think there is a separate anchor accreditation if they're installed in the tension zone of a member?
There definitely used to be at least, I don't know if it has been wrapped up into other qualifications now (Cracked or C1/C2)

- C1/C2 accreditation requires maintaining strength in certain width cracks etc so this kinda double dips on the Cracked concrete etc

 

[EngDM]

Can you guarentee that the concrete will remain uncracked for its entire design life? If no (which is basically always) design for cracked concrete, I.e. don't design for capacity you may not always have. I design pretty well everything for cracked, similar to what others have put here.

 

[Arun238]

Thanks everyone for the valuable thoughts on the subject