Development Length

[dl5150]

We are constructing pilecaps at site now which measures 1.6m x 5m x 1.3m deep and are each supported by 2 bored piles 800mm diameter. The piles are anchored 70mm from the base of the pilecap. The reinforcement of the piles are 12 pcs 25mm diameter epoxy coated bars and with 12mm spirals 80mm pitch. I have calculated the required development length in tension of 25mm to be 1.6 m. From the top of the pile, the 25 mm reinforcement can only extend at a maximum of 1.15m (juat a little below the 2nd layer top reinforcment of the pilecap. This is obviously not enough base on 1.6m which I have calculated.
In ACI 12.5 there is a 0.8 development length reduction factor for a 90 deg bend bar if stirrups are spaced not > 3db perpendicular to the bar being develop. I know this does not apply to our problem because the bars are straight vertically.
Is there any provision in ACI which states of a reduction in development length of straights bars in tension by enclosing them with ties? Thanks in advance

 

[Strukter]

You can reduce the development length by the ratio Calculated Factored tension/ Allowable Factored tension.

ie actual stress divided by allowable stress

 

[TXStructural]

There is no provision which allows a reduction to tension development length (below a 1.0 factor) because the bars are enclosed by ties, since the basic values consider that bars are enclosed or have sufficient confining cover. You can get a reduction for compression bars if you use spirals meeting 12.3.3 (b)

 

[asixth]

I take it with the 5m pile cap length that you probably require some moment capacity and hence the reason for the tension reinforcement in the piles.

I don't work with ACI but I can't see how ties would provide development. For extra development you need either a cog or a head to the reinforcement. Not sure whether you can provide cogs with epoxy coated reo but that is what I would be looking to detail for this application.

 

[hokie66]

If you need full tension capacity, I think you need hooks. What is the epoxy coating for?