Grade Beam Construction Joint on Augercast Pile

[bumbler]

Hello all,

We have a 5-on-2 with a foundation system consisting of augercast piles connected by grade beams. We have a pour strip at our podium slab that is roughly centered in the building floor plan. The contractor is now requesting that we add construction joints at all slabs-on-grade, concrete walls, grade beams, and the lower PT slab near this upper pour strip so that they can construct in two phases. I figure that because the grade beams are supported on the augercast piles, the best locations for the construction joints are centered on the piles with a pinned condition at the construction joint. The piles are embedded into the grade beams with headed deformed bars.

Any thoughts on this approach or on the overall feasibility of the phased construction? See attached sketch where I've marked the proposed construction joint and highlighted piles for one of the affected grade beams.

 

[hokie66]

Construction joints in grade beams over piles is appropriate. But I fail to see why you would consider it a "pinned condition". If the reinforcement continues through, especially the top bars, the beam is continuous.

 

[le99]

I would consider placing the construction joint in between the pile and the column.

 

[driftLimiter]

I also see the beam as continuous across the joint particularly if you ask for an intentionally roughened surface. Shear Friction across the joint to transfer shear from one side to the other, flexural reinforcement continues, these can be used to reason why the beam is essentially continuous.

 

[bumbler]

hokie66,
I had assumed a pinned condition because the contractor plans on pouring the second half of the grade beam a few weeks after the first half of the grade beam. If I'm interpreting what you said correctly, then the grade beam remains continuous if we keep the reinforcement continuous. So my initial design assumption of a continuous, multi-span grade beam holds up and the boundary conditions remain the same. Is that correct?

le99,
Can you elaborate on why this would be a better approach?

Thanks for the replies so far!

 

[bumbler]

driftLimiter,
Thanks for the reply, ensuring adequate shear friction transfer is one of my main concerns here. Good to hear more support for a continuous beam.

 

[hokie66]

Yes, a construction joint should have the reinforcement through the joint. In your case, made over the pile, there is no concern for shear transfer, as would be the case if made at centre span.

 

[le99]

@bumbler,

In general, construction joints should be placed away from locations with the potential of having high stresses. The quarter-point in an interior span of the continuous beam seems to be satisfactory.

 

[dik]

Is it a construction joint or a control joint? Is there supposed to be any movement? and detail it accordingly.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hokie66]

Some confusion or disagreement. Dik, the OP said construction joint, and he prefers a continuous beam, so it is not a control joint.

le99, construction joints within a span should ideally be placed to coincide with minimum shear, so typically at centre span. Flexural stress at the support is not relevant, as the continuous beam will be fully supported by the pile.

 

[le99]

hokie66,

The congestion in pile-grade beam connection turns me away, as well as the concentrated force3. But, the same as you and others, I'll not reject placing construction there, but avoid it for the sake of better-practice consideration.

 

[hokie66]

le99,

I agree that bar congestion is a factor in choosing construction joint location.