Drilled Pier Minimum Reinforcing, ACI 336, IBC code

[kennyb04]

I have read several threads on minimum reinforcing of drilled piers but am going in circles on a solution. I am trying to determine the minimum reinforcing for drilled piers required for expansive soils. I understand that ACI 318-1.1.6 states 318 does not address drilled piers and so I should use ACI 336. The issue with using 336 is that the IBC does not have this document as a reference standard. Is there any way to justify min. reinforcing in drilled piers by code? IBC 1810.3.9 (Cast-in-Place Deep Foundations)only says reinforcing is required if there is a net uplift or moment requires it. The IBC does not reference ACI 336 as a referenced standard. IBC does reference ACI 318, but ACI 318 does not cover drilled piers.

Is the only option left for designing per code to design the drilled piers as a continuously supported column therefore requiring the minimum reinforcing ratio to be 0.01 (1%) per 10.9.1? Or if there is no net uplift, design it as un-reinforced concrete per ACI 318 22.7 or 22.8 which requires minimum reinforcing only in seismic areas?

The drilled pier I'm trying to provide reinforcing for is due to expansive soil, however, the geotech only gave required bell to shaft ratios to handle the uplift force. I do not have an actual uplift force due to expansive soil so am unable to design it as a continuously supported column in tension.

I know I may not get any black and white answers but any comments or code references would be appreciated.

 

[BAretired]

I have always used 0.5% minimum reinforcement in a drilled caisson based on the CSA minimum reinforcement in a column which is architecturally oversized. Don't know if the ACI code is similar in that regard.

BA

 

[JedClampett]

Can't you press the Geotechnical Engineer to get you uplift forces? After all, it he/she who's specifying the belled bottoms, so they must have a force in mind.
But in similar situations (where I needed to reinforcing piers, but didn't have any forces), I've used the .5% that BAretired mentions. It might be a lot fo steel, but at least I have some code coverage (ACI 318, Section 10.8.4 and 10.9)..

 

[JAE]

I think section 1810 of the IBC (I'm looking at the 2006 version) has some min. limits on reinforcement in seismic classifications C and higher.

 

[haynewp]

IBC 1810.1.2.1 and 1810.1.2.2 have 0.25% and 0.5% based on the respective SDC. I didn't see any recommendations for minimums in expansive soil, I would get the uplift from the geotech and run the reinforcing full depth of the piers.

 

[VoyageofDiscovery]

Looks like IBC has a hole in it. Document it and then use your judgement.

 

[dcarr82775]

I have always gone with 0.5% minimum, but checked it on a smaller cross section where the steel equates to 1%. Get the Geotech to give you the full length tensile load requirements

 

[JLNJ]

In areas of low seismicity with deep shafts I have seen a nominal amount of reinforcement for the top section and none at all in the lower section.