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Re: Piers & Transverse Ties

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Section 1809.5.2.2 states that "Piles shall have transverse reinforcement
meeting the requirements of section 1921.4.  
Section 1921.4 Frame Members Subject to Bending and Axial Load.  This section
applies to frame members 1) resisting earthquake induced forces AND 2) having
a factored axial force exceeding Agf"c/10.  

Did you check the Agf'c/10 versus the factored axial load?  My experience has
been that unless the pier is resisting large dead load plus seismic
compression you will not exceed Agf'c/10.   ( Discuss this with the plan
checker to make sure he/she accepts this).  If you exceed the Agf'c/10 axial
load then you should provide the ties.

Section 1921.4.4.2 specifies the maximum spacing as 4 inches.

I believe the requirement to have ties per 1809.5.2 &1921.4 is to maintain
confinement of the core to resist large seismic and axial forces.  This
provides for a ductile failure mode.

Good Luck,

Tom Jakaby, SE