Transmission Structure Pier Foundation - Circular Ties

[tildeme]

For pier foundations of transmission line, what is the ties spec everyone is using? My company uses the standard below. I just want to ask those on this forum who are far more experienced than me about this and why this seems to differ from other foundation designs I've seenby people who have been in the industry for years.

For the longest time we've had our circular tie overlap length follow ACI 7.10.5.4 even though ACI does not really address pier reinforcement per ACI 1.1.6

Where longitudinal bars are located around the perimeter of a circle, a complete circular tie shall be permitted. The ends of the circular tie shall overlap by not less than 6in and terminate with standard hooks that engage a longitudinal column bar. Overlaps at ends of adjacent circular ties shall be staggered around the perimeter enclosing the longitudinal bars.

We've been told we must use ACI chapter 12 for tension development length to calculate that circular overlap length properly and then add in hooks. But really the requirement for foundations including drilled shaft is found in the IBC Chap 18 for deep foundations. Except for seismic applications, longitudinal reinforcement is required in shafts that are subject to moments, and only in the portion of the shaft where the moment exceeds the cracking moment as defined in Chapter 18. When longitudinal reinforcement is required, it must be tied together with transverse ties or spirals. Except for seismic applications, where specific requirements must be applied, the transverse reinforcement is constructibility reinforcement and does not need to meet ACI 7.10.5.4 requirements for compression members transverse reinforcement.

 

[transmissiontowers]

I don't know much about foundations. I do the above ground steel design for towers and poles and substation structures. I believe our foundation engineer uses LPILE or MFAD to do the drilled pier design. Back in the ancient days, we used a program called beam-column to design the piers. If you are a PLS-CADD user, there is a Caisson program they have available but I don't know if it does the reinforcing bar design.

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