concrete column with 2 layers longitudinal reinforcement

[mjl23]

Guidance for when cross ties are needed for concrete columns is provided by ACI 318 7.10.5.3 and AASHTO LFD 8.18.2.3.4. AASHTO requires longitudinal bars be restrained every 24" instead of the 6" required by ACI.

Does anyone know how this applies to columns with multiple layers of longitudinal steel? Does the interior layer of longitudinal steel need a tie and lateral restraint? I would think the outer tie would provide confinement, but I'm not sure about the lateral restraint of the individual bars that the above code provisions address.

 

[civilperson]

The 6 inch requirement of ACI is measured along the tie,(perimeter), and is the clear distance between longitudinal bars. The enclosure requirement in a corner of a tie can be met by one tie for bundled bars or by one tie for bars in different layers.

 

[mjl23]

civilperson:
I'm not sure if I understand your response (well, I'm sure...I don't)...
To clarify, in a rectangular column that has two layers of longitudinal bars, the outside layer will have bars that have a restrained bar which "has a lateral support provided by the corner of a tie having an included angle of not more than 135 degrees". This lateral support shall not exceed 6" per ACI or 24" per AASHTO. I guess this means that the interior layer of longitudinal bars needs it's own tie, otherwise the interior layer has no direct support.
Originally I questioned whether the outer tie/lateral support would meet the requirements for the INNER longitudinal bars.