Type B construction joint in Australian Standards

[silver2164]

Hi,

NZS has quite a clear definition on the requirements of a construction joint. Typically a Type B construction joints (where it is necessary to develop shear friction across the joint) are specified and NZS 3109 has clear definition of what a type B CJ is, and how the contractor is to create a type B CJ (green cutting, roughened to a full amplitude of not less than 5mm). ACI has a similar clause.

Is there an equivalent in Australian Standards?

 

[hokie66]

I don't think Australian standards recognize the concept of shear friction.

 

[silver2164]

What!

How do engineers specify the CJ requirements, other than "intentionally roughened"? Even with reinforcement tying two separate pours together I would still expect the surface to be roughened, not smooth.

 

[bugbus]

For bridges, there is a TfNSW technical direction (B80) that spells out the requirements for construction joints:
Deliberately roughen the surface of concrete at construction joints to a pronounced profile with a surface roughness not less than 3 mm. Remove loose aggregate particles and laitance.

I believe in the AASHTO bridge code it is specified as 1/4" roughness.

I'm not sure how it is normally specified in the building world.

@hokie66, I disagree. What about the shear friction provisions in AS 3600 and AS 5100.5?

 

[hokie66]

I could well be out of date. The last time I asked the question was in 2019.

thread744-456716

 

[Just Some Nerd]

Does section 8.4 technically cover shear friction? It's only mentioned in the context of composite beams, and doesn't give any guidance on construction joint standards, but the theory seems to be there.

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Why yes, I do in fact have no idea what I'm talking about

 

[bugbus]

Now I see where you're coming from. Agree that Section 8.4 is mainly written in the context of composite beams, but in the past I and others in my office have relied on it in other situations that you might describe as shear friction. E.g., checking for potential planes of shear failure in plain concrete, joints subject to external post-tensioning but otherwise unreinforced, etc.